I Learned About Air-Cooled Engines From That
Third Edition Vol. 1
After the Yamaha shop was sold, I found out that in three months, I would be unemployed by that establishment. After my departure from the Yamaha shop, and now with plenty of time on my hands, I started hanging around Jerry’s shop and one day he asked me if I needed a job, and of course I respond with a cheerful “YES”! I spent all of that first summer taking apart fifty-three VW engines in every condition imaginable.
The following year I removed the old tired 1300 cc engine out of my ’66 Bug and we built a new 1600 cc engine. Jerry went through the transaxle to rectify the “falling” out of fourth gear problem so my trips back and forth from Big Bear to Victor Valley College in Victorville could be accomplished safer and a little more quickly. As a side note, I had been reading the Hot VW’s magazine, and read an article about installing an auxiliary oil cooler that bolted to the front side of the fan shroud over the cooling fan intake. This article claimed a huge decrease in oil temperature and was advertised as dropping the oil temperature by 20°. “Cool”, (no pun intended). Just what I need for this new engine running up and down the back grade in the summer heat of the SoCal High Desert. After my week-end engine swap at home with the new oil cooler installed per the instructions, and new firewall insulation, I was ready for my test drive around my hometown test track. This track is merely the loop around the lake. After my first lap, I pulled into Jerry’s shop and he asked how it was running. I responded by stating that is was much more powerful, but seemed to run hotter. He asked what I thought might be contributing to this increase of heat, especially at 6,500 ft MSL? I said that I wasn’t sure. Maybe it’s the friction of the new piston rings and cylinders? He asked what other mods I had done, and I said “nothing. Other than that oil cooler, but that couldn’t be it. It’s supposed to drop the oil temperature by 20°”. He said, “I’ll give you your old cooler back and you go home and change it back to the way it was, do another lap around the lake, and then let me know”. I did this as instructed and later that day cruised into Jerry’s driveway to report my findings. “Well? How did it go”? I excitedly exclaimed “It’s running a lot cooler”. “Yeah, I thought it would” he said. I asked him that if he knew it would run cooler with the original oil cooler stuffed in the fan shroud than the “Rapid Cool” oil cooler bolted to the front of the fan shroud, then why did you let me go ahead and install it? He said, “ I tried to explain it to you, but you had to have it”. I said, “O.K., explain it to me again”. And, the following was his explanation.
“The “krauts”, (I say that in an endearing way, as they are my peeps), knew what they were doing when they designed the car and its’ engine way back in the late 1930’s. Remember, the oil performs two functions in an air-cooled engine. Other than the obvious function of lubricating under pressure the vital engine parts, about 40% of the engines cooling is performed by the oil in an air-cooled engine. If you look inside the fan shroud, you’ll notice some airfoil shaped “vanes” strategically located within the fan shroud housing. You’ll also notice that there are these “vanes” just downstream of the cavity where the oil cooler would be, that direct the cooling air down over the number three and four cylinders. Now, when you remove this “obstruction”, (the oil cooler), you create a void, and the air no longer is directed over the cylinders, but now all of the air is dumped over onto the number three and four cylinder head. Now that the cylinders themselves are not receiving the air they once were when the stock oil cooler was installed, the cylinders run hotter, increasing the oil temperature. The hotter oil is now being routed through your new “Rapid Cool” oil cooler, which is mounted over the cooling fan intake and partially covering the air intake area by about 80%. Now, the oil cooler is doing its job by rejecting the heat created by the hot oil flowing through it. And, rejecting that heat through its fins and coils, by the passing air being sucked into the fan shroud, which is then being directed over your already hot cylinders and cylinder heads. You’re essentially “pre-heating” the cooling air used to “cool” the engine. It’s counterproductive and is a big circle that compounds itself very quickly as the oil temperature rises”. I understood this completely, and then asked the obvious. “Then why do they sell these things, if they don’t work”? He said, “well they do, in the right configuration and position”. He then took me out to his ‘66 Panel Van and proceeded to show me a set-up that made more sense. In the engine compartment, Jerry had installed a very large specimen of one of these same type oil coolers close to the left side engine compartment cooling air intake louvers. On the inboard side, he had a thermostatically controlled fan that could pull cooling air through it when the oil temperature rose to a pre-determined number within the thermostat. Now, even though this cooler was mounted in close proximity to the air intake louvers, and that this “warmed” air from the cooler was still entering the engine cooling fan, there is also a set of louvers on the other side of the engine compartment to allow for unobstructed, unaltered cooling air to enter the cooling fan. In addition, these louvers also had those big fiberglass scoops bolted over them. He did explain that this set-up was still not optimum, but it was better than having the oil cooler covering the fan intake. This engine is “full-flowed” and also has the famous “dog house” style oil cooler and fan shroud set-up installed as well.
The optimum set-up would be like what we installed on Chris’ ’64 Bug. In conjunction with the “dog house” style oil cooler and fan shroud set-up, the oil cooler on that car is located on the left side, under the car just behind the torsion housing, and just ahead of the left axle tube. We used the Mesa brand, 48 plate oil cooler set at a 30° angle, housed in a scoop type ducting that exits out the top in the direction of the starter. This set-up is the best, as no rejected heated air enters the engine compartment or subsequently, the fan. We also installed an HP-1 oil filter in the system. On Terminal Velocity, we again used a 48 plate Mesa oil cooler, but mounted the cooler with a HP-1 oil filter behind the driver’s seat, and fabricated an internal air deflector panel, and used the outer body side panel to direct the slipstream air through it. No fan needed, as we still used the “dog house” style oil cooler and fan shroud set-up on both engines as well as both being “full-flowed”.
On the same side of this coin, aircraft engines are no different when it comes to cooling the oil. The same cooling affect the oil has on the VW or Porsche air-cooled engine, has the same affect on the air-cooled aircraft engine. Just about every air-cooled engine has some sort of oil cooling apparatus to aid in cooling the oil. The oil is what carries the internal heat generated by the combustion process, ring to cylinder bore friction, etc., away. The heated oil is then sent to an oil cooling device of some sort, (oil cooler, heat exchanger, etc.) then back to the engine to start the process all over again. In a liquid cooled engine, the coolant flowing through the water jackets provide this vital function of picking up the generated heat, carrying the internal heat away and sending it to a heat exchanging device, (radiator), which, by the same action as the oil cooler, reduces the coolant temperature before it gets pumped back into the engine to start that process all over again. The oil in a liquid cooled engine is merely there for lubrication purposes and related functions only. Very little cooling of the oils is used in most production cars. (Some later vehicles do have this feature though). This is why most late model cars recommend the use of 10W-30 or even 5W-15 multi-visc oil.
I will discuss the importance of oil viscosity at another time. But I will say this. Multi-visc oil has no place in your air-cooled engine. Stay tuned to find out why.