The Story of the Oil Temperature

Reprinted from 1958 Christophorus Magazine

   Recently a letter from America reached the Editor's desk and it will be answered here coram publico because it touches questions and problems which are probably of common technical interest.  It is written by Melvin W. Cole, an engineering student who bought a 1953 Porsche coupe with a Super engine in which, however, the roller bearing crankshaft-why he didn't write us-was replaced by the plain bearing model.  He is now worried about the oil temperatures and asks: Is this a common occurrence, these high oil temperatures, or do they only concern my motor and what can I do about it?  "Here in Bakersfield," writes Mr. Cole, "The summer temperatures often lie above 105 and even after relatively short drives I get oil temperatures of over 250.  My best friend, however, has a 1955 Porsche and in his the oil temperature never goes over 195.  I have never," Mr. Cole reports further, "driven a car in my life that gave me as much pleasure as the Porsche and therefore the high oil temperature is a particular headache."  Dear Mr. Cole, I would like to start my answer, your worries are not new and we have often been queried on this point but I believe that this theme has never been handled in "Christophorus"-certainly a sin of omission!  Where does the limit actually lie?  That depends on the maximum oil temperature we can accept in the car without suffering damage to the soul-that is, to the motor.  What do the Porsche engineers say to your worries?  Well, we will ask them.  The oils of well known firms-trademark oils, we might say-are so far advanced today that even at a temperature up to 320 the oil film in the bores does not break down and you can still consider the lubricating ability to be sufficient.  The Porsche engineers are of the opinion that the maximum oil temperature that our motors can be expected to sustain without serious damage is 280.  However, there are some thoughts to be noted.  For instance, only since July 1957, have Porsche motors done away with the camshaft drive gears of plastic.  Now they are made of light metal.  The plastic wheels are somewhat more susceptible to temperature than the light metal ones and when you drive a long period between 250 and 280 degrees the life span of the plastic cogs sinks and you must not be surprised if one gives out some day... The performance of a motor decreases at such high temperatures.  An engine usually reaches its horsepower maximum at 175-195.  At a greater motor heat the filling degree is lessened-warm air needs more room and that decreases the performance.

   A remark inserted here.  Of course we are talking here only of pushrod motors, not of the Carrera engines.  For them there are different values.  A Carrera motor should usually never go over 210-230 which is assured by the special oil cooler in this model.