nicolas-eric

Hello.

We have a problem with a 5.2L ZJ.
When the engine is cold it runs ok.
But after a few minutes when it becomes warm the oil pressure goes down and the engine has a knocking sound.
We thought it could be the oil pump and installed a new one. But the problem is still there.
The ignition works.

Now I need your help.
What could cause this knocking?
Perhaps a broken bearing?

Here's a video:

Thanks for your help!
Nicolas-Eric

Bustedback

That is a rod knock caused bt a spun or worn out connecting rod bearing. Time for a rebuild my friend. The oil pump does not make oil pressure, it only makes flow. The tight clearences between the bearings is what makes oil pressure. The more clearence between the bearings the less oil pressure you will have. Excessive clearence is what causes the knocking sound, that sound is actually the connecting rod banging into the crank, not good for either part. Keep running it and the big end of the rod will get pounded into an egg shape until the rod bolts can't handle the stress anymore and will break and cause the rod to escape through the side of the block.

The87XJ

what he said above me. i freaking love you. LOL.. now i know more about oil pressure ! thanks!~

lngliv3

Bummer ....

nicolas-eric

Thanx for your detailed answer!

Can a worn out connecting rod bearing cause the low oil pressure?
Or are there some other worn out bearings?

How hard is it to replace these bearings?
A friend could do that.
But is it worth the money and time?
Or should I better buy a used engine and replace the complete engine?

Bustedback

Worn out bearings is the main cause of low oil pressure. You should have a machine shop lok at the crank and rods to see if they could be resized and polished and then replace the bearings. It does require some specaility measuring tools in order to get the clearences to the correct spec. Just replacing the bearings won't fix the problem. It would be more cost effective to replace the engine with a used one from a reputable auto recycler. Money wise for a used engine could be between 300 to 800 bucks. Having yours rebuilt would be a minumum of $1500 because of the machining that would be needed, if you needed a crank or rods the price would only go up. A new crate engine would be close to 3000 bucks for the engine and then you have labor to install it if you didn't do it yourself. The Pick-n-Pull in my area charges $600 for an engine that has been pulled and $150 for an engine if you pull it yourself. I want to pull an engine and then freshen it up with new rings, bearings and seals and then just swap it in over a weekend. The actual pulling the old out and installing the new is not too hard as long as you have the proper tools and take your time.