I believe you can buy vacuum fill devices to avoid this problem, which might be improvisable

www.youtube.com/watch?v=2QQHykK_RIw

Dunno if I'd buy one though, even if you could get them here. Pretty sure my cooling system has never been under significant vacuum and it might not thrive.

Nature is a mother, and abhors a vacuum.

Every cloud has a sooty lining, especially if its from China.

OTOH, Eric O's never had a problem, so it should be OK.

www.youtube.com/watch?v=cPMSzA2wOmw

renewed on my diesel car last year and found the reservoir empty when I got home - the techy just hadn't run the engine enough for the thermostat to open fully.

A lot don't realise there are sometimes two bleed points, or fail to run the engine at a higher speed than tickover

I didn't realise there are sometimes two bleed points.

I did, however, realise that there are sometimes no bleed points, because I think that's all I've ever had on any of my cars. Can't remember it being a problem before.

I fail to run the engine at a higher speed than tickover, because I've found that running the engine at a higher speed than tickover on this car doesn't work.

With the scary boiling...er...method that I now use, I don't want to run the engine at a higher speed than tickover, because I dont want any more local heating (particularly around the exhaust valves, which are probably the area at greatest risk) than is necessary to get it to boil.

I suppose I could mist water into the air intake to slightly reduce the risk but there's a bit too much happening as it is.

Edited by edlithgow on 01/12/2020 at 14:12

The leak has definitely been repaired and despite the coolant bubbling after every trip to/from work, it doesn't look to have decreased in volume in the reservoir. The running temp (on the dashboard at least) seems to be normal, the only thing that's changed is that the fan boots in a lot sooner than it ever had done beforehand (I don't really expect it to have to come on for a 25 minute drive on residential roads). One thing I have noticed is that the fan doesn't seem to come on if I run the heater inside the car. Not entirely sure why this is, but in all honesty I know next to nothing about the internal workings of cars, hence why I went to a mechanic in the first place!

Heater in a car acts the same as the radiator under the bonnet, which is why when the engine starts overheating its a help to use the heater in the car on max hot to help keep engine cooler

on older cars in the 70s 80s a lot of people when in town used to keep heater on hot even in summer to help keep engine cooler, modern cooling systems are more efficient usually...

The leak has definitely been repaired and despite the coolant bubbling after every trip to/from work, it doesn't look to have decreased in volume in the reservoir. The running temp (on the dashboard at least) seems to be normal, the only thing that's changed is that the fan boots in a lot sooner than it ever had done beforehand

That sounds to me the result of changing the thermostat. A petrol engine will usually open its thermostat after a couple of miles or five minutes, a diesel may take quite a bit longer. A thermostat may stick open or closed, or just react slowly.

If it is blowing hot water into the engine bay, the tester may refuse to test it as unsafe.

If it is blowing hot water into the engine bay, the tester may refuse to test it as unsafe.

Have we been told that is happening ?

Eaux contraire. We've been told that it isn't

Apart from my above contributions, I thought of something else. Has the cambelt been changed recently - and badly? I doubt if the Fiesta has variable valve timing, which can vary by more than 30 degrees in more sophisticated engines. Assuming a camshaft sprocket has about 46 teeth, if it's a tooth or two out that could mean an eight or sixteen degree timing error applied to the valves the camshaft controls. I assume it's a DOHC arrangement so it could be either the inlet or exhaust valves if just one sprocket is awry. This might explain why the engine struggles and overheats.

I remember a similar problem over fifty years ago with my mother's Triumph 1300, which gradually lacked power and got hot quickly. The distributor mounting had slipped so the spark was many degrees out of synch with the valves.

Edited by John F on 09/06/2021 at 15:08

Only reasonably practical desperate improvisation I can think of would be removing the thermostat. This will potentially increase circulation in the cooling circuit, allowing it to remove more heat.

Not necessarily a good idea. A colleague did this on a Maxi many years ago, resulting in engine damage. The theory being that the back pressure caused by the t/stat evens the flow around the engine. Removing it allowed the coolant to circulate around the path of least resistance, causing overheating elsewhere.

I can’t say that doesn’t happen, but I would have thought it was fairly unusual, since thermostat removal is/was quite a common bodge/workaround for overheating problems.

I suppose you could “tune” it with a blanking plate with a hole in it, to provide less but still some restriction.

The OP is unlikely to want to bother with that though, especially as he already has some blowing from the coolant reservoir so couldn’t easily detect any local boiling due to modification.

Flushing the radiator might improve its cooling a bit.

IF the water pump is belt driven, I suppose it might be possible to change the pulley to increase the pumping rate, but I doubt it would be worth the trouble.

Edited by edlithgow on 10/06/2021 at 10:33