Let's Talk Oil Pressure

[North Coast Cab]

Wanted to do this for some time. Here are the oil pressure my car reads. What do you think?

Cold Idle 3.8-4.0
Warm Idle 1.2
2000RPM 3.3
3000RPM 3.8-4.1
4000RPM 4.2
5000RPM 4.4

JG

[rstoll]

Looks pretty much like mine.

[North Coast Cab]

I've got 127,000 miles and no major rebuild I'm aware of. So you've got an '83 SC in the same shape. Are these good number or bad numbers and do they indicate anything? I'd love to find someone who recently did a rebuild and compare.

JG

[rstoll]

I think they are fairly normal readings. I have about 20,000 more miles on mine. Still running strong. I have had it for about 2.5 yrs. Has been a real dependable car, although not a daily driver.

[fogcity]

Thats weird. If we're talking about the Druck Press, I have an '84 with considerably higher readings. It has 178,000 miles with no major engine work done as far as I know. The mechanic just did a compression test and all checked out fine (I think the numbers where between 135-155). The Druck Press wasn't working for quite some time I was told (I bought the car a month ago) and I just fixed it a week ago (the wire under the shrink wrap came off the sending unit).

cold idle @ 3.5-4
warm idle @ 2.2-3.2
Whenever I check the gauge at speed it reads @4.2-4.9, although I'm usually at around 3k rpms. The temp gauge needle always stays just below the first SMALL (skinny) white line and in bad traffic it creeps up to just above the white line.

[North Coast Cab]

Mine drops quickly as the RPM's drop. Drive it a little and then see where it settles at idle, it will probably drop below the figures you show. Now where's the post on the newly rebuilt engine?

JG

Oh, and congratulations on the choice of car.

[sammyg2]

What kind of oil are you running and at what viscocity? that makes a big difference.
My owner's manual for a 1980 SC states: " with the engine at operating temperature (194 degrees f, 90 celcius) and an engine speed of 5000 rpm the oil pressure should be about 4.5 bar.......a drop in oil pressure at higher temperatures is normal. At idle speed, with the engine oil hot, it is permissible for the green control light to light up-this does not indicate any loss of engine performance. "

Thicker oils will show higher oil temperatures, thin synthetic oil will show lower pressures in most cases.

[North Coast Cab]

Castrol GTX 20-50

The 4.5 Bar @ 5000RPM sounds right on. I'm, more concerned at lower RPM and when Idling. I have a new set of cam oil lines to install and I purchased the newer adapters with the smaller orifice to provide increased oil pressure. I juts want to cover my bases before I install.

JG

[fogcity]

It doesn't drop that much. I use Valvoline 20/50 All Climate. I'd imagine that there's many a subtle differance from guage to guage as well.

[TimT]

are you guys using the oem oil pressure gauge?

check your gauge against a known mechanical gauge sometime.

one of my engines shows 0 psi at 1000rpm (on the oem VDO gauge) when I hooked up a mechanical gauge i had 15 psi AT 1000RPM.

[jwetering]

The rule of thumb is 1 bar or better for every 1000 rpm when the car is hot. So 3000 rpm should be 3 bar or better, 4000 rpm should make 4 bar or better, etc. At idle it doesn't really matter what the oil pressure is because the engine isn't working so it doesn't need oil pressure, and the guages aren't that accurate at those low pressures. Also, when the car is cold, the oil is thicker so oil pressures are higher - also not readings you should pay much attention to when evaluating an engine's health.
Hope that helps.

[fogcity]

Does "better" mean that you can't have too high of an oil pressure reading?

[Mike Kast]

Originally posted by jwetering
The rule of thumb is 1 bar or better for every 1000 rpm when the car is hot. So 3000 rpm should be 3 bar or better, 4000 rpm should make 4 bar or better, etc. At idle it doesn't really matter what the oil pressure is because the engine isn't working so it doesn't need oil pressure, and the guages aren't that accurate at those low pressures. Also, when the car is cold, the oil is thicker so oil pressures are higher - also not readings you should pay much attention to when evaluating an engine's health.
Hope that helps.

My engine rebuild has about 8 or 9000 miles on it. jweterings post is on the money from what I have heard and seen

[jwetering]

Does "better" mean that you can't have too high of an oil pressure reading?

Unlike blood pressure - high oil pressure is a good thing. I don't think the oil pump would give enough pressure to do any damage. There are a couple of pressure relief valves which control the oil pressure at the high end, but when these fail, it's usually that they get weak, or stick open and don't allow oil pressure to build. In the unliley event that they were to stick closed, I doubt any damage would be done.

I've sure never heard of too high oil pressure.

[HawgRyder]

Too high an oil pressure can wash out bearings.
By too high...I mean very high....in the 100+ area.
Oil flow is more important....a good high VOLUME oil pump is normally called for in very long life engines.
And...the oil pressure relief valves can be checked for operation (and should be) whenever you change the oil (if only by checking the higher pressure relief by reving the engine when it is fairly cold).
The pressure should rise quickly then stay at one point reguardless of revs (higher)...this shows the high press relief is working.
Oil is the lifeblood of the engine....keep it cooled...keep it clean.
Bob

[silverc4s]

Guys,
Before anyone gets panicked and tears their engine down, let's get a good hold on the numbers here.

First of all, Druck means Pressure in German, so Druck Pressure is redundant usage..

The Druck gauges are in bar, 1 bar = 1 atmosphere at sea level, or about 14.7 psi

I think the gauges labelled Pressure are all calibrated in PSI increments of 10 psi per line - NOT THE SAME THING as 1 bar!!!

The rule of thumb, going way back to something writtten by BA in the good old days, was "about 10 psi per 1000 rpm" as a good minimum oil pressure for a warmed up 911 engine.

The pressure should bypass at about 60 to 70 psi some where, if it is not, that's a problem too.

So, to close 1 bar per 1000 rpm would be on the high side of expectations, not an average reading...

[fogcity]

I thought "Druck" meant "Oil"? Man, my German needs some help

[jwetering]

Oil in German is OEL - that's on your oil level guage next to the temp guage.

With respect to guage labelling - I'm pretty sure the ol' DRUCK PRESS guage is incremented in bar. I can't see the germans using pounds per square inch since they don't really recognize pounds or inches as valid units of measure (we canadians don't either).

My SC used to produce just over one increment per 1000 rpm of engine speed. Over time this dropped to just one increment per 1000 rpm.