[SOLVED] Low Oil Pressure at Idle but Only When Warm

[usury]

This summer I finally tackled a problem I experienced with my 250K mile 1987 na. At cold idle, oil pressure indicated between 4 and 5 on the dash gauge. This was confirmed with a mechanical oil pressure gauge adapted to the oil pressure sending unit opening.

At warm idle, oil pressure dropped to below 1 on the dash gauge (and also the mechanical gauge when it was attached), resulting in a "!" light and a noticeable stumble. Blipping the throttle resulted in a return to about 3 on the gauge, again dropping below 1 when the RPMs dropped to idle. This happens, of course if you hold the clutch pedal down or put the car in neutral in stop and go traffic, too.

I know the manual says an occasional excursion below 1 on the gauge is nothing to sweat (which never sat right with me, but hey it's in the manual). My problem wasn't occasional. It was repeatable. Conditions weren't grueling - mine is a street car only. This occurred regardless of ambient temp. Idling in the driveway on a 55F day would do it.

It took about 20 minutes for the engine to be warm enough to experience low oil pressure, but it always happened. It could always be "remedied" by holding higher RPMs.

Of course, I had read several forums posts (RL, Pelican, etc) where people experience this problem but no "here's what I did to fix it" solution was ever posted, at least that I discovered. The only consistent recommendation was to try heavier oil and make sure the crank pulley bolt is torqued to 155lb-ft.

I tried 20W50 oil - no real difference.
Crank bolt was torqued properly.

I know the oil pickup tube can suffer cracks, which results in the oil pump sucking air from above the oil level in the oil pan and producing low oil pressure. However, those cracks seem to happen to race cars or cars run without balance shafts or with collapsed motor mounts for extended periods (lots of vibrations).

Also, due to the design of the oil delivery system, the #2 rod bearing can wear, resulting in out-of-tolerance clearance which affects oil pressure.

So I finally ordered parts and seals. New pickup tube. New rod bearings. New rod nuts. And most importantly in my case, the new oil pickup tube seal.

Underside for orientation - left side of photo is front of car
Notice the oil pickup tube (with the round mesh screen) near the rear of the engine.

Underside, front of car to the left of photo

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Close up of crusty looking seal between pickup tube and crankcase
It isn't supposed to be squishing out like that.

Oil Pickup Tube Seal, Detail 01

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Oil Pickup Tube Seal, Detail 02

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Close up of Seal Itself
It isn't very supple any more, and there are fine cracks along the inner diameter surface that contacts the oil pickup tube.

Seal Closeup 01

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Seal Closeup 02

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Seal Closeup 03

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The Results
Turns out, my 250K+ mile oil pickup tube wasn't cracked. Turns out my rod bearings had only the slightest signs of normal wear, and the crank itself was pristine. However, that seal was shot.

Now, the car idles cold with 5+ on the dash gauge (nearly 6 bar on the separate mechanical gauge when it is attached). It idles warm at about 4 on the dash gauge.

My low oil pressure problem was solved by a cheap seal.

I performed quite a lot of "while I'm in there I should also do XYZ" parts replacements (like new pickup tube, rod bearings, pan gasket.) Perhaps those new parts also contributed to the cure.

I suspect when the crusty seal got warm, some cracks in the seal widened and it became possible for the oil pump to suck some air. Or perhaps the metal pickup tube and/or the hole it connects to expanded with heat and the crusty seal couldn't accommodate, resulting in a gap through which the oil pump could suck air. This probably happened at all RPMs, but only resulted in dangerously low oil pressure at idle.

Potential Gotchas
There are two versions of the oil pickup tube, each with a different diameter mesh screen portion. To my knowledge, they are NOT interchangeable. If you decide to tackle this project and you want to have an oil pickup tube on hand prior to opening the engine, you'll have to do some homework to determine which model years or engine versions used which pickup tubes.

edit: Supporting the engine from above may compromise the cork gasket at the back of the cam housing, detailed in this post.

If you replace rod bearings:
- you need new rod nuts as well
- connecting rod caps CANNOT be interchanged (the rod and the cap are machined as a set and have matching numbers stamped into them)
- connecting rod caps MUST be oriented properly - get just one flipped around and it is completely impossible to turn the engine by hand (with a socket wrench at the 24mm crank bolt).

I had read some anecdotes (in forum posts not specifically related to low oil pressure at warm idle) regarding engine seal kits that contained undersized/oversized oil pickup tube seals. I ordered the seal separate from any aggregate kit getting the part number from PET. But there were also anecdotes of separate seals bagged with the wrong part number on the packaging, or rather the right part number but the wrong part. Order from a reputable Porsche-specific place.

[Tom]

Great post, thank you for taking the time to write that up! Any chance that seal had been changed before? I know the Victor Reinz lower gasket kit comes with a seal that "looks" like it would work for the pick up tube, but bulges out like that when you try to use it (ask me how I know). If you root around in that kit, they also include a seal that fits perfectly. On the other hand, if it's the original seal, I'd say you got your money's worth if it lasted 250k miles!

Sounds like a great repair, and one that may have saved your motor! Nice work.

They changed the pan somewhere along the way, and with it the pick-up tube and dipstick -- so you are exactly right about making sure you have the right parts...

[usury]

Any chance that seal had been changed before? I know the Victor Reinz lower gasket kit comes with a seal that "looks" like it would work for the pick up tube, but bulges out like that when you try to use it (ask me how I know).

Indeed, it's likely that seal was previously changed.

I've owned this car since 1999. I'm the second owner starting from about 130K miles. About eight years and 40K miles ago, as part of a much more sweeping set of repairs, the engine was out of the car and resealed all around. It was done by a reputable and well-respected Porsche shop in my old home town. Even then, it's possible a junior mechanic or trainee put the wrong seal in, especially if the gasket kit came with a pair of similar-looking seals that fit the pickup tube. I mean, anyone can make a simple mistake. I hold no ill will.

Honestly it was a simple repair and really required only one new tool - the engine support bar I got from Harbor Freight for $85.

It did take a long time since there are a lot of components to remove to get at the oil pan. If a person powered straight through without stopping to clean/paint any of the parts that came off, and you find nothing else broken (like motor mounts, suspension bushings, etc), and you don't have to order parts after you've started the project, you could have it done in a weekend - like two 8-12 hour days, but still. It's all straight forward work.

[usury]

These YouTube videos were super useful in getting my head around the significant disassembly required in order to remove the oil pan.

[notny41]

i have an 86 951 that will get down to 2-3 when it is warm and comes to an idle (like at stop signs/lights). wondering if this is something I should be concerned with? my car leaks oil pretty good but when i checked the oil level it was sitting at almost the full line.

[Tom]

i have an 86 951 that will get down to 2-3 when it is warm and comes to an idle (like at stop signs/lights). wondering if this is something I should be concerned with? my car leaks oil pretty good but when i checked the oil level it was sitting at almost the full line.

When hot, my car idles at 2 bar. Still going strong.

[notny41]

Oh, thank goodness! Thanks Tom!

[notny41]

These YouTube videos were super useful in getting my head around the significant disassembly required in order to remove the oil pan.

I love watching Van's videos! Learned a lot from him. I bought that same harbor freight engine support bar as you mentioned. Was wondering how it worked for you? I bought it years ago and haven't gotten it out of the box yet. was intending to do motor mounts but still haven't mustered up the motivation to do so - and wasn't sure I could trust that bar. LOL Also wondering how the fender tracks faired after bearing the weight of the engine?

[usury]

I love watching Van's videos! Learned a lot from him. I bought that same harbor freight engine support bar as you mentioned. Was wondering how it worked for you? I bought it years ago and haven't gotten it out of the box yet. was intending to do motor mounts but still haven't mustered up the motivation to do so - and wasn't sure I could trust that bar. LOL Also wondering how the fender tracks faired after bearing the weight of the engine?

The HF engine support bar was fantastic. When working under the car while the engine was supported, I was always cognizant of the potential danger, but I got used to it in about an hour.

The fender rails were unaffected by the experience. The area near the shock towers is pretty strong in general.

I recall needing to move the mounting brackets out of the way for the cruise control actuator, or perhaps it was for the brake pad sensor connector barrel. Regardless, it was something small.

I looped one end of the chain around the left side engine mount. Air box had to come out for that. I also removed the throttle body and anything else that the chain wanted to hit or apply pressure to.

I used the support loop on the back of the cam housing on the right. I managed to make more work for myself by crushing the cork gasket on the back of the cam housing, which I wrote about in another post (link is in the "gotchas" section of my original post in this thread). If I have to support the engine again, I'd try to find a way to loop the right side chain through the right side engine mount, too.

[gruhsy]

viewtopic.php?t=1097&start=90

Not sure if you saw this.

Oil pick up tube potential hazards/issues.