Ford Fiesta weird overheating issue

EdGasketTheSecond

Bigphil1474 wrote: »

Norman, yep it's only happened since the thermostat was replaced last month.

Sounds like the thermostat is faulty then or not fitted correctly. There is a bleed hole in the thermostat that needs to be uppermost and the thermostat needs to be fitted the right way round. It will still basically function if either or both of the above are wrong but as you have discovered, will cause problems.



The fiesta's run too hot anyway imho; the fan needs to come on sooner and the thermostat needs to open at a lower temp.

Ganga

EdGasketTheSecond wrote: »

Sounds like the thermostat is faulty then or not fitted correctly. There is a bleed hole in the thermostat that needs to be uppermost and the thermostat needs to be fitted the right way round. It will still basically function if either or both of the above are wrong but as you have discovered, will cause problems.



The fiesta's run too hot anyway imho; the fan needs to come on sooner and the thermostat needs to open at a lower temp.

The thermostat HAS to be fitted the right way up as the incoming hot water will not heat the stat and force it to open.

EdGasketTheSecond

It will work both ways; just not so well or reliably.

Bigphil1474

Got the car back. Dave the mechanic said he checked the whole system, no issues found. Said all the bits heated up as expected, no air locks etc. He has replaced the temperature sensor. Will see how it goes.

EdGasketTheSecond

Thanks, though you said the fan was working OK so no point replacing the temp sensor. But keep us posted as it is interesting to know the outcome.

AdrianC

EdGasketTheSecond wrote: »

Thanks, though you said the fan was working OK so no point replacing the temp sensor. But keep us posted as it is interesting to know the outcome.

Is there only one temp sensor? Rather than two - fan and ecu?

Back in the day, when temp gauges actually told you the temp, not what the ECU thought you needed to know about the temp, there would often be three temp sensors - fan, gauge, ecu.

EdGasketTheSecond

It's one sensor on that age Fiesta; does the gauge and ecu. The ecu turns the fan on low speed through a resistor or high speed without the series resistor.


BigPhil: You might like to idle the car and check that first the fan runs slow when up to temp. If it only runs at high speed, then your resistor pack is faulty (thermal fuse blown most likely) or the low-speed relay is faulty.

Bigphil1474

Thanks Ed.
Just been on a 20 mile motorway run. Not sure it's sorted tbh. Warning light didn't come on, but fan was on full blast when I stopped which I don't think it did before, and definitely a bit of a whiff of a hot engine. Not sure if it is relevant but the bonnet was cold when I stopped which I wouldn't expect? I'll try idling it and see what happens.

AdrianC

The bonnet has cold air passing over it, so it wouldn't necessarily be hot.

Do you have aircon on? If so, that usually puts the fan on, too, to flow air over the condensor to prevent icing up and increase efficiency. Aircon is, of course, massively useful at this time of year because it dries the air, which can then be warmed by the heater matrix - so you blow dry air at the screen, clearing it almost instantly and keeping it clear.

Bigphil1474

Adrian, just thought it odd that it was stone cold, not just not hot.

Don't usually use the air-con except when it's hot - just run it once a week for about 15 minutes. I did read somewhere that you can check the fan is working by putting the air-con on when you start the car, and it does come on when I do that.
Also if I put the heating on full, the warning light goes off. Don't want to be doing that in the summer though.