Fuel Mixture and Engine Temperatures

[Jandrews]

Hello,

My '73 RS spec coupe seems to wnat to run excessively cool. I know that is not a typical problem for 911 owners and it used to not be for me. I added a front mounted Mocal oil cooler and dropped the average running temperature by nearly 50 degrees!

The problem that I have now, is that as Fall is approaching here in the Midwest, and temperatures are lingering in the 50's and 60's, I don't seem to be able to get my engine up to "operating temperature". I will drive for 45 minutes to an hour in stop and go and highway, and my guage still reads around the 140 or 150 degrees mark.

Granted the guage may not be completely precise, but I think I am definitely running cool. The oil lines to my front cooler do not get warm, indicating that the thermostat is not opening. I have verified operation of the thermostat, as on track days during the summer, my temp gets in the 210 range and the oil lines to the front are hot.

Anyway, now for my question. My car has MFI, and seems to run rich. I don't think it runs richer than anyone else's MFI, as it doesn't smoke and has lots of power. I know about the concerns of raw fuel washing the rings down, diluting the oil, etc..., and I know that MFI and rich running cars in general will cause cooler engine temperatures. My question is just how rich would you have to be running in order to get these super cool temperatures? Also, any other ideas on what might be causing this 911 to be too cool? No pun intended!


Thanks,

JA

------------------
John
70/73 RS Spec Coupe

[Bill Verburg]

Most likely what is happening is that the engine mount cooler is dissapating the entire heat load. Though there are 2 thermostats which nominally open at the same temperature, the engine mounted one sees the hot oil first, cooling it enough to prevent the wheelwell one from opening. this phenomena manifests itself as 2 shelves in a time vs temp plot. If ambient temps are low enough the second shelf is never attained. It is normal, both my 72 S, and 76 Carrera 3.0 exhibited the same behavior.

I am no longer as familiar with MFI as I once was, but I seem to remember that the main temp dependant item to check on was the heat riser and free movement of the injection pump thermostat rack. I'm sure that Warren can provide better info in that area.

------------------
Bill Verburg
My Home Page My Pelican Gallery page My Porsche Owners Gallery Page

[Superman]

No, I don't think a rich mixture can be blamed for cool engine temps. The mixture contributes to cylinder heat temps, but does not contribute to oil temps much at all. Oil temps in Porsches and also, (believe it or not) engine temps generally, the main and rod bearings are making the heat. that's primarily where engine heat is generated not the cylinders. Lean mixtures can melt spark plugs and pistons and burn exhaust valves, but they won't boil the oil.

In the winter, when we have thick, very humid 25-40 degree morning air, my car also never gets a warm front, trombone cooler. The oil temp never gets to the first line on the gauge. Normal. Relax.

------------------
'83 SC