911 3.0L SC oil cooler system.

[srf911]

Hi,

Just in the process of an engine refit and general tidy up of my 1978 SC. I'm looking at the oil cooling lines all the way to the "trombone" style cooler and I have to ask, "How important is the auxiliary oil thermostat/pressure relief valve, just behind the right rear guard"?

Could you simply delete this and run fresh lines to a cooler mounted at the front? as the engine already has a primary thermostat/relief to regulate engine oil temp. I'm in Australia so the climate might not necessitate this extra cooling regulation anyhow?

Would appreciate any thoughts others may have.

Cheers,

[Dr J]

Once a mechanic removed the innards of the thermostat to the front cooler, thus allowing it to be activated all of the time. I went back and told them to put it back, because the oil temperature was too low. I would drive in traffic for half an hour in Miami and it would be difficult to reach 170F. Best operating temp is about 180-210F. My oil cooler is in the front spoiler and is much better than the trombone cooler.

[boyt911sc]

An oil circulation system for 911 with auxiliary cooler (trombone or carrera cooler) must have an auxiliary thermostat. Otherwise, it would cool down the oil prematurely causing to prolong the time to get to operating temperature. It might not even get to the operating temperature when weather is cooler if you don't have an auxiliary thermostat.

The engine thermostat opens @ 176°F while the auxiliary thermostat opens @ 186°F. As the warm circulating oil from the engine reaches the 186° temperature range, the auxiliary thermostat would start to open and allowing the hot oil to circulate through the cooler. The colder the environment, the more is the need for an auxiliary thermostat.

Tony

[chrismorse]

I don't know what the pressure is in the scavenge side of the oil system, but the pressure side is showing 100 psi when cold @ 3000rpm.

Without the pressure relief, it may be possible to rupture the cooler when cold. Take a look at the diagram. The factory put in the system for a reason. I could also be reading the whole thing wrong too.

chris

[srf911]

Thanks for the info., DrJ and Tony. Thanks also Chris for the oil flow schematic diagram. I think your right, the factory would have thought about this in far more detail than myself.
The more I think about it, without the relief valve the system it is "open ended" and might cause too much "foaming" in the oil tank. Worse than that, the scavange pump may need a degree of back-pressure to prevent excessive cavitation on the suction as it scavenges oil away from engine.

I think I will be leaving well enough alone, leave the thermostat/relief in it's original designed location!

Thanks,

Scott.

[Walt Fricke]

Scott

Good decision. But I don't think the scavange pump needs back pressure, at least not more than is provided by moving oil through all that piping, not to mention a cooler or coolers. I don't run a thermostat on my race motor, so the oil eventually just dumps into the tank which is, via a breather, open to the atmosphere. Haven't had any problems. But I fuss with getting the oil somewhat warm (a heater if really cold, cardboard over part of the coolers, some time idling to wrm things up), which would be a bother if you wanted to jump in the car and go somewhere in cool weather.

[srf911]

Thanks for the info., Walt. Looks like the only issue may be as you mentioned, excessive cooling which is not ideal on cold start up in relation to engine wear. I'll probably leave as is I think.

Cheers.

[MBruns]

We had a cust. that had direct - 16 plumbing through an Oberg filter to a big ruf front cooler, with 50wt oil and a cold Fla. morning a blip to keep it running jacked all the 3/8' threads out of the filter housing, so I installed a press guage in a temp fitting before the cooler and tested it and pegged the 250 psi guage with a blip of the throttle, so yes you need a press bypass and a thermostat or be very careful when cold. The scavenge pump does not have a bypass so it can produce enough to possibly split the pump if something else doesn't fail first.

Mike Bruns

[Steve@Rennsport]

Originally Posted by MBruns

We had a cust. that had direct - 16 plumbing through an Oberg filter to a big ruf front cooler, with 50wt oil and a cold Fla. morning a blip to keep it running jacked all the 3/8' threads out of the filter housing, so I installed a press guage in a temp fitting before the cooler and tested it and pegged the 250 psi guage with a blip of the throttle, so yes you need a press bypass and a thermostat or be very careful when cold. The scavenge pump does not have a bypass so it can produce enough to possibly split the pump if something else doesn't fail first.

Mike Bruns

I'll mirror Mike's comments and experience and simply add that I've seen the same thing happen with 20w-50 oil.

Everyone certainly has their own opinions about this, however I'd never do an oil cooler system installation anymore without that factory thermostat/pressure relief valve in the system. Its cheap insurance.