Ford Fiesta weird overheating issue

AdrianC

Bigphil1474 wrote: »

Don't usually use the air-con except when it's hot - just run it once a week for about 15 minutes.

Use it all the time. Ignore the scaremongering about how polar bears will die if you do - it uses very little fuel, and usually cuts in and out automatically when needed.

Also if I put the heating on full, the warning light goes off.

Modern heaters are "airblend" - they run water through the matrix (a second rad in the dash) all the time, and just vary the amount of air over them. But, of course, when there's air flowing over the matrix, the coolant sheds heat...

EdGasketTheSecond

Looking at the symptoms:



"The engine bay seems too hot. The coolant levels are all fine as is oil. Putting the heating on full stops it overheating."


"he wasn't sure if it was kicking in at right temperature, but was definitely working. We also had a drive round the block with the computer connected up and he said the temperature dropped whilst the car was moving."


It looks as though the fan is not operating correctly as the engine should have been at the correct temperature when stationary and then the temp would not have dropped whilst the car was moving.
The fan should come on at slow speed when the air-con is switched on. Check that first. Turn the air-con off.
Then idle the car and check that the fan comes on slow speed once the engine has warmed up. It should come on for a bit and then switch off as the coolant is cooled by the airflow through the radiator. Then it should cycle like this every few minutes.
If you hear boiling in the cylinder head and the fan has not come on then the fan switch-on point is your problem. Please report back on the above.

Bigphil1474

Ed - will try that at the weekend. Thanks

Bigphil1474

Ed - managed to find half an hour at lunch time to try it out.

From a cold start - When I switch the air-con on the fan comes on. I wouldn't describe it as slow speed but not full blast. Turned the air-con off.

I idled the car for about 20 minutes occasionally revving the engine to speed up getting to temperature. Fan didn't come on, and lunchtime was over. Do I need to leave it longer or is that enough evidence of an issue? Couldn't hear any boiling.

EdGasketTheSecond

I guess it is inconclusive as presumably the engine did not overheat either. You need to idle it for longer, until either the fan comes on or it starts to overheat e.g. coolant boiling/blowing out of the expansion tank or you hear it bubbling in the cylinder head. If the latter happens, feel the top and bottom hose and make sure both feel hot showing coolant is flowing properly.


At least the fan works with air-con so the relay and fan work.


Is this a fiesta MK 6 (traditional shape) or the new 'ecoboost' version?

AdrianC

Bigphil1474 wrote: »

I idled the car for about 20 minutes occasionally revving the engine to speed up getting to temperature. Fan didn't come on, and lunchtime was over. Do I need to leave it longer or is that enough evidence of an issue? Couldn't hear any boiling.

20 min idling in these ambient temps, I'd be surprised if it was much above 'stat opening temp.

Bigphil1474

Okay, thanks both. It's an 09 plate Mk6 1.4l petrol 5 door Titanium which I've owned for 4 years and always been pretty sweet mechanically. I'll try running it at the weekend for longer and see how I get on.

Bigphil1474

Looks like it is resolved, though not 100% sure how.
I didn't find time to do the checks you said Ed, as it was chucking it down weekend before last. However, had to take it back into garage last week as front wheel was chuffing. When I took it in, I spoke to the mechanic and she said she'd sort the chuffing out, and she asked me about the overheating. I told her I didn't think it was fixed, as I was still getting a hot engine smell in the car, so she said she'd look at the thermostat etc.. When I went back for the car in the afternoon, she wasn't there, but Dave the mechanic said they'd checked the front and back brakes, and sorted out the chuffing issue - build up of corrosion on the front brakes. He didn't know anything about what she'd done with the thermostat or anything else to do with the overheating. There was no bill for their work so nothing written down for what was done (it was free).
Anyway, went for a long drive on Saturday (same journey as previous problems) and no overheating, no hot engine smells etc. and no need to have heating full blast.
I suspect that she may have looked at the thermostat, and as Ed suggested, it might have been fitted incorrectly. Alternatively, it fixed itself. However, no issues now.

Jumblebumble

Bigphil1474 wrote: »

Looks like it is resolved, though not 100% sure how.
I didn't find time to do the checks you said Ed, as it was chucking it down weekend before last. However, had to take it back into garage last week as front wheel was chuffing. When I took it in, I spoke to the mechanic and she said she'd sort the chuffing out, and she asked me about the overheating. I told her I didn't think it was fixed, as I was still getting a hot engine smell in the car, so she said she'd look at the thermostat etc.. When I went back for the car in the afternoon, she wasn't there, but Dave the mechanic said they'd checked the front and back brakes, and sorted out the chuffing issue - build up of corrosion on the front brakes. He didn't know anything about what she'd done with the thermostat or anything else to do with the overheating. There was no bill for their work so nothing written down for what was done (it was free).
Anyway, went for a long drive on Saturday (same journey as previous problems) and no overheating, no hot engine smells etc. and no need to have heating full blast.
I suspect that she may have looked at the thermostat, and as Ed suggested, it might have been fitted incorrectly. Alternatively, it fixed itself. However, no issues now.

Sounds like a self bled airlock somewhere
I recall some cars (Renault? ) were an absolute pain for this

Exemplar

Jumblebumble wrote: »

Sounds like a self bled airlock somewhere
I recall some cars (Renault? ) were an absolute pain for this

Yes they were I had 2 x Scenic's (standard and Grand) that did this. Replaced the £5 bit and Voila!!! (see I got a French word in there!).