MattGibson1

Hey guys,

Ok, '89 305 TPI. Always held 30lbs for the past 2 years. Lately has been racing between 25ish to 30lbs very erratically. At low speeds and in park sometimes dips to 15lbs, and today when I pulled into the driveway it dropped very low and and the whole car vibrated very hard, but I didn't hear and metal on metal. Has plenty of oil, changed it last weekend. Car has had a SLIGHT tick for awhile, but only when cold. Once it warms up it sounds fine. I was thinking a bad oil pump but I've read/heard they rarely go out. So maybe a oil pressure sending unit? Any help would be GREATLY APPRECIATED. Thanks.

AlkyIROC

When a pump fails, it will usually completely fail. There's always a possibility that the pickup tube screen is partially plugged (silicone etc that got into the pan) or the tube is sucking air (cracked/loose).

The first thing you need to do is put a mechanical gauge on the engine. Sending units fail regularly.

You could still have an internal problem. The best way to tell is by cutting open the oil filter, cut a chunk of filter material out of it and squish it in a vise to squeeze out the oil. Then open up the material and look for metal.

There's always a possibility of a main bearing or cam bearing failure. Neither will cause any noise until the engine seizes up. Finding lots of metal in the oil filter is your first indication that something is wrong inside and a teardown is required to pinpoint the problem.

Without confirming actual oil pressure with a mechanical gauge, you're only guessing that something is wrong. If the mechanical matches the dash gauge then cut open the oil filter. If you don't have the old one, buy another new one.

MattGibson1

Ok thanks a lot. When I changed the filter last week I looked at it pretty good and didn't see anything. And is a mechanical gauge install hard? Any links?

MattGibson1

Also it drives completely fine, so I feel like there can't be a serious problem.

AlkyIROC

Bad cam bearings will drive fine, won't make any noise but will allow the pressure to drop when the oil is hot. Bad main bearings usually don't last very long before they overheat and seize up the engine. Only bad rod bearings will cause noise.

Like I said, you need to cut open the filter and squeeze the oil out of some material to do a proper examination. Very large metal flakes can be easy to see but the smaller stuff can't be seen if the material is full of oil.

To install a mechanical gauge, you only need to plumb it into an oil gallery port. Spare port near the filter housing, oil pressure sender port etc. It doesn't need to be a permanent installation. You just need to compare it to what the gauge on the dash is reading to see if it's accurate or not.

JunJun

A failure of an oil pressure sending unit is very common.
So replace it first.

MattGibson1

I'll definitely replace that. Is it hard to replace? Do I need any special tools?

86LG4Bird

iTrader: (1)

I think you've transposed cause and effect here. My guess: you have a tune-up issue causing your idle to fluctuate, which in turn causes the oil pressure fluctuation.