Couple of radiator fan questions

EJP

EJP

Daily Driver
My car is a '79 Non A/C car. Don't think my fan is working at all.

When warmed up, about where is the temp gauge needle supposed to be? Mine is a bit above the 190 mark on the gauge.

How do you know when the rad fan is on? Can you hear it running when driving the car?

Should the fan continue to run after the car is turned off after driving it for a while? I think it should be.

Can you test for power to the fan when the car is cold or does it have to be warmed up. I think the sensor on the rad sends a signal to a relay, relay closes, and the relay sends power to the fan? (Not great with electrical diagrams.) I thought about testing the blue wire at the connector before the fan with my test light with the key turned on. Will that work as a test?

Where is the ground located for the fan? Is it in the left headlight bucket with that cluster of other ground wires?

I checked the fuse on the fuse panel and its good. I assume the relay is working.

Thanks for the replies and help.

Ed
 
If the cooling system is in good shape, it would, in my experience, be unusual for the fan to come on while driving. Mine cycles on and off while idling, and I can definitely hear if from inside the car with the top on.

The fan should not run after you turn off the ignition (unlike the carburetor cooling fan, which can run with the ignition off).

On my '85, the needle normally stays a hair over 190. Keep in mind that the gauge reads the temperature at the head, and the thermoswitch for the radiator fan is on the radiator. There will be a temperature difference between the two.

If you remove the radiator fan relay and jumper terminals 30 and 87 of the relay socket, the fan should come on, even if the ignition is off.

If you disconnect the thermoswitch (left side of the radiator, on the side facing the driver, you can jumper the two wires (ignition on, but no need to have the engine running), the fan should turn on. Be very mindful of where your fingers (and hair, if so equipped) are while doing this test. The radiator fan can do serious damage to human flesh and bone.

Also have a look at the 1980 - 81 Electrical Diagnostic Manual. It has good descriptions of how each circuit works, and lists the location of relays, connectors, grounds etc. Much of it would apply to your '79.
 
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You should be able to tell when the fan runs. On my 85 the whole care resonates from it or at least that is the way it feels to me.

By and large mine does not run unless it is hot out (@90) and only when the car is at rest at a light, low speed/rpm in traffic or coming off the highway. Although it doesn’t run after shut down, a minor rewiring could allow it to do so by moving the power supply to the relay to an always hot circuit in the fuse box (easy to do on a ‘79).

My car’s temp gauge I think reads low, I need to do a full clean out of my cooling system (may happen today we shall see, my gas tank clean out takes precedence) with a flush of clean water, flush materials and then new hoses (the existing hoses are OE to when the car was built) and new coolant of course.

The fan is controlled by the radiator temp switch grounding the relay leg switching the relay to on to provide power to the fan. The ‘79s were prewired for a second fan to support AC which would require adding a relay into an existing opening in the fuse box and making some of the final connections along with either using a three connection radiator switch from a VW or a switch in the cabin. You can scout around in the fuse box and under the plastic housing on the right side of the front trunk for the correct wires and connectors. The pertinent section of the wiring diagram is shown below:

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All of that said, the one fan should be sufficient in a properly clean system, properly bled and with new coolant. This system is quite adequate for a stock car, the biggest issue is all the parts are old, there is likely some scale or other buildup in the radiator and at this point many radiator thermo switches are failing.

Cleaning the system out using radiator flush chemicals along with strong rinsing of the pipes and the radiator will go a long way towards ensuring the system works properly. You may find you need a new radiator if it is clogged or has lost the many of the thin external fins which do the majority of shedding the heat from the coolant travelling through the radiator.

Hope that helps.

Karl
 
Hey Ed, I'm sure there are several other guys closer than myself to you that can probably help but I might have an extra (wouldn't be able to confirm til this evening) working fan if you find that yours is dead? You can have it for the cost of shipping if I do in fact still have it? Anyhow, let me know and I'll check. Looks like you're in PA so hopefully the shipping wouldn't be too awful from Ontario?
 
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My fan does run when directly connected to battery. Might be an electrical problem getting power to the fan. Thanks for the offer on the replacement fan
Also, many thanks to Karl and Bjorn for their comments and suggestions on searching out the problem.
The link to the Diagnostic Manual was really helpful. Pretty cool book
 
In follow up to my questions of the other day and the suggestions I received, I jumped the terminals in the relay socket on the fuse panel and the fan came on. Great news I thought. At the front of the car, I pulled apart the connector that is a few inches from the radiator thermo switch. It did not look like the 2 black wires going into the thermo switch were meant to come off. I jumped the white/black wire and the black wire going into the connector expecting the fan to come on. Nothing happened. No fan running. I checked all of the grounds in the left headlight bucket and all seem to tight and clean. Maybe I am not testing the correct wires? Any thoughts on what to check next? Thanks in advance for the replies.
 
EJP said:
In follow up to my questions of the other day and the suggestions I received, I jumped the terminals in the relay socket on the fuse panel and the fan came on. Great news I thought. At the front of the car, I pulled apart the connector that is a few inches from the radiator thermo switch. It did not look like the 2 black wires going into the thermo switch were meant to come off. I jumped the white/black wire and the black wire going into the connector expecting the fan to come on. Nothing happened. No fan running. I checked all of the grounds in the left headlight bucket and all seem to tight and clean. Maybe I am not testing the correct wires? Any thoughts on what to check next? Thanks in advance for the replies.
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1. You did put the relay back in place, right?
2. When you jumper the wires for the thermo switch, the ignition needs to be on for the fan to come on. Was it?
3. You jumpered the wires going into the car harness, not the wires coming out of the thermoswitch, right? Sorry, I had to ask :).
 
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A further test you can do is to turn on the ignition, then jumper the WHT/BLK wire that is supposed to go to the thermoswitch, to ground (a good body ground, or directly to the battery). This should turn on the fan. If it does not, remove the jumper and measure voltage between the WHT/BLK wire and ground. You should have battery voltage with the ignition on. You should use a voltmeter for this, rather then a test light. If you have voltage, you should suspect a grounding problem. The 1980/81 wiring diagrams show that the thermoswitch is grounded in the left hand headlight cavity, '79 is probably the same.

If you do not see battery voltage on the WHT/BLK wire, you should start looking for a break between the relay socket and the plug for the thermoswitch.

When I leave the ignition on for testing, I usually disconnect the coil primary to avoid running current through the coil for any length of time.
 
EJP said:
At the front of the car, I pulled apart the connector that is a few inches from the radiator thermo switch. It did not look like the 2 black wires going into the thermo switch were meant to come off..
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Yes, some years had spade connectors on the thermoswitch body, other years had wires coming out of the thermoswitch and a connector at the end.
 
In response to your questions..
1. Yes, relay was back in place.
2. Yes, ignition was on.
3. Yes, I jumped the white/black and black wires coming out of the main harness and not the two black ones from the switch.

Will follow thru on your other suggestions for testing. Wiring in my left headlight bucket is a bit of a challenge. When the car was painted by previous owner, they painted all of the wiring as well. Have to do a little scraping to see which ground wire belongs to the fan
 
You can get rid of the factory setup and use a better version. Replace the radiator temp switch with a dual temp switch. I posted a wiring plan using a Volvo fan relay on another thread. You can also use the same prinicple with a temp switch fitted in the hose that goes from the engine to the radiator in the engine bay. You can then fit a small fan in the side vent to duct air back into the bay after shutdown. You can also fit a timed switch to this fan to get rid of radiant heat.
I've done this a number of times on quite a few cars. I also done the engine vent fan on a Boxster. Worked a treat. The Volvo relays are cheap and very reliable. You can also get cheap two speed fans from an auto dismantling yard.
 
Follow up to earlier post.
Well, I feel like the biggest idiot! I followed all of the suggested tests for the fan with almost no positive results. Defeated, I figured I had a broken wire somewhere from the fuse panel to the rad thermo switch connector. Here we go. This isn't going to be fun. Looking at the fuse panel sitting on the passenger floor and noticed the horn and fan relays had the same Bosch part number stamped on the top. I "assumed" the relay to be good when I started this task. Why not switch them around and see what happens? I did and jumped the black/white and black wires that feed the thermo switch at the front of car and fan started running. Horn doesn't work now so new relay will be bought. If I had done that 3 days ago...
Sorry to waste everyones time. Geez, what a dummy I can be at times.
Ed
 
EJP said:
Follow up to earlier post.
Well, I feel like the biggest idiot! I followed all of the suggested tests for the fan with almost no positive results. Defeated, I figured I had a broken wire somewhere from the fuse panel to the rad thermo switch connector. Here we go. This isn't going to be fun. Looking at the fuse panel sitting on the passenger floor and noticed the horn and fan relays had the same Bosch part number stamped on the top. I "assumed" the relay to be good when I started this task. Why not switch them around and see what happens? I did and jumped the black/white and black wires that feed the thermo switch at the front of car and fan started running. Horn doesn't work now so new relay will be bought. If I had done that 3 days ago...
Sorry to waste everyones time. Geez, what a dummy I can be at times.
Ed
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That's usually how troubleshooting goes. Glad you found it.
 
How do I make this fan run when connected like its supposed to be? I got it to run by jumping the wire connectors up front at the rad. Got it to run by jumping at the relay panel. Went for small drive today. High 80's and humid. I kept trying to hear the fan turn on. Didn't hear it.
Let the car idle for a while thinking the temp would rise enough to start the fan. No run.
Any thoughts on a bad thermo switch on the radiator??? It looks to be original.
Car does not run abnormally hot. Maybe they just don't come on very much???
If I do replace it, how much coolant will run out of the radiator?

Thanks for advice.
 
I believe the standard-temp unit should switch on at 92°C (198°F) and off at 87°C (188°F ). That's pretty hot--above normal operating temperature, I think. That said, mine wasn't working at all after I pulled the car out of storage. I think the switches have been known to fail. If you're going to replace it, you can do so with a switch from MWB that comes on at a lower temperature.

If you're quick-fingered with a new switch, you won't lose all the coolant. But the switch is at the bottom of the radiator, so it'll come rushing out.

If you're not ready to refill and bleed the system for whatever reason, you can wire a simple interruptor switch that bypasses the temp switch instead of replacing it.
 
In general unless it is very hot out the radiator fan won’t run while going down the road.

The fan should start running when in stop and go after driving on the highway or in extended low speed running. The fan doesn‘t run often in my car’s use.

The thermostatic switch does fail over time. Mine has. I have a manual contact switch under the car for when I know I will need it, such as at an autocross or when I expect to be in traffic.

I will be replacing it next week when I replace all the primary hoses, thermostat, heater valve and coolant. I will likely change over to the three contact VW switch and eventually add the second fan to make use the other other contact to ground the AC fan relay.
 
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kmead said:
I will likely change over to the three contact VW switch and eventually add the second fan to make use the other other contact to ground the AC fan relay.
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I'm sure you already know what I'm about to say, but just in case. If you only have one fan (for now), then the three contact switch isn't the right choice (unless your single fan is a two-speed unit). The switch has two temperature levels, one for each contact. So a single speed, single fan will only run at one of the two temps. Having a second fan, each activated by one of the two temp levels will work, or the same with a two-speed single fan. The AC compressor could activate either or both fans/speeds, independent of the coolant switch. I'm confident you have this covered but thought it might help avoid confusion for anyone else reading the thread and considering the mod. ;)

What got a bit confusing was wiring two two-speed fans and AC to one of these bi-temp switches on one of my VWs. But at the same time wanting to operate the two fans independently for different functions. o_O
 
Clever catch swapping relays like that!

There is a way to test the radiator switch. Once removed it is immersed in a pan of hot water on the stove with a thermometer to read water temp and a continuity testor to read when the switch activates. Don't just assume you have a good contact when it clicks. The contacts could be trashed up. Or, you could just spend $12 on a new one from our suppliers and switch 'em quick before you get wet.
 

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Dr.Jeff said:
I'm sure you already know what I'm about to say, but just in case. If you only have one fan (for now), then the three contact switch isn't the right choice (unless your single fan is a two-speed unit). The switch has two temperature levels, one for each contact. So a single speed, single fan will only run at one of the two temps. Having a second fan, each activated by one of the two temp levels will work, or the same with a two-speed single fan. The AC compressor could activate either or both fans/speeds, independent of the coolant switch. I'm confident you have this covered but thought it might help avoid confusion for anyone else reading the thread and considering the mod. ;)

What got a bit confusing was wiring two two-speed fans and AC to one of these bi-temp switches on one of my VWs. But at the same time wanting to operate the two fans independently for different functions. o_O
Click to expand...

It is just a ground. A switch can lead to ground for the one or both relays. Multiple grounds can lead to the same point, which one is actually possessing continuity is up to you.
 
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