Engine knocking oil pressure flutter

[tripletdaddy]

I have a 95 Ford Windstar with a 3.8l engine with 140k miles on it. To be brief, the engine oil got gas in it. The oil light came on, it died, and it wouldn't crank. It may have actually vapor locked, but I wanted to play it safe and towed it home. Changed the oil and filter. It now has a loud knock. When I first started it on and off real quick several times as I was concerned how bad it was, it wasn't noisy. I then took it for a drive. When I went over 2500 rpm, the knocking sound became apparent. Since then, with every start up, any revving of the engine, and sustained engine speed much above idle causes the sound. I think it can be heard faintly either real close to the intake or with a listening "tool." The sound does seem to be from deep within the engine. I measured its oil pressure, a real PITA to do on this engine. At start up its 70 psi, then with warm up settles around 55 to 60 psi. When I increase the rpm, it will max out at 70 to 75 psi. The pressures are great, but the idle pressure flutters or fluctuates rapidly by maybe 5 psi, seen as a very fast moving or vibrating gauge needle. Unfortunately, I was only able to put on a 300 psi gauge instead of a 100 psi one, so I was not able to see with more detail the needle movement.

Anyway, I'd be interested in what you folks think what's going on and what I will need to do, etc., etc.

Thanks in advance.

[MagicRat]

I think you have 2 problems.
First of all, 70-75 psi of pressure is a little high, assuming your gauge is accurate. The oil pressure relief valve may be stuck closed.
Usually, the valve opens to bleed-off excess pressure, so it is limited to 35-45 psi, regardless of engine revs. . Also, pressure 'flutter' (at pressures that high) is usually never observed, again because excess pressure is bled off, which serves to moderate such fluctuations.

High oil pressure puts excess stress on the oil pump drive mechanism and may cause your oil filter to rupture.

As for the gas in the oil... people have used gas, diesel, kerosene etc to clean-up sludge deposits inside an engine, so I wonder if a bit of sludge has broken free, got sucked up by the oil pump and has jammed the pressure relief valve??

Also, gas in oil obviously thins the oil and can easily cause metal-to-metal contact in the crankshaft bearings, causing damage.

At the very least, consider dropping the oil pan and removing all bearing caps. Inspect the bearings for wear, damage etc. If the damage is moderate, the crankshaft could be machined and all-new, undersized bearings installed. If you are lucky, the engine does not need to be removed to do this job.

It sounds like the damage is not too severe right now. Badly-damaged bearings tend to "spin", that is, the bearing shells are overheated so much they weld themselves to the crankshaft journal and start to spin in the bearing saddles. This means the bearing saddles and caps need to be re-sized before installation... which is a major machine-shop job and requires engine removal from the vehicle.

Finally, replace the oil pump too.

[534BC]

You probably have a couple of spun mains and thus a couple of rod bearings worn or spun. I would guess hat it is the two closest to the oil pump and are turned to plug the oil hole. It will need rebuilt or replaced.