My '92 Volvo wagon overheats in summer stop and go traffic (with a/c on) - meaning that the indicator goes up almost to the red section. Normally it's 'level'. Turning the heater on brings it down to the normal position. Today, when it happened, I stopped and looked at the electric fan in front of the radiator and it was not running.

One morning a few days ago I started the car and let it come up to temperature and the fan cycled on and off to maintain normal temperature.

I figure it's something that is heat soaking and fails to switch on the fan when it gets too hot.

The dealer could not duplicate the problem at their shop; it seems to need to have been running for awhile in city traffic in hot weather.

Suggestions for where to start would be greatly appreciated;

 

Having your temperature gauge go into the "nearly overheating," range and not kick on the fan tells me your Temperature Compensation Board might be faulty, giving haywire readings. Either that of your Gauge Temperature Sensor is faulty. This is not the Engine Coolant Sensor which gives reading to the ECU and should tell the fan to kick on if it is hot.
How involved do you want to get? I would start by removing the instrument cluster and take out that circuit board that could be faulty. You'll need some solder and a gun.
Or you could try testing the sensor on the block, but I really think you should try the dash fix first, seeing I had the same problem and removing that circuit board worked for me.
I have some picture and I could walk you through it if need be.

 

I agree. It sounds like either a sensor is not performing it's function properly. Sensors are usually pretty reasonable cost wise. I don't have any experience with the dash fix. Good Luck

 

The fan seems to operate properly when starting from cold, meaning that it cycles on and off to maintain the normal temperature. I watched it do that for a half hour or so at idle. The only time the gauge moves up to almost red is in traffic on a hot day and when that happens, the fan is not running.

It seems like it's something that takes a while to heat up and finally fail.

What component would fail in this manner?

 

if its hot and the fan isn't coming on, i'd be trouble shooting the fan.

its also possible your radiator is partially blocked, so the high temp sensor that enables that fan isn't seeing the hot water.

 

Suggestions so far:
>>Temperature Compensation Board, Gauge Temperature Sensor:

I don't understand how the parts that provide a signal to the gauge can be faulty, since the gauge reads correctly (hot) when the engine is actually hot because the fan isn't running, and the gauge returns to normal when the heater is switched on to provide additional coolant cooling. It seems to be telling me exactly what's happening.

>>Fan:

I think this is a possibility since whatever is preventing the fan from coming on under heat soaked conditions needs to be somewhere near the engine. Perhaps a winding or connection within the fan that opens up when it finally reaches a certain temperature, but remains closed when I (and the Volvo service department) idled the engine and watched the fan cycle on and off properly. When it fails in traffic (rather than at idle), I think it's because the engine block gets heat soaked over time and happens quicker if the car has been making power (the 'go' part of stop and go traffic).

>> Blocked radiator:

Since the fan cycles properly and the gauge reads normal until the fan fails to come on, I think the radiator is doing its job. It never fails on the highway, only in traffic; again pointing to a heat soaked component like the fan, fan connector, fan wiring, or ?????.

Anyway, that's my theory based on a sample of exactly one, and little knowledge of the Volvo systems. Anyone have a counter theory, and/or experience that points to a component that fails in exactly this way?

 

could be a stuck thermostat, I suppose. that would prevent the hot water from getting to the radiator, but your heater plumbing bypasses this and gets the water right off the head, so when you crank up the heat, your heater is acting as an auxilliary radiator.

 

My '91 240 did similar to yours last year. It was the radiator.

 

I have similar issues with my 86 240. i dont have a cooling fan tho. I have noticed most of the time my temp guage doesnt go up at all, this occured when i replaced the in tank fuel pump. the fuel level and temp level guages were not working, so i unplugged the connection thats in the trunk, wire brushed the connection, and it works now..execpt for the temp* i could go try wire brushing it even more, but thats not the whole problem i feel. when the temp guage turned on (example im using is from yesterday on my commute home) i realized mty car was very hot, not to the red tho. i was getting ready tpo go up a couple hills when i noticed it. once i got onto the highwaty tho, i turned the AC on high and the temp went down to about half way, then it went down to zero.
any suggestions? radiator? different coolant? new guage?

 

the dashboard temperature sensor is on the engine block, not back in the gas tank.

btw, turning on the AC makes the engine work harder and generates more heat. its the heater you want to turn on to help cool the engine

 

ya know i feel like an idiot for saying such a thing, not 5 minutes later i thought about it and was like, no, that couldnt be..the temp sensor that is, thinkin it was the same as the fuel level guage:P im no mechanic, but im learning.
whats a way i could check that sensor and see if its faulty? or is that something i just need to go purchase.

 

there's a series of sensors screwed into the engine under the intake manifold runners. the one with a single yellow wire is the dashboard temperature gauge. the one with two blue-red wires is temperature for the ECU and ICU. you may have a knock sensor, this is a flat sensor with a 2 pin connector on the side. and.... mmm, I can't remember what else offhand. the Oil pressure switch is on the other side, near the oil filter.

 

oh okay, sounds easy enough. is the yellow wire something i can go unplug and clean? ive found many things that dont work in my car, just need cleaning, which has been pretty convienient

 

im at work thats why im not out looking for myself:P

 

aha, oh:P well it must of been something else making it colder, obviously.
i have mostly water with slight discoloration, so im gonna take it all out and put in the correct coolant:water ratio