High Oil Pressure on start up - 1977

[kach22i]

High oil pressure on start up, Running Castrol 20/50 dino oil.

A few months ago before I put my car into winter storage and pulled the battery for charging in the house, I noticed on the progressively colder days that the oil pressure was high on start up and until warm.

I think the standard should vary between zero and 20, if I recall correctly.

It should be 20 on acceleration and then dropping to zero at idle, right?

Once the engine was warm I remember getting the 20/0 oil pressure readouts. However because I was driving the car until the first of December in Michigan I was seeing 100 on start up (foot on gas), then dipping down to 40 or 20 until it gets all warmed up.

Running Castrol 20/50 dino oil.

Does the oil really get that thick when it gets below freezing?

Does thick oil mean higher oil pressure?

At what point would you switch to a lighter oil, or is there a problem elsewhere which starts to show up in the cold first?

[wowzer911]

You should be hitting 60 at startup, then lowering to 20 and below.
I always change viscosity for the winter months, just makes sense.

[Richard Burns]

I am using a 20/50 dino oil and I get 4.5 bar of pressure on cold startup(about 60 psi.) with my '77 Carrera 3. Once it has warmed up the pressure can be as low as.5 bar at idle( about 7 psi). Oil when it is cold does seem to be thicker and with the extremes of temperature that you get I would be looking to change to a thinner oil for winter if I was going to drive it of course that is not a problem here as my winters only get to about zero centigrade.

[72 four door]

Your in michigan i would be running a lighter oil in the winter. Upon start up pressure will be higher 60psi then once hot 10psi.

[tcar]

10-40 is better in winter. Or even 5-30 in Mich. That's why it's so high when cold, it's like cold honey.

Should never be zero. Hot, at idle (1000 rpm or so), should be around 5-10 psi.

Should oscillate w/ engine rpm, about 10 psi +/- per 1000 rpm. (1 bar is just under 15psi).

[RoninLB]

running 15w-50 and high cold start up psi.


i keep revs low for a short time after starting till psi lowers then increase for warm up.

[T77911S]

20-50 synth castrol here. if i start driving as soon as i start up i see close to 100 psi, even in the summer, so i take it very easy until warm. hot idle mine is around 15 to 20 psi. 77s in south carolina. porsche changed the pressure to scavenge ratio over the years. the 77's must of had a i much higher pressure pump than the earlier years. maybe someone out there knows the specifics

[kach22i]

Thanks to everyone for the input.

In the spring I'm going to adjust one of my valves which is making a ticking noise. I did my first valves adjustment in the fall, and like all newbies must "do-over" or go back and tweak again.

I just figured that while I have it open that perhaps I should be looking for something related to high oil pressure when very cold.

There was some carbon and gunk which I cleaned off with PB Blaster and WD-40 when I had it open. I'm still wondering if some lines or oil holes (don't know the proper term - sorry) could be clogged.

If an engine is like a heart, then I just want to make sure my arteries are not clogged with fat.

I've read warnings about old air cooled engines and "engine flushes".

If it's not broke - then don't fix it , right?

[tcar]

Still wondering about your oil pressure...

20psi is way too low when accelerating, even when it's hot, should rise w/ rpms. Should never be zero.

[kach22i]

Originally Posted by tcar

Still wondering about your oil pressure...

20psi is way too low when accelerating, even when it's hot, should rise w/ rpms. Should never be zero.

I guess it depends on how hard you accelerate, right? When cold I thought the pressure was way to high, over 100, almost 140 with a pump of the gas. I thought I was going to blow the dial up.

I'll watch what's happening in the spring. The whole 20-0 thing was from what I recall in an old thread. The guy who first made the statement never answered a follow up question so I've been hanging on this for a while. This rule is close to the truth for my engine from what I remember.

I started this thread so that I have time to think about these things, and when spring comes I know what to be looking for.

[wowzer911]

Below 20 is common for the 2.7L when hot, even below 10.

[tcar]

Originally Posted by wowzer911

Below 20 is common for the 2.7L when hot, even below 10.

Yes, at idle, but not at 4000 rpm.

[kach22i]

There must be a chart or graph which shows temperature, rpm and oil pressure.

If I find one I'll post it in this thread.

May take a while.

[tcar]

There was a brief one several months ago, basically said that, within reason, at full operating temp, oil press increases at about 10 psi (.66 bar) per 1000 rpm.

[AshEvan]

Originally Posted by tcar

There was a brief one several months ago, basically said that, within reason, at full operating temp, oil press increases at about 10 psi (.66 bar) per 1000 rpm.

That is a good way to gauge oil pressure. As your RPM increases, so should the oil pressure proportionately, when the engine is warmed up.

Just my 2 cents.

[tshih]

Make sure that the wire from the pressure sender is getting good ground, otherwise the gauge pegs high.

[djdsc]

Having personally had two motor mounted oil coolers blow on a ‘77S I would caution just letting this go. My circumstances were much as you described, cold weather, still using summer weight oil and very high oil pressure on initial startup.

With the first cooler blowing I just wrote it off as a failure even though few professionals I spoke with had ever seen a cooler split like this one. When the second one went a year later under the same winter conditions, everything to do with pressure was checked and replaced. An old timer finally mentioned that the horizontal pressure piston on these motors can get sticky and result in an over pressurization of the system on cold start-up. It seems that seals would have blown prior to two oil coolers.

The car is long gone so I have no knowledge of the long term effects of the repairs; just telling a story.



You can see the split line running down the middle of the weld.

[spuggy]

Originally Posted by kach22i

High oil pressure on start up, Running

Once the engine was warm I remember getting the 20/0 oil pressure readouts. However because I was driving the car until the first of December in Michigan I was seeing 100 on start up (foot on gas), then dipping down to 40 or 20 until it gets all warmed up.

Running Castrol 20/50 dino oil.

Does the oil really get that thick when it gets below freezing?

I've got a '77 tub, so I've got the 140 PSI pressure gauge as well.

Unlike you, I've got a '78 930 motor. I always run the motor @ 2,000 RPM for good oil flow for a little while after starting.

That's 100 PSI. Spring, summer, winter or fall. More revs == higher pressure, but I like to keep it down.

After about 90 seconds, two minutes or so, I see the engine thermostat open, and the pressure will dip quickly (to about 70-80 PSI, there's no markings there so I'm just estimating) once or twice as it allows hot oil out. If I wait long enough, pressure will stablise around 70-80 PSI (engine thermostat fully open), but I generally drive away as soon as I see two or three dips in quick sucession.

When I drop the revs to select gear, the pressure will fall to just over 60 PSI. Spring, summer, winter or fall.

I think the rest is specific to the 930 (like hot idle is 20-25 PSI, and if I didn't have better than 60 PSI @ 3,000 RPM I'd pull over and stop), but the startup is identical to what you describe.

Right now, I'm running Shell 15/40 Rotella T Heavy Duty, but it really doesn't seem to vary at all regardless of the oil. Although I could always tell when my 944 was about due for an oil change, because hot idle pressure would drop from 2 bar to 1 bar...

[kach22i]

Originally Posted by djdsc

Having personally had two motor mounted oil coolers blow on a ‘77S .............

Six years ago and just a few weeks after I first purchased the car the rear oil cooler failed. It was October and the mechanic said it was rare to see one crack like that.

It's hard to tell from the diagram, where are parts 29 thru 32 exactly?

[stevemfr]

No real need to make a chart - unless you want to be very scientific about things. As mentioned above, very high oil pressure is the norm on cold start. Taking it easy is a very good idea, and not alone for the oil pressure. During my tenure as a mechanic in a Porsche shop near Munich (10+ years ago), this was a discussion topic every winter. New pressure relief pistons didn't really seem to make a difference. I don't remember ever hearing of a blown oil cooler, but then again a good %age of these cars had hoop-coolers.
As far as hot pressure goes (80deg C), the Porsche Tech Specs booklet calls for ~1bar/1000RPM's. The mag case motors suffer from out-of-round main bearing saddles at higher milage - which in turn leads to lower hot oil pressure. As this is a prob only rectified by tearing down the motor, there's not much to be done other than living with it until rebuild time. I remember my 2.7 being very near the top of the 10 bar (150psi) pressure guage in the winter and worrying while 'bahn-storming on hot summer afternoons with the motor at 5-6000 rpm's for very long stretches (very long. 20+ mins) with the oil pressure at ~4bar. That motor ran strong for many km's before being torn down for a hp increase - and showed no excessive wear probs on tear-down.

All that being said, the oil press. sending unit and guage are not precision pieces (especially at 30 years of age). If you really want to know where your pressure is, you'll have to (temporarily) install a mechanical guage at the motor. But I really don't see the need in making a sience of it.