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Cooling System in Vanagons: Explained

The following write-up is an article Lucas Valdes (Prez & Resident Mechanical Engineer of GoWesty) wrote to provide some info on the Vanagon cooling system operation.

All water-cooled Vanagons have an automatically controlled electric fan on the radiator. The way the system is supposed to work is like this: after the engine is started, the thermostat on the engine stays closed until the coolant temperature at the engine reaches 87°C (189°F). The thermostat then begins to open and allows hot coolant to flow to the radiator, which is located up front between the headlights. The temperature of the coolant continues to rise as long as there is no movement of air past the radiator, like when you are stopped in traffic. When the coolant temperature in the radiator gets up to 85°C (185°F), a thermostat switch on the radiator tells the electric fan on the radiator to come on. The fan continues to run until the temperature drops enough for the thermo switch to open, and then the fan shuts down. The coolant temp starts to rise again, and the process repeats. The indication on the temperature gauge (the needle) while this is happening should be about 2/3-3/4. This is normal. No need to freak just because the temperature gauge is up there. If you are driving at a speed that is low enough—a speed wherein air flowing past the radiator is not sufficient to keep the temperature of the coolant below 85°C—then the fan will cycle on and off in the same manner. If you are working the engine hard, like towing or climbing a steep hill on a hot day, even if the fan comes on the temperature may continue to climb. In that case, if the temperature gets up to 95°C (203°F), the fan comes on at a higher speed (loud!). This all happens at a temperature gauge reading of about 7/8. This is also normal, but start paying close attention. If the high-speed fan is not enough to control the temperature, the gauge will continue to climb and at about 15/16, the red light will start to flash. This is NOT NORMAL. That means slow down or even pull over.

So, when everything is hunky-dory, driving down the road at 65 mph on a 75° day, the temperature gauge needle should be somewhere around half way on the gauge, somewhere around the flashing bubble. Contrary to popular belief, if the temp is too low, that is not good. It is the responsibility of the THERMOSTAT on the engine to keep the coolant temperature from running TOO LOW. If the temperature is too low, your thermostat is either the incorrect one or it is no good. If the temperature runs too high, that is not good either. It is the responsibility of the RADIATOR to keep the coolant temperature from running TOO HIGH. However, if the temperature is too high it is not necessarily the radiator.

Vanagon cooling systems are a bit peculiar because the engine is in the back and the radiator is up front. The pipes that run between the two are BELOW both, so if air gets into the system it ends up in the highest point, which is the radiator. If air gets in the radiator it will stay there. There is a bleeder screw on the top of the radiator next to the right headlight used to get the air out. But if air gets back in, it will end up accumulating in the radiator again. That is why it is so important to address any loss of coolant IMMEDIATELY. If coolant can leak out, then air can get in, and you have to find out why. Like I have always said, if you can keep oil and coolant in one of a waterboxer, you can’t break ‘em. They will just go and go...

There were two different radiator fan systems used on Vanagons from 1983-1991. All 83-85 models, with or without AC had the smaller two-speed 200/300-watt radiator fan motor. Starting in 1986 the Vanagon either had that same system or, on vehicles equipped with FACTORY AC (not dealer-added “in-dash” AC), had a larger, one-speed, 450-watt fan motor. The higher wattage fan motor is easily distinguishable because the wiring bolts right on to the back of the motor. The lower wattage motor is a plug-in type. NOTE: With either system, It is NORMAL for the radiator fan to continue to run after the engine is shut of and the key is removed! It will run until the coolant in the RADIATOR cools off enough for the thermo-switch to open.

The low wattage system is comprised of:
1) Radiator (up front)
2) Two-stage thermo-switch on radiator
a. First stage comes on at a radiator temperature of 85C (185F)
b. Second stage comes on at a radiator temperature of 95C (203F)
3) Electric cooling fan on radiator, 200/300 watt
4) Fuse for fan first stage on fuse panel
a. #7 fuse on 83-85 models, 16 amp
b. #1 fuse on 86-91 models, 30 amp
5) Second stage relay for radiator fan high speed,
a. Under dash, to right of speedo on 83-85 models (round headlights)
b. On fuse panel, location #5 on 86-91 models (rectangular headlights)
6) Water pump on engine
7) Thermostat on engine
8) Hoses and pipes throughout

The 200/300-watt motor system is a two-speed design. The first stage activated by either the AC being turned on, or automatically by the radiator thermo-switch, second stage by the later only. With AC off, all the current for either speed flows through one fuse on the fuse panel, fuse #7 up to 1985 (German type ceramic bullet type fuses), fuse #1 on 86 and newer models (US blade-type ATC fuses). When in the first stage mode (low speed), current flows directly through the fuse, to a medium-gage wire (red with white stripe), which conducts current that enters the first stage contact on the thermo-switch, which is in first stage mode (85C/ 203F coolant temperature). Current travels through the switch and comes out of the switch via the wire that is red with a black stripe (same gage as red/white wire), the other end of which is connected to the first stage of the motor. In second stage mode (high speed), current flows through the same fuse and same red/white wire to the thermo-switch, which is now in the second stage mode (95C/203F coolant temperature). Now the current exits the switch via the red wire with the blue stripe (lighter gage). That wire goes back into the vehicle and under the dashboard and triggers the second stage relay, which in turn sends current via a larger gage, solid red wire to the motor’s second stage (high) mode. If a low-wattage vehicle was fitted with AC at the dealership, the AC system is wired such that, when the AC is switched on, the radiator fan operates at first stage through a separate fuse, and cycles on and off with the AC compressor. The exact location of the various AC electrical components, and the means by which the AC system wiring and vehicle wiring were interconnected varied with the type of A/C system used, who did it, what day of the week it was, and how high that person may or may not have been at the time. Sad, but true... The first thing to check when troubleshooting is the FUSE! If the radiator fans work when the AC is turned on, but not in automatic mode, it is probably the fuse. If nothing operates the fan, it’s probably the fan motor or the ground path (brown wire) to the motor. Another quick check is to unplug the thermo-switch and check for power at the red/white wire. If power is present, jumper the red/white wire to the red/black wire and the fan should come on at low speed. Jumper red/white to red/blue and high speed should come on.

The 450-watt system is comprised of:
1) Radiator (up front)
2) Two-stage thermo-switch on radiator
a. First stage comes on at a radiator temperature of 85C (185F)
b. Third stage comes on at a radiator temperature of 95C (203F)
3) Electric cooling fan on radiator, 450 watt
4) Resistor behind left headlight
5) Fuse for fan first and second stage on fuse panel, #1, 30 amp
6) Relay for fan second stage on fuse panel, location #5
7) Relay for radiator fan third stage under dash, to left of speedo
8) Fuse for fan third stage, strip type 50 amp right next the third stage relay
9) Water pump on engine
10) Thermostat on engine
11) Hoses and pipes throughout

The 450-watt system is a three-speed design. This system is found only on 86-91 vehicles fitted with factory AC. The resistor behind the left headlight can drop the voltage to the motor so it can run at one of two lower-than-full speeds. So the 450-watt fan motor, even though it is a one-speed motor, is actually made to run at one of three different speeds because of the design of the electrical system that controls it. The second stage (middle speed) comes on whenever the AC system is turned on, and cycles on and off with the AC compressor. The first and third stages are controlled by the thermo-switch on the radiator.

Mystery condition: On a super hot day charging up a long grade with AC blasting, you may hear the third-stage fan speed come on, even though the temperature on the gage is nowhere near 7/8’s. This contradicts everything I have explained above, and for some time puzzled me to no end. So, I put it out there for about three years for someone smarter that I to solve, and posted this on our site:

"Now, I have studied the wiring diagram for this system very, very carefully. I consider myself an expert at reading a wiring diagram. There is nothing in the wiring diagram that would indicate that the AC system can make the radiator fan come on at any speed other than the second stage. However, my experience with my own 87 Westy with factory AC is that, on a super hot day charging up a long grade at 80 MPH with my 2.4 liter engine and AC blasting, I have heard the third-stage fan speed come on when I KNOW FOR SURE the temperature on the gage is nowhere near 7/8’s. I know that the AC system is involved because I can feel the compressor shut-down as soon as the turbo-speed 747 fan comes on. Furthermore, it WILL NOT do this with the AC off. This condition--AC apparently tripping the radiator fan third stage even though the engine coolant temperature IS NOT too high--cannot be explained by reading the circuit diagram. So, maybe someone smarter than I can figure this one out..."

Enter: Chris Corkins a GoWesty customer from, you guessed it, the great HOT state of New Mexico. The folks down there rely on their AC to stay ALIVE. Chris correctly surmised the situation. In reading the circuit diagram it is clear that the AC compressor is automatically shut down when the third stage fan comes on. The designers did this to prevent overheating. They figured if the coolant was hot enough to trip the super turbo high speed 747 fan, it might be a good idea to shut down the AC compressor until the temperature dropped. This interaction between the radiator cooling fan and AC system was not something that escaped me, it is obvious by looking at the circuit diagram. And I was kinda right, that is that the AC system cannot control the radiator fan ELECTRICALLY. What I failed to grasp was that the AC system CAN control the radiator fan--not electrically--but instead THERMALLY. The coolant temperature as indicated on the temperature gage is measured back at the ENGINE. The radiator fan thermo-switch is measuring coolant temperature in the RADIATOR. It never occurred to me that the coolant in the radiator could be even HIGHER than the coolant leaving the engine. After all, the engine is where the heat is being GENERATED, right? Well, yes, but that is not the only heat source. In FRONT of the radiator is the AC condenser! That is an ADDITIONAL source of heat into the cooling system. So, under certain conditions, it IS possible for the coolant in the radiator to be hotter than the coolant leaving the engine, which is what you can see on your gage. So, in effect, the AC system is controlling the radiator fan speed THERMALLY. When this condition arose, I seemed to me that the AC system was controlling the radiator fan speed, which it indeed was, just NOT ELECTRICALLY (boy, is this guy Lucas a nerd, or what. What the hell is he talking about!). Well, lucky for me, there are other Vanagon nerds out there! Great work Sherlock, uh, I mean Chris! Thank you! Say, by the way, how are you fixed for work...

So, to summarize, the way the system is supposed to work with AC OFF is as follows:
1) Engine starts cold, thermostat closed
2) Coolant to radiator is shut off by thermostat
a. Note: Coolant to heater(s) is allowed to flow regardless of coolant temp
3) Thermostat begins to open at 87C (189F) allowing coolant to flow to radiator
4) Coolant temp rises until the temperature in the RADIATOR reaches 85C (185F)
5) Thermo-switch first stage closes, fan comes on at lowest speed
6) Fan stays on until temp in radiator drops enough for thermo-switch to open
7) Cycle repeats until you start to drive
8) At highway speed on flat ground on a 75 degree day temp reads about 1/2
9) Cooling fan stays OFF
10) Climbing a grade and/or on a hot day, temp will climb until first stage comes on
11) Continued hard running, temp will climb until second stage (on 2-speed systems) or third state (on three speed systems) comes on
12) Continued severe hard climbing, call GoWesty for a fresh engine.

Cheers.

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GoWesty! Camper Products is a privately owned company specializing in parts, accessories, sales and service of Volkswagen (R) campers. It is not affiliated in any way with Volkswagen of America or Volkswagen AG. "Vanagon", "Bus", "VW", "Volkswagen", and "Eurovan" are registered trademarks and should be considered as such throughout our entire website.

 

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