Jeep TJ vacuum problem

Here's the problem, my son flooded his Jeep in water. He drain oil and dried out everything, did 3 oil changes and now there is a vacuum when he open the oil cap. You can ear a lot of air being sucked thru the hole. What can it be? No unusual noise from engine. He pulled out the oil pump and he can turn it by hand, no debris was found in the pump. His friend has the same Jeep and no vacuum when he open oil cap.

Thanks.

check the pcv valve

My son changed the pcv valve, no changes. What's next? A lot of people are telling him the oil pump might be defect, how do we test? We can't see oil coming up when motor is hot by opening oil cap and pressure gage shows low pressure. No codes nor engine light.

Is this the 4 liter 6 cylinder engine? As I recall, these engines do not have a PCV valve.... they have a metered orifice in the vacuum line. This orifice is actually just a restriction in the vacuum line.

If this restricted piece is missing, or the vacuum lines were incorrectly installed after drying-out the engine, then the engine is sucking far too much vacuum out of the crankcase.

This problem could be made worse by a blocked vent pipe that runs from the engine to the air cleaner.

Also, I am quite certain the oil pump has nothing to do with this problem.

It's the 4 liter I6 engine. Is the PCV valve located on top of valve cover? That piece is 90° shape and is connected between valve cover and vent pipe with flexible hose. If it's not the PCV, where is it? Vent pipe is not clogged we checked that. He didn't removed anything while drying out except oil pan. Thanks for help.

It's the 4 liter I6 engine. Is the PCV valve located on top of valve cover? That piece is 90° shape and is connected between valve cover and vent pipe with flexible hose.

That should be it. As mentioned before, the PCV pipe does not have a valve, just a restriction in the hose.

When the engine is running, remove this pipe. It should be sucking a small amount of vacuum through it.

When removed, are you getting a vacuum-sucking effect coming from the hole in the valve cover?

If yes, and if you are sure the vacuum lines are hooked up right, you may have internal engine damage.

If the Jeep was driven into deep water, then sometimes water is sucked through the air intake, past the filter and into a cylinder . Since water does not compress, the water stops the piston from going up all the way in the piston. It stops dead. When this happens, there is a momentary tremendous amount of pressure in that cylinder..... which bends connecting rods, breaks pistons, etc.

It does not take much water, either. About 50 or 60 ml is all thats needed at one time to do this

A compression test might tell you if one piston is cracked or broken.

http://autorepair.about.com/od/enginetroubleshootin1/ss/compress_test.htm

We do have suction while PCV valve is removed from valve cover. What's annoying is that the motor runs smooth, no clanking noise or whatsoever. I'll do a compression test and let you know the results shortly. I'll double check vacuum lines again to make sure they're connected right. BTW, he use 10w30 oil, is this ok? I know that using thicker oil is a temporary fix but which grade of oil is recommended?
Thanks for the info.

there's 2 vaccum lines on the top of the valve cover the 1st one near the rad fan goes to the left of the air filter box and the 2nd one goes beside the brake booster vaccum line

All lines are cleaned and connected. Jeep is at our local mecanic for investigation.
Chances are crankshaft seals.
Merci et bonne soirée Nova73noir.

hope its not too bad!!
bonne chance!

Update,

After a huge and expensive investigation, results are bad.
Crank kit
Rear main seal
Pilot bearing
Associated gaskets
Etc.

Over 1000.00 for repair, next time, think twice before getting off road.
Now my son will add the snorkel kit, LOL too late...