Overheating under 20MPH

[e30onBBSs]

When the engine is cool, feel your rad hoses. Do they feel like they have air inside of them instead of coolant? That's why my car used to overheat.

You can ground out the temp sensor to see if that's the problem. stick a wire in the plug and see if it jumps all the way to the right. When you pull the plug off the sensor it should just go all the way to the left. If these don't happen then there is a problem with the wiring to the gauge, or the gauge is messed not the sensor.

[LJ851]

I just got an IR gun, how should I use it to diagnose my overheating problem?

You can measure the temp at the outlet of the head, the other side of the thermostat, temp at inlet of radiator, outlet of radiator.


When my thermostat was failing, i had 200+ degrees at the head and almost that going into the rad but like 90-100 degrees coming out of the rad.

[Dzdimi14]

It would if the thermostat failed closed, my car would still stay around the middle of the gauge on the highway (maybe a little warmer than usual) and then climb up to near the top of the gauge when i stopped.


Do you have an infrared heat gun?

I just got an IR gun, how should I use it to diagnose my overheating problem?

[Dzdimi14]

Do you have a fan shroud installed ?

yup

[Dzdimi14]

Harbor freight, like 9-15 dollars for a ir gun.

sick, ill pick one up. I can see myself just playing around with one of those for hours haha

[efficient]

Harbor freight, like 9-15 dollars for a ir gun.

[Dzdimi14]

It would if the thermostat failed closed, my car would still stay around the middle of the gauge on the highway (maybe a little warmer than usual) and then climb up to near the top of the gauge when i stopped.


Do you have an infrared heat gun?

I do not, are they reasonably affordable

[LJ851]

could be, Ive noticed that when the engine is still really hot( intake manifold, valve cover) the radiator is barely even luke warm. Wouldn't that also effect cooling while im driving though?

It would if the thermostat failed closed, my car would still stay around the middle of the gauge on the highway (maybe a little warmer than usual) and then climb up to near the top of the gauge when i stopped.


Do you have an infrared heat gun?

[Dzdimi14]

A failing thermostat can cause the fan clutch to not engage. Air heated by the radiator is what heats the fan clutch and causes it to engage.

If the thermostat is not acting properly and blocking too much coolant flow, the car will run hot and the radiator will still be cool thus not engaging the fan clutch which makes the car overheat at low speeds. A failing thermostat can be slightly random in it's behavior as well.

Ask me how i know. Don't buy a shitty aftermarket thermostat either, buy a nice bmw or oem unit.

could be, Ive noticed that when the engine is still really hot( intake manifold, valve cover) the radiator is barely even luke warm. Wouldn't that also effect cooling while im driving though?

[jeffnhiscars]

Do you have a fan shroud installed ?

[LJ851]

A failing thermostat can cause the fan clutch to not engage. Air heated by the radiator is what heats the fan clutch and causes it to engage.

If the thermostat is not acting properly and blocking too much coolant flow, the car will run hot and the radiator will still be cool thus not engaging the fan clutch which makes the car overheat at low speeds. A failing thermostat can be slightly random in it's behavior as well.

Ask me how i know. Don't buy a shitty aftermarket thermostat either, buy a nice bmw or oem unit.

[jlevie]

While the aux fan temp switch could be a problem, it's primary purpose is assist when A/C is being used. Cars w/o A/C have no aux fan. Thus I'd explore the possibility of a bad fan clutch, misbehaving temp gauge, air in the system, or a bad thermostat first. The fan clutch is easy to test with a rolled up newspaper and the head temperature can be checked with an I/R temperature or contact gauge.

In this case, I'm inclined to suspect that the engine is running hot since the temperature comes back down when the car is moving faster. Which tends to exonerate the gauge as a suspect. If the easy suspects are eliminated as a cause, my next step would be to replace the radiator as it could be partially clogged.

For bleeding the system see http://www.r3vlimited.com/board/showthread.php?t=364705. You might also gain some benefit from flushing the cooling system (http://www.r3vlimited.com/board/show...07&postcount=8) before replacing the radiator if it comes to that.

[Dzdimi14]

if you have a late model its pretty simple to check the aux fan operation. theres only 3 pins at the temp sensor connector. if you jumper the power pin to each of the other ones, the fan should turn on at a low speed and at a high speed. if it does that tells you the fuses, relays, wiring and resistor to the aux fan are ok. in this scenario you most likely just have a bad temp switch. and imo it would not be worth it to do a conversion since you already have an electric fan(the aux). and the oe system is designed pretty well. really with a properly working system you could probably throw the mechanical fan in the trash and be fine. i use the factory setup with an e34 aux fan and no mechanical myself on my s52. with a fan clutch and working aux system you should be more than ok.

Can you elaborate a little bit on how I would jump them, sorry im a bit of a noob at electrical stuff.

[atldohc]

but yes a faulty reading could be the cause as well, ive had that happen to me myself when i had my m20. the gauge would go to 3/4 sometimes while waiting at stoplights but after tightening the ground nut on the back of the cluster it never went above half. it might be a good idea to get an infrared thermometer and start checking temps at your rad, thermo housing, hoses, engine etc. other possible causes for overheating at a stop or slow speeds could be a partially clogged rad, lazy/partially opening thermostat, water pump with damaged impeller fins, air pockets in the system,etc. basically anything that won't support enough coolant flow volume to cool the engine down.

[atldohc]

if you have a late model its pretty simple to check the aux fan operation. theres only 3 pins at the temp sensor connector. if you jumper the power pin to each of the other ones, the fan should turn on at a low speed and at a high speed. if it does that tells you the fuses, relays, wiring and resistor to the aux fan are ok. in this scenario you most likely just have a bad temp switch. and imo it would not be worth it to do a conversion since you already have an electric fan(the aux). and the oe system is designed pretty well. really with a properly working system you could probably throw the mechanical fan in the trash and be fine. i use the factory setup with an e34 aux fan and no mechanical myself on my s52. with a fan clutch and working aux system you should be more than ok.