Always has to be something.
Now that the XK8 is back from the dead it has a new problem. Or maybe one it had all along but just turned up now because its cold. This is the first winter I've had this car. The car has sat for more than 2 weeks while I was dealing with the ECU issue. Since then it has gotten *** numbing cold.
The new problem is as follows:
If it is around 20F or less and the car has been sitting over night in even colder temps and the engine is started you get between 3-5 fairly loud "clacking" sounds from the engine right after it starts and then it goes completely away and will not do it again unless it sits overnight and is started at 20F or less again. If its warmer out in the morning no noises. Never does it again on subsequent starts all day either.
It only does it for a few seconds at most so no time to get out of car and listen for its exact location. I've never owned this car when its been this cold so no way to know if its always done this or not. I listened to some youtube videos of timing chain rattle and its nothing like that sound at all. Sounds more like a large solenoid clicking fairly loud.
Any ideas?



Dave

 

First guess is that it is oil pressure related. Are you sure that you have a filter that has a back flow valve to prevent oil from draining back into the slump? It takes 1-2 seconds for pressure to get up even with the valve, 10 or more without it. I had installed one of the 'free' with oil purchase filter without the valve and it didn't take but two of the 10 second episodes to jerk that thing out to replace with a proper filter.

Of course, temperatures like we are experiencing aggravate oil pressure issues.

 

Yes I made sure I used a filter with a back flow valve. I put that and Mobil One in it just a few hundred miles ago. I know the oil pressure gauge is useless but the oil light goes out and the gauge goes to its "on" position right away.
Its definitely a problem being brought out by the cold temps. For all I know it could have been doing this for years but this is the first winter I've had it. The car came from an even colder part of the country so I bet this is a long standing problem.
The noise doesn't happen at all when its cranking. It starts doing it the instant it starts but only makes the noise 3-5 times and never does it again until it gets cold soaked overnight again and the temps are 20ish or less.


Dave

 

Startups for me are always a little noisier when it manages to get really cold. Not a clacking, but you are more aware of the mechanical bits moving. Not loud enough to be concerning.

And I use the correct filters, but I do use 5-30w oil, which is thin at freezing temps.

 

Agreed. I think you're hearing typical cold weather-related start-up noises. Just wait until Thursday/Friday when temps are predicted to drop to zero or below. You may need earplugs to start your car....

 

Its a worrisome noise as its almost like a rod knock except its not like a deep from the engine thud, more like a clank. Just 3-5 clanks like someone is tapping the engine with a wrench and then its quiet the rest of the day no matter how many times its started again. And its all over in a couple of seconds so no way to get out fast enough to trace exactly where its coming from.
There is also a "whirring" sound from the front of the engine when iys cold but it goes away as it warms up.
Supposed to get MINUS 7F Thursday night. I'm more worried about the pipes breaking in my house at this point.


Dave

 

Dave, not related to your knocking but you are worried and rightly so about the pipes freezing. Lived in Danville many years and I known the housing is not built for that, so we have the same issue here with our house that is up for sale. Cut the water off at the street and open all taps, go to the lowest tap, generally outside and drain the system. Put enough water in some containers to flush the toilets and have coffee for a couple of days and this extreme to us, temperatures should end. I wouldn't worry to much about getting a lot of company, so full showers aren't needed, unless the lady friend is coming over to keep you warm.


Wayne

 

Already planned on doing all that. About a month ago when it got down to 9F several neighbors had broken pipes. I'd shut mine off at the curb that night and had no broken pipes.


Dave

 

Started the car this morning when it was about 32F and nice normal startup with no funny noises. This Jag only complains when its 20 ish or less.


Dave

 

Have a buddy crank the engine next time when it is cold, while you carefully observe the BELT tensioner (a flashlight might come in handy here). If it jumps back and forth with the 'thuds' you found the problem. It is usually due to wear and thickening of the grease in one or both of the idler pulley bearings.

If so, the pulleys can be replaced for around 15-$20 each aftermarket, or you can just ignore it.

 

I was thinking along those lines also but it doesn't do it when its just cranking. The noise appears as soon as the engines fires. Unless it needs higher rpms than the starter provides before it starts bouncing around.

Dave

 

When I have seen it, it was right after starting, not cranking, so it is probably rpm related.

 

I'll check it out. Hard part is I live alone so no one around on a cold morning to start it for me while I watch the belt tensioner.


Dave

 

Could also be a cam phaser or a chain tensioner.

 

Variable Valve Timing?

https://www.jaguarforums.com/forum/x...lenoids-26827/

 

The BELT tensioner noise is easily found or eliminated as a potential cause with a simple visual check. This is why I suggested this first.

 

I listened to several youtube videos of tensioner noises and they were all more like rattles that sounded like chains hitting things. This noise is more crisp and louder like a wrench being tapped on the engine. Not thud-ish like a rod knock.
Also I would think if a tensioner was bad enough to make a noise that loud cold it would be making noises at other times.
I thought of the VVT also but didn't think it could be so loud but maybe when its that cold it could be if its sticking at first.
Its going to be hard for me to troubleshoot this as I don't have anyone to help me and it only does it on very cold mornings and only for a few seconds at engine fire up. Not enough time to get out and trace the sound.
Dave

 

Dave, I bet that sucker would have rattled this morning. You stay in the warm, it will warm up in a couple of days.
No broken pipes I hope.


Wayne

 

Fortunately I don't have to go anywhere today. Its still -4 windchill and 10F out. The cats want out but no way. No frozen pipes as yet but its supposed to be even colder tonight. At least its warming up some this weekend. One thing that makes it worse is my downstairs furnace ductwork is messed up and the only way to fix it is to tear up the wood floor in the hallway. So no heat to the 2 bathrooms at that end. Have space heaters there now, Not looking forward to that.

The sound it makes is crisp like it isn't being muffled by coming from inside the engine so my bet is the belt tensioner.
There is also definitely a chain noise at startup when its cold like a whirring sound of the chain links traveling until they get enough oil and it goes away. Its not a rattle like the youtube video noises.
Otherwise the car has been acting perfectly normal since the ECU fix. No more errors or codes. Engine sounds normal when warmed. Heater even works once it has time for the coolant to warm up.

Dave