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High Oil Pressure: Too much of a good thing?

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Andy Blackley

Andy Blackley

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Today I replaced my crank thrust washers with Scott Helms nifty replacement, and since an oil change was in order I also took the opportunity to replace the stock oil filter with a spin-on adapter and a Bosch filter. I put in Castrol 20/50 "High Mileage" started her up and checked for leaks. Seeing none I took it out for a spin. The cold oil pressure was pegged at 100 psi, which it usually does on start up. Typically within a few minutes the gauge would read high, but not be pegged out. Previously the oil pressure would drop as engine temps increased so that after 20 min or so it would be a 70 on a cool day at 2000 rpm and 60 on a 90 degree day. Stinking hot it never goes below 30 psi. Satisfactory oil pressure.
Now tonight driving around the gauge would peg at anything above 1000 rpms for the first ten minutes, and dropped to 90 psi when fully warmed. Hot idle pressure is around 45 psi. On acceleration it pegs again, which tends to spoil the fun.
The high reading makes me worry. I suspect the filter element is too small/restrictive. The oil preesure relief valve had been replaced a few months back and before the conversion the oil pressure was great as described.
Anyone have a thought or similar experience?
Thanks!
Andy
 
Andy,
Your repair should have had no affect on oil pressure if just the TW's were replaced. If so, the only thing that has changed is your oil. Your reading are high. I would take the car on a short run at highway speeds for about 30 minutes & see if they return to normal. This will give the oil sufficient time to come to temp & viscosity. If they return to the high readings check the gauge for acuracy with a cheap VDO gauge.
Oil pressure that high is overkill & a waste of HP.
 
In addition to wasting HP, it puts tremendous strain on the oil pump drive, causes increased leaks, increased oil consumption, & can even blow an oil filter can or seals.
D
 
I would guess that the "high mileage" oil formulation contains an additive package to boost viscosity as a way of compensating for bearing wear in high mileage engines.
Possibly your car does not need this assistance yet; I would change back to your regular oil and see if you get back to normal readings. I think you will.
Simon.
 
Simon: Using 10W40 is my fall back position. I was using the same 20W50 Castrol High Mileage oil with the old filter and did not have the same problem. I think the oil pressure benefitted from it, especially on hot days. The only really new change is the spin-on filter. I am going to install a PH3600 or equivalent tonight to see if anything changes.
 
Isn't the oil filter on the "take-up" side of the oil pump? i.e. normally at negative pressure and so high oil pressure should not cause the oil filter can to "blow"?

Rob.
 
Hi Rob,
the filter is on the pressure side of the pump & down stream from the pressure regulating valve. There is usually a coarse screen on the pump intake side to remove the large chunks.
D
 
[ QUOTE ]
On acceleration it pegs again, which tends to spoil the fun.
The high reading makes me worry. I suspect the filter element is too small/restrictive. The oil pressure relief valve had been replaced a few months back and before the conversion the oil pressure was great as described.
Anyone have a thought or similar experience?
Thanks!
Andy

[/ QUOTE ]
Hi Andy,
Another thought. The filter is down stream from the relief valve & the pressure gage is down stream from the filter, so restriction at the filter would lower the pressure readings. I suspect that the relief valve may be blocked or sticking. It should be set to around 60 psi with the engine cold. A higher setting will not raise pressure when the oil is hot, since it only releases/bypasses when the pressure goes above 60.

On some filter adaptors it might be possible for the wrong gasket, on the adaptor to engine, to block the relief valve bypass channel & cause very high oil pressure. An adaptor which was not properly matched to your engine could do the same thing.
D
 
Update: This evening I changed the filter to a Mobil M1-209. As it turns out it is almost identical to the Bosch, and about as big a spin-on filter as you can get with the relatively small diameter. No difference. Still read at 100psi at any rpms above 2000. I drained the 20w50 and installed 10W40.
The pressure readings are still higher than usual for the first twenty minutes, but after a good warm up the idle pressure is at 30psi like before, and at 3000 rpm around 80 psi, which is higher than previously. At sustained 4000 rpms the gauge is a tick below 100 psi, say 90-95. I am going to drive it gently and see if it changes as the oil ages. I am fairly confident that I installed it correctly, it is canted just slightly to avoid the slave cylinder. It came with a large o-ring for the outer circumference and thick rubber cicular gasket where the adapter meets the block. I dont see what I could have done wrong.
 
[ QUOTE ]
Update: This evening I changed the filter to a Mobil M1-209. --- No difference. Still read at 100psi at any rpms above 2000. I drained the 20w50 and installed 10W40.
The pressure readings are still higher than usual for the first twenty minutes, but after a good warm up the idle pressure is at 30psi like before, and at 3000 rpm around 80 psi, which is higher than previously. At sustained 4000 rpms the gauge is a tick below 100 psi, say 90-95. I am going to drive it gently and see if it changes as the oil ages.

[/ QUOTE ]
Hi Andy,
It appears that the filter is installed ok & is not causing problems. The only thing left is the pressure relief valve or it's spring. To repeat - filter restriction could only lower the pressure.

The pressure should NOT go over 65, hot or cold. You stand a real chance of blowing a gallery plug or shearing the oil pump drive pin or blowing the filter, with the pressures that you are quoting. I would not drive it at all until the cold pressure is down to about 65 max at ANY rpm. Correcting this will not drop the hot idle pressure. The pressure relief valve is intended to reduce maximum pressures to a safe limit.

Either the relief valve plunger is sticking or you have the wrong spring in it or the relief passage is plugged. You said earlier that you replaced the relief valve. Was it doing something wrong? I suggest you do what ever is necessary to get the pressure down where it belongs. I would try another spring & not the optional high pressure spring which is sometimes available.
D
 
Andy,
Like you and everyone else I'm somewhat at a loss. But someone did mention getting a auxiliary gauge to double check and I would recommend that. Those numbers at the upper end would spell potential problems on a race engine eg, bearing metal washout. Check it out if you can.
Tom Lains
 
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