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I've shared the tale of my ongoing search for a solution to a high oil pressure problem in my '87 924s on this forum before and now I may have something new to add. I was sure that the high oil pressure (150#) resulted in two leaks: one at the oil filter and the other at the port-side aft part of the valve cover gasket. It turns out I might be wrong about the valve cover gasket.
Yesterday I started the gasket replacement procedure and when I went to disconnect the sensor that might be attached to the rear engine lift (using irina's youtube video) I found another area that was leaking! It was the valve cover lid (8). Actually, one bolt was missing and I was able to remove the remaining three by hand. There was a good 2-3 mm gap at the bottom. Anyways, I hope I found out why the oil pressure is so high.
Search on the photo about 1/2 way down with the title Rear end of the camshaft housing with rear cover removed. Note oil return passageway.
The oil at that location is bleed oil from the camshaft bearing. Normally it returns to the main gallery of the cam cover through the oil return passageway shown in the photo. I guess if the passageway was blocked off, that might create problems but not high oil pressure per se. And in your case, the return oil is simply leaking out through the gap. Certainly needs to be fixed but probably not your problem.
Harvey, your article is canon (as is 944onthefloor's). I have referred to it a number of times while trying to sort out my car's high-pressure issue. I started the search for a solution by attempting to de-gunk the motor with something like Rislone (can't remember). Nothing notable showed up in oil after removal. So, the likely culprit, as you have pointed out, is the OPRV. I rebuilt it and the pressure fell to a more reasonable 90#. Believing this to still be too high (idle!) I removed it to change the gaskets yet again. I haven't tried it as I have the car prepped for a valve cover gasket change. And now I can add a rear valve cover gasket to the mix!
You're getting 90 psi at idle. Fully warmed up? Wow! I assume you've ruled out the sending unit and gauge. My most recent go-around with the OPRV on my track car (resulting in too low pressure) was added recently to my "canon". If you haven't read it, there may some ideas for you there. I'd probably considering springing for a new OPRV at this point.
Its kind of a pain in the neck experiment but if there is gunk in the engine, the pressure should drop if you were to experiment with a low viscosity oil, like a 20 weight. But if it's the OPRV, then there wouldn't be any change with a low viscosity oil, since it just operates as a spring resisting pressure over the area of its plunger (or whatever you want to call it).
I never thought about it much but the oil pump is a "positive displacement" pump, which means if you could somehow block off the outlet, tremendous pressures could theoretically be developed before something breaks.
Lower viscosity would cause a lower indicated oil pressure when at operating temp just by it's propensity to escape more easily from the same existing clearances.
90 psi at idle...?
Hmmm,
What is the pressure at 1000, 2000 and 3000 rpms...?
Wow! I assume you've ruled out the sending unit and gauge.
It's a new gauge (digital) using the existing sending unit. But this would merely 'report' the oil pressure rather than cause it, no???
I'd probably considering springing for a new OPRV at this point.
As soon as I exhaust my box of Harbor Freight O-rings.
Originally Posted by 951and944S
90 psi at idle...?
Or higher.
Hmmm, what is the pressure at 1000, 2000 and 3000 rpms...?
150#
So, how do I know if I have high oil pressure if the gauge can't be trusted? My 'evidence' is the leak at the top of the oil filter and maybe the valve cover gasket. The latter spot might be a coincidence and, in fact, is coming from the wide open lid at the cover's back. It reminds me of trying to find the source of a water leak that was showing up in the suspended ceiling in our basement.
Screw on a mechanical gauge and see if there is a difference ... like i mentioned previously in another thread , my faulty OPRV caused me two engine fires !
It's still cheaper than having your car burn to the ground , especially if you don't have an adequate fire suppression system ...
Screw on a mechanical gauge and see if there is a difference ... like i mentioned previously in another thread , my faulty OPRV caused me two engine fires !
It's still cheaper than having your car burn to the ground , especially if you don't have an adequate fire suppression system ...
Just sayin ...
The reason I switched to the digital was the analog (original) meter was pegged at the right.
Anytime I work on this I keep your experience in mind! At least I know where to get new ones for $185.
I would buy a new sending unit. They are less than $50 as I recall, from Paragon.
Folks more electrically astute than me can chime in but I don't think the sending unit is designed to report pressures in the 150 psi (approx. 10 bar) range.
After all the various threads about oil pressure, I think I'm going to take an oil filter and thread/tap it to fit a simple mechanical gauge. There's nothing like checking the pressure at its source!
I would buy a new sending unit. They are less than $50 as I recall, from Paragon.
Folks more electrically astute than me can chime in but I don't think the sending unit is designed to report pressures in the 150 psi (approx. 10 bar) range.
After all the various threads about oil pressure, I think I'm going to take an oil filter and thread/tap it to fit a simple mechanical gauge. There's nothing like checking the pressure at its source!
Thanks again for your advice, Harvey. I'm trying (can't access Province drop-down options) to order a new OPRV from Paragon as they are only $185!!!
As for the 'adapter' might I suggest one of these? Or one like it as they come with different sized side plugs. I bought it from wish dot com.
And a great big thank you for the offer of a loaner. You know that this would be rewarded with lots of Canadian bacon. Or 🍺
.
A web link to where it is sold, or just the make/model of the gauge.
I think I could find spec on it.
Let's see the signal range, Harvey might have been on to something.
If the sender and gauge are compatible and your reading is actual, we'll set up me sending you an OPRV to further your tests.
It's interesting though, that there are some reinforcement ribs on the pump body's aluminum housing that are there to address distortion, expansion of the aluminum and potential cracking.
It's possible that if your pressure reading was legitimate, the pump would have failed by now.
A web link to where it is sold, or just the make/model of the gauge.
I think I could find spec on it.
Let's see the signal range, Harvey might have been on to something.
If the sender and gauge are compatible and your reading is actual, we'll set up me sending you an OPRV to further your tests.
It's interesting though, that there are some reinforcement ribs on the pump body's aluminum housing that are there to address distortion, expansion of the aluminum and potential cracking.
It's possible that if your pressure reading was legitimate, the pump would have failed by now.
T
This is a head-scratcher alright. I can find lots of thoughts on low-pressure situations here and on other forums but not much more than that a high-pressure situation can exist.
OK Curt, you going to force me to get technical on you
The reason I am suspicious of a 150 psi reading is as follows. I went down this rabbit hole last year when the oil pressure on my 944 was reading low. I wanted to rule out the sending unit and the gauge. So my thinking was that I could hook up my multimeter to the sending unit and read pressure directly, after applying some math. But what math. I consulted with Jason at Paragon and we came up with a part number for a sending unit manufactured by FAE. The one that he sells for much less than the Porsche labeled item. I'm sorry, I don't have the part number handy but it led me to a FAE catalog on-line. A portion is reprinted below. Now FAE is European and my best guess at deciphering their catalog is that Presion means precision and the number there is the recommended pressure measurement range for the sending unit in Bars. Part number 14110 is typical for what we use in the 944, which is a combination pressure sending unit and a switch to turn on the oil pressure light. That unit has a precision of 8 bars and the light turns on at 0.60 bar. And I'm pretty sure that the unit that I bought from Paragon has a precision of 5 bar, which makes sense as that is sympatico with the gauge, which reads up to 5 bars. Now 5 bars is roughly 75 psi.
Furthermore, I'm pretty sure the sending unit is a variable resistance. It doesn't read pressure per se, the resistance is converted back at the dash to pressure by applying the resistance to a voltage divider circuit. Now I'm really getting to the limits of my I&C knowledge so anyone, please, jump in here but my point is that the 944 was never set up to read 150 psi and your digital gauge has to make certain assumptions regarding the source of its information. But if for instance, your system voltage at the dash was degraded to say 6 volts rather than 12, the gauge would read incorrectly by a factor of 2. On my really old cars from the 60's, all the dash gauges make a sudden movement when cranking on the starter because the system voltage drops to 9 volts. Newer cars have a voltage stabilizer circuit to resolve this issue.
So all of this is a long winded way to say you can never be really sure of what your pressure is unless you circumvent all the stock parts and go with a mechanical gauge. Thus my crack about mounting a mechanical gauge on the oil filter.
In my case, the problem was the OPRV, but in your case, I still have to question if your pressure readings are real.
Just how close to the magnetic north pole are you, anyway
04-30-2019, 10:01 AM
The last place I'd look for an oil leak...
