[rkeysor]

My '92 coupe's fans have begun cycling on and off more than normal, apparently a common problem.  I assumed it was the thermal fan switch, pulled the radiator, installed a new switch, and got no change. I next used the Clark's Garage test procedure for the fan relay in the fuse box.  This basically entails jumping poles in the plug for the thermal fan switch, operating the AC switch, etc.  My relay failed each test.  I then purchased a "used" fan relay from a West Coast parts source, the exact version in my car.  This unit had been resealed suggesting it had been opened and possibly had connection (s) resoldered.  My fan operation continued to be erratic, sometimes switching on while driving even though the temperature needle was just above the first marker. It was essentially unchanged from the behavior with the original relay. After reading some previous posts on this topic, I sprayed the fuse box where the relay mounts with Tuner/Control Cleaner & Lubricant spray, let the car sit overnight, reinstalled the relay, changed the coolant for good measure, and got the same result not long after the engine came up to operating temperature.  I haven't used the Clark's Garage test on the replacement relay.  Also, there is mention in some posts of a ballast in the system.  I am unenlightened on that topic.  Appreciate any assistance.  I have already upbraided myself for buying a used relay, it's worthiness unknown.

Partial Post: Please Login or Register to read the full post.

[flash]

most likely the big relay (not the small ones).  that was the case with a couple of cars i've had in here

 

however, the ballast resistors on the firewall over by the battery, underneath the heater cover, can cause erratic behavior.  most commonly it is the connection there, and not the resistor itself

Partial Post: Please Login or Register to read the full post.

[rkeysor]

I've now replaced the thermal fan switch and the relay in the fuse box with new units.  I've also changed the coolant.  I'm still having the fan come on during normal driving, though the temperature gauge has never approached the second hash mark.  My memory is that I rarely heard the fan (s) run on this car except upon shutting down a warm engine.  There was mention of a "ballast" that I recall was said to be located in the vicinity of the battery, a matter raised on earlier fan operation questions.  What is the ballast, where is it located, and how is it trouble checked?  Thanks for any help.

Partial Post: Please Login or Register to read the full post.

[MCL968]

Did you burp the air out of the cooling system? My 92 had an air pocket that caused the gauge and the fans to do strange things.

Partial Post: Please Login or Register to read the full post.

[flash]

you could be chasing a ghost.  higher mileage engines will also run hotter than lower mileage ones.  higher rpms will generate higher temps.  you could also just have a clogged radiator.  it is important to make sure you never use tap water, and only phosphate free coolant.  water wetter is also an excellent addition to the system

 

that being said, a few things to know:

 

obviously the system has to be bled correctly (fully warmed up, heat on high, heater fan on high).  it is important to make sure you have a bleed screw and not a regular bolt.

 

use a laser thermometer to determine the temperature at which the fans are coming on.  do not trust the dash gauge.  if it were working though, the 8 o'clock line is 176 and the 10 o'clock line is 212.  it should run right in the middle with the OEM fan switch, and a good needle's width lower with the low temp switch

 

the OEM fan switch will bring the fans on low speed at 197.6F and the high speed at 215.6F.  the low temp switch at 185 and 199.4

 

the thermostat begins to open at 185F.  if the thermostat is wonky, the fans will act up

 

if any of the lower body pans (front apron, plastic belly pan) are missing, the fans will come on more than normal, because the engine will run hotter.

Partial Post: Please Login or Register to read the full post.

[rkeysor]

Thanks for the info.  I did "burp" the system during the refill.  The car got a new radiator and thermostat 12 years ago, and the temperature (prior to that event) has never gotten very high.  It generally takes a rest just above the first mark on the dial.  But it is indeed a high mileage car, 164,000 or so.  While I think it is unrelated, I had my heater fail ON as they do a couple of years back.  I fixed the two clips in the driver foot well and installed a new Audi heater valve without curing the issue.  I then used a cable tie to close off that Audi valve and continued to drive it for a year or two--I'm in Florida.  When I got working on the current problem and wanted to change the coolant, I clipped the cable tie and turned the heater to full on during the process. This included opening the bleeder, which is a stock item.  The funny thing is that after I turned the heater off and continued to use the car, it did not turn itself back on.  I will recover my thermal gun from a fellow car guy and check the turn on temperature.  The full body pans are in place on the car, I will add.  

Partial Post: Please Login or Register to read the full post.

[flash]

the heater control valve is vacuum activated, and defaults to "on" when vacuum fails.  your problem there may just be a bad vacuum connection or hose.

 

the ballast resistors are on the firewall near the battery, under the heater cover.  those connections are known to corrode and cause issues.

Partial Post: Please Login or Register to read the full post.

[ds968]

The cooling fans are now starting to act up in this manner : they both turn on simultaneously at their full speed , run for 4 or 5 seconds, then stop , and within a couple of seconds start again . This pattern repeats continuously seemingly without end ...until I remove the key from the ignition . It’s NOT the big relay , I switched it with the one which works perfectly fine in my other 968 , but it did the very same thing in this one . They kick in as expected at the right temp ( at least according to the dash temp gauge ) , and they kick in whenever I turn on the AC, but the rapid on and off pattern is the same in both cases . This just started happening, they worked perfectly fine a month or two ago when Imlast drove the car . No work was done on the engine since that time ..for whatever that’s worth ..


So what could it be ? Ballast connections is going bad would make the fans act this way ? Fan switch seems to work ok since it triggers the fans to kick in when they should , the thermostat is fine , the system has been burped last year, but the car has only been driven about six times in the last six months ( yes, I know, shame on me ) so doubtful any air bubbles have formed since then .


Any ideas ? Thanks ,

Partial Post: Please Login or Register to read the full post.

[pdxmike]

Are you saying that they are kicking in at low speed at the indicated gauge temp (as would be normal), or are they kicking in at high speed when they should be running at low?

 

Is it always the same amount of time that they turn on/off or does it vary?

 

Do the fans still run at low speed for a minute or two after you turn off the engine or are they cycling then also?

 

Regardless - first thing I would do would be to make sure the thermofan switch connector on the radiator is actually well-seated. Second would be to clean the thermofan ground and connectors to the ballast resistors. I believe the thermofan switch grounds at ground point IV which is on the chassis just behind the driver's side headlight. It's easy to access.

Partial Post: Please Login or Register to read the full post.

[ds968]

They’re kicking in only at high speed, where the gauge temp indicates they should ( slightly above the middle line ) They never run at low speed, in any situation.

And even if the gauge temp is below the bottom 1/3 line, if I turn the AC on they immediately kick in at high speed .

Always the same amount of time on and off , no variance at all.

When I turn off the engine they stop , no continuance running at all, high or low speed.


Thanks , will check those out !

Partial Post: Please Login or Register to read the full post.

[pdxmike]

It's your thermofan switch (or wiring to/from it). 

 

The thermofan switch on the radiator has two contacts - one for low speed that closes at 92C and one for high speed that closes at 102C. The low speed contacts aren't closing correctly on your car. So what's happening is that your coolant heats up, and at 92C the contacts should close for the low speed fans but for some reason, on your car they aren't. So the coolant eventually reaches 102C closing the high-speed contacts. The fans come on, the coolant cools down, the fans turn off. What SHOULD happen is that the low speed fans should still be on until the coolant reaches 92C. But because your switch's contacts aren't working, the low speed fans never come on - so the coolant heats up again, triggering the high speed switch to close again - car cools, high speed fans turn off, car heats up, high speed fans come back on. That's your on/off cycle, because you're missing the low speed fans. 

 

The fans don't stay on when you turn off the ignition because they are designed to only run at low speed with the ignition off. Your low speed contact is faulty, so the circuit remains open and the fans just cut out when you shut off the ignition. 

 

I would still check the connector and clean the contacts as it could be part of why the low speed circuit isn't closing. Definitely there could be a wiring disconnect somewhere between the thermofan switch and relay causing the problem.

 

7a on the amazing cooling system troubleshooter should help you confirm if your low speed switch itself is buggered. 

 

http://www.968forums.com/topic/9029-elec...ng-system/

Partial Post: Please Login or Register to read the full post.

[ds968]

Thanks, that is very helpful info !!

Partial Post: Please Login or Register to read the full post.

[ds968]

[quote name="pdxmike" post="186956" timestamp="1555721433"]


It's your thermofan switch (or wiring to/from it). 

 

The thermofan switch on the radiator has two contacts - one for low speed that closes at 92C and one for high speed that closes at 102C. The low speed contacts aren't closing correctly on your car. So what's happening is that your coolant heats up, and at 92C the contacts should close for the low speed fans but for some reason, on your car they aren't. So the coolant eventually reaches 102C closing the high-speed contacts. The fans come on, the coolant cools down, the fans turn off. What SHOULD happen is that the low speed fans should still be on until the coolant reaches 92C. But because your switch's contacts aren't working, the low speed fans never come on - so the coolant heats up again, triggering the high speed switch to close again - car cools, high speed fans turn off, car heats up, high speed fans come back on. That's your on/off cycle, because you're missing the low speed fans. 

 

The fans don't stay on when you turn off the ignition because they are designed to only run at low speed with the ignition off. Your low speed contact is faulty, so the circuit remains open and the fans just cut out when you shut off the ignition. 

 

I would still check the connector and clean the contacts as it could be part of why the low speed circuit isn't closing. Definitely there could be a wiring disconnect somewhere between the thermofan switch and relay causing the problem.

 

7a on the amazing cooling system troubleshooter should help you confirm if your low speed switch itself is buggered. 

 

http://www.968forums.com/topic/9029-elec...ng-system/

 

 

Checked everything on the list, all seems to be clean, good contacts everywhere , resistors tested just fine, so I had the thermo-switch replaced just for good measure .   and.... NO CHANGE !!   Still the same cycle , both fans come on simultaneously, right when it should kick in, slightly less than half way between the 8;oclock and 10 oclock bars, with on and off repeating patterns ( about six seconds each, with an interruption of about two seconds between) and then stop as soon as the needle drops right below the 8 oclock bar again . After trying three different relays, I'm at a loss as to what can cause this.  My mechanic is just as puzzled.    

Partial Post: Please Login or Register to read the full post.

[pdxmike]

Well that is quite frustrating.  :angry:

 

Clearly it is not the relay. 

 

It is also of course unlikely to be the thermofan switch.

 

The fact that the low speed fans NEVER come on argue against there being an air pocket in your radiator.

 

It seems clear to me that there is SOME problem with the low speed circuit. Nothing else would explain why the high speed fans cycle on and off. They are doing their job by cooling the coolant. The problem is  that somehow you have lost your low speed circuit. 

 

So somewhere there is a problem with the low speed circuit. You have already done all the checks in the very nice PDF which means the problem lies somewhere outside the fuse box and the wiring leading directly to and from the relay. Most likely - there is an open or short in the wiring between the components of the low speed circuit. 

 

1 Signal from thermofan switch to Relay - to verify the wiring itself - check circuit TS for continuity, between the thermofan switch connector and at TS on the fuse box

 

2) That out of the way: here is where I think the money is. Relay switched power to fans through low speed resistors - CHECK FOR POWER at the resistors when the low speed fan should be running - i.e., right after the high speed fans come on and then cut out. What is the voltage going INTO the resistors? What is the voltage coming OUT? If your thermofan switch is working (it's brand new, so it most likely is), and your relay is working correctly, and #1 above checks out, and you do not have an open between the relay and the resistors - then you MUST have 12VDC going into those resistors when your coolant temp is between 92 and 102C. I'm not sure what the voltage should be coming out of the resistors, but obviously it should be lower, as V=IR. In fact, if you measure current going into the resistors you can use that equation to tell you exactly what the voltage "should" be exiting. If it's 12VDC, the resistors would be your problem. 

 

I think the problem at this point is most likely with that circuit, coming to and leading out of the resistors. Because you do not even get low speed with the AC switch on. The fact that you get any fans at all with the AC switch indicates that power is getting through (sorry, I should have paid more attention to this before, as it argues against the thermofan switch being the culprit). So the circuit is intact. But, the relay-switched power may be too high, due to too little resistance, causing the low speed circuit to "become" a high speed circuit. The simplest explanation would be a fault with the resistors - which you checked - therefore something else is going on with the wiring in that area. Just my hypothesis.  :glare:

 

3) If 2) checks out OK, then CHECK FOR POWER at the leads coming from the low speed resistors, at the fans themselves - at the time when the low speed circuit should be active as in 2) above. You or your mechanic will want to devise some leads for this as obviously you do not want to be sticking your fingers near the blades while the engine is running! 

 

4) If all this checks out OK - is it possible there is a problem with the fans themselves? I.e., is it possible that with age, use, heat they have too much internal resistance to spin with the relay-switched power coming from the low speed resistors? 

 

Best of luck. 

Partial Post: Please Login or Register to read the full post.

[ds968]

Thanks again, willl ask him to check into that ( focusing on what you noted in the last post ) when he gets back from vacation in a couple of weeks . I drove the car today for about two hours in this condition, ( keep in mind my AC is always on ) so I’m wondering if, in spite of the gauge indicating the cooling works ok, and in spite of both fans going on for a brief time after I shut off the engine, if in reality these short bursts do not sufficiently cool the system , or, while I’m driving it may eventually overheat , boil over , cause undue stress on the radiator , or maybe even cause the fan motors to just burn themselves out with this abnormal m.o. ? I drove the car for about two hours today, in pretty hot weather, and it seemed ok , but any risks if I continue to drive it this way for a more extended period of time ? Not that I need to , it can go back in the garage for as long as it takes until the culprit is identified and fixed, but just curious ...

Partial Post: Please Login or Register to read the full post.

[pdxmike]

If your temp gauge stays in the acceptable range, I don't see how driving it would hurt things. The cooling system doesn't care if your low speed or high speed fans are cooling it, just that it gets cooled. If you had a problem with the high speed fans not coming on, that would be more worrisome and in that case I would say park it.  

 

My fans stay on high pretty much throughout the summer - I drive in a lot of stop-and-go - and they seem to be holding up fine. I would think having them cycle on and off would actually cause less wear-and-tear, as they have a chance to cool off between cycles.  

 

You definitely should keep an eye on the temp gauge, but I wouldn't park it just based on this. JMO.

Partial Post: Please Login or Register to read the full post.

[ds968]

Makes sense, thanks.    

Partial Post: Please Login or Register to read the full post.

[ds968]

Only a little off topic, but there is a majority school of thought which subscribes to the argument that any additives ( oil additives, gas additives, transmission fluid additives, etc ) are nothing but snake oil , but I have used Water Wetter in my coolant for years and I can categorically state I can detect a material difference in the gauge reading with and without that additive ; with it, the gauge needle does not rise nearly as quickly to the point where the cooling fans kick in, nor does it go to the same higher level as it did without that additive. Just my experience .

Partial Post: Please Login or Register to read the full post.

[MCL968]

We used it in our race car and it worked great. Very noticeable difference from the moment we started using it.


As for your gauge,I noticed mine became much more accurate after I cleaned the posts on the back of the instrument cluster. That was actually true for all of the gauges where I cleaned the posts, my fuel gauge became more accurate and almost goes to full now.

Partial Post: Please Login or Register to read the full post.

[ds968]

Well, well, well... so my mechanic's vacation actually starts tomorrow, not as I had thought that he was already on his way, so he had some free time this morning to run some more tests on various things that  PDXMIKE mentioned.   

He disconnected the wires going to the resistors and cleaned all the contacts, noting that one had just a little bit of corrosion on it.   Put it all back, and guess what..?!   Yup,  everything is working just as it should now !!    :clap:                  

Partial Post: Please Login or Register to read the full post.