9113300709 Low Oil Pressure Issue

[Haasman]

9113300709 Low Oil Pressure Issue

Background: I acquired this 73S this past summer. The car has 100k miles on it (I believe to be accurate). I was told it has a 2.8-liter motor. The MFI pump space cam was recalibrated by Pacific for 2.8 and installed by Canepa.

I haven’t pulled the plugs to check for heat range/correct specs, but I did check the timing and adjusted it from 3 to 5 ATDC. This BTW cured spitting in the intake at idle.

It is a very fast car, a screamer with a tractable engine that pulls easily from just above 2,000 RPM. I’ve been working through a lot of issues including interior, suspension etc, but in all a wonderful very fast car.

The car lives in northern California, in a temperate area so until yesterday I hadn’t driven it in temps greater than high 70 degrees. Yesterday after going to EASY in Oakland, the temperatures were in the high 80s to low 90s. This is when I saw the oil pressure plummet. The car is running Brad Penn 20W-50 partial synthetic that was replaced a week ago. It has a Porsche parts filter.

A side note: I replaced the oil pressure sending unit thinking that was the culprit, and also tightened the OP sending unit mount with correct crush washers, since there was evidence of oil seepage. No change.

When starting the engine cold with ambient temps of approximately 55 degrees the oil pressure is just under 100 PSI (per the dash gauge) and this seems normal to me.

As the car is driven and the engine temp comes up to just below 180 degrees the oil pressure starts to lower, and this I would also expect to some degree. Up until yesterday the rough ratio of 10PSI per 1,000 RPM was pretty close, but still seemingly a bit low at 60 PSI at 3,000 RPM.

Then yesterday with the ambient temps climbing to the low 90s is when the pressure got very low: just above 20 PSI. This scared me. Since I was at the top of the coast range where the weather will be cooler I carefully drove (low RPMs) until the ambient fell to the mid 70 degrees again. It never got below 20 PSI but as I slowly moved closer to cooler ambient temps (coast) the engine temperature came down and the oil pressure improved a bit.

The engine hasn’t gone above 220 degrees, it seems it the oil pressure that is the issue.

Does this ring a bell with anyone? I have search through and read many, many threads on this forum and on The Bird.

Unsure how to proceed. Suggestions and recommendations greatly appreciated.

Additionally- I do have a trombone-style loop cooler but would need to source the hoses and hardware to install it.


Cold start-




Yesterday was a hot day-

[edmayo]

The first thing you do is to make sure you have the correct sender. Remove the sender and look at the hex fitting, it should be stamped 10 bar ie. 140 psi range. If it is the correct sender then next I install a 'temporary' mechanical oil pressure gauge by removing that electrical sender after recording the readings, then screw in your mechanical sender and compare readings. Do this at the high ambient temperature, ie. when you're getting those low readings. Assuming it is still low I would remove the oil pressure relief spring and measure the wire diameter, it should be 1.8 mm and about 68 mm free length (trusting to memory here, don't have the spec books at home) If the wire diameter is 1.2mm and the free length is 74mm (or thereabouts) someone has put in a late model spring (probably when the oil return mod was done) use the proper spring and that should raise your pressure. If not you're in deep poo-poo! All my cars will run about 70-80 psi under your conditions as a reference.

[Haasman]

Thank you Ed. Your advice, experience and clear descriptions are appreciated. I will double-check the new OPSU.

I realize after posting that a mechanical gauge verification is next. Any suggestions on this? I need to find a male threaded connector that matches the thread on the OPSU. Any company/product that you can suggest?

Is the OP relief spring located on the bottom of the engine?

[edmayo]

I just use a generic gauge such as you could buy from any auto parts store, a 1/8th" SAE pipe thread will screw into your metric sender thread. The oil pressure relief is the bottom hole of the case, the one on the side is the over pressure cold oil by-pass that opens around 140 psi. to protect the filter from extreme cold oil pressure.

[Haasman]

Thank you Ed. Will measure and report back.

[jameshtaylor]

Your two pics show superb oil pressure on a motor acting perfectly normally. I see a hot motor at 3k rpm with probably about 40lbs of oil pressure. Tell us again what the problem is?

[M_deJong]

Is your OP sender at the flywheel end of the engine or fan end? If its at the fan end you need a weird adapter to connect a mechanical gauge to the large diameter thread of the sender. Also possible to connect the mechanical gage to the oil temperature port near the fan belt.

In my limited experience with my 2.2 T at high temp, the oil does thin out a lot at 210 vs 185 and the oil pressure is lower. But not that low. At 210 I would see 55 at 3000. Since I added the loop cooler I haven't been over 185.

I just finished playing with the oil pressure relief springs in my 3.2 as I wasn't satisfied with the hot oil pressure. It is the vertical spring. My engine, being a 3.2 had the long (I think its 86mm Ed) spring and never went above 60psi warm-hot. That long spring set up is really efficient at dumping oil pressure and keeping it steady across a wide range of oil viscosity.

So I installed the early 70mm spring (but with the later hex head cap) and whoa momma did I have oil pressure. 100++ cold, 110 hot (185) at 5k rpm. Thinking that's a little high I modified the cap to "early" dimensions (12mm deep vs 9mm deep) and that brought me down to 100 cold, 60 hot at 2500, 90 hot at 5k. I think I like that. Maybe this summer I can get up to your 210 degrees and see what it reads, but I doubt it with a Carrera cooler.

Good luck. I think 1) verify the gage; 2) verify the sping; 3) if short spring you can shim it with two washers; 4) if still low then...


Edit... seems I'm a slow typer... the two above weren't there when I started!

[Haasman]

James- the temp went lower than the "above 20 PSI" as the temp got close to 210. That concerned me. Having 40 years of experience with these engines, 20PSI at 210F at 3,000 RPM indicates courting with disaster.

M_deJong- Thanks for that experience. I with you in your first run at it seems too high. I will keep this thread updated as I complete 1), 2) and 3)

[jameshtaylor]

Sorry if I have the wrong data. Your original note says nothing about dropping TO 20psi at 3000rpm (which I'd agree is worrisome.) And the pics show a perfectly normal motor with about 15psi at 2600 rpm and very near 210° if I'm reading the gauge correctly.

[kentf14]

I'll be interested to hear the group consensus here, but in my opinion, you're seeing 10PSI/1K RPM. I believe this is the normal range (what's your opinion here Ed)?
An engine @ temp with ~30PSI @ 3K seems normal for a mag case engine, does it not? What do you see at temp for higher revs?
Also, I recently discovered a stuck MFI thermostat that I believe led to fuel dilution in the oil. When I discovered this, my pressure was in a dangerous range. I'd examine your oil to see if you are diluting it with fuel causing it to thin out.
I cleaned and replaced my thermostat and all seems well after 1K miles.

Good luck!

Kent