Engine noise video (tapping starts at around 17 seconds)

My 1997 XK8 developed a tapping noise when cold started after a few days of rest, which only occurs at mid-level RPMs...not at idle and not past about 2,000. After about 5 minutes of warm up, it tends to go away, but can be heard in mid-range RPMs if you're under the hood and flipping the throttle. The car has about 67,000 miles, had the upper timing chain tensioners replaced in 2011 (about 10,000 miles ago), and these were observed by a mechanic who changed the valve cover gaskets several months before the noise appeared. He reported that they were OK in appearance. He did note a lot of carbon buildup, cleaned the fuel system and recommended fuel cleaning additives in the gas for the next several tanks.

I then thought that it might be VVT related, but from what I've read, VVT tends to exhibit noise at idle. With my regular mechanic stumped, I took the car to a Jag specialty shop, and the mechanic there said he'd not experienced a noise like this either. He suggested that the only way to diagnose it was a frontal lobotomy on the engine to inspect the timing chains and all tensioners, plus possible VVT at a price range of $2,500-$4,000 depending on what's found. For a car that is street valued at around $10k, that was a non-starter for me...better to just drive it and assume the risk of engine failure and parting the car out to recoup some of the loss if it goes.

I also noticed that the car was burning about a quart of oil every 500 miles (no visible smoke though) and displayed low oil pressure if it isn't warmed up for at least 5 minutes after a cold start before driving. After being driven, no issues with oil pressure later in the day on subsequent starts. That leads me away from thinking that it's a clogged pickup tube screen or a failing oil pump.

Then, a car enthusiast friend suggested that I try an using engine oil flush to get rid of carbon buildup and refilling with specialty oil and supplements. He recommended Liqui Moly products, and I decided to give it a try since I felt like I had nothing to lose. I contacted Liqui Moly's technical support representative in the U.S. to ask for their recommendation, and after describing the symptoms, he suggested that I try the following (which I did): Liqui Moly engine flush in the oil, idled for 10 minutes and drained. Replaced with Liqui Moly 5W-40 (I know it's beyond factory spec, but it's what the Liqui Moly rep recommended for this car at this mileage), added Liqui Moly Ceratek (which is supposed to smooth worn engine surfaces after a few hundred miles by adhering to the surfaces) and Liqui Moly Motor Oil Saver (which is supposed to recondition seals to reduce oil consumption). I also installed a Jaguar brand EAZ1354 oil filter to replace a Bosch 72209WS filter that was on the car. The Bosch is specified for this car, but it is about an inch shorter vs. the Jaguar brand filter.

Since changing the oil, I have not noticed any issues with the noise, and on the contrary, the engine is quieter than before and idles smoothly. I've done nothing else to the car, so I can only attribute the change to what I did with the oil. I'm guessing that the engine flush may have made a lot of difference since the my trips tend to be about 20 minutes long, although partly at highway speed, and the car is not driven frequently. My purpose in posting is two-fold. First, to attach a video of the noise to see if others might have experienced something similar and identified the source, and second, to suggest that the oil change procedure that I followed might be helpful to others who find themselves in a similar situation. I'm certainly not intending to post an ad for Liqui Moly products, but that's what was recommended to me. And, it seems to have worked.

 

interesting, perhaps an oil passage or the VVT actuator screens were plugged with gunk and you flushed it out. now would be the time to simply change just the oil filter as it probably caught a lot of material early on. moly is a very good lubricant and most high end oils have a lot of it. it essentially replaces zinc. 5w-40 is not really out of line. it is the final step up in the oil recommendations after 0w-40 which i use. given that you are in a warm climate, it is probably perfect.

most people do not realize that thick oils are not good and cause VVT noise. perhaps a previous owner was using something too heavy or worse waited too long between changes.

it is not a difficult job to do the lower guides. if you are handy and have a place to patiently work, it will extend the lifetime of the engine greatly.

 

Thought that I'd post an update on my engine noise issue and the oil change that seemingly solved it. On the plus side, the engine runs smoother, I don't smell any burning oil in the exhaust, and the "Liqui Molly Motor Oil Saver" works extremely well. I went from burning a quart every 500 miles to absolutely no loss of oil anymore. On the minus side, the noise that I had still occurs occasionally when the engine is cold and rev'd above idle. After a minute or two of warm-up at idle, the problem goes away, so I just never start driving the car until it warms up for a few minutes.

 

These are Classic signs of out of tolerance at the engine tappets esp. as noise disappears when engine warms up.

On my previous 1972 Triumph GT6, I had a threaded adjustment at the valve tip and different thicknesses spacers.

Theoretical Question - Is that adjustment possible on the AJ V8?

 

unfortunately, no.

 

I had a mechanic speculate that it might be a primary tensioner that is sticking until the oil/engine warms up, but that's just speculation. I'm not one who would undertake removing the front of the engine from a car by without "adult" supervision, so looking at "exploratory surgery" on my engine at a cost of $2,500, which is the quote that I received, with no reasonably guarantee that the issue would be fixed, I've opted to just live with it and be sure to let the car warm up before driving it. True, I might be risking a blown engine, but the car is only worth $10k at this point, and $2,500 on exploratory surgery vs. taking the risk seems too pricey vs. living with it.

 

I disagree. I would do the exploratory surgery myself if money is an issue, but I would not live with that noise.

 

IMO the noise is a rattle not slack tappet: more like loose chain(s).
Low oil pressure possibly plastic detritus in the pump strainer? Mileage isn't high but she's 22 years old and I'm thinking primary chain slippers/tensioners.

Like giandaniel, I'd want to know what's going on in there. -10k + 2.5k = -7.5K I don't follow if the car is otherwise sound.

 

Hi Onfire, if you haven’t addressed the issue I would also recommend getting your hands dirty. There are plenty of resources available, the most recent ones I found give a very detailed step by step video guide of the process. My car has exactly the same symptoms, both cold start chain scratch and the tapping. In 2 weeks I’m starting the job and can post some updates if you’re interested.

 

https://www.jaguarforums.com/forum/x...ioners-214569/

I did the primary and secondary timing chains, guides, and tensioners about a year and a half ago and this is my story.
If you decide to dive into this I hope it helps.
I explained every challenge I came across and how I resolved it so that nobody else has to go down the dead ends.

 

On a Porsche 928 (35yo) it was suggested by a fellow Porsche and Jag XJS owner told that oils high in ZINC content (one of the ingredients in Liquid Moly) AND intentionally overheating the engine (in a semi controlled way) would one, create a smoother run condition on a tappet valved engine AND two, to liquify the sludge built up in the tappet and hydrolic lifters themsleves which would cure tapping. Low and behold it worked...

Because of the inaccuracies of the temp gauge in the xk8/r the intentional over heating scares the BeeJesus out of me but I think I might be willing to give it a try - maybe.

 

intentionally overheating the engine is a marvelous way to take a possible minor irritating issue and make it into a full fledged unmitigated disaster.

Z

 

Hmm, lol. Ok. Can't say it's not scary...

It's not an uncommon practice for people who work on cars. Especially older cars and especially with the hydraulic style lifters, 32 of them, in the case of the 928. A million nooks and crannies.... Remove some of the oil, replace with a marvel mystery, even diesel or kerosene, cycle the engine thru 3, 4 or 5 "controlled" heatings or high heatings simply using a piece of cardboard over the rad and you wouldn't believe what pours out of the plug when you change the oil... Takes and hour. Anyways, lol, I didn't make it up. I did it and it works... Maybe intentional "overheating" was the wrong choice of words...?

Full Fledged Unmitigated Disaster, hahaha...
Sounds like a modern news broadcast.