Overheating 928s4, Cooling fans not kicking on
 

I recently pulled my 928s4 out of storage. It's been sitting for about 2 years. Everything seemed to be fine on test drives. I started driving this week. First time ever it overheated. Temp shot up after about 5 miles, red light came on as I got to my development. She started dumping coolant about a block from the house. When I stopped I noticed the fans were not running. Checked the fuses - they are OK - however they do not spin while car is running.

It's been so long since I have driven the car I don't remember how/when the two fans operated.

Ideas?

What year is your car???
remove the coolant cap and start the car see if there are bubbles in the coolant while its running. This would be a head gasket or cracked head or block
If the coolant temp shoots up to hot after 5 mins or less than you may have a bad water pump
Did you happen to notice if the front cooling flaps are closed . If so pull the fuse and then remove the cover over the flap motor and spin it open
Try turning on the AC switch see if the fans come on.
if no then try pulling the connector from the bottom of the front Driver side radiator turn on the key see if the fans come on

The fans depend on having some coolant flow through the radiator when the AC is off. A stuck thermostat, air bubble at the top of the water bridge, water pump non-op.

Refill the car with water after you let it cool off. Fill the reservoir all the way to the top, and try to have the car nose down so it has a better chance to self-burp. Start the engine and let it warm up normally. Keep that reservoir absolutely full. When the gauge reads in the middle, at normal operating temp, bump the throttle some so that the water circulates faster. At first as it warms you'll notice that the top hose is hot and the lower hose is colder. Reving the engine pushes any entrained air in the crossover bridge over into the reservoir. Keep the reservoir full to the top. At some point before the temp gauge reaches the hot mark, the thermostat should open and you should start to feel more serious heat in the lower hose. Once you do, the hot coolant routing through the radiator now will also start the fans, thanks to the temp sender at the bottom forward driver's side of the radiator. If that doesn't happen and the gauge makes it to the hot mark, shut the engine down and report back.

Remember also that the fans run when the AC is on. You can also test the fan basic function using the temp switch at the top of the intake manifold. With the engine off, connect the two wires that run to that switch. The fans hould start and run in low speed. The hood switch is sometimes part of that circuit (WSM reports that it is but on my car it isn't) so you may need to push the hood switch down to get the fans to run.

If the fans still don't run with any of this, go back to the battery and double-check the wire connections to the positive battery terminals. There are several red power feeds attached there besides the big cable that runs to the starter and the alternator. Those smaller wires need to be tight, with clean shiny connections. Two of them feed the fans, one feeds the fuel pump and injectors. There may be another there for something else per other owners' reports; My car has only these three. No matter, they all need to be clean, shiny and tight.

You do need to provide more info but since it was such a short distance my guess is your thermostat is stuck closed. With it closed coolant never circulates to the radiator where the temp sensor is for the fans so your car overheats but the radiator is stone cold. Happened to me on the way to the 2000 OCIC in Wichita, you don't get very far once the thermostat fails closed.

Nice Bob, this had me going nuts last summer. Sneaky engineers...

Hood latch - interesting
 

Thanks for all the great input guys. The hood got me thinking. Just this week I noticed the driver side hood hing was catching up. Like something was stuck in it. I need to investigate further. I will also work my way backwards from easiest to hardest tasks to perform and see if it works. I will report back.

Thanks again...

Husker--

One of the normal maintenance tasks that normally gets ignored is lubrication of the hood hinges. When ignored, they get stiff and don't always allow the rear of the hood to go down where it should. A little lithium grease in the spray can takes care of this problem. Just back up the spray with a paper towel so the stray/overspray from the tube doesn't go all over the place. Anyway, if a sticking hinge causes the hood to sit high, it may --possibly-- keep that safety switch from opening.

If you want to test the hood switch function, lock the doors with the driver's window down, then reach in and pop the hood release. Mine will come all the way up to the finger latch position and be OK. Release the finger latch and raise the hood, and the car messages you load and clear. Reset by cycling the key in the driver's door switch. Proves alarm function at the same time. :)

Did you check the fuse? The 2 fuses for the fans have a tendency to cook and pop. My fuse panel for those 2 fuse looks brown by all the heat. I put in 2 self resting circuit brakers that plugs right in. No problem anymore.

I believe on all years the hood switch only controls the 'after-running' of the fans not the normal operation while the engine is running.

I think the idea is that if you put your fingers near the fan blades while the engine is running you are claarly suicidal and its not their fault.

However if the engine is off and the fans are stopped and you have your hands in there when suddenly the heat soaked intake causes the controller to decide to turn the fans on - then your missing fingers might spark a bit of litigation against Porsche... so better safe than sorry...

Alan

Thanks for all the great suggestions. I think it's time to take my girl to the shop.
The air condition is not coming on as well.
Checked the fuses - check OK
Disconnected the fan motor wires and hooked them to my battery charger to make sure the motors work - they do.
Not sure if it's a relay or not - not sure how to test that.
Made sure the flaps were open.
Checked the thermostat - it's opening and closing.
My guess is the air conditioner and the fans are in the same electrical circuit - maybe the air con shorted out and took the fans out. This is officially outside my wheelhouse.
Best Regards to all.
Dave

The very first thing you need to do is make sure the RADIATOR is hot to the touch!

If so, it shouldnt be over heating that fast, and if it is truely a fan controller issue, you will be able to know if the radiator is very hot when then engine temps go toward the 2nd white line . dont let the red light come on. that can often mean engine damage!

mk

I'm having a similar issue. The car is new to me, so I don't know the history.

I am able to:

1. Jumper the relay and get the driver's side fan to run on full. The second fan does not run.
2. I can jumper the temp sensor on the intake and make both fans run on low.

If it works by jumpering the intake sensor, does that mean that is bad, or do I need to pull the radiator temp sensor and replace that?

Husker Dave--

There's a parallel thread that's been resurected related to the X-bus relay, and the effect on cooling fans, AC operation, and your fog lights believe it or not. So, when the engine is running and you can't get the fans running right, does your AC engage and do your fog lights work?

Otherwise, I recommend that you take some time to clean and reseal the battery connections, especially the smaller red accessory power leads that attch to the positive cable clamp with a smaller bolt. Disassemble, clean with a small wire brush or fine sandpaper until bright, reassemble, tighten the bolt snug, and coat the whole terminal with Vaseline. Do the negative side while you are there, and the ground point where the negative strap meets the body inside the rear tool compartment. Two of those accessory power wires are for fans. One loose or poor connection there will cripple the fans.

After that, go fuse hunting. Those two fat power feeders from the battery go to the fuse panel, where each has its own fuse. The fuses are OK since you can get both fans to run slow with the intake temp switch. But the sockets in the fuse panel may be melted or otherwise damaged a bit. Visual inspection for melting and damage. You don't state what year S4 you have so I can't be sure of the fuse numbers for the fans. I think they are 28 and 29 on my '89 S4.

Try this easy stuff, and let us know if the AC and/or fog light operation is erratic with the cooling fan problems.

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One of the many benefits of Rennlist membership is that you can add the year of your car to a signature that shows up with every message. Worth the investment IMHO. In the meanwhile, you'll have to make do with adding it manually to your messages. I can get a lot more specific about what fuses and what relays to check if I know what year your car happens to be.

I wonder what the final resolution was? Looks like he joined in January 09 and was gone by March of 2009

Hi guys I have a cooling issue! It’s been a while since I last posted on here my 92 s4 UK car has been in the paint shop for 2 and a half years I’ve finally got her back on the road and the first thing to happen was she got very hot �� the vents are opening and one cooling fan runs at varying speeds the car isn’t overheating but the fans don’t continue to run when the ignition is switched off any thoughts please?

Thanks Nige