Hello All,
I have a 1997 Jaguar XK8. The engine has been gone through and the main bearings were plastigaged and within spec. The car runs fine but after it gets up to operating temp when I stop the oil pressure goes to the red zone and when I give it throttle it comes right back up. It only does it when it is warmed up. Any ideas.
Thanks,
Jay111

 

drain the oil, drop the oil pan and check the sump - may have a clog similar to what I experienced

https://www.jaguarforums.com/forum/x...s-sump-184905/

 

This might be because I had a problem with mine (not a 97 but an 04, different looking pick up) and it's my go to answer,,, but try dropping the pan and having a look at the pickup in the sump pan. They can and do get gummed up. Also, of the PO had issues with cracking and deteriorating plastic bits in the chain guide and tensioner set up, those little bits and pieces could still be in the pan and causing grief - again, the pickup. Have you laid eyes in it?

 

Besides possible sludge at the pickup, there are lots of places in the engine where oil pressure can drop: cam bearings, variable cam timing valves, cam chain tensioners, rod bearings. Any of these could be a little loose and dropping oil pressure as well.

 

As the oil pressure sensor is just a simple on/off switch, you might want to try changing the sensor.

 

Have you changed the oil pressure sensor ..cheap and quick but if that does not cure it take the sump off ...
Use thicker oil ?? If they have checked the bearings they must have had the sump off so any debris would have been cleaned out ......
Sorry Typed this while dibbit was typing .....

 

OK so I replaced the oil pressure sending unit and if anything it got worse! The main bearings were plastigaged when it was apart and were within spec.
So what is the most likely culprit? This car is driving me crazy!
Jay111

 

Did you check the pickup screen for clogging debris as suggested ?


Z

 

he rebuilt this engine with the bedplate out of course the oil pan pickup is going to be clean. hook up a mechanical gauge to the oil pressure switch i forgot the size but it's pretty uncommon.

also a plastigage is not the most accurate tool in the world.

 

TSB info for you. (I wish people would download and read ALL TSBs for their cars!)

 

I know it was clean then, but is it still clean ? As mentioned previously, there are many plain bearings besides the mains that could be the issue, Bur before tearing the engine down I’d first install a permanent oil pressure gauge (sorry if I missed that it has already been done). Then examine the pickup and the pump too.

Z

PS: oil pressure issues right after a rebuild do not speak well of the rebuilding processes. Errors can be made that will impact oil pressure.

 

Sounds like the rebuild didn't go well and something is broken.

 

If it was apart why did they not change all the shells? And why was it taken down to start with?
You mention the crank but what about the big ends?
Why not just change the oil for 20-50 and see what you have ? If that puts it right sell it.
proper oil pressure gauge of course.

 

Reason for rebuild was old engine dropped two valves went through piston. Block, head, and two pistons replaced. Stupidly didn't replace oil pump but it seemed OK ( no grinding, or bad spots when turning). All the bearings looked fine and were plastigaged and within spec, crank journals were cleaned and polished.all tensioners and chains were replaced, everything was cleaned before reassembly. Car ran fine, no noises or issues, now this. Also I may not be a certified Jaguar mechanic but I do know my way around engines and I think most people come on here for help and assistance, not to be criticized for their work.
Jay111

 

Hey, Man. When you say worse what do you mean exactly?

 

Now we know why and what I still say put some 20/50 in it and see what happens.

 

I think you are taking suggestions that mistakes might have been made in the rebuild the wrong way.

You yourself say “….Stupidly didn't replace oil pump….” , your words, not mine.

so if it’s pointed out that mistakes may have been made, it’s only the same thing you are considering as well.

No one on the forum has eyes on the car. We are just throwing out ideas. Good and bad, on target or off.

I’ve been rebuilding engines and restoring 2 & 4 wheeled vehicles for 55+ years. And I’m not above making mistakes. It can happen, and no reason to be thin skinned about being human.

Not saying it’s guaranteed that the current issues are the results of the rebuilding process. But if they turn out to be, so what ? No one should expect perfection from others or themselves.

Z

 

Before oil pressure reading was fine until engine warmed up, then oil pressure reading would drop at every stop but came back as soon as I accelerated, now when engine gets to operating temp the pressure bounces down when I slow down and drops completely when I stop but comes back under acceleration.
Jay111

 

Are you sure the pressure releif valve is shut? If it's open at idle you will loose all the oil to the sump.

 

Not sure. How do you check?
Jay111