Oil Pressure Relief

#1

Has anyone installed shims (washers) under the spring in the engine oil pressure relief valve, to raise the pressure? If yes, what thickness washers have you used, and how many?

Thanks,
Alex

#2

Interesting question, wish I had an answer…

I have never changed my relief valve but mine does seem to stay closed longer than normal. In most other cars I own and have ridden in, the oil pressure never goes above 75psi and drops to 15 +/- 5 at idle. Even when hot, I will see 35-40psi at idle and up to 90psi at high RPM’s in my car. Occasionally my relief valve will open and my oil pressure will drop to 15psi at idle.

I am assuming this is a relief valve issue, but I may be wrong.

Does anyone have experience rebuilding/modifying oil pressure relief valves? Does anyone know what the factory specs are?

#3

This is pretty common on e30 M3’s, where I shimmed about 1/4 - 3/8 during my rebuild a few winters ago. I can’t remember if I used washers or a cheap spacer. Probably washers.

Been observing oil pressure Cory describes (5-15 idle when hot) on my (new to me) 325is and started thinking about shimming this motor too, if this morning’s oil change does help (not sure what weight is in it now). Looking on realoem, the M20 oil pump design is fairly different than the S14, but seems like it would work there too. Would love to hear empirical evidence before I try it though!

  • Chris

(e30 HPDE lurker)

#4

Cory1970 wrote:

[quote]Interesting question, wish I had an answer…

I have never changed my relief valve but mine does seem to stay closed longer than normal. In most other cars I own and have ridden in, the oil pressure never goes above 75psi and drops to 15 +/- 5 at idle. Even when hot, I will see 35-40psi at idle and up to 90psi at high RPM’s in my car. Occasionally my relief valve will open and my oil pressure will drop to 15psi at idle.

I am assuming this is a relief valve issue, but I may be wrong.

Does anyone have experience rebuilding/modifying oil pressure relief valves? Does anyone know what the factory specs are?[/quote]

35-40psi at (warm) idle is too high. I’d be surprised at anything over 10psi at idle. I don’t know how a relief valve could cause this idle oil pressure symptom. Maybe the engine isn’t warmed up yet, or maybe you are using 50W oil.

If I recall correctly, the purpose of the oil pressure relief valve is to protect the oil cooler plumbing from the high pressure that builds up when the oil is cold. Or if the filter gets plugged. So it doesn’t play unless oil pressure spikes. I dimly recall 90psi being the trigger prassure.

I think that a valve at the oil pump controls system oil pressure.

Note that when I was playing with oil types I found that it took a lot longer for my oil temp to stabilize then I thought. Don’t reach any conclusions about oil pressures unless your engine has been running for at least 30min.

A reasonable pressure rule of thumb is 10psi/1000 rpm. So if your motor is at 3k rpm, your oil pressure should be around 30psi. 26-40psi would probably be ok. Just be sure that your oil temp has stabilized before you play with this sort of thing. Consider also that most gauges are not very accurate.

Here’s an interesting thread:
http://forums.roadfly.com/forums/bmw/bmw-3-series-e30/9238978-1.html

#5

The old-time SE crowd might refer to the oil pressure relief valve by the fond nickname “don’t frick with it, rookie!”

One of our esteemed dudes had his relief valve literally come apart, leave a few choice clips and washers on the track, and dump a motor’s worth of oil at RRR in said rookie’s first race about 2 years ago. He still gets the occasional zinger about it.

If not for the kindness of Pantas, the downtime would have wiped out our Sunday race.

#6

and after that incident I ran with the eta housing / minus oil cooler but didn’t like the temps I was seeing.

I went to a machine shop with the “I” housing and had them weld a cap over ‘presure relief’ section and never worried about it again.

As far as I can tell or see there is absolutely no downside to doing this. The car doesn’t see thick oil, or cold temps.

Anything that is held in with a 20 year old snap ring that can pump every drop of oil out in 2 min or less and seize your engine if you’re not paying attention isn’t anything I need.

and yes I’m sure this (the eta housing and the cap) are illegal somehow.

#7

IndyJim wrote:

[quote]and after that incident I ran with the eta housing / minus oil cooler but didn’t like the temps I was seeing.

I went to a machine shop with the “I” housing and had them weld a cap over ‘presure relief’ section and never worried about it again.

As far as I can tell or see there is absolutely no downside to doing this. The car doesn’t see thick oil, or cold temps.

Anything that is held in with a 20 year old snap ring that can pump every drop of oil out in 2 min or less and seize your engine if you’re not paying attention isn’t anything I need.

and yes I’m sure this (the eta housing and the cap) are illegal somehow.[/quote]
I presume that you are referring to the oil filter adapter found on cars equipped with an oil cooler by reference to the snap ring. The assembly held in by the snap ring isn’t a “pressure relief” and is in fact a thermostat that enables/disables the oil cooler based on oil temperature. Removing the thermostat and welding up where the cap went will result in very little oil flowing through the cooler. To have full flow trough the cooler, but no thermostat, move the spring to the other side of the thermostat.