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Escort MK4 Overheating


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I'm working on a Ford Escort MK4 from 1989. The 1400CC engine has an overheating issue I can't quite wrap my head around. The waterpump and timingbelt have been replaced, the thermostat has been replaced and the radiator has been replaced. We hoped it was enough to fix the overheating issue, though when flushing it with distilled water, the termperature gauge in the interior went all the way up within ten minutes. So the car is overheating again. The radiator fan is not switching on, though even with the fan connected directly to the battery, the overheating issue returned (so fan full blast).

The temperature sensor in the block and the thermostat switch in the thermostathousing have both been tested by measuring the resistance, then putting them in hot water and measure again. Resistance dropped as the sensors got warmer.

Heatercore in the interior is not heating up at all. Eventhough the sensor says the car is overheating, the water is not boiling in the coolant expansion tank, you can just hold the tube coming out of the thermostat, it feels hot, but not enough to burn you. Pressuretest on the engine returned about 110 to 115 PSI on all four cilinders - so I doubt it's a blown headgasket. I have no idea of the actual temperature of the actual thermostathousing/tubes, but I'll test with an infrared-meter.

My plan for this weekend is to: 

1) Disconnect the heatercore to exclude that issue.

2) Disconnect the temperature-sensor as termperatures start to climb: I'm starting to wonder if the temperature gauge on the dashboard isn't reading the values of the radiator fan. 


What else can be done as tests to pinpoint the issue? Anyone else experienced issues like this - how did you fix these?


Best regards.

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  • 1 month later...

Turned out to be an electric problem in the dashboard. Here's how to diagnose it, if anyone is ever stumped:

1) Take out the thermistor sensor in the engine block, the part that threads in the block is the negative (-); the part where a wire connects to is the positive +. If I remember correctly these two should be isolated from each other. If you measure for continuity it should not beep. 

2) Take out the dashboard and take out the temperature gauge unit. It is fitted with the fuel gauge. There are three pins on each dial (Plus, minus and a resistance). You can deduct which one is the resistance by looking at the layout of the circuit where the gauge fits in. The fuel gauge and the temperature gauge share the plus and minus. 

3) Connect the plus of the gauge, to the plus of the 12V battery

4) Connect the minus of the gauge to the minus of the 12V battery

5) Connect the minus of the thermistor to the minus of the 12V battey

6) Connect the plus of the thermistor to the resistorleg of the gauge.

7) Put it in lukewarm water ==> shouldn't overheat. 


If it does overheat:

Take another thermistor ==> Try again

It overheats again: probably a broken gauge. 


You can do the above test in the car or outside. If it doesn't overheat using your own wires, but does when using the wiring in the car, then something is broken there. 


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