divil

I'm seeing the coolant temperature get out of control after track sessions on hot days. The needle is at about the halfway point while I'm driving and pitting in. But once I stop, it climbs up - and if I switch the engine off, even after a few minutes of idling - it shoots way up. Not quite into the red, but yesterday it did get above the top white line, and the light came on. The odd thing is that the fans turn on at about the right temperatures (both speeds), but they don't seem to be doing a very good job. The temperature climbs anyway, and the fans just turn off after a short time regardless. I thought they were supposed to run based on temperature only, so they should keep going as long as the coolant is above the threshhold? Is is possible that the gauge is simply off and the temperature is fine? Is there any way I can verify that? I have an infrared temperature gun, but I'm not sure if it can be used to reliably check coolant temperature. Checking at various places around the head/coolant pipes/water pump etc., I was only seeing temps in the low 80s (C). But I'm not sure if that's a good indication of the actual temperature of the coolant inside. Any suggestions? Thanks!

Paul Waterloo

If the fans are turning off, could it be that you have a bad resistor for the high speed setting and once it gets to that stage the fan motor is open circuited? I have not looked at the wiring diagram but there should be a series of resistors for low and high speed operation, I would start there.

divil

Yes there are resistors for the fan speeds. The fans do run on high speed though...just not for very long. But the wiring to those resistors is in pretty rough shape, so maybe that has something to do with it.

Willard Bridgham 3

Surface temps of metals in contact with coolant are representative of coolant temperatures after operation. Stick with metals out of the airstream. I Use an IR sensor all the time and they work fine.

Have you burped ALL the air out of the coolant? Air in the coolant will cause this problem.

divil

Once it cooled down enough, I removed the bleed screw and hooked up a pressure tester. A stream of coolant came out on the first pump - no air. I didn't try the normal bleed procedure again yet. Today the track was undriveable due to weather so I left early. I'll try it soon though.

When you say air will cause this problem, do you mean it causes the fans to switch off too soon, or that it causes the gauge to read high?

Tom M'Guinn

It's entirely normal for the temp gauge to rise for a while after you shut off the motor. Virtually all cars do that. Idling the car to bring the temp down before shutting off the car helps, and I often turn the heater on for a minute too before shutting down the car. The coolant in the heater core is nice and cool, so brings the temp down quickly at first. If you suspect the fans aren't turning on quickly enough or long enough, you can always disconnect the thermoswitch in the radiator and jumper the connector to run the fans on high when you come into the pits to see if that helps. I've seen guys who just wire the connector to a toggle switch so they can turn it on as needed. Running at the mid-point on the gauge isn't terrible on a hot track with lots of boosting, but you probably can bring it down. Assuming everything is working as designed, I've found that bringing the temp down is often a combination of little things -- make sure the duct work is good and not cracked/leaky/missing; make sure there is zero debris in in the radiator and a/c condenser; run a bottle of water wetter; use a Wahler thermostat and make sure the bypass seal in the pump is good; make sure you are vented 100% (so you hear no gurgling when you put the heater on); run a higher percentage of distilled water v coolant up to 80/20 or so if you can; buy a factory new radiator if yours is 27 years old -- they flow less and less as they age; don't block the front with a license plate on the track; run an oil cooler; -- every little bit helps.

divil

Thanks...the radiator was replaced a few years ago, but it is pretty clogged with flora and fauna at the moment. I can clean that easily enough...I was more concerned about why the fans won't stay on. It seems to me there must either be something wrong with the fan thermo switch or the temp gauge.

Tom M'Guinn

Get the debris out for sure! Keep in mind that the temp gauge and the fan switch are driven by two different sensors, one in the radiator and one just under the head -- so the fans and gauge won't always sync up. In particular, when the engine is not running, the fans will lower the temp of the coolant in the radiator (and turn off the fans) even though the coolant in the block and dash gauge keeps going up for a while. Having said that, Clarks has a complete diagnostic for the thermo switch and the temp sensor /gauge, which is free and easy to do if you can use a multimeter. To confirm accuracy of the gauge itself, you can pull the spade connectors off the temp sensor on the block and put a 50 ohm resistor between the connectors instead of the sensor -- the gauge should sit about at the middle. (If you can't find a 50 ohm resistor at your local bankrupt radio shack, you can twist two 100 ohm resistors together to create 50 ohms (twist them together side-by-side to they run in parallel).

jerome951

I've had the same symptoms before. Cure was to bleed the cooling system again. Try raising the front of the car and see if you get any air out.

Could also be dash grounds, though you'd like see this as a fluctuating needle. Do any of your other gauges (esp voltage) act funny when the temp gauge rises?

divil

I do actually get the odd fluctuation in the temp gauge and fuel gauge. The others are more stable.

Another thing I thought of was checking the resistance of the DME temp sensor. I'm not sure how accurate it is but it might give me an idea of how close the dash gauge is.

CO951

I've had this same "problem", although it's not a problem. As Tom said fans turn off because the radiator cools off enough, but there is no water pump to move that cooled water to the head. When really hot I would come back after the car has been off about 5min and idle it for another 30sec just to move that water. It cools down a lot, but will go back up again for the same reason. On very hot days I may idle for another 30sec after about 5min. Temp always comes down and then goes back up. There's just no good way to move the cool radiator water to the head when the car and water pump aren't running.

divil

Hmm I thought the radiator was in bad shape, but on second thoughts I think I am looking at the AC condenser. I should know this because I replaced the radiator but I forget which one is in front lol! Either way whichever one is in front is definitely blocking some air, so that will be first on the list. As Tom said there are a lot of other things I could improve. I was thinking about switching to pure water anyway for safety on the track. I've also been running without the undertrays for a while, and I've heard that causes the engine to run hotter. Then there's the dodgy wiring for the fan resistors...they are working, but maybe not optimally.

Any tips for clearing out the debris from the condenser/radiator? It looks like I might be better off removing them and soaking them in something. Although I will probably just replace the condenser if i have to remove it.

333pg333

Also worth attaching a secondary 'relief' tank off the stock expansion tank. Medium size drink bottle can do the trick. There are probably some pics somewhere in this forum showing what I mean.

divil

Update...I cleaned out as much as I could from the condenser. The radiator itself is perfect. I also drained the coolant and replaced it with pure water, bled it thoroughly and re-installed the plastic under tray, which I've had removed for a long time. I didn't install the metal one because the studs are in bad shape, but I just finished another track event at Watkins Glen and there is a huge improvement in the situation now. The needle shows about the same while driving, but the sudden surge in temperature when I shut off is not there now. It was pretty warm today so I think I would have seen the problem if it was still there. Thanks everyone!

Spidey944

Make sure you add a water-wetter product or some coolant to your system. You need that for lubrication and corrosion protection.

Also since it freezes in Indiana - you kinda need to prevent that lol