Oil pressure at full operating temp

[Hatari]

I just completed a top end on a 72' 2.7 (yep, it is a 2.7...converted as Mr. Anderson prescribes in the handbook). I did not split the cases as there seemed to be no reason to. The #1 head gasket blew precipitating the rebuild. Engine runs great, no smoke, no compression losses, etc. I can report (according to the almost 39 year old gauge) respectable (60lbs. at 3k RPMs) oil pressure until the point the engine reaches full operating temp. I am running 20w50 Castrol GTX. At full temp, the pressure averages reading about 60% of when the engine is cooler. I installed a new ground strap during the restoration, but no new gauges or sending unit. The 81' SC I am temporarily custodian of seems to have much better oil pressure at all temps. Any thoughts?

Thanks,
Jack McAllister

[rstoll]

39 yr old?

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Robert Stoll
83 SC
83 944

[Hatari]

Almost 30yrs. old. My mistake.

[Joeaksa]

Jack,

One bar per one thousand RPM's is the standard oil pressure at normal operating temp. This is usually measured at 4000 and thus four bar. The bar is plus/minus 15 psi (believe its 14.6 or so), so your 60 PSI sounds good.

Personally I would recommend switching over to Mobile One if you get too much past 220 degrees on a regular basis. Anything over this temp is just too high for me and "dino"
oil... IMHO...

Joe

[BRAINIAC]

The older engines (pre-77 I believe) have a smaller pressure pump than the later engines like your SC. 10-15 psi per 1000 RPM is the spec. My owners manual for my 72 says that oil pressure should never drop below 70psi @ 5500 RPM. That's probably where the gauge is most accurate. At idle I don't think they are that accurate.

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Tyson Schmidt
72 911 Cabriolet
92 C-2 Cabriolet

[wayne savage]

In my onwers manual for 72S states: "The engine oil pressure should be read when the engine is warm, that is 176F and running at 5500rpm. oil must not drop below 70psi" It dos not say at 210F it should be 70psi. So I too am a little confused on this one. At 176 I have alot more than 70psi but at 210 I am struggling to get 60PSI.. at 5500rpm ..I think this needs some clairifcation.

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You can stick a Beetle motor in a 911.But you can not! Put a 911 motor in a Beetle....
Wayne Savage 72S MFI

[Early_S_Man]

Jack,

It was the '76 models for which the scavenge pump size was reduced and pressure pump was enlarged ... that could be one reason for SC pressure being higher.

But, there are other possibilities, too ... including weakened bypass springs, and unless modified/updated, both of your springs are probably the 70 mm size, and probably should be replaced. If your oil system has been modified to the '76 bypass, per B.A. then you would have the later solid, grooved pistons in place of the early perforated pistons.

It is possible that one or both of your bypass pistons is stuck in the bore.

If either of the springs is significantly less than 70.0 mm, then the left, horizontal one should be replaced, and an updated 86 mm spring and guide installed in the vertical, right case one's place.

Removal of the plugs requires a very precise-fitting drive bit, approx. 1/8" x 3/4" and it should be filed/ground to fit.

Finally, even if your sender is OK, corrosion in various wiring harness connectors could be playing a part in low gauge readings! The wire goes through both 14-pin connectors in the engine compartment before heading towards the dash area!

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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[Early_S_Man]

Jack,

I'm not sure that this is a clarification, as it just points out another discrepancy from the elves own publications from the Black Forrest, but:

Per '72-'73 spec book -- min. 78.2 psi, max. 99.6 psi (5.5 - 7.0 kp/cm^2) at 5000 rpm and at 80 degrees C, 176 degrees F.

Per '78-'81 spec book -- 4 bar, 55.6 psi at 5000 rpm, at 90 degerees C, 194 degrees F. ...

Seems to me the new SC is being held to a somewhat less stringent spec, especially considering their larger pressure pumps! Maybe we should give the older gals a break and use the SC spec, you reckon?

My recommendation, Jack is to give both cars a test, uncluttered two-lane road, 200 degrees F oil temp ... 5000 rpm steady for 10 to 20 seconds in 2nd gear ... take note of oil pressure gauge reading!

My thinking at this point is that you DON'T HAVE AN OIL PRESSURE PROBLEM!

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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[Hatari]

Thanks all for the feedback. I'll recheck the reading at 5,500 RPMs this week...based on memory, I'm probably in spec at that engine speed. Warren, as you point out, I probably do not have a pressure problem. As you coached me through the rebuild, I paid close attention to the internal parts of the engine that did not get replaced and they were in seemingly good condition. Even the old piston rings were in BA's side gap spec. After a little touring in the SC, I just got concerned. For all I know the oil pressure guages in the two cars (72' vs. 81')may actually work on a different scale.

I have Mobil 1 for the post rebuild oil change which is coming up soon.

I will check the bypass valve and condition right away.

Thanks again to all.

Jack McAllister

[not_sure]

@ idle, mine is just above zero, but goes up well with the rpm range.

[Hatari]

Well, I'm good at the 5,000 RPM and 190 degree mark. Got the full (maybe even a little extra) 55 PSI. Thanks to all of you.

Sure sounds good up there too.
Jack McAllister

[J P Stein]

This may be much ado about nothing, but when you're new at the 911 engine rebuild game, you worry about everything.

Like Jack, my 76, 2.7L reads about 2.5 bar @3000 rpm when hot. I did all the latest oil thingys, with the exception of the improoved
pick-up screen (which I will rectify at the next oil change).

I hear that the case squirters begin to work at around 43 psi. I would prefer the were doing their job at 3K, rather than being along for the ride.

I have also read that the newer Carreras had a smaller dia. hole in the hollow bolts at the cam towers, designed to improve low rpm oil pressure. One would hope that this is not detrimental to the top end oiling.
Any info here?

JPIII