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Vangon Articles - How to Troubleshoot your Radiator Fan System (83.5-91 non-diesel Vanagons)


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How to Troubleshoot your Radiator Fan System (83.5-91 non-diesel Vanagons)

August 6, 2014 35 Comments Ask Ken, Cooling Ken Wilford

How-to, very simply, trouble shoot the Radiator Fan system on 83.5-91 watercooled (non-diesel) Vanagons.

  1. Remove lower grille
  2. Unplug the radiator fan temp switch plug on the front of the radiator
  3. Make a short jumper wire out of some 10-14 gauge wire
  4. Plug the jumper between two of the holes in the plug (there are three) until the fan comes on. (I forget which holes but you can figure this out easy).
  5. When the fan comes on, try swapping one end of the wire out into the other hole until you get the second speed working.
  6. You should be able to have two speeds (low and high and you will be able to tell the difference as high is like huricane force).
  7. If the two speeds are working then everything in the wiring is good (fan, relays, wires, plugs etc).
  8. If only the high speed is working then your radiator fan resistor is bad and needs to be replaced. We have these in stock just give us a call.
  9. Now run your van up to temperature.
  10. Not far past the center on your coolant temp gauge (to the left of the LED) the fan should come on low.
  11. If the fan comes on, then you should be OK. I don’t think you can get the van hot enough to check the higher speed just with the van idling.
  12. If the fan doesn’t come on at all or only the high speed comes on at a higher temperature then your radiator fan sending unit is bad and must be replaced.
  13. This is just a simple trouble shooting plan for this system but it works well and will tell you in a very short time exactly what your problem is and how to fix it.

    Hope this helps,
    Ken Wilford
    John 3:16


Steve January 6, 2020

Ken I’m not sure my radiator fan is coming on when it’s suppose to, I thought I remember it working in the past but haven’t heard it running in some time. I performed the jumper wire test in the 3 wires connecting to the sensor on the radiator and I do have 2 speeds (high and low). I’m thinking about changing out the sensor on the radiator! Thoughts ?

Deon April 27, 2018

Heya 2.3i microbus cape town I have a radiator fan that stays on. I have to unplug the battery when I park the van. I can't find any diagrams for wiring or workshop repair manual. My only option left is putting a toggle switch on the fan which will be a bit dangerous as my temp gauge doesn't work. Could the problem be with the temp switch screwed into the radiator. Please please please help. My fixer upper is turning into a real head scratcher

Laura April 22, 2018

Hey. 84 vanagon here. Had it parked for over an hour after driving just over 100 mi then radiator fan started up. Couldn’t get it to turn off until I pulled the switch. Left it off until I had to start it up again. Drove about another 80 mi turned it off to park and radiator fan starts up again

Ken Wilford November 14, 2017

Have you done the test at the thermoswitch to see if you can make the low speed come on by bypassing the switch with a paperclip or short piece of wire? You want to bridge the connections inside the plug that plugs into the thermoswitch until you get the high speed fan and the low speed one. If you can't get the low speed one then most likely your low speed fan resistor is burnt out and you need a new one. Happens all of the time. Doing the test should tell you this one way or the other. Let me know what you find. Ken

Ryan November 12, 2017

Hi Ken, After having issues with the fan kicking in, I have replaced the coolant and installed a new thermo switch, however the fan still doesn’t want to behave. As the engine (stationary) heats up the low speed on the fan won’t kick in and the temperature starts to rise. Once it gets to 3/4, the high speeds cuts in and then almost immediately cuts out without reducing the temp which continues to rise ? if I short the fan with a small wire it works fine both low and high speed and brings the temperature down. Not sure what else to check ? any ideas? Thanks ? 2.1 injection

Ken Wilford August 17, 2017

Mike D August 17, 2017

Can you give me the part numbers for the radiator and the fan switch. I have ac

Mike D August 17, 2017

Got the temp gauge to almost max. Checked bleed for air and got hot water only. Opened the under dash valve no difference. During these checks only low fan ran. Took you suggestion and got an IR temp reader. 87C at the top of the radiator and 45C at the bottom. Not hot enough to trip the high speed. I agree that a radiator and sensor are ready to be replaced. By the way, I was just up north from Florida visiting family in Ocean view. I was born and raised in Somers Point. I saw your address in Millville. If I would have known then I would has come by. Thanks again for all your help. I will be getting my parts from you website.

Ken Wilford August 17, 2017

Bob, have you checked the low speed resistor for the radiator fan? That is usually the culprit when this speed doesn't work. The fan itself, if it is working on the high speed, is fine. Ken

Ken Wilford August 17, 2017

Possibly just because the radiator isn't actually getting hot enough to turn the fan on. If it is flowing poorly the engine (where the temp sensor is) is getting hot but the radiator might still be cool or at least cool enough for the radiator fan to not come on. You could pull the upper grill and see what the radiator feels like when the gauge is saying the engine is fully warmed up. Or better yet, get a cheap IR thermostat and get some temp readings. Should be around 87C when it is fully warm. Ken

Ken Wilford August 17, 2017

The valve to the front dash heater core should not cause problems. I just installed one myself on a customer's van and it was running the same on temperatures before and after, except now you don't get that hot leg syndrome on trips (Yes!). I am still leaning toward the radiator being the culprit. Try turning on the heater valve on the front heater and running the fan and see if your temp goes down. If yes, then it is new radiator and fan switch time. Ken

Mike D August 17, 2017

One more thing. When the gauge is near max why doesn't the high speed fan go on?

Mike D August 17, 2017

I found that the rear heated was shut off and the front heater had a shutoff valve installed on one line under the dash. Would the restrict the coolant flow? The prior owner said he put the valve on the front to reduce heat on the floor while driving. Thanks for the quick response to my questions.

Ken Wilford August 16, 2017

Mike, it could be a problem with the radiator itself. Try bleeding the system of air at the radiator and see if there is any air. If not, then try turning on the front and rear heaters with the fans when the van goes above half and see if that lowers the temperature. If it does, then most likely your radiator is clogged and you need a new one. The radiator fan switch is what controls when the fan turns on, although if you turn on your AC it will come on and run all of the time. If you have tried that and the van still is overheating then I am still leaning toward a bad radiator. We have them for $195 if you need one. Ken

Mike D August 16, 2017

I have a 1986 gl camper. On the road temp gauge is about half way. When I slow down or get caught in traffic, it goes up to max and light flashes. I did the fan speed test with the jumper and all works. Low speed runs with ac on when used.. The fan will only run low speed when gauge is near max. Does the sensor on the radiator trip the high speed fan? The water levels look good.

Bob August 7, 2017

Hi Ken, I have an 89 with AC. I unplugged the wires at the radiator switch and tested the connections. When I jumped the two outside instead of getting fan I could hear a click under the dash. I jumped the pairs looking for low speed fan and still did not get a fan response. Is the problem the relay at the fuse panel or should I go in and try to manually put power to the fan to see if it is defective? This van has been completely rebuilt by me after it sat in the rain for 10 years and the fan used to come on when I turned on the AC or sat at idle after a run. Thanks in advance Bob

Michael June 28, 2017

Thanks! The #7 fuse was good, but not connected on the back side! All fixed now.

Ken Wilford June 27, 2017

I would look at fuse 7 on the fuse panel. The AC system has a alternate source of power for the radiator fan when you turn it on but the radiator fan switch on the 1.9l Vanagon is getting full time hot power from fuse 7 to the fan switch on the radiator. It is either blown or the wiring to it is messed up in some way. Ken

Michael June 26, 2017

Ken, Funny one here for you. 85/1.9 factory AC. Fan comes on when AC is on. No power any of the ports in the plug of the radiator sending unit. No fan on when the jumping the ports on the plug. Where to look next? Thanks.

Ken Wilford January 12, 2017

Check your coolant level in the tank that you have to remove the engine lid to access (the one to the right with the blue pressure cap on it). Check to see if this tank is full to the top. If it isn't then top it off and add coolant to the tank behind the license plate until that is at Max line as well. Now run the van. I think you were just having a low coolant level and not an overheat, because that light can be just blinking for low coolant level. Let me know what you find out. Ken

Ferch January 12, 2017

HI Ken. I have an 87 2.1 gas. My temo sensor light started flashing when I was in line waiting for the kids to get out of school. Turned it off then back on and drove home very short distance and temp dropped. (Previously I believe my thermostat was stuck open by the way...always ran cold according to the temp gauge). Got home ran the van a bit and light came on again no fan. Then turned it off for about a minute then turned it on again no light and now low speed fan coming on fine again. So I say all this to say why would my fan come on now and not earlier? Is my relay starting to go bad? Any advice would be greatly appreciated

Ken Wilford December 16, 2016

What can be happening is that your cooling system has a vapor lock. You want to remove the upper grill and actually feel the upper portion of the radiator. When the temperature gauge says the engine is fully warm, the radiator should also be hot. If it isn't then the coolant isn't circulating and then even though you have a good working radiator fan, it isn't flowing to cool the hot coolant. The hot coolant is staying in the engine area and just getting hotter and hotter until it finally boils over. Check this for me and let me know what you find. Ken

Steve December 14, 2016

Great info. Cross wired fan feeds and both speeds came on. That proves fan unit and wiring fine. Took sender off radiator and dangled sensor into boiling water and did continuity test. I got positive readings which would indicate sender also ok. If that is correct, why does my coolant boil over through expansion tank?

Ken Wilford October 26, 2016

For the early Vanagons 83.5-85 and also 86-91 with no factory AC, the second speed resistor is built into the fan itself. So I would unplug the fan and try to power it directly. There should be three wires at a round plug and you will have to drop the spare tire to see it. One is ground and the other two would be the two speeds. See what you can make work. It could be the fan itself that is having an issue. You can also check the ground there with a meter between the brown ground wire and the body to see if it is good or not.

JB October 25, 2016

Thanks for the run down. I have a 83.5, No ac. Mine does not turn on when driving. I can jump it like you say above but only one speed comes on. I changed out the radiator switch, but the symptoms are still the same. And ideas what I might need to look for next? Could it be a bad ground?

bugeye August 24, 2016

Thanks for this, same thing happened to me. AC doesn't work but the kids had turned the switch on, had no idea it affected the radiator fan.

Ehsan June 27, 2016

I figured it out. My three year old had turned the a/c on. I guess this keeps the fan running?

Ehsan June 27, 2016

Hi ken, My radiator fan is kicking on prior even starting the van (in the start position, radio on power windows functioning). Van has been sitting for a couple hours so engine isn't hot. I noticed the fan continues to run even at high speeds. Basically the fan never shuts off. What gives?

Ken Wilford June 22, 2016

Thanks for letting us know what the final result was. Bad grounds are the bane of the Vanagon. Ken

cjvango June 22, 2016

Thanks Ken I really appreciate your response and availability for help! I did get things figured out. We ran the switch originally just to get the vanagon back on the road with a working fan in case things got hot. The switch was wired to the plug. Anyway the reason it worked with the switch was we also ran another ground from the back of the fan. So after further consideration and research I tried your test with this new ground hooked up and it tested as it should from the plug - two speeds. I ran a more permanent ground from the back of fan to chasis and everything works as it should again. The ground was my problem and rather then fishing for which wire in was on the grounding tree or wherever it resides creating a new ground from chases to fan works great. I have to remove my dash in the coming weeks to change the blower motor and wiper motor I'll tend to the grounds and wires back there further then.

Ken Wilford June 22, 2016

CJ, I am going to help you the best I can but when folks start wiring extra switches, etc. into the system, I have no idea how they are wired and what was cut to make them work, etc. Your radiator fan system should work properly with just the sending unit. Extra switches, etc. are just a problem waiting to happen. Example: You lend the van to a friend and forget to tell them about the switches. They drive the van and let it overheat because they don't know any better. Etc. Once you get the radiator fan system set up properly it is all done automatically. If you have a new fan switch then we can pretty much rule that out. Get a test light or a 12 volt tester and check the three holes that are in the plug end that plugs onto the fan switch at the radiator. One of those three should be full time hot even if the van is shut off. If it isn't then that is the problem with the system not working properly and you are going to have to figure out why that wire isn't hot. It could be a cut wire, a fuse, etc. Does that help you out? Ken

CJ June 21, 2016

I don't understand. I have a new sending unit installed, but it is out of the equation when unplugged so how can it be that? I can put a wire as suggested and connect said wire into any of the two holes in the plug that attaches to sending unit, in any combination of two holes on that plug, and the fan does not come on at all with ignition on or car running. The fan runs fine in both gears when hooked directly to power and a toggle switch on the dash. It does not work at all otherwise.

David Beierl August 3, 2015

Ken, Bentley calls that a thermoswitch. Don't forget that non-A/C vans have the lower-power fan with internal resistor and two wires running to the fan instead of one.

Ken Wilford May 21, 2015

Yes the radiator fan sending unit, aka the temperature switch that is physically screwed into the radiator and measures the coolant temperature, turning the fan on and off. Does this clarify? Ken

Ed Templeman May 13, 2015

Ken, please forgive my ignorance, but in point #12 by "radiator fan sending unit" do you mean the radiator fan temp switch or some other sensor, like the gauge temp sensor? Thanks for your reply!

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