Cooling Fans Not Coming On 86 Porsche 944
 

Hi all -

Since my previous post on April 4th, I have replaced the thermostat (even tested it in boiling water before installing just in case), lower & upper radiator hoses, hose from expansion tank that goes across top of radiator toward passenger side of radiator and expansion tank cap. Also replaced thermofan (cooling fan) switch and the cooling fan relay (ouch over $100). I performed the Clark's garage test and jumpered the the cooling fan switch and both fans came on so i though the cooling fan relay must be bad (this is after i have replaced the thermofan switch. I got the cooling fan relay in yesterday put it in thinking my overheating/non working fans problem would be over. Well, it did not solve it. The fans will come on now but only when I turn the A/C on, but they shut off as soon as i turn the A/C off. I tried multiple times yesterday of the letting the car warm up and each time the temp gauge goes all the way up to the 3rd white mark and continues to rise so i shut it off. I have also felt the lower and upper radiator hoses after letting it run and they both get hot. Replaced both cooling fan fuses as well although both tested good.
When my son and I installed the thermostat we found an 82C one i think the original was an 80C...and the thermofan switch i think was 90C to...can't remember upper limit at the moment.

Is it possible I still have air in the coolant system and this is causing no signal from thermo fan switch to cooling fan relay to make the fans turn on once the car warms up to temp?

Or are there other possibilities that I am overlooking?

Looking through the threads I saw lots of different issues on fans not working, thermostats, bleeding the coolant system. But I did not see anything posted that air in the system would cause the cooling fans not to come on...my car is equipped with two cooling fans but it is non-turbo. 86 NA 5 speed

The issue is driving me crazy to try and resolve.

Take a look at the connections and the wiring going to the two 50mm diameter ceramic fan resistors.

On the early cars, they were mounted in the engine compartment, under the plastic shroud, near the battery. On later cars, and my '86, they were mounted [on a bracket] inside the cabin, to the firewall, behind the glovebox. My suspicion...your connectors and wiring have seen better days.

Thanks to 931 guru and mel_t_vin - the cooling fans finally engaged but not until between the last 3rd white mark and the orange hot line so well over 100 C - I did replace the cooling fan switch with a lower degree setting (83 to 95 C) - tested it out yesterday and the fans kicked on right at 100 C (last white gauge mark) this time. Fans did not come on at low speed but high speed, when I shut the car of they ran for a few minutes in what I think was low speed.

It seems i may need to take the dash apart to get to the resistors behind the glove box. I was hoping they were under the plastic shield below the windshield under the hood. I suppose it is possible that they could be corroded not causing fans to kick on at low speed when they should. It is odd when shutting the car off they seemed to be engaged in low speed as well as when i turn the A/C on they run in a lower speed.

You should not have to take the dash apart. At most, you may want to remove your glove box...but even that may not be necessary.

Slide your seat back, lay on the floor, take a flashlight, and look up toward the battery near the firewall. You are looking for a ~6" aluminum bracket carrying 2 silver dollar sized ceramic pucks. Examine the wiring and associated terminals...

Thanks I’ll try to check that out this weekend. Fans still come on at 3rd white mark on temp gauge one car gets hot enough. So they do work, just would like to see if they’ll come on sooner.

@Bowhunter1974 how did your 944 cooling fan issue workout? I searched the forums when my son's car started having this problem but somehow didn't find your thread. It's a frustrating one...

Well I replaced the thermo fan switch and allowed the second fan to kick on. The silver dollar resistors underneath dash were absolutely fine. The fans still do not kick on until the third mark, but they do work.
We don’t get nervous until we have to idle along time or in hotter months. Again they work but it seems like the engine gets pretty hot before they do. I read through so many posts and replies. I never found anything that I hadn’t already tried. Some owners posted they just run hotter.

I don't know if this could be of help for you guys, but I had a very similar issue where my fans would kick on way too late, and it was purely because of air in the system. I had just finished refilling the whole system after a water pump replace, and my forgetful self didn't remember to bleed the system after doing so. I understand earlier you said trapped air could be a possibility, although if you haven't already tried bleeding the system out for a while, that may be the issue. Even if you've bled the system already, worst case scenario you just need to buy some more coolant to refill if you lose any. Although obviously just make sure to keep an eye on the engine temp so the car doesn't overheat while idling (in case the problem isn't air in the system).

You may know how to do it already, but I just took my reservoir cap off, unscrewed the bleeder bolt, waited for the car to warm up (with the heat all the way on), and then bled it until a steady stream of coolant came out of the bleeder bolt. Because RaceKarl on YouTube made a pretty good video on how to bleed the system without losing any coolant/spilling it everywhere, which involved using a grease fitting and a hose to redirect the lost coolant back into the reservoir tank - (starts at 2:31). I haven't personally gotten a hose/fitting to do this method yet (although I plan to soon) so I've been doing it the messy way, but it still worked fine, I just had to keep ample paper towels on standby.

After doing this my car's fans kicked on right about the middle mark of the temp gauge, so the 3rd mark definitely seems too hot for it to kick on. Again I'm not sure if that's the real cause of this, but either way hopefully it's relativity easy fix!

Thanks for the information and the video link.
We did bleed the system repeatedly in the garage, take it for a drive and then bled. At startup, idle, and anything in between. If there’s air in the system I can’t imagine how. Haven’t done it in several months. Definitely colder here in KY so almost zero issue with running hotter now. If we do drive it longer it will get up to third mark, both fans engage and it drops back down to second mark. 🤷🏻‍♂️

You can always throw a toggle switch in to allow fan to run a little extra longer.

Fan Resistor Complete Re-Wire
 

My resistor wires are falling apart under the cowl cover and under the dash. I want to replace them all the way home. Where are the other ends of the four wires? I don’t want to unwrap everything if it isn’t necessary.

944 Fans not coming on Low Speed
 

I just had a head gasket replaced on my 86 944 S2, but I noticed the temp was still going up and down during slow (bumper to bumper) traffic, still within the white lines. Only the right side fan was coming on at low speed. Based on what I found here, it appears that one of the low fan speed resistors (behind the glove box) has failed, one shows as OPEN, the other reads 0.9 ohms. I'm now waiting on the replacement part to arrive, and anticipate that should resolve the fan issue. Thanks for all the valuable info.

You need to test your fan relay, which based on everything I have read, you have not done... That is what triggers the high/low speed fans based on the thermo fan switch. This is likely why your high speed fan is activating but your low speed fan is not.

Read through clarks, as already posted - look at the bottom where it says "Testing Late Model Fan Relay"
http://www.clarks-garage.com/shop-manual/cool-01.htm

This is the last piece of the puzzle which you havent tested yet

Resistors = fan speed
Thermo switch = measures temp and sends signal to relay
Relay = triggers high/low speed fans based on signal from thermo switch

PS thanks @Joe Hewlett for ressurecting the thread and me replying to a 3 year old post....Next time make a new thread