This article, originally written in 1989 has been redone as a retrospective look at the form and function of Porsche oil coolers. Since the original article, I have had additional personal experience and gathered further information about Porsche oil coolers.
The purpose of the article is to provide a basic understanding of oil coolers offered in recent Porsche history, and assist you in coming to the best possible decision, should you decide to add or upgrade a Porsche oil cooler.
My original ventures into exploring oil cooler options proved to be an expensive process for me; it didn't have to be. My overly enthusiastic approach was to gather my data first hand, purchasing and installing the various coolers in a staged process and evaluating their utility on street and track. I don't recommend this approach: Too costly. Do your research thoroughly; you will make the appropriate decision to best meet your needs.
Perhaps you recall the moment you first became aware of shortcomings in your present oil cooling system. For me it occurred on a warm summer day, driving my 911 at a Time Trial. Routine checking of gauges is part of the driving process. While doing my checks, I observed the oil temperature indicator needle had risen well past the middle of the gauge, indicating a very warm engine on the way to becoming extremely warm. For those without numerical indicators on their 911 oil temperature gauge, midway in the scale is approximately 230 deg F.
I wanted that oil temperature to drop, immediately! As an immediate corrective measure, I got out of the throttle, took a cool down lap and brought the car in. Decreasing engine demands did bring the temperature down, but also made serious inroads into my Time Trial practice.
Should you experience a warm, to hot 911 engine in heavy traffic, step one, turn off your air conditioner; this may remedy the situation temporarily. However, should oil temperature remain very warm, or continue to rise, consider getting off the well traveled road and find a less crowded surface street where increased speed will help optimize air circulation around your fender mounted cooler, assuming you have a 78 or later 911 SC. Recall that from 1969 through 1977, oil coolers were optional on many Porsche models. They only became standard upon the introduction of the 1978 SC's.
So why the concern with 911 engine oil temperature? How important can it be? After all, the Porsche factory oil temperature gauge in 911 cars delivered after 1975 no longer indicates the oil temperature in degrees. This would seem to indicate that knowing engine oil temperature is not all that important. Can this be true? Not!
Here is what we know for certain: Heat is the major enemy of the air cooled (oil cooled) 911 engine. Excessive engine heat resulting from inadequate oil cooling robs the engine of horsepower and may serve to drastically shorten engine life.
As a possible first step, consider modification of your oil temperature gauge to indicate temperature in degrees, the way it was done on the earlier 911's. Obviously this fix won't cool your oil, but it will let you know your actual engine oil temperature, contrasted to the vague estimate provided by the standard Porsche non-numerical oil temperature gauge.
A calibrated replacement gauge is available from various aftermarket sources for approximately $60.00 and is easily installed with a screwdriver once the oil temperature/oil pressure gauge is removed from the dash.
With 1978 to 1989 911's, gauge removal is accomplished by firmly grasping the outer lip of the gauge and rocking it side to side while applying steady pulling pressure breaking it loose from the large rubber grommet holding it in place in the dash. First apply this technique to the tachometer. It has a large surface area and is generally easiest to remove. Once the tachometer is out and set temporarily off to the right, reach in behind the combination oil temperature/pressure gauge and gently press it out of the dashboard. Disconnect the gauge, noting where the wires are to be reconnected. Unscrew the old temperature portion of the gauge and replace with the calibrated temperature gauge. Reconnect the wiring and press the gauge back into position. Replacement of the tachometer completes the job. From this time forward, you will have an accurate indication of your car's engine oil temperature.
What has Porsche done to address potentially excessive engine oil operating temperature? Since the first 911's, they have supplied the 911 engine with an internal oil cooler. Trust me, it is there; you just can't readily view the cooler.
Over the years, Porsche has recognized that excessive engine oil heat must be addressed and produced an evolution of cooling devices. For U.S. cars delivered since 1969 and through the 1989 Carrera, Porsche has offered four different styles of oil coolers, either installed as an option, or included as standard equipment. The open aluminum radiator available from 1969 to 1972, the loop cooler (Often referred to as the trombone cooler because of it's trombone like shape.) from 1973 through 1983, the 28 tube brass cooler first introduced to the U.S on the 1984 Carrera, and the shrouded aluminum cooler delivered on the 1985 Carrera, with an "active" fan added to these coolers in the 1987 through the 1989 Carrera model run.
The first aluminum radiator coolers, available from 1969 through 1972, are located in the right wheel well, exposed to the elements. As a result, the radiator is subject to corrosion and could potentially be damaged by road debris coming off the right front wheel. These factors led to the demise of the open aluminum radiator and the birth of its replacement, the loop cooler first appearing on the 1973 911S.
U.S. delivered 911 SC's, from 1978 through 1983 have the loop cooler. This system consists of the initial flexible hose connections from the engine connected to tubing running forward to a thermostatically controlled valve located in the right rear, wheel well. When the proper oil temperature is reached (approximately 182 deg F.) the valve opens, and the pressurized warm oil is routed forward through tubing to the loop cooler mounted in the right front fender well, ahead of the wheel. Once at the loop cooler, the oil is pumped vertically to the top of the cooler, making a 180 degree turn, falling to complete another 180 degree turn upward, around and down to complete the cycle.
Once the loop cooler cycle is complete, the cooled oil is redirected rearward through a brass lines to the engine, passing again through the thermostatically controlled valve, and making the final connection to the engine using flexible tubing.
Both the aluminum radiator and the loop cooler are "passive" in the sense that the coolers perform their function by passively transferring heat from the oil pumped through them into circulating air. There is no fan directing air to optimize the process. Passive coolers denied circulating air, such as when sitting in traffic on a hot day, lose their efficiency.
The 1984 U.S. Carreras were delivered with a "passive" 28 tube brass radiator first seen on the 1980 R.o.W.(Rest of World/non-US) SC's. 1985 and 1986 911 U.S. models were delivered with a "passive" shrouded aluminum radiator, as well as front bumpers incorporating a notch in the right lower corner, added for the purpose of providing increased air flow to the radiator.
1987 to 1989 U.S. cars come with an aluminum style radiator, complimented with a powerful electric fan placed at the front end of the radiator. The fan, transforming the "passive" radiator into an "active" unit, is energized when a thermocouple device built into the top of the radiator senses oil temperatures reaching 118 deg C. (244 deg F). Bruce Anderson suspects the thermocouple triggering device is set high as the fan generates it's optimal cooling with the oil in the radiator at these higher temperatures.
Next time I'll discuss options and alternatives to the stock Porsche factory oil coolers. Until then, stay cool.