RE: Fan goes on and off, on and off...

[Z-man]

At idle, and at slower speeds, my fan keeps switching on and off, repeatedly. (I see the volt meter drop and hear the fan switch on) After I switch the ignition off, it will do the same for a short amount of time too.
It doesn't appear to be happening once I'm at cruising speed.
My temp guage stays steady at the 2nd tick from the bottom, but I've seen it move a little around there. Also, my coolant in the overflow reservior is warm, so I have to assume that it is cooling the block. After driving for an hour or so, the reservior is at the MINIMUM level. Not good?

I did have a lower temp thermo installed recently, and have driven the car HARD at DE events.

Could the switch just be going? I'd like to try to repair it myself: it this ia difficult job? My car is a 1989 S2.

Thanks,
-Zoltan.

[Lawrence Coppari]

I think the switches are sealed and there is no getting them apart. The quick on/off is probably just a quirk of this particular one. Evidently, it is very sensitive.

My coolant level rises a little when I drive the car (and shut engine off) due to expansion of the coolant. It drops as the system cools off.

[DennisR_944]

I'd wait awhile before doing anything with it. The lower temp TS could be causing it. If it doesn't get too hot I'd go with it. Good luck.

[Z-man]

UPDATE: My mech checked it out: it is a air temp sensor unit thingy (technical term!) that is causing this cycling: hopefully the part can be installed today, so it will be back to normal and I can attend this Sunday's autocross!

The fan switches/relays are all functioning properly, everything else in the coolant system was ok too.

Thanks for the feedback guys!
-Zoltan.

[Lawrence Coppari]

Where is the air temperature sensor located?

[PorscheG96]

Originally posted by Lawrence Coppari
Where is the air temperature sensor located?

Seriously, I need to know too. C'mon Z.

[Z-man]

When I pick up my car tonight, I'll ask where the air temp sensor thingy is.

I'll try to post some pics too.

-Z.

[Z-man]

The "Air-inlet temp sensor" is mounted in the intake.

Unfortunately, that didn't fix my problem yet: the mechanics are puzzled....

-Z.

[divezic]

Z-Man,

I hate to mention this but I think your mechanic does not know what he is talking about. There is nothing in the cooling system that takes and "air inlet" reference temperature. That is solely a fuel injection sensor on the air flow meter.

If your fan is cycling very often at slow speeds/idle and not at faster speeds, I can think of three things:

1-Partialy clogged radiator OR a failing water pump. Don't be alarmed yet. I don't think there are the problems because you'd probably get the same indications when running high speeds, especially during DE.

2-Air bubbles in your coolong system. These cars are very sensitive to air in the system and they are a pain to bleed properly. You mentioned that you had a lower temp fan switch put in your radiator. Who did it and is it possible they did not bleed the system properly (like the guy who diagnosed a cooling problem related to a FI component?) On a 944 NA it isn't difficult after you get a good technique to do it. Ya just gotta do it right.

3-I think this is most likely the problem. New lower temp fan switch will kick the fan on around the 1/2 tick mark (OEM switch kicks it on around the 3/4 tick mark). OEM thermostat keeps the coolant around 90 C, which roughly correlates to an engine temp around the middle tick mark or a little lower. So if the old thermostat tries to keep the engine temp little less than 1/2 and the thrmo fan switch kicks the fan on at 1/2 then it takes very little time at idle (aka no air cooling flow) to cycle the fans. I believe that your system components are working perfectly, but not working together properly. If this were my car I'd change the thermostat to a lower temp unit (80 C). This will keep the engine temp at about the 1/4 tick mark or a little less. You will find that your fans cycle less but when the fan is on it will stay on for a little longer than before.

Please note that I have a 1984 944. The temp gague markings are probably different, but the function of the cooling system is the same. The gague had 5 tick marks. I call them: low, 1/4, 1/2, 3/4, and blow your engine up. My car has a lower temp thermostat and an OEM fan switch. When driving, my car always remains at the 1/4 mark and the fan kicks on at the 3/4 mark when in traffic.

The fact you mention that your temp always stays steady reinforces my theory. There is a very little temp spread between the thermostat and the fan switch. Hence the quick cycling and the steady temp. Furthermore, there is no cycling at speed because there is enough cooling air flow to keep the temp out of the fan switch range.

Good luck and keep us informed about your progress.

[Z-man]

Dave,
Thanks for the tips.
I do have a lower temp thermo in my car, and they also replaced the fan switches at that time with lower temp units. They checked everything for proper functioning. Through this process, they did find the air inlet temp sensor was faulty in my car. Was it related? No. But is was faulty.

If the fan would kick in and stay on earlier than before, I would expect this to be normal, but the fan keeps cycling every 7-9 seconds: on again, off again. Also: I believe this only started happening when I switched my defrost on, thus kicking in the compressor. Before then, even after I had the lower thermo put in, this on/off on/off was not occurring.

Puzzling situation....
-Zoltan.

[PorscheG96]

I can hardly wait until your mechanic finds out what the problem is. My cooling fans do the same thing with the AC on and my initial cooling isn't working. I've replaced the fan switch, the fan relay, checked the fuses, and taken the car to the mechanic...cannot figure it out.

[DennisR_944]

My vote still goes to it's working properly. It doesn't take much for the fans to cool these aluminum blocks down. You put in lower temperature components so it's not getting as hot as before thus the fans are cycling shorter times. I see lots of people that don't understand the cooling systems on our cars and they are always comparing them to older non-electric fan cars. Idling in these cars doesn't cause them to heatup more like a car with belt driven fans would. Increasing the engine speed doesn't cause the temperature to go down like a belt driven fan does, it causes the opposite. I'd get an expert opinion, but I think your OK.

[Z-man]

Originally posted by DennisR_944
My vote still goes to it's working properly. It doesn't take much for the fans to cool these aluminum blocks down. You put in lower temperature components so it's not getting as hot as before thus the fans are cycling shorter times. ..

I understand what you're saying, but this is the cycle I'm experiencing:
2nd fan goes on and goes to FULL speed (5 seconds)
As soon as it hits full speed, it stops.
While it is slowing down, it kicks in again.
This cycle repeats over and over again.
If you heard this cycling process, you'd know that something is not setup right.

There are many components to the S2 cooling system: not just the thermo and fan switches. There are sensors in the throttle body and the intake. They run coolant through the throttle body to prevent icing of the throttle in cold conditions. (Ever hear of icing in the carbs? The coolant is to help prevent this type of condition in our throttle bodies!) So when the throttle body gets hot enough, the sensor tells the fan to switch on. For now, they removed the coolant in and out hoses to the throttle body to bypass that sensor. (Actually, that may help with performance, since theoretically, the air going into the engine will be a little colder!)

The intake has a similar sensor: it's underneath and toward the firewall. And of course the AC system is also hooked up to the whole system too.

My car will be back at the mechanics for further investigation (I took it for the weekend autocross!) John took home a working FAN relay to try to figure out how it works.

My take: when I switched to the lower thermo and fan switches, somethings causing a loop: there must be a higher temp sensor somewhere that turns on the fans, and then the lower temp stuff turns them off: kinda like two kids playing with 2 light switches conected to the same lightbulb.

I'll let you guys know ASAP what's going on.
-Zoltan.

[DennisR_944]

Don't take this to the bank, but it seems like I read somewhere where there is a sensor underneath what would be the air cleaner box on the n/a cars, attached to the chassis. Maybe check that location in your S car.