Cooling the air-cooled VW motor in the winter is obviously not an issue. At least it shouldn't be. (If it is, something is wrong.)
But, cooling in the hot summer months is a common problem for folks with old VWs ... especially folks with modified engines who live in the HOT places. The original stock VW motor/exhaust system actually works pretty darn well -- in hot or cold.
We all run into the heat issue when we increase the displacement, add bigger valves, taller cams, add dual carbs or larger carbs, merged exhaust systems, etc.
Sure, the engine tin and engine compartment seal need to be installed correctly. However, that alone won't solve the problem.
First of all ... what is considered to be a HOT oil temperature? The VW books say the normal operating temperature should be between 180F and 220F. Again, these figures are based on a non-modified VW motor, but, modified of not, an air-cooled motor can only get so hot. (Side note: VW motors are pretty amazing. I've seen engine blow demonstrations at car shows where they drain the oil and then rev the thing wide-open with a weight holding the carburetor throttle arm down. I remember seeing one run for 11 minutes before blowing. Incredible.)
A VW mechanic friend of mine says the upper limit of the temp range can be higher than 220F. Most people start to freak out when the temp reaches 240F, but he says it's not uncommon in the hot weather states to run them up around 250F. Perhaps not uncommon, but it's not advisable either... In my opinion, you're really flirting with disaster if you run your motor like that for very long. And, who wants to risk blowing up their expensive new motor, and spraying oil and metal bits all over their shiny new paint job?
Having said all that, I think a modern oil temperature range on a modified engine could safely fall between 180F and 230F. MPO
I think that super beetles cool better than bugs. That's kind of a given. They're uglier (sorry super beetle fans), but they were designed MUCH better -- from the ground up. No comparison. They finally got the correct amount of air circulation through the engine compartment by adding the side intake scoops. I think that the old bug hard tops cool better than convertibles. I think that convertibles cool better with the top up rather than with the top down -- especially the older models. The deck lid only has two sets of little slits, and the air seems to get deflected around them when the top is down. So, if you're like me, and you're running an old convertible bug with the top down, you're at about the worst configuration possible for cooling your motor. Add a modified motor to that equation and it's even worse.
Anyway, here's what I did to my car to help the situation:
Here's a decent shot of the fan from the rear - and an electric thermo-switch that I also installed. Its purpose is to automatically turn on the fan when the oil temp reaches a certain temp (I forget what it is) ... and only when it reaches that temp. Until then, the fan doesn't come on. However, it didn't work very well for me. It wouldn't switch on at the right time. Maybe I screwed it up during the installation? I'm not sure. Anyway, instead of an "automatic" switch, I ran the wires up to the front and installed a manual switch. It was not a planned modification, but I really like it this way. During summer driving, I have the ability to reach down below the dash and turn the electric fan ON and OFF at will. I can monitor the oil temp on my VDO gauge while driving, so I have complete control over the fan. The manual switch I installed also came with a green light that activates when the fan is on, so I get a good visual when driving. The fan is a powerful little sucker ... uh, blower. If the motor is off and the fan is on (no need for this, but this is the result of how I connected it to the fuse box), you can certainly hear it running. But, you can also see dust getting blown around below the car.
It's hard to get good pictures of the thing after it's installed because of the location. I mounted it on the driver's side, left of the tranny, forward of the axle, and just underneath the heater channel intake. (no flex hose there because I'm not running a heater.) I used all stainless steel braided lines with AN fittings. (I also left the doghouse cooler in place. I didn't see any reason to remove it.) I mounted the right side of the cooler onto the little flange on the left frame "fork", and mounted the left side via a custom bracket that I welded together and mounted to the car above.
Cooling the Old Convertible VW
During our 118F summer days, my oil temp was reaching 240F quite easily. Honestly, it may have gotten higher, but I never gave it the chance. (In the winter months, it would peak at about 220 - no problem at all) I looked around at all the different types and brands of external oil coolers, and finally settled on a Setrab Fan/Pack unit like the single unit in the picture to the left.
Now, the oil temp is only reaching 210F - maybe 220F - during the hottest driving conditions I could find last summer ... and it takes quite a while to even get that high. It hangs right at 180-190F for a long time. Idling in traffic or driving on the freeway, the temp stays the same - 180-210F. The tiny little setrab oil cooler and fan do a super job. I would recommend them to any VW owner that needs some additional oil cooling. I bought my stuff at aircooled.net.
Some additional things that could cause over heating (list below taken from the Haynes VW book -- my comments added to the right):
- Fan belt slipping. (hopefully not)
- Fan air intake behind shroud could be blocked. (probably not)
- Thermostat faulty (most of the modified engines don't even use them anymore - folks just rip 'em out).
- Incorrect engine timing. (this is a big one - make sure you get it right)
- Carb air/fuel mixture incorrect. (another big one - kind of a mystery to us "weekend" mechanics. Bottom line is this ... if you're still having heating issues, and don't have the expertise to set up your carb/carbs yourself, pay someone to do it.)
I've added a few below:
- Incorrect fan size ... the alternator was running on my old motor (before the resto) with a 29mm cooling fan inside a stock-sized fan shroud (although I didn't know this for sure until I took it apart to check). I didn't have the knowledge in this area to know any better. So, without checking the fan, I installed that alternator with the 29mm fan on my newly rebuilt 1776 with a wider, after market doghouse-style fan shroud. The shroud was meant for a 35mm fan, not a 29mm. I finally decided to take it apart and check.... sure enough, it was a 29mm. So, the 29mm was not pushing the air around very efficiently because of the width difference, and not cooling the motor like it should. I ordered a new oil cooler and 35mm welded fan, and I installed them both (quite a while ago now). It's not a very fun job - hint, use an impact wrench to get the 36mm fan nut off! Easy.
- Incorrect or missing engine tin.
- Missing engine compartment seal.
NEW:Use caution with the after-market, early style fan shrouds, too. A fellow VW enthusiast wrote me with some thoughts: "After some heating problems, I inspected the inside of the shroud and found it was cheaply made with less cooling veins, incorrectly aimed. After changing it to a modified doghouse shroud (closed heater vents) the problem was solved."
So, the aftermarket stuff strikes again. Some of it is good, some of it is junk, and some of it is just incorrectly made. And, to make it even more difficult, those of us who run modified engines probably have slightly different configurations - like different displacements, different quality internal engine parts, engine tin from different manufacturers, different exhausts, different grade and quality of engine oil, different spark plugs, different compression, different carburetor configurations, different distributors, and live in different climates around the globe.
But honestly, you really have to give Dr. Porsche kudos for his air-cooled engine design. These engines in their original state, with their original displacement and parts manage the heat very well!! It usually isn't an issue until we start modifying these cars that we have problems with engine heat. So, in my opinion, we can't complain too much about it. That shiny new 1914cc motor you just put in will give your car some get-up, but may indeed require some extra cooling!
Maybe all this information is old news to you. Maybe not. This car is the first convertible VW I've owned. I've owned many other hardtops with modified engines, and never really had a cooling issue. Of course, back then, I lived in a cooler climate area, too. For you folks that have never lived in a HOT climate area with your old VW ... air temperature does make a difference. Sometimes a BIG difference.
Anyway, I hope my trials and tribulations will help someone out there.
Drive and enjoy those old VWs! They are a dying breed.
I also installed an oil cooler sandwich adapter thermo-switch in-line at the filter. No need to super-cool the oil when the engine is trying to reach operating temperature. It's best to let it warm up naturally, then< start managing the oil temps. When the car first starts, the oil cooler is completely by-passed and routed back to the motor until the oil temp reaches 160F. After 180F, the oil is then routed through the cooler/fan after being filtered. Pretty cool.