91 240 wagon occasionally heats up above normal temp

[e777]

For some months now my 91 240 wagon will get a bit too hot for no apparent reason. It never reaches the red zone thankfully, but it will rise to halfway between the dot on the gauge and the red zone under normal driving conditions (no excessive ambient heat, no long periods idling in traffic, etc.).

In trying to trouble shoot this vexing problem, I have replaced a few inexpensive parts that, given the car's mileage (250k) would probably need replacing anyway. The parts are: the thermostat, temp sender and temp sensor. I also blew out the radiator with compressed air from the inside outward. I also verified that the auxiliary fan works and verified that the connectors on the harness to the auxiliary fan are working properly. That being said, I noticed when the car was hot (needle between dot and red zone) the auxiliary fan was not on.

I did the recommended check (hold blade connector from temp sender to ground) to verify that the circuit board is not faulty.

The water pump is relatively new as is the coolant.

So, with this in mind, I have a couple of questions:
1. Is there some other part of the auxiliary fan circuit that I should be checking out? Unfortunately, the Bentley Bible has no information on this (at least I could not find it).

2. I have read that this just might be a symptom of a faulty radiator. if so, is there a way to verify the radiator is faulty, filled with sludge, etc?

Thanks!

[Jesse8931]

You can use a infrared temp gun to check for hot spots on the radiator.

[e777]

Thanks. I had never even heard of such a tool. Surprisingly you can buy one on Amazon for around $20!

[93Regina]

91 240 wagon will get a bit too hot for no apparent reason.

1986-1993 240 models are equipped with circuitry that is designed to keep the coolant temp gauge needle positioned in the normal zone (9:00 position) even if the engine is running a bit hot. The idea is to prevent minor variations in coolant temp from causing worry for the driver. As these cars age a common problem is the failure of the circuit board and connectors resulting in erratic readings or no reading at all. We have put together a simple bypass harness that reverts the function back to the earlier trouble-free design.


1993 240 Temperature Gauge not working

Temp Faker removal:

[jimmy57]

+1 on the temp gauge system.

Grounds can cuase this when cluster gauge comp board has no issues but that will usually show as an erratic gauge that is consistent with high electrical loads.

The irony of this is the gauge compensation (gauge lying) is to address the temp gauge being honest and going up when climbing hills or idling in a burger drive-thru or traffic and then going low if you coast down a grade. When the comp board has issues the gauge goes up and down when the temp of coolant is stable.....

[e777]

Thanks very much 93Regina and Jimmy57 for the very useful info! I will have a go at the temp gauge.