By: Ray T. Bohacz:
The most irritating aspect of valve-lash adjustment is its awkwardness; too many components require removal to perform a ten-minute task.
Hydraulic valve lifters, on the other hand, require no adjustment for the most part. When adjustment is necessary, instead of setting lash, as you would with solid or mechanical valve lifters, a hydraulic system requires pre-load. There is no lash. This is usually required only when the cylinder head is being reinstalled.
The need for lash or free play
The camshaft is responsible for the valve’s timing, its lift and its duration—the periods it remains open and closed. In a cam-in-block engine, this is accomplished by the camshaft working with intermediate components: valve lifter (or tappet), pushrod, and rocker arm. With an overhead cam design, the intermediate components differ, using some style of follower in lieu of a pushrod and possibly a tappet. This discussion focuses on the hydraulic tappet employed in cam-in-block engines.
It’s the profile of the camshaft lobe that determines the valve action, and that motion is first transmitted to the valve lifter and onto the pushrod and finally the rocker arm that contacts the stem of the valve.
When the parts are cold, they shrink and as heat is generated they expand. For this reason, free play is required to prevent parts binding when heated. Free play is created between the rocker arm and the valve stem tip.
Valvetrains that required lash were often identified as employing a solid lifter or mechanical camshaft. Today’s engines provide either a hydraulic or mechanical lifter, based on the manufacturer’s decision.
Improvements in metallurgy and valvetrain design now allow a mechanical tappet to stay in adjustment much longer and work efficiently with less operating clearance or lash. Often these are referred to as a tight-lash design.
When the engine is cold, operating clearances recede and when hot they expand, depending upon engine materials. If the engine block and heads are entirely of cast iron, expansion will be minimal. Alternatively, if they are of aluminum, expect expansion because aluminum expands twice as much as steel—and both lifter and pushrod are made of steel. Aluminum block and heads will increase the lash 0.010in – 0.020in cold to hot.
In addition, the lash setting means that the effective valve lift is less than the height of the cam lobe. This is the result of the multiplicative effect of the rocker arm ratio, which is the offset of the fulcrum from the rocker mounting.
For example, if the cam lobe is 0.350 inch and the rocker arm ratio is 1.6:1, the valve lift would be 0.350 X 1.6 = 0.560 inch, if the engine used a hydraulic lifter, which has no lash. However, if it were a mechanical design with 0.020-inch lash, then the valve lift would be 0.540 inch.
This decrease may sound inconsequential, but it represents approximately six percent less valve travel and a corresponding impact on air flow both in and out of the cylinder. Furthermore, as the parts wear from constantly colliding as the lash reduces, the performance of the engine degrades and emissions output is altered.
Also, it’s a false impression to assume a solid lifter camshaft makes more power than a hydraulic design. A solid lifter has the potential to follow a more aggressive camshaft lobe and also work effectively at higher engine speeds. But racing engines aside, this argument is irrelevant.
The difference in lifter design
For our discussion a solid lifter is as its name implies: one piece of metal. It can be considered simply a means to transfer camshaft lobe action to the pushrod. In contrast, a hydraulic lifter is hollow, has an internal piston, spring, and allows oil to enter and exit.
Similar in operation to the hydraulic piston of a tractor bucket, engine oil flows to the cavity in the hydraulic lifter. When the valve is closed the lifter is on the base circle of the cam (the round part of the lobe) and its cavity fills with oil. The internal piston is now at its maximum travel upward since the oil is below it.
As the camshaft rotates and opens the valve, the piston is forced down and a check ball is usually employed to close the oil inlet orifice. As oil is considered incompressible, the piston cannot move because oil is trapped below it and the bottom of the cavity. The tappet now operates as a solid lifter and transfers the motion from the camshaft lobe to the pushrod.
During the lift of the camshaft and due to valve spring pressure, oil is forced from the lifter cavity by the time the lifter dwells on the nose of the lobe. Once the travel of the lifter on the lobe is complete, the pressure from the pushrod is decreased on the piston and it enters its at-rest position. The cavity is now replenished with oil.
Diagnostics and adjustment
If an engine with hydraulic lifters is noisy, either the internal spring has lost some tension or the check ball is not sealing or allowing the oil to fill the cavity. The remedy is to replace the tappet.
By changing the engine oil regularly and avoiding over-revving the engine, hydraulic lifters will work as designed indefinitely. Most hydraulic lifters fail due to poor maintenance.
To determine which lifter is noisy, remove the valve cover, start the engine, and let it idle. Anticipate oil spray: take precautions. Then, using a long extension 3/8-inch drive, push down gently on the rocker arm where it connects to the pushrod. This will absorb some of the internal piston slap in the lifter and should change the sound.
Due to the effort required to replace a failed lifter, it’s wise to renew all of them. If one is worn the remainder will soon follow. Also, during starting, avoid dry lifters operating against camshaft lobes by coating their bottom surfaces with engine assembly lubricant before installation.
Some engines use a threaded nut on the rocker stud to adjust preload while others place a shim under the rocker stand. In further designs employing a rocker shaft, adjustment is self-regulating if the valve installed-height is correct and pushrod of the proper length.
Regardless of the design, a good rule is to rotate the pushrod between your fingers and when rotation is no longer possible, correct preload has been achieved. If a stud-mounted rocker is used, add one-quarter rotation to the nut once the pushrod preload is established.
This was a VERY helpful and informative article. I have a 1997 Jeep 4.0L that suffers from a stumbling idle; the vehicle has never demonstrated adequate vacuum at idle since I bought it with 125k miles. I’ve tested for vac leaks, checked compression and done a number of things to try to remedy the situation. The 4.0’s are known for some ticking that normally disappears as they warm up, which mine does as well. Recently, I tried to measure my valve lift at the pushrod side of the rockers. Each appraised within the range of 0.122 to 0.162in. I let the lifters “bleed” down at the top of the camshaft lobe travel, so that each would come to a stop. However, with this wide range of values and even adding 0.060 or 0.080in of piston travel, valve lift is far from factory specs. Could this be the reason for my poor idle manifold vacuum and irregular idle? Would you replace both the camshaft and the lifters or just the lifters if these are the problem? Again, thanks for this informative article. It’s the best thing I’ve read yet, indicating that maybe my camshaft\lifters have been causing the problem all along.
Rob, Thanks for reading my article and the kind words about it. I too am confused about your measurements at the pushrod. But first I need to know a little more. How does the engine run off idle? The idle instability: is it there when the engine is cold? Is it a misfire that you can hear and feel at the tailpipe? What is the mileage on the engine now? I do not want to jump to conclusions until I hear back from you with some answers but I think the issue may be with an injector(s) and not internal to the engine. Please send me an email at: email@example.com so that we can open a dialog on this and get the 4.0 L humming as it should! Thanks, Ray
In my old 1965 Ford engine, I am told that if I install new lifters only they can rapidly wear the cam lobes as the lubricating oil properties have changed over the years. I was told to run it at a fast RPM immediately. Lastly, is there an oil additive now available for the older engines?
From author Ray Bohacz:
There is a requirement to fast-idle the engine for around 20 minutes when a new flat tappet camshaft and lifter set is installed. This procedure, which was valid even before the chemistry of the oil changed, breaks-in or mates the lifters to the lobes.
If the new lifters are being installed to a stock camshaft, there is no concern with modern engine oil. Just coat the bottom of the lifter and the cam lobe with engine assembly lube. However, if it is a performance camshaft with a more aggressive lobe and higher than stock valve spring pressure, you can use a ZDDP additive in a modern oil of your choice or choose one of the many brands that have a blend for older, non-catalytic converter-equipped engines. Applying assembly lube to the lifter and cam lobe is still necessary.
There is severe metal-to-metal knocking noise in the 2 liter engine of my 2007 Nissan Xtrail. It occurrs only on starting, then stops. I’ve been told it is caused by faulty hydraulic lifters, and to add a Wynns’ product to the oil and after 500km the noise will stop. Is this true?
What is throwing me off base is the term that you use to describe the sound… metal-to-metal knocking. A slow to pump-up noisy valve lifter will make a tapping and not a knocking sound.
I need to know how long it takes for the sound to go away and if it happens on only the initial start of the day or on subsequent restarts?
Your engine is an OHC design and does not employ a traditional valve lifter as the article is about. It uses a follower. It can be a hydraulic follower and will share the operating principles in the text.
Adding something to the oil would not hurt but most likely will not cure the issue if the lifters are slow to hydraulically pump up.
Listen to the sound again and let me know about the restart and how long it takes for the sound to diminish. If the truck has an oil pressure gauge, see if you can determine if the sound is linked to a slow rise in oil pressure on initial start-up.
If the engine needs an oil filter with an anti-drain back valve and the one you are using does not have it, that can cause a noisy valvetrain on starting, especially with an OHC engine.
Let me know and we can go from there.
I have a Chevy 402 engine with cam lobes and lifters that don’t match. Is this normal? So far, the lobes and the lifters of the cams I’ve tried don’t match.
Reg, When you say that they do not match, are you referencing the contact point on the lobe. Please expand on this and I will gladly provide my best advice. Thanks! Ray Bohacz
My 2018 Ssangyong Korando 2L petrol engine suffers dry start in the morning. It sounds like cams / tappets dry of oil. Ssangyong insist this is a feature of the engine. I say, as do others who are mechanics, this rattling noise is caused by lost of oil returned to the sump overnight or cam wear. What do you think? Regards Rob.
I agree but I wouldn’t jump to the conclusion of cam wear. As we don’t have Ssangyong vehicles in America, I assume the engine is an OHC design. Most modern OHC engines, if not all, use an oil filter with a check valve to prevent the entire lubricant returning to the oil pan. In some applications, the check valve may be in an oil gallery and not the filter. So, my first suggestion is to examine your oil filter. Even with a check valve, the system will not prevent total drain-back over a long period of time. Here in the States, most modern engines use either 5W-20 or 0W-20 engine oil. My four Ford vehicles are of OHC design and employ an oil filter with a check valve. Thus, they can remain stationary for weeks and on starting the low viscosity oil travels to the top of the engine so quickly they never exhibit dry-start. My next suggestion is to determine the viscosity of your oil. If Ssangyong is correct and it is the nature of the engine, it does not speak well about their engineering prowess. If I can help further please let me know. Ray in America.
Hydraulic lifters big-block Chevrolet: When I preload and adjust, I lose compression on whatever cylinder I’m working on. Can you diagnose my trouble?
Please supply me with more information. How are you determining the loss of compression? What is your procedure to set the preload? Is it by twisting the pushrod? With more data, I will do my best to assist you. Thanks! Ray
Ray – Very informative article, thanks for providing it.
I have a 1967 Ford F100 with 352 FE V8 engine. We removed the heads due to a burnt valve and performed a complete valve job. As we had the heads off, I replaced both the push rods and lifters with Melling parts. There isn’t any adjustment capability of the rocker arms. Now, the engine is making a clattering noise. When you wrote about rotating the push rods by hand to assess the preload, was this executed at cylinder TDC, or at any point in the cam rotation? And, should the lifters be full of oil to perform the test?
In previous decades, Ford engines, though excellent, had many different variations even in the same family. Today, that is not the case.
Ford engineered for the best application and was not concerned with cross over to other powerplants in their family. As an engineer, that is the best way to do it: make it what it needs to be. But to the enthusiast and those working on the project, it brings frustration that one would not find with a Chevrolet. Nonetheless, these are my thoughts but please don’t accept them as gospel, as many capable aftermarket companies provide these products today.
Ford recommends that the lifters be full of oil but that is often hard to accomplish unless you either remove the distributor or keep bumping the engine around with the starter.
Given your non-adjustable valvetrain, the pushrod length sets the preload. It is my professional opinion (and I may be mistaken) that you are suffering a stack-up of tolerances. During the valve job, the seats were cut which affected the installed height of the valve. If the valves were not renewed, the tips were ground square which affects the length. Also, I am quite sure that the replacement pushrods and lifters, though correct, are of different lengths (albeit minor) than the factory parts. With these factors combined, the preload and often the rocker geometry becomes skewed and, in your case, results in excessive clearance.
The prescribed Ford method is to obtain the proper length pushrod. I recall that Jeg’s and others sell shims to insert under the rocker shaft but, in theory, that would increases the clearance, and based on what you’ve said, it is already excessive.
I would talk to the machine shop that performed the valve job and hear what they suggest. Candidly, they should have made you aware of this potential problem and calculated the equation to provide you the correct pushrods or at least make a suggestion.
Engine building shops use an adjustable pushrod that determines the proper length with the twist method I describe. Then with the accurate measurement the parts are ordered.
You could also guess the length and purchase a pushrod that is 0.060in longer. Ford (the company) used to offer 0.060in longer and shorter pushrods to compensate the effects of machining operations.
I am sorry that I cannot offer more help and hope I have steered you in the proper direction.
Being a car guy and a farmer I wondered if your truck is a resto or a vehicle that is being used. When young, a country neighbor (about 2 miles away) also had a 1967 model with a 390, 4 WD, stamped steel wheels and skinny tires… nothing could stop that beast!
Please let me know what you find.
Have a blessed day,
Firstly, thank you for taking the time to publish your article. I found it very informative and it may have helped answer some of my questions regarding hydraulic flat tappets. I posted my questions recently on a forum but, so far, haven’t had any replies. So, I’d greatly appreciate if you could read through my notes below and offer any further insight?
I’m hoping to get some technical advice regarding hydraulic flat tappets. I have a Chrysler 318 engine with a Comp Cams CRS XE268H-10 utilizing their 867-16 Pro Magnum lifters. I’ve previously had a low-idle oil pressure issue with this engine and as a result had lifters ticking. Currently, the engine is removed from the car and have rectified the oil pressure issue. However, I’m hoping to get some further advice on the typical characteristics of automotive hydraulic lifters. My experience has been predominately in the aviation field where our hydraulic lifters remain constantly pumped up regardless of whether the engine is operating or not. As many would know, aircraft engines operate at a low and constant RPM, and I’m told the lifters in my 318 are of the anti-pump style for higher rpm ranges.
I have emailed Comp Cams with my tech question but have yet to hear from them. Basically what I would like to know is the following: Currently, I have the intake manifold removed and when rotating the oil pump with a drill, the lifters appear to pump up somewhat. However, the ones that are positioned with a valve open don’t appear to, or at least not fully. Also, some of the lifters seem to bleed down pretty quickly. Is this normal behavior when operating the oil pump with the drill?
I appreciate any advice or suggestions, and I thank you in advance.
Hi! Thanks for reading my article and reaching out to me. I will do my best to provide my opinion.
From what I gleaned from your letter, you are receiving oil to each lifter but some are responding differently than others.
Based on your description, I believe all is fine. I would be concerned with each lifter being fed oil and not necessarily how it receives the oil under the current conditions. Also, how did you set the preload? I would set it for zero lash (pushrod twist method) and maybe 1/2 turn based on the camshaft design. It does not surprise me that some lifters are bleeding down at a quicker rate and that those working against valve spring pressure are not filling to capacity. The speed and thus oil flow from the pump along with all of the other dynamics are skewed and, thus, the hydraulic response will not mimic a running engine.
I now have a question for you. How do the lifters stay pumped up with the engine off on an aviation design? I would assume that they must bleed down, over a period of time, and especially those with an open valve. If you could acquaint me with a resource, I would greatly appreciate it. Are they truly hydraulic lifters (on the aviation engine) or a solid lifter that has an oil cavity for cooling and as a conduit to the rest of the valvetrain?
I trust you will hear from CompCams. Please let me know what they tell you so that I can learn too.
Sorry I was not more help.
Ray Bohacz, http://www.farmmachinerydigest.com
Thanks for the article. I have a 1974 SBC 350 flat tappet, and I’m confused about how high the lifter should be outside of block and full of oil primed. Should the plunger be locked solid or should it be able to be depressed slowly to bottom of it’s travel? I ask because when I prime and install and then set pre-load (3/4 turn past 0 lash) all the valves are open because lifters are locked solid.
Thank you so much for reading my article. Please reach out to me at firstname.lastname@example.org so that I can try to help you with this issue.
I have a few questions such as are you setting the pre-load with the lifter on the base circle of the lobe? Are the lifters the same length as the ones you replaced? Are you using the pushrod twist method to determine zero lash?
Thanks so much, Ray
I needed to replace one of my exhaust valves (#5 due to low compression) on my Gen 1 Chevy 350 and am getting ready to re-install the head and perform a valve adjustment to both sides while I have the intake manifold off. I have hydraulic lifters with a Comp Extreme 262H cam (its more for torque improvement than high horsepower) with roller rockers. After researching the internet thoroughly, I found your article provides more clarity to how the hydraulic lifter works (thanks).
I am confused though if I need to drain my lifters in order to verify proper lash. It seems that I need to adjust each to where the valve piston is slightly compressed and does not come back into contact with the retaining wire at top of piston in lifter. Currently with all rods removed, the piston is at top of lifter and I cannot force the piston down by hand with a rod. I’ve also received conflicting info on once the free-play is removed from rod: some say to make a 1/4 tighten turn at rocker (so as prevent the valve from slightly being open) but most say to do 3/4 tighten turn.
If the piston and spring would compress when valve is fully closed and I could watch the movement in the lifter (both with valve open and closed) to verify and I could make a judgement as to the amount of preload I need (1/4 – 3/4).
Do I need to drain the oil from each lifter (disassemble them) or should I just insure the proper free-play and make the pre-load by 1/4, 1/2, or 3/4 turn, then let the engine do its job by loading each lifter as you described in your article.
Any advice would be helpful.
Thank you for reading my article and for reaching out to me.
I would not over think the adjustment procedure. I would get the lifter on the base circle and do not be concerned with it having oil in it. With a hydraulic lifter you are setting preload and not lash, so to a certain extent it will not be very sensitive.
I would use the “twist the pushrod between your fingers” method and set the preload at 1/2 turn and if possible, run the engine and see how it sounds and if it is happy. The theory being that most engines with even a slightly more aggressive than stock cam, historically do not like the higher end of the preload index. If the lifters are noisy, then go to 3/4 turn.
If the application does not lend itself to pulling the rocker covers off once it is back together, then I would go for around 3/4 turn or just under and let it rip.
Please make sure that the rocker geometry is correct by watching the orientation of the roller on the tip of the valve stem after you adjust the preload and before you close it up. My concern is more toward geometry, especially if the engine has been apart. There are some excellent videos that go over checking the geometry since it does not lend itself to a written explanation.
I wish you the best and if I can be of any more help, please do not hesitate to reach out to me.
Ray… the Hot Rod Farmer!!
I realize your article is over three years old but I think it is the best one I have found anywhere.
I have a problem with my GMC 5.3 L truck engine which started with two failed AFM/DOD lifters. My issue involves the replacement lifters (I did replace all 16) the new lifters when compared to the new ones appeared to be about 0.125 inches longer than the original ones and I attempted to adjust preload to this only to find that the rocker arm studs could not be torqued to GM Spec of 22 Ft lbs. When I attempted to start the engine I found that when cold the engine misfires on multiple cylinders until it warms up. I refuse to drive it due to this but am at my wit’s end when it comes to what to do next.
The truck has good vacuum readings, compression, and everything else looks alright when monitoring live data with my scan tool but the engine runs extremely rough at idle if I bump the rpm from 600 to about 750 the engine runs real smooth. I am wondering at this point if the lifter length could be my problem as this is the only thing left I have not condemned other than the PCM. I am not sure if I can obtain shorter push rods to allow for the difference in lifter length.
Any suggestions would be appreciated.
Thank you for your kind words regarding my article.
This is not an easy matter to diagnose. You make valid data points regarding the lifter length being 0.125 inches longer than the original and the engine running poorly until it warms. However, the longer lifter may not be the cause. If the engine has developed a vacuum leak, it presents the possibility of poor running until the fuel control circuit goes into closed loop. Then it would have some authority to add fuel to compensate for a vacuum leak. On your scanner you should examine the fuel trim to ascertain if it is adding injector pulse width.
You make no mention if the valve train is noisy when the engine is cold or even when it is warm. Did you buy GM lifters or aftermarket ones? You need to determine why the lifter is longer. Does the extra length affect the distance from the plunger to the top of the pushrod? If it is just the longer body causing the plunger to be more recessed within, then it should have no effect.
How did the engine run before the lifters failed? I assume it was fine.
I am uncertain as to why the rocker studs could not be torqued to specification. Is it because of the lifter length and its interaction with the pushrod?
Based on that, it appears that even if the engine ran fine there is a concern with the rocker arm stud.
This is what I would do: determine why the lifter is longer by asking your supplier. If it is wrong, then get the proper length lifter and that should take care of the rocker stud issue, or so I believe. I would also search for a vacuum leak. A smoke tester is the best tool for this. Here’s an excellent article on finding/preventing vacuum leaks: https://torqstorm.com/detecting-boost-leaks-capturing-horsepower-you-lost-or-perhaps-never-had/
Acquiring shorter pushrods is straightforward, as custom-length pushrods are readily available but should not be required for an engine that is being repaired.
Yours is the hallmark of a vacuum leak on an engine with fuel injection. If it were lifter geometry it would not correct itself.
If I can be of more help don’t hesitate to ask, and also please let me know your findings.
All the best, Ray
I will be installing a hydraulic roller cam into my engine and need to verify adequate piston to valve clearance since not only is the cam being changed but so are the rockers and heads. Most cam manufacturers recommend using a solid lifter to perform this task. Must I purchase a single solid roller lifter from the cam manufacturer or is there a way I can utilize one of the new hydraulic roller lifters as I check this clearance?
Since yours sounds like a street/strip engine you can make this easy. Take the lobe lift of the cam and multiple it by the rocker ratio for total valve lift. For example, if the lobe lift is 0.350-inch and the rocker is a 1.6 ratio, the total valve lift is 0.560-inch. Install a valve checking spring on both the intake and exhaust valves along with a dial indicator with the tip on the valve retainer. You do not need to have a lifter in place. Bring the engine up to TDC, then with your finger open the valve until it hits the piston crown or runs out of travel. Read the dial indicator. Let’s say the dial indicator reads 0.760-inch and you ran out of valve travel and did not hit the piston crown. Then you have more than 0.200-inch clearance. If the valve touches the piston crown, that reading is your interference point, so anything less than that is your clearance. The exhaust valve chases the piston so there is not much worry there but check it anyway. This is a quick, easy, and accurate method to determine that you will not have an interference issue.
I have a general question regarding hydraulic lifters. I have an aircraft engine (a Lycoming 0-360) in my airboat in which I am replacing one cylinder. The manufacturer states if lifter was in contact with a magnet it must be replaced. Unfortunately, when placing the lifter on the workbench it was magnetized by a magnetic flashlight base. My question is, have you ever heard of a hydraulic lifter failing from magnetization? And secondly, if I demagnetize the lifter, wouldn’t it negate the manufacturer’s warning.
This is a partially educated response to your question.
I would not worry about it at all since the engine is in an air boat. FAA rules are quite strict and often go to an extreme, which I respect, understand, and appreciate. It is my belief that the FAA is concerned about the potential of an attraction between the lifter and some other part such as the block, pushrod, or camshaft. If this were to occur, depending on the point of magnetic attraction there is the potential for a catastrophic failure. Though I believe the possibility is extremely rare, but when one is in the air, safe is better than sorry. The truth be told, I never checked for any magnetic attraction of any engine part during my career. If you learn more on this subject, please let me know so that I can be enlightened.
I have a 1956 Cadillac Coupe Deville with a 365 engine. It has just been completely rebuilt due to a collapsed lifter on the #4 cylinder. Yet, it has developed an intermittent lifter noise that appears to be coming from #2 cylinder. I’ve checked that the oil level is correct and the oil pressure is to spec. Alas, I’ve not been able to test the lifter when noise occurs, as it is audible only for a limited time. However, there is no evidence of a lifter problem when I have checked them when there is no noise. I’ve driven a total of 250 miles over 3 trips with no noise and then on another trip it occurred after 35 miles. One possibility is that the 250-mile journey had been driven at varying speeds and of the 35-mile trip, the latter 20 miles were traveled at a more constant speed and load–between 55 and 60mph. The new lifters installed are Johnson brand. Supposedly, they are most reliable. Do you have any suggestions please?
Thank you for reading my article. I have a number of thoughts which I will condense and share with you.
From your note, I have gleaned that the engine has run fewer than 300 miles. Thus, I would not be too critical of a powerplant that is 67 years old. In contrast, you may have been expecting more from your recently rebuilt engine… well that would be a broad and inconclusive statement that requires qualifying. For example, were the dimensions of the lifter bores checked versus the dimensions of the new lifters, as the noise, which I assume is a tapping sound, comes and goes intermittently? At this juncture, I would give the engine a chance to break-in and for the new lifter to break-in. Also, what oil are you using in the engine?
From experience, I could assess a litany of possibilities, but, first, drive the car and accumulate some miles. Renew the oil and filter and, if you like, have an oil analysis conducted and proceed from there. If the problem persists with 1,500 to 2,000 miles on the Caddy, then please reach out to me via this website, and I will lead you into some diagnostic steps. However, I suspect it will heal itself over time.
Have a blessed day, Ray.