Oil pressure readings on 3 litre turbo

[Mark Crowe]

I have a 1977 3 Litre Turbo, engine number 6770162, that was rebuilt about 10 000 km ago, due to oil leak and a cracked stud. When the engine was started, the oil light came on, and the builder decided to replace the oil pump. The original was no longer available, so he used the upgrade( not sure what this was) The oil light went out, but the guage showed low pressure when running medium speed to high speed, about 3- 4 bar. At idle it shows about 1 bar. Reason for my concern is friends SC and Carreara 's oil gauges run off idle at 5 bar- is this difference normal on a turbo?

Waht should normal idle, mid and high speed oil pressure reading should be?

I believe the relief valve needs to be matched to the pump, how can I check this was done without stripping engine down? A mechanical guage plumed into the oil lines confirms the dash guage is reading correctly

[Eagledriver]

The oil pressure on a 911 should be between 10 PSI and 1 Bar per 1000 RPM. I believe the factory spec is 5 Bar at 5500 RPM when engine at operating temp (196F, 90C). I assume the 930 needs the same oil pressure. If you are getting at least the 10 PSI per thousand RPM you should be ok. That is on the low side but a common thing to see on high milage 911's. They seem to still run a long time this way.

I have run several different rebuilt engines over the last 5 years and with new bearings and used oil pumps they run at 1Bar (15PSI) per 1000 RPM. When cold they run much higher and when very hot (racing) they run a little lower. Thicker oil will also give you a higher oil pressure.

-Andy

[Eagledriver]

Idle oil pressure can be very low (under 10PSI).

The pressure relief valves were changed in 1976. I think all the 930s had the newer valves but I'm not sure about that.

-Andy

[BReyes]

Can you scan the oil pressure and tach and see the value on the oil pressure always reading a little more than the value on the tach.

Regards,

[Dennis Kalma]

Oil pressure is such a subjective thing...in spite of all those guages.

My Kremer shows virtually zero oil pressure at idle (I'd say less than 10psi), when cold or partially warmed up it gives about 20psi per 1000 rpm, peaking at about 100 psi (which I figure is 6 bar or so), but then it settles down to about 15 psi per 1000 rpm when fully warmed up (after about 30 minutes of driving).

I swear I can tell when the external oil cooler thermostat opens as that seems to be when the pressure rated drops off a little...

So my point is that there is apparently some variability in the pressure, it seems each engine and oil combination is a little different.....from my experience you seem to be OK....

Dennis

PS - it is odd to see the oil pressure shoot up when the engine is dead cold (like 10 degrees ambient).....makes me careful warming it up though

[Mark Crowe]

Glad to hear that there are some variances out there! Busy with an upgrade to the turbo(s) so will check how it acts after this mod, before I put in a front mounted oil cooler to replace the serpentine loop so I don't distort the picture even more!

[BReyes]

When is starts gives the highest reading. I had my switch replaced to get a good reading. I was driving my NA 3.2 yesterday and the oil presure was at approximately the the same value as the rpms (actually a little less when hot)

[One-more-time]

I have a 1980 911SC, and changed the brand
of oil and corresponding viscosity last year. Was
concerned about the hot pressure and whether the
gage on the dash was working properly. I found
a mechanical gage that replaces the coupler on
the engine, and still uses the stock sender. I
now see that Pelican carries it. As far
as I'm concerned a very inexpensive piece of mind.

PEL-PBOOGBZZN

Cheers

Matt