Tom92

2003 1.6 focus overheating

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Hi guys, hoping some ford guru’s may be able to help me with this issue I’m having, seems a fairly common one but not getting anywhere at the minute... Well might of done, I’m about to order some bits but wanting to pick some brains too!

 

Right so focus has been overheating badly without cure for a while now, have made some progress....I’ll go through what’s been checked/ renewed 

1. Rad replaced

2. Thermostat replaced (didn’t work, so temporarily removed, will come back to this)

3. Water pump inspected

4. Coolant hoses all removed inspected and flushed through

5. CHTS resistance checked, signal voltage checked at connector (all appears good) 

6. fan relay checked (works, ish)

7. Fan itself will work but not when I want it to

Right moving on.... so for some reason the thermostat (74C) when tested in slowly heated pan with thermometer started opening at 78C and within 5C was fully open, functioning as it should and what I’d of thought was within tolerance. When put into car it got to the point that the coolant in expansion tank was reading at 90C on the thermometer and hose from thermostat was cold indicating it wouldn’t open 😤🙄🤔, anyway removed and ran without so I could focus on next issue which is one I'm wanting more help with....

Fan not kicking in.... so on OBD port using diagnostic machine live temperature reading from CHTS has gone as high as 102C and fan not cutting in, unplugged  sensor fan will run constantly, checked resistance at varying temps and seems to adjust accordingly indicating it is working and the fact ECU recognises when it’s there or not (unplugged shows an error code) now when checking relay voltages and they’re there but not signal voltage from ECU to tell it to close and power fan. If voltage is applied relay will close and fan runs, if sensor is unplugged fan runs and relay closed, am I to think regardless of 5v signal at connector, varying resistance based on temp and the fact the ECU recognises the sensor, that it is not functioning correctly???

Also anyone had issues of a perfectly functioning thermostat not working when in cooling system?? Not ever had these issues before.

Any help would be greatly appreciated 🙏🙏

 

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1 hour ago, Tom92 said:

when tested in slowly heated pan with thermometer started opening at 78C and within 5C was fully open, functioning as it should and what I’d of thought was within tolerance. When put into car it got to the point that the coolant in expansion tank was reading at 90C on the thermometer and hose from thermostat was cold indicating it wouldn’t open

I can think of two causes for a thermostat to work in the pan test but not in the car:

Something like a displaced gasket is jamming the 'stat shut when installed.

Gas is building up in the 'stat housing, and this will not convey the heat to the wax element. There is usually a small vent pipe from the top of the housing back to the expansion tank. If so, check it is not blocked somehow. The most common cause of gas in the coolant is a cylinder head leak. If it is a small leak, then it can often be fixed (at least for a while, maybe a few years) by K-seal or similar.

As the OBD readings via the ECU stack up with the CHTS resistance, it does suggest the CHTS is ok.

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