1992 240. My temp gauge always shoots right up to just below the red once the car is warmed up. Last summer I replaced the front electric pusher fan for the AC, and the fan clutch and the temp needle stayed between 9-10 o clock all summer. This last spring the temp gauge stopped working--I already checked the "temp faker" compensation board and it has already been addressed. So then a week ago I replaced the temp gauge sender under the intake manifold and the needle works again. After a coolant flush didn't bring the needle temp down, I ordered an infrared thermometer to check various temps. Thermostat housing never gets hotter than 200 F. The cylinder head, right next to the recently-replaced temp sensor, also reads about 200 F. The hose from radiator to Tstat is 160 F. Driver side of the radiator reads 200. The top and center of the radiator drops to 115 F. Lower hose reads 160 F. Water pump 200F.
I should add that after the car gets to almost in the red and I turn the car off, the fan has zero resistance. This also points to a faulty gauge, since the fan clutch isn't hot enough to engage yet.
Are these actually overheating temps? Or is the gauge temp needle showing inaccurate readings?? Is the cold spot on top of the radiator a blockage?
I am at a loss.

 

the thermostat should come open in the 180-190F range and the operating temp should be in the 195 to 210F range with the fan coming on somewhere in the 200 to 205 F range (not 100% sure for your model). Volvos used closed systems so it will pressurize which raises the boiling point. Anyways, here's an older thread you might find interesting:

https://volvoforums.com/forum/volvo-...mp-sens-75312/

 

Let me check out this thread you shared.

 

I read through that thread. Seems to address the IET, which send engine temp to the ECU. To my understanding, that sensor has no bearing on the needle reading.
That thread inspired me to clean the spade connector (even though it's not the ground) that goes to the gauge sender. No difference :/

 

If the engine warms up to the corect temp (in the middle of the guage) and on hot days continues to climb into the red - Replace the radiator - it is clogged. (as long as thermostat/head gasket/etc is good) My shop has replaced hundreds and solved that problem in Atlanta Ga summers. (back when 240's were common) The older copper radiators could be "rodded" - taken apart and cleaned. The aluminum radiators can't be cleaned, just recycled.

I've had many "discussions" over the years with techs who want to change a fan clutch, or another part to solve that problem. After they swap the fan clutch from my car onto the offending vehicle and it still runs hot - they believe me that the radiator must be partially clogged and simply not releasing the heat to turn the fan clutch on and cool the car.

Have you tried turning the heat up full blast, full hot, full fan, when the temp gauge is up? Uncomfortable but is a test of the cooling capability of the radiator. (you can run the ac at the same time - but it won't make the inside of the car comfortable with the heat full blast)

 

Thanks for response. Radiator looks original, and its a NE car no less so a lot of exterior corrosion. I have already tried driving the car with heat on full blast and it doesn't lower the needle temp.
It makes sense that the fan clutch is not the problem like you said. It hasn't been hot enough to engage (based on ambient and engine temps). I even shot the IR thermometer on it when the temp needle was way up: clutch was only about 160 F, so naturally is wasn't engaging.
I found a section on this page that says that the gauge cluster has a voltage regulator for the temp gauge, and if I understand correctly, can give faulty needle readings if it fails:
https://www.240turbo.com/240gaugewiring.html

 

Yes there is a voltage stabilizer that powers the temp and gas gauge to keep them accurate. The early style stabilizers would go bad. (pre 1985 maybe) The later ones look like a three prong transister on the back of the cluster - and I've never seen a bad one. When early ones went bad the gas gauge was not accurate also.

 

It's worth a shot fixing. Modern replacement for the voltage regulator is cheap enough. The temps measured with my IR thermometer shouldn't equate to a near-the-red reading at the gauge from what i understand.

 

Just wanted to update this thread. I’ll eventually come to a solution so I hope this thread serves other drivers in the future, if at least to show the process.
Yesterday I replaced the voltage regulator for the the temp gauge. No difference.
Also yesterday I switched out the thermostat. No difference. I’ll test them both in pot.

Today I drove out to the beach and made a few observations. It’s a good long drive both ways, so I made sure to spin the fan after we parked to see if the clutch engaged at all. Some resistance. But probably an appropriate amount for the outside temp.
On the drive itself, while the needle showed just below red, I tried blasting the heater. No difference.

I’ll take a compression test to see if we have indications of a bad head gasket. But the oil doesn’t look like chocolate milk and the coolant has stayed neon green since the coolant flush.

Barring a bad head gasket, there’s really nothing left but the water pump and radiator to replace. Like I said in the original post: I do have different temps throughout the rad.

 

Volvos don't do that. The oil drain passages are too far away from the coolant passages. Hondas, yes - old alfa romeos, yes.

 

Updating this thread again. I just replaced the radiator with a new Nissens unit. The radiator that I pulled out of the car had maybe half of the fins completely missing. Started it up with the heater on full blast at idle: the temp gauge already started exceeding 3/4 and I shut it off.
I should add that I filled coolant past the MAX line on the overflow tank before starting the car up (after the rad replacement), thinking that it would circulate through the motor, past the thermostat etc. But the coolant level did not go down. Could this indicate bad coolant flow somewhere? Maybe the thermostat not opening up? I did see SOME burping.
I have replaced every cooling part but the water pump at this point. No symptoms of a bad head gasket (except overheating).
Shall I "throw" a water pump at it at this point? Externally, the pump looks as bad as the radiator did.

 

No, you should remove the pump and inspect the impeller (and shaft seal) If there is a problem with the impeller (or it's leaking from the shaft seal) then replace it (with a pump that has a metal impeller)

 

Okay so the problem is mostly solved. I drove the car home last night and alternated the heater on and off a few times and the temps finally read at the 9 o clock mark. Then right before pulling up to the apartment the needle dropped dead. So the temp is finally right where it should be. Not sure why the needle could be dying at this point.

 

So I wanted to update this thread since I have since fully resolved these issues.
First off, the high readings at the gauge were caused by an aftermarket temp sender. I replaced it with a genuine Volvo part and the temp reads much lower--where it should be based on IR thermometer readings.
After I created this thread, I had intermittent temp gauge functionality. I was stumped as the compensation board had already been bypassed. I went ahead and ALSO did the direct-wire method outlined on cleanflametrap.com and have since had reliable gauge functionality.
In the end, the temp gauge is always where it should be, generally running nice and cool. Problem officially solved.