Low oil pressure

food · 04:18 PM

I recently picked up an 87 with 70k miles and the oil pressure gauge is always showing very low. At startup and idle, it's just above 0 and the idiot light is on (when power is cut, the gauge moves down below 0). If I blip the throttle, the light goes out and the oil pressure gauge moves just a bit, but while driving it never moves to or past 1. The light stays off until I take it out of gear, and is on while idling.

In the paperwork with the car, I see a mechanic swapped out the sender 2 years ago and it still had the same problem, but they didn't see any knocking or particulate in the oil to cause concern. I pulled the connector off the sender and the gauge pegs to 5 so I'm pretty sure the gauge is ok.

It seems to run and idle just fine. The oil level is right in the middle of the dipstick and on the gauge when warm. Is it really possible the oil pressure is that low? Wouldn't it be having trouble idling and all kinds of other issues?

Update: turned out to be an oil pressure relief valve

Trackrash · Trackrash's Garage

Has the pressure been checked with a mechanical gauge and confirmed to be low? If confirmed low, start by checking the pressure relief springs. Also confirm the correct sender is installed.

Solamar · 12-01-2019, 10:09 AM

The oil pressure light and oil pressure gauge use separate senders at opposite ends of the engine. Id certainly be concerned.

manbridge 74 · 12-01-2019, 11:54 AM

Idle pressure is irrelevant on these. Factory spec is 50psi at 2500 rpm. And 65psi at 5500rpm. This assumes operating temps 176-180F. Check with mechanical gauge as wrong sender may have been installed.

bpu699 · 12-01-2019, 01:42 PM

If you have 1 bar max oil pressure then something terrible is going on. Stop driving, check the pressure with a manual gauge...

stownsen914 · 02:16 PM

Quote:

Originally Posted by bpu699

If you have 1 bar max oil pressure then something terrible is going on. Stop driving, check the pressure with a manual gauge...

What he said - hopefully it’s a bad or mismatched sender or something. But if that number is real, your engine will be ruined in short order if you keep running it. Not worth risking that. Check pressure with a mechanical gauge where the stock sender goes. That will tell you if you have an issue. If it were my car, I wouldn’t start the engine again (except to do the test) until you confirm that.

Scott

Harpo · Harpo's Garage

This is what I used to check my oil pressure.

https://www.pelicanparts.com/More_Info/PELPBSCECZZN.htm?pn=PEL-PBSCECZZN&msclkid=8c32d96e539810142b74848a1cd0a09d&utm_source=bing&utm_medium=cpc&utm_campaign=Shopping%20Ads%20-%20Porsche&utm_term=4580428003593808&utm_content=%24100%20-%20%24200

Harpo · Harpo's Garage

This is not my photo

bpu699 · 12-01-2019, 03:08 PM

Quote:

Originally Posted by Harpo

This is not my photo

I’ve got one of those and it’s handy. The gauge fails every so often and needs replacement...

bpu699 · 12-01-2019, 03:11 PM

I do wonder how long a motor car run with 15 psi oil pressure... probably longer than we think.

Some YouTube videos show motors running with no oil...they go 2-3 minutes...

tailwind22 · 12-02-2019, 04:33 AM

Serious situation and need to verify with a mechanical gauge at idle 2000 rpm, 3000 rpm and 4000 rpm and record. I had a similar situation with a 930 motor a few years ago with max pressure of 2 bar at 4000 rpm. Turns out one of the crankshaft galley plugs had fallen out, shattered and was clogging the crankcase strainer. Only found it after pulling the motor apart. As one suggested, the oil pressure reliefs are a good place to start.

juanbenae · juanbenae's Garage

do you know what the oil weight is in there now? I used a break in oil in a new motor and was getting little to no oil pressure due to viscosity. 20/50 is advised.

food · 12-06-2019, 04:56 AM

Oil pressure test revealed 3psi at idle/900rpm, 10psi at 2000rpm, 15psi at 3000rpm.

I think the previous mechanic put in 0w-40.

Ian Comerford · Ian Comerford's Garage

I understood that idle pressure didn’t really matter but that you need 3 bar at 3k revs and 4 bar at 4K revs. Oil type may affect this of course

stownsen914 · 12-06-2019, 06:17 AM

Oil pressure test was done with a mechanical gauge? (i.e. important not to use the sender or gauge in your car while troubleshooting)

food · 12-06-2019, 06:22 AM

Quote:

Originally Posted by stownsen914

Oil pressure test was done with a mechanical gauge? (i.e. important not to use the sender or gauge in your car while troubleshooting)

Yes, the shop took the sender out and manually tested it. They're saying it probably needs a top-end rebuild to sort it out ($$,$$$).

manbridge 74 · 12-06-2019, 06:31 AM

Top end has nothing to do with oil pressure!

They (actually someone else please) should be looking at lubrication schematic to analyze possible pressure loss areas. I’d be looking at relief valves etc before condemning engine to tear down. And 0w40 won’t cause these low readings by itself.

stownsen914 · 12-06-2019, 08:35 AM

I'd want to check some other things before deciding that a rebuild is warranted. And agreed that I wouldn't think a top end rebuild would address whatever the issue is. It sounds like your engine is bleeding pressure somewhere in the pressure side of the oil circuit. There are a number of places this can happen, some can be checked externally without disassembling the motor. As suggested, I'd start by checking the pressure relief valves in the crankcase since they are externally accessible. If one of those is jammed, it could cause low oil pressure.

Incidentally, was a PPI done on this car? If so, someone missed an easily detectable major problem. And I hope you aren't taking it to the same shop for the work now.

Scott

cabmandone · cabmandone's Garage

Quote:

Originally Posted by food

Yes, the shop took the sender out and manually tested it. They're saying it probably needs a top-end rebuild to sort it out ($$,$$$).

I'd go find a shop that knows what the hell they're talking about. Next I'd consider going to 20w50 dino rather than 0w40 which is typically full synthetic and pours like water.

Coastr · 12-06-2019, 10:30 AM

Quote:

Originally Posted by food

Oil pressure test revealed 3psi at idle/900rpm, 10psi at 2000rpm, 15psi at 3000rpm.

I think the previous mechanic put in 0w-40.

15 psi = 1 bar

You have a serious oil pressure problem somewhere - as stated 3k rpm should be 3 bar or so. My 145k mike engine that uses oil a bit still does well over 3 bar at those revs.

Suggestion to top end rebuild is not confidence inspiring in the person you’re talking to, absent other details as to what might be fixed in the rebuild. Maybe if they told you which bit of the top end is likely to be causing low pressure.

If it were me I would drop the 0W 40 immediately and put in 20w/50 or 60, and see where you’re at. I doubt this will make a big change though.