Low idle oil pressure (gauge sits on zero)

[Ye'OleAstrologist]

I am fighting a steadily declining oil pressure issue with my van now. I am suspecting the electric gauge, but I wanted to send a feeler out first.

On start up. Oil pressure pegs the gauge all the way past 80 psi... at idle. Using 10w30 Mobil 1 synthetic. Driving along cold/warm/hot oil pressure stays pegged. Always has, always did until now. In the past few weeks the oil pressure has steadily declined when hot (after driving 25~ miles) and continues to drop the further you drive until it reads 35psi driving and dead zero at idle. Pull over.. pop the oil fill off, no blowby, but if you pull the dipstick, the oil is incredibly hot (in my opinion anyway) I know the dipstick runs right by the pass. side header, but still.

Normally the OP would drop to 35 psi at idle when hot, but it has steadily declined over the past three-4 weeks to the point it's dead on zero.


So, I thought "you know what, the oil cooler must be clogged" But I don't see any evidence of one on the van. Maybe I'm not looking in the right spot or something. I don't know. So ruling out that there is or is not an oil cooler, could I have something coming apart in the motor... like cam bearings, etc? I am hoping it's a problem with the two oil pressure sending units, and when I get some money I'll toss a sending unit at it, but I figured someone here must have ran into this problem at some point...

Thanks, Brian

[Matrixx]

What year is the van, and how many miles on the motor?

Has the engine ever been over heated at anytime?

Thanks.

['cudapaul]

I think that you may have a misbehaving sending unit and I would change that first before tearing into the engine.
You may want to do that right away to rule out mechanical problems in the engine.

[Big_kid]

I'd put a test gauge on it before spending $ on a sending unit. The symptoms you describe are classic for excessive clearance in the crank bearings. Try an oil change, see if that helps. "They" say 10psi for every 1,000 RPM is sufficient pressure. Let us know what you find.

[astro355]

What kind of oil filter are you using?

[Ye'OleAstrologist]

Sorry I forgot to include that info.

It's a 1988 with 150~k on it with about 67k on the engine. Reman engine at 87~k due to cracked pcv? plate under air cleaner housing letting unfiltered air in engine. The engine supposedly has a "lifetime warranty" but we cannot find the paperwork on it.

Here's some history. This issue came up in less than 3,000 miles. Van sat for about a year, and I made the mistake of driving it a little bit on the oil that was in it initially. I changed it after less than 100 miles with halvoline 10w30 and a purolator filter and drove it about 2000 miles (to the point it turned black again) and changed the oil with halvoline again using a purolator and changed at 3,000~ to mobil 1 10w30 with a WIX filter, which is what it has now. About 2,000 on this oil change now. I don't use Fram, or Bosch filters. I tried a bosch filter on my taurus and as soon as I took it out the box and squeezed it i was like "heeeel no" and took it back for a purolator. I use Wix, Purolator, or AcDelco/Motorcraft only. I am more apt to use wix because most are made in North Carolina.

During the last 500 miles of the last halvoline change it began the issue, but was only dropping to 20~ on the gauge. It has progressively gotten worse from there. Just before the low OP there began a rumbling noise in the front of the engine bay which turned out to be the water pump bearings. I have not flushed it out as of yet, but the engine is not overheating at this time. I thought "aha, the pump wasn't circulating properly so the oil was taking the slack from the pump" but I replaced the pump (reverse flow) and that did not help the issue at all. The engine did overheat quite bad about 5 years ago when the radiator sprung a leak and we didn't realize it until the gauge had hit about 240. Radiator was replaced with a new OEM GM UNIT and this was about 25,000 miles ago. This work was done at a chevy dealership, and I assume that they flushed the system seeing as this was an old vehicle that they could take their time on. However, they may not have. The engine may have overheated slightly or severely right after I started driving it again because I blew a LOWER radiator hose about 1.5 miles from home (had been only driving about 3 miles, happened right when the thermostat opened I think. By the gauge it didn't heat up, but it may have gotten hot on the topside of the motor.


What I have done so far is, I had to drive the van about 50 miles on a pretty hot day a couple days ago, so I drove it and when I got to my destination the gauge was on zero at idle. I left it in drive with the parking brake on and I could not hear anything which would suggest lack of oil to anything in the motor.

Since this began, when cold/warm the gauge jumps around some at idle, during the transistion from being pegged at 80 psi all the time.
It's like 5-10 psi up and down randomly, and it does not look like a mechanical variance, it's a real spastic movement up and down very quickly and randomly which is another reason I feel it's the sending unit. When I get the time, hopefully this weekend I'll take it to a friend's shop and we'll hook a mech. gauge up to it to see what it is really doing.


But on the flip side of that, the oil is getting REALLY hot (in my opinion, but the dipstick DOES go right by the pass. side header) To compare it to, I have a 1999 7.3L diesel f-250 which even after driving 200 miles the oil is hot but not so hot that you cannot take it straight from the dipstick to your finger.

[Ye'OleAstrologist]

The van is also getting poor mileage, and someone had said that it could be a fuel leak in the plenum, and I considered "maybe the oil is getting diluted with fuel" However, the oil pressure did not return to normal at all for any length of time after this last oil change.

After changing over to the synthetic the engine seems freer than it was before. The oil is also still clean, which could be a good, or a bad sign (the engine is either clean, or the synthetic isn't cleaning... because the first two oil changes came out black)

[rev_les]

just off the display description on the gauge, it sounds like a sending unit , wiring, or the gauge itself.I'd put a mechanical pressure gauge on it and see where it stays.Both of mine have over 200K and have 30 plus PSI at idle, and around 50 on the go. I had an isuzu pup that suddenly "lost" oil pressure going down the road, that had a sending unit just go out spontaneously.( which I figured it was because in the time it took me to safely pull over, it should have been clacking.. i fired it back up, let it run a sec, still no "signs" of low pressure, and drove it home, replaced the sending unit, and it was fine.)

[Big_kid]

Since this began, when cold/warm the gauge jumps around some at idle, during the transistion from being pegged at 80 psi all the time.
It's like 5-10 psi up and down randomly, and it does not look like a mechanical variance, it's a real spastic movement up and down very quickly and randomly which is another reason I feel it's the sending unit.

AAAhhh.... I'm leaning toward the sending unit too now. Mine does just about the same thing. No knocks or noises, but very erratic needle movement at idle when it's warm. A test with a mechanical gauge wouldn't hurt though.

[astro355]

Before you get another sensor, I would try cleaning it with brake cleaner. Remove the sensor and give it a good spray/soak session and see if anything odd comes out.

If you had fuel leaking into your oil, you would smell it when you check the dipstick.

[Ye'OleAstrologist]

Thank You for taking the time to reply fellas.


As soon as I have the spare time I will do the above mentioned things. I looked the sending unit up, and it's not that expensive fortunately. about $30 at advance assuming I have the right part.

Am I looking at the big thing which looks kinda like a fuel filter, mounted next to the oil filter, or am I looking at the one which is somewhere* on the engine? Do both of them make up what the gauge reads, or is one solely for the gauge, and the other for the Fuel pump relay override?

[astro355]

It looks like this:

http://www.oreillyauto.com/site/c/detail/MPI0/S4088.oap?year=1989&make=Chevrolet&model=Astro&vi=1027943&keyword=oil+pressure&partType=03438&parentPartType=C0039

On mine, it was mounted on the top of the engine behind the distributor but I have also seen them mounted by the oil filter.

[Leeann_93]

Mine's also behind the distributor.

[Ye'OleAstrologist]

I went to advance and auto zone and all they could come up with is the oil pressure switch by the oil filter which is a big ol' thing about 3" long from what I remember, 1 wire connection. I told them I didn't think that's what I needed. Your van is a 1993 and mine is a 1988 maybe they changed some things?

[astro355]

Mine is an 89 and the oil pressure switch is behind the distributor and uses a three wire connector, just like Leeann's

[Ye'OleAstrologist]

I want to thank everyone for the help you guys gave me. I never could find someone with a manual gauge who would let me use it, oh well.

I finally found the little OP switch. I got it to the van, and opened up the doghouse.. found the one by the distributor, and un-plugged it. Cranked van, gauge still worked. So I go "hmm" and I unplug the connector off the big one by the oil filter. No gauge. If only I had done that in the first place, right? Live and learn I guess.


So anywho, so I take the other sensor back and get the correct one. I install it, everything went smooth. Cranked it up from cold, gauge did not peg out to 80+ psi, but instead came up to about 70. I saw this as a good sign, so we piled in and we drove it to Raleigh and back. (50 miles) Totally hot after driving 50 miles idle in gear is 35psi by the gauge and cruising is about 50psi, WOT runs up to about 65 psi.

So... We're good, right?

Everything I know about cars I learned myself. From saving $20 doing oil changes myself a few years ago to doing Ball Joints on my F-250 (what a fun job that was... bleh.) To replacing the water pump on this van to diagnosing a problem with my taurus. When I have the time to take the time, I take my time (lol) and with a helping hand I can get just about anything fixed (or so I think)

Again, Thank You For the Advice, Brian.