Thread: scary noise
View Single Post
spuggy spuggy is offline
Registered User
Join Date: Jul 2003
Location: Glorious Pac NW
Posts: 2,831
Originally Posted by Alan L View Post
But when it was labouring at about 300-500 rpm (and running a bit roughly) you could hear a definite knock.
Errr. Just about any engine will do that running at half their idle speed.

Don't let it do that.

Hell, the only time I drop down to 1,000 RPM after starting the car and before the oil is 190 degrees is when I'm shifting into 1st or reverse. (and Grady Clay's tip of shifting into 2nd before 1st or 3rd before reverse is golden for preventing "clang" without waiting 30 seconds with the clutch in for the shafts to stop rotating for me).

I keep the revs up to about 1200-1400 at stop lights until the oil is hot - the difference is the difference between 25-30 PSI and 60 PSI oil pressure - and who knows how much more flow?

Folk lore says that most wear happens when the motor is cold and oil isn't flowing well. In aviation, the life of a piston engine is not only measured by hours run, but cold and hot starts are also logged...

3 bar at idle just seems weird, I think.

If cold, mine would read around 60 PSI (4 bar), if I ever let it idle (and the owners manual says not to do that as well). But this is meaningless - and depends on what oil is in it too.

At a 2,000 RPM fast-idle it reads 100 PSI (nearly 7 bar) when cold until the internal thermostat opens. And then it maxes out at the "protect the external oil cooler" pressure of 70 PSI (5 bar) once that happens.

If it's hot it generally reads just over 20-25 PSI at idle.

That darn well better be right, it's got about 5,000 miles on a complete rebuild...

I think the rule-of-thumb for all 70's and later Porsche is "1 bar at idle, 1 bar per 1,000 RPM and peg @ 5 bar". When hot. If you have those minimum figures, you're good.
'77 S with '78 930 power and a few other things.
Old 12-12-2007, 10:18 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)