Debugging the Cooling System

After getting my beetle through the Dutch safety inspection (APK), it was testing time. The cooling system wasn't good enough. When the engine reached the operating temperature of around 90 degrees it became hotter. The cooling fan turned on, and wasn't able to get the temperatur down. The temperatur stayed at 100 degrees celsius, with the fan on all the time. Even when the car was standing still and just idling, the temperatur didn't go down. I discoverd that when I opened the engine lid, there was much more hot air leaving the engine compartment. The fiber glass decklid I installed was too restrictive. So I re-installed the original decklid. You can see that this decklid:

Does not vent as good as this decklid:

I had to cut out a piece behind the license plate to make room for the alternator pully. It would have toched (barely) the engine lid otherwise. This also is a great extra venting hole. But what you really need is venting holes in the upper part of the decklid. There is the hot air directed that's coming from the fan.
This made a difference, it could get the temperature slowly down when standing still. But it still wasn't enough while driving.

I suspected that the hot air from the fan is drawn back into the radiator through the other side. I installed a air-deflector next to the fan:

I also installed some (heater)radiator foil because the radiator box got a little hot on the outside.
The deflector changed almost nothing. So it probably didn't re-use hot air.

I think this radiator air-box isn't working:

I assume the two air channels that direct the cool air to the radiator only cool a small part of the radiator. It doesn't spread the air over the radiator surface. My plan now is to remove the floor of the radiator air box and shorten the air-channels so they will spread the outcoming air. This might also be better for the fan, as it can suck cool air better, without the restriction of the air-channels.

Another thing I want to do is box-in the K&N air filter, it's picking up a lot of hot air when standing stil.

edit 20-05-2007: I modified the radiator airbox, I removed the floor of the box:

This is what the rear parcel shelf looked like:

Clearly, I had to cut that too:

I also removed the air-channels, which where between the air-scoops and the radiator air box. I just left them out, the scoops are now aimed at the radiator:

It took a longer time before the fan was switched on. This is an observation based on "feeling". It is very difficult to make two comparable testruns, because of different traffic on different days with different outside temps.

These changes made it a lot easier for the cooling fan to draw air through the radiator. Once the fan was switched on, it took less time for it to cool down the radiator to a temperature at which it turned off again. But, after driving it hard (city traffic with lots of aggressive accelerations) the temp went over 100 degrees and the fan was on all the time.

A strange thing I noticed is that the temps were over 90 degrees, and the fan switched off.. I thought that the temp-gauge was'nt giving a accurate reading.

I also noticed that the performance decreased when the engine warmed up. I suspected this was caused by the engine sucking in hot air through the air filter. The air filter is located in the engine room, in the neighbourhood of the radiator:

As you can see I did have a fresh air hose from under the car aimed at the airfilter. But that doesn't work in slow city traffic. Then it will suck in warm air from the radiator.
To solve that I made a box for the airfilter to which I can attach the fresh air hose:

In this picture I temporary used ducttape to seal the box. I was eager to test it at the end of the saterday afternoon. I will remove the ducttape and use sealant to seal the box.
This change solved the bad performance after warm-up and it took the temps down, I think... I accidentally switched the temp gauge to oil temp instead of water temp... D'OH! But, after the testrun, I switched it back and it read around 95 degrees. I'll have to do another test-run..
But it might be the hot intake air caused the in-accurate readings of my temp-gauge. It heated the intake manifold and the temp sender is screwed into the intake manifold.

edit 3-06-2007: The beetle is now doing fine in city traffic, once the temps get up, the fan switches on and cools the engine down again. When driving at higher speeds (80 km/h and higher), the temp gets to 95 degrees and the fan switches on, and doesn't switch off again. Only when I stand still for a while it will switch off. I suspect this is due to not enough airflow to the radiator, as airflow is much more important on outside-city driving.
I wanted to know what the airflow was to the radiator. I don't have a wind tunnel at my disposal, so I had to improvise. I used a blower from the dashboard of the Alfa 33, which I still had lying around. I aimed it at the airscoops:

(picture shows testing the passenger side airscoop)

Then I held a small rod with a tiny piece of string attached to the end in the airflow on the exit side of the airscoop:

(picture shows testing on the drivers side)
This test prooved to be more usefull then I thought. It showed that part of the air was hitting the underside of the parcel shelf area. And the that was hitting the radiator wasn't spread enough. Bending the alumium at the exit side of the scoop solved this.
BUT this test learned that only the sides of the radiator where getting airflow. About 15 cm's on each side got airflow and the middle, the part that is above the gearbox, didn't get any airflow.
These "aiming" did do some good, only after driving it for 10 km's on a steady 80 km/h speed, the temp got so high the fan switched on and didn't switch off.
I plan on using flexible tubes to direct air to the middle of the radiator.

edit 24-06-2007: I made an extra hole in the rear decklid, it is behind the license plate light:

It can't be seen from the outside, unless you look under the license plate light cover. This extra hole reduced the time the fan is on a little.

Furthermore, I placed some flexible tubes under the car. These are the flexible tubes normally used in the aircooled engine to guide air from the doghouse to the heat exchangers. I placed them along side the big airscoops and routed them to the radiator. I had to be careful not to block the air that comes from the big airscoop.
This is the front left one, I mounted it under the car on the rear swaybar bracket, and then routed it upwards along the bodywork that's under the rear seat.

The other one is under the leg of the gearbox fork, and then around the rear axle, and then upwards to the radiator.

I did the same on the passengers side of the car.

This is what it looks like under the car:

I now have four of these flexible tubes guiding air to the middle of the radiator and two big airscoops guiding air to the sides of the radiator. You'd think the extra four tubes delivering extra air would make a difference?! Well, it didn't do a thing! Again after 10 km's of driving at 80 km/h the fan came on again and didn't turn off, and the temp rose slowly to 100 degrees celsius. Which I think is very strange, because the extra air should have done something...

Now, I am suspecting two things: the too low gearing of the gearbox, or the thermostat is stuck.
If the thermostat is stuck half way open, it could explain a lot of things. It would explain why I am seeing a higher water temp at the engine (manifold) than at the radiator. I sometimes see the fan being switched on and/or off while the temp gauge is at a steady 98 degrees... If the thermostat is stuck half open, it would be logical that the water in the engine is at a higher temp then in the radiator.
I also noticed that it takes a long time to get to operating temperature, 86 degrees celsius. This is a sign of a bad thermostat. The thermostat on this engine looks like the original sinds new, and that's 113.000 km's ago.. So I am going to replace it with a new one.

edit 22-07-2007: I replaced the thermostat with a nice shiney new one:

I also replace the flexible tubes to the thermostat. These are not standard hoses but had to be ordered at the Alfa Romeo dealership.
The car warmed up a little faster, but it still had the same problem at 80 km/h. So the old thermostat wasn't stuck halfway open.

For good fun and education I cut the old one open:

I wanted to know if the thermostat needed the heater-circuit to function properly like the Subaru engine has. But, it doesn't need the heater circuit. The warm water has to go up for it to enter the return channel to the pump. When it goes up it heats up the thermostat. I placed a valve in the heater circuit, but I can keep it closed safely.

I wanted to get more airflow to the radiator, so I made an extra airscoop for the two middle hoses I attached earlier. I hoped to create more effective airflow to the radiator through the hoses. This is what it looks like:

For testing it, I made a trip to a little beetle meeting nearby in the german city Bad Bentheim. Sadly enough, the extra scoop didn't make a difference. It looks like all the extra airflow I create doesn't have any effect...strange.
The meeting, however, was small but fun! When I parked the car there, I removed the engine lid. I got lots of attention:

I believe the most people liked the conversion. I didn't see a purist shaking his head in despair.. :-) This was the first meeting I attended with the conversion.

edit 26-08-2007:I am running out of ideas to improve the airflow to the radiator. So, I've decided to fight the symptoms. This is the standard fan on the radiator:

I have another one lying around, so I placed that one next to it:

I removed the shrouds because otherwise it would be too restrictive for the "normal" airflow. I wired the second fan through a relay, because I was afraid to overload the temp switch.

Finally I got some positive results!! Now at 80 km/h the fans still go on, but they bring the temperature down en switch off again. Now the fans switch on and of and they keep the engine temp at a nice 90 degrees! It might not be the best solution, but now I can drive longer distances without the worry of overheating.
This result proves that there is not enough airflow delivered by the airscoops from under the car.

From this point, I've got three choices:

edit 9-09-2007:A guy on the keversite forum who also drives an Alfa beetle gave me the idea of running the two fans in series. This way the fans will run at half the speed all the time. When the temps get too hot, both the fans can come on at full speed. This sounds easier than it is to wire up... After a long thought and talking to some guys at the keversite I came up with this wiring diagram:

After a lot of soldering and wiring, this is how it looked:

I connected the half-speed setting to the wire that goes to the fuel pump. This way if I put it on contact, but don't start the car the fans will come on for about 2 seconds and then stop. When I start the car, the fans will turn at half speed. I allready did a test-run, and the temps stayed at a good 90 degrees. But I don't know how often the full speed was engaged because the indicator led in my dash stopped working... It is the second time it goes bad, it probably has something to do with peek voltages after switching the full speed off.

edit 23-09-2007: I changed the wiring diagram you saw here above. Now it includes an diode that's wired in the opposite direction of the LED. This should let the high peek voltages generated by the relays safely back instead of overloading the LED. This is how it looked when I soldered it together on my workbench:

Of course, this is before soldering it to the wiring in the car. I've got such long wires on it because I didn't have enough room around the LED to hide the diode.

After I installed this I did some test runs, and the LED is still working..

Now, during city driving the fans hardly go on at high speed anymore. After driving at 100 km/h for about 10 km, the fans switched to high speed and stayed on for a long time. But the temps did'nt move much past 92 degrees celsius, so that is looking good.

edit 28-12-2007: De engine still runs hot when driving 120 km/h for a longer time, so I decided to move the radiator up front. I created a new to-do item in the list, see this page.