Ford Fiesta weird overheating issue

Bigphil1474

My 10 year old Ford fiesta (petrol) has started over heating. It only happens on a long drive - after 40 miles or so the temperature warning light comes on. The engine bay seems too hot. The coolant levels are all fine as is oil. Putting the heating on full stops it overheating.
The car was MOT'd and serviced 3 weeks ago. Also had the timing belt, water pump, thermostat and thermostat housing replaced, and coolant was fully replaced. Garage is a local indy I've used for a few years and trusted. Had the RAC out when it started overheating as I was 100 miles from home, and they couldn't find any problem. They did a test for gas getting into the coolant (not sure what exactly that is but he had some liquid in a tube and wanted to check it didn't change colour, which it didn't). He also said water pump was circulating coolant okay, and thermostat was working okay. The radiator fan is working okay as far as he could tell - 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. After all that, I drove on for another 40 miles or so and the overheating symbol lit up again.
I'm pretty sure it is an overheating issue rather than a dodgy warning light, as it sometimes 'smells hot' and the in-car heating seems to be hotter than normal - usually have set at 26oC on a morning to get nice n cosy, but have had to turn it down to about 22oC as it was getting too hot.
It's back in the garage this week for them to investigate, but my concern is that they'll find the same as the RAC guy. It's been suggested that it could be an air-lock, but if anyone has any suggestions, would like to know before it goes in. Thanks

AdrianC

Bigphil1474 wrote: »

My 10 year old Ford fiesta (petrol) has started over heating. It only happens on a long drive - after 40 miles or so the temperature warning light comes on. The engine bay seems too hot. The coolant levels are all fine as is oil. Putting the heating on full stops it overheating.

Which suggests the radiator's not shedding the heat properly - blocked rad would be the most likely cause, or it's lost all the fins through external corrosion.

The car was MOT'd and serviced 3 weeks ago. Also had the timing belt, water pump, thermostat and thermostat housing replaced, and coolant was fully replaced.

What state was the old coolant in? How long since it'd been replaced?
Did they flush it all through?

And... what coolant did they put in?
If blue-green has been mixed with red OAT, then gelling can result in blocked waterways.

Garage is a local indy I've used for a few years and trusted. Had the RAC out when it started overheating as I was 100 miles from home, and they couldn't find any problem. They did a test for gas getting into the coolant (not sure what exactly that is but he had some liquid in a tube and wanted to check it didn't change colour, which it didn't). He also said water pump was circulating coolant okay, and thermostat was working okay. The radiator fan is working okay as far as he could tell - 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. After all that, I drove on for another 40 miles or so and the overheating symbol lit up again.

No mention of the most basic check - seeing if the rad is evenly hot all over the surface. Ten quid of IR thermometer will give accurate results, including how much difference between top and bottom hoses - but the back of a hand will show whether there's cold spots.

and the in-car heating seems to be hotter than normal - usually have set at 26oC on a morning to get nice n cosy, but have had to turn it down to about 22oC as it was getting too hot.

That sounds like either psychosomatic expectations, or a completely different issue - if it's actually marked in degC, then it should be thermostatically managed, so 22deg is 22deg is 22deg, no matter the temp of air coming out. It'll just cut back on the heat quicker.

Bigphil1474

Adrian - thanks
The radiator looks okay to my untrained eye - minimal corrosion on the outside, but it is the orginal one so could be that.
The old coolant was what was put in at the last service a year ago. They told me a few months ago that there was a minor leak from the thermostat housing, so I've been topping up the coolant now and then so it may have been diluted a little bit over the last few months, but not significantly. Hadn't noticed any issues with it, and I was checking weekly. Old was red, new is red. I was told it was flushed out when they fitted water pump.
The RAC guy checked the top and bottom pipes and said they were as expected temperature wise but don't know what that meant.
Re heating - you are possibly correct that I am imagining the temperature difference.

AdrianC

Bigphil1474 wrote: »

The RAC guy checked the top and bottom pipes and said they were as expected temperature wise but don't know what that meant.

That the return is cooler than the feed.

If he was using an IR thermometer, fair enough. If he was just using his hand, we're talking about a ~15degC difference at ~90degC or so...

I take it the front of the rad isn't easy to get to?

Bigphil1474

Yes, the front of the radiator is difficult to get to. I'll see what they say on Thursday. Thanks

Ganga

Did Ford not have a major problem with some of their engines overheating which resulted in new engines having to be fitted?

AdrianC

Ganga wrote: »

Did Ford not have a major problem with some of their engines overheating which resulted in new engines having to be fitted?

EcoBoost, newer than the OP's. A hose went pop, and the faulty parts were recalled four years ago.
https://www.autocar.co.uk/car-news/new-cars/ford-ecoboost-engine-failures-customers-receive-refunds

Norman_Castle

Sounds like the thermostat is intermittently failing to open. Did the problem start just after it being replaced? They can be cheap and easy to replace, if they are on your car thats where I'd start.

tiggerbodhi

Had the same issue on a Fiesta, get the heater control valve changed, doesn't seem logical, but it fixes the issue of intermittent/odd overheating

Bigphil1474

Norman, yep it's only happened since the thermostat was replaced last month. Most of my driving is under 15 miles and maybe once a month do a long trip over 100 miles, but I had been on a long trip the weekend before the car went into the garage and no issues. Had it back a week of doing short trips no problem, but first long trip, overheating started. Having driven it a few days since my post above, I still think it's definitely overheating as there is a more noticeable fumey hot smell. Will find out tomorrow.

Ganga

I hope they have fitted the correct thermostat,Pekins engines used to use a by-pass thermostat that had a extension at the bottom with a plate on it that used to block the flow off making the coolant flow thru the radiator etc,the fitting of a standard thermostat allowed the coolant to flow from the head to the block and go round and round and by passing the radiator! the damage used to be expensive.