Radiator fans not coming on

So I just got a beautiful 1987 328, runs great, but I noticed that the radiator fans do not seem to come on ever. When I am moving, temp stays between 170-195F, but when stopped it starts creeping above 195F. According to the owner's manual, the fans should kick on at 183F and back off at 167F. I let the car idle at my garage so temp would creep up well past 183F and confirmed the fans aren't kicking on.

I'll do some troubleshooting this week -- first will check for +12V at one of the leads going into the thermal switch on the radiator. If there is +12V at the switch, I'll jumper across the switch, which should make the fans come on. If they don't then the issue would be the fans I assume. Or some wiring problem. Anything else I am missing?

If no +12V at the thermal switch, the problem would have to be upstream, such as a relay (or wiring issue). Looks like right and left fans have separate fuses and separate relays (I checked both fuses, both are good).

If both fans are not kicking on, I feel like it's got to be a common cause -- the thermal switch would be the most likely culprit. Unless there is some sort of staging, or other conditions where right and left fans operate independently and not together.

Any other advice or suggestions that would help?

thanks,
219

 

You’re on the right track. I’m betting the switch. Do the jumper thing.

 

It's the dreaded thermoswitch. Gotta be.

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Pull the connector off the switch and short the pins with a paper clip. The fans should run it the switch is bad.

 

I had the same issue back in July with my 308. Turned out to be the fuse block. Birdman made me a new one, which also fixed the a/c - bonus!

 

I was looking at the 328 wiring schematics and found the thermal switch (77) and motors (27 and 28). I was wondering if a ground point could also be a common link to both fan motors but the schematic seems to suggest each fan grounds to different points on the chassis. So for sure the thermal switch (or its wiring) is the common link.

The switch has a yellow/green wire going to the fan relays and black wire (which I assume is +12V). On the schematic, that black wire points to "AL 1 / TO THE 1" -- top is Italian bottom is English. I can't find "1" anywhere on the schematics but I assume maybe it refers to a connector or point hanging off +12V bus. There are similar messages elsewhere in the schematics referring to other numerical connections.

Anyway, I'll test the thermal switch tomorrow and that will give a big clue...

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Are you basing the (non) turn-on diagnosis on the temp gauge? My 328 fans do not activate until the needle is slightly past the index mark at the 6-oclock position. IOW, maybe the coolant temp has not actually risen to the point where it is hot enough to activate the fans. Easy enough to get a decent check with an IR gun aimed at the thermostat box from a couple of inches away.

 

After my first extended drive on Saturday (was just going for a ride around the block that turned into 20 miles) I found it surprising that the fans never kicked on at all, and that was before I knew anything about the thermal switch range or normal engine temp ranges of the 328. Just seemed to be running warm->hot with no utilization of the fans.

After that I started looking up numbers and comparing to the temp gauge, which of course could be inaccurate since it's probably hooked up to a 34 year old thermistor. So it would be good to verify with an IR gun. Bottom of the gauge is 195F. Needle can swing and point well to the right of that with no fans ever kicking on.

I am hoping to have some time to troubleshoot after work today.

 

No, it's a ground connection. "1" is one of the front parking light assemblies (see Fig 6 -- it, likewise, shows "to the 77"). When the thermoswitch 77 is open (cold), the GV wire will be +12V relative to the N wire. When the thermoswitch 77 is closed (warm), the GV wire will be connected to the N wire (ground) = closes the relays that run the radiator fan motors.

 

Thank you! That is great clarification to have. I looked at those diagrams many times and never spotted the "1". And there it is prominently in the upper right corner of figure 6...

So then the thermal switch is really just opening/closing the path to ground for the relay coil to actuate. I guess I ought to verify that the N wire is running to ground as part of the troubleshooting.

 

Yes, if "jumping" the connections at the thermoswitch does not cause the radiator fans to run, check that the N wire is well connected to the chassis ground (i.e., measure the resistance from the N wire to some known good metal chassis ground point or the negative battery terminal -- should be a very low resistance).

They did a little better in later wiring diagrams to include the "to the..." items in the text description of the figure where the "to the..." appears (even if the "to the..." item itself is not in the figure) -- but not the case for the 328 wiring diagram so takes some searching in the other figures to find them.

 

What causes the thermal switch to close? That is, how does the switch know when the engine temp has reached 183° ?

 

I have seen a few kinds over the years. Most use a temperature sensitive shape-memory-alloy or bi-metal construction that will flip a lever or spring to close contacts. Basically, some type of metal mechanism that expands/contracts or warps according to temperature.

 

OK, so I was able to test everything.

Black wire to the thermal switch is 0.2 ohms from ground (I tested to the nearby bracket on the AC filter/dryer), so that seems good.

Yellow/green wire to the switch had +12.3 volts when the ignition was on, so that seems good.

With a jumper between the two wires, both fans kick on when the ignition is on, so that seems good.

I think this means one of the following:
1) thermal switch is bad
2) thermal switch is not reading properly for some reason (air?)
3) my expectations for temperature, or correlation with the temperature gauge, are misguided.

I've heard these cars are fussy about air in the system -- does anyone know how likely it would be to have an air pocket down in that lower corner of the radiator where the thermal switch is mounted? My thinking is that it would be very unlikely to have an air pocket down low next to the return line but I am not familiar with these systems.

I should confirm temperatures at the engine thermostat and the lower corner of the radiator near the switch to make sure I am being realistic with regards to what the temperature gauge shows. I don't know what sort of temperature drop happens between those two points other than to say temperature in the lower outflow corner of the radiator should be noticeably lower than coolant leaving the engine. So I think I'll run the car, let it get nice and warm and measure temps with an IR gun to get some data. As it happens, I can't find my IR gun, so I ordered a new one and should get it tomorrow.

 

# 1 and #2 seem to the same, the switch is bad.

Me? I would just replace the switch, they aren't expensive. You can do it without draining the radiator, if you are quick, (on a 308 anyway) you will lose maybe 1/2 pint of coolant.

Doug

 

I am sure the switch is easy enough to change if everything goes right, but I never make that assumption on an old car! I've had too many 5-minute repairs turn into projects. I got my new IR gun tonight and want to measure a couple temps first before I conclude the switch is bad. Probably tomorrow if weather cooperates.

If the switch seals with an o-ring or gasket, I'd hope I can replace it quick enough to not lose much coolant. I'll probably fill the expansion tank to the top for some extra margin

 

Well, I'm not a mechanic, and I know zero about automobile electricity; in such matters I defer to experts like Steve above.

However, FWIW...a bit of "return of experience". I have two 328s, both '89, and have owned them for about twelve years now. As discussed a lot on this forum for many years, 328s are not temperamental regarding their cooling circuit, certainly less than some 308s seem to be. Air in the cooling circuit is a rare occurence, and should be easy to cure with a good purge, including driving after the purge with the heating circuit wide open for about 30 miles or so (unless something is very wrong, such as a head gasket).
Do not overfill the expansion tank to the top, the circuit will spurt the surplus out. Once correctly filled and the heaters purged, the circuit should stabilise at its operating level, that is, as per the owner's manual, exactly 6 cm (a bit more than two inches) under the tank's neck; or exactly at the seam between the two parts of the tank, at its middle; and it should STAY there. All the time. That's what both of my cars do; anything above that level is spurted out.

As for the fans behavior...I don't know the weather in your place, if you have city driving, etc...on my cars, the fans work just fine, as expected, with coolant temp at a bit more than 90°c on the gauge, but actually they do not kick in AT ALL in "normal" pleasure driving that is on country roads, no city driving. Had a 60 miles drive with the GTS on Monday: no fans needed. (Standard operating coolant temp is about 75° c on the gauge on both cars)
They only start doing their work if there is some city driving, and even that, not very often; I do the same driving in a city from time to time, with 37 red lights in succession one behind the other; depending of the traffic speed, etc, I might from time to time have to stop at most, or even all, the 37 red lights; in such case, the fans use to kick twice or three times, that's all.

You're in good hands on this forum and I'm sure you will find very soon if your gauge is accurate or not.

Rgds

 

Yes, that's why I want to get temperature measurements with a gun, to make sure the gauge is reading right and that my expectations are reasonable. There is also a substantial temperature drop across the radiator and the switch is on the downstream end, so I want to measure there too. All of this will give a very solid picture and dictate the next step. I did order a replacement switch ($14) just in case, but it's possible the temperature data will be normal and I don't need to do anything. The previous owner was generous with maintenance and the car had a pretty thorough PPI before I purchased it, so I am thinking a faulty switch would have been noticed, but you never know. I tend to be more perceptive about these nuances so it's possible I am the first to notice.

BTW, filling the expansion tank to the top is only done to offset coolant loss and minimize air issues while changing the switch. Afterwards the level will be adjusted back to normal as needed.

 

I let the 328 idle outside my garage for a while today. Started taking measurements with an IR gun. Best readings were in the upper and lower corners of the radiator where coolant flowed in and out, respectively. I was seeing about 20-30 degrees F drop in temperature across the radiator with the fans off (ambient temp was 55F).

I went to take some readings on the engine and when I came back to the front of the car, the fans were on! Temp on the dash gauge was reading about 210-215F eyeball. Temp in the lower corner of the radiator was ballpark 175F but with the fans on I didn't get as close as I would like to for a pinpoint reading, so there was surely some averaging going on (the IR beam spreads the farther the gun is from the area being measured).

I'd say things are working as intended more or less. Because of the temperature drop across the radiator and the fact that the fan switch is in the coolest corner of the radiator, it's normal for the engine temperature gauge reading to be 20-30 or more degrees F higher than the temperature that the fan switch sees. This surely varies with outside temperature -- in hot weather there will be less cooling, so the temps will be closer together. In cold weather they will be farther apart.

I could swear I got the engine just as hot the other day without the fans coming on. I am wondering if the fan switch connectors might not have had good contact before (one of them was about halfway on but appeared to be in contact). Perhaps when I pulled the connectors off for testing, I got a better connection when they went back on. I did give the female connectors on the wiring harness a squeeze with pliers before putting them back on, and then coated the connections with Fluid Film afterwards.

I guess I will keep an eye on this as time goes on to make sure things still work right. Thanks for all the input and help, I appreciate it.

 

By the way, since I didn't have to replace a fan switch, I used my free time to get in other trouble. I had the (in retrospect, dumb) idea to pop a cassette adapter into the vintage Alpine head unit (model 7284) in the car to see if I could play some music from my phone. Sound was lousy and then I discovered the cassette adapter would not eject. With a cassette in there, of course radio mode could no longer be used (AM/FM had been working great). So I spent a couple hours carefully extracting the head unit from the dash and taking it apart to get the cassette out. For sure the unit won't play cassette now since I had to remove a couple parts of the eject mechanism to get the tape out, but at least I have AM/FM back. I cleaned up some of the 34 year old radio wiring while putting things back together. I suspect it's common knowledge in the classic car world to not try using ancient tape decks of unknown function, but I found out the hard way. I won't ever try that again.

 

I had a cassette tape fail to eject or play in my Mercedes AMG. I left it in there for a few weeks and tried the ejection button several times each time I drove the vehicle. The machine finally ejected the cassette after about 20 or so attempts. That cassette no longer goes into that machine. Figured I was lucky.

 

The dealer-installed Pioneer KEH-5060B, a gift by the french importer Pozzi, the one with the little horsey badge at left still works fine in my 328 GTB, cassette, radio, etc...I don't use it while driving, but I try it from time to time with a "The best of Sam and Dave" cassette. Sound is certainly not great, but hey: 100% period correct.
The GTS has a "modern" (end 1990s?) head unit, a Sony with a CD reader (no cassette) and removable front part; I have never even tried to put the front part on in the 11 years I have owned that car, so I don't know how it sounds.

Rgds

 

I used to carry gallons of coolant for 100 miles of driving during our Monterey car week, until I learned about my cooling system and fixed it. Water pump and radiator are still original 1974. The air blockage on my 308 was actually in the thermostat housing. Aftermarket bleed screws in the thermostat housing and top of radiator help a lot. They only function when the system is warm enough to open the thermostat. Radiator cap, thermostat, and fan relays are very inexpensive. I agree that you just overfill the coolant tank and let it "pee out" the excess to find the correct level (same as my modern KTM). Birdman fuse blocks will guarantee that there is no failure there. Search this forum or my post for "Lucas radiator cooling fans, and why they need to go away." Keep asking questions and check the little things until everything is right.

 

It's located in the bottom of the radiator...