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Fiesta overheating - a weird solution

Hi guys, this is my first post but Ive done a fair bit of lurking!

My Fiesta 1.25 Zetec began genuinely overheating (bubbles in the expansion tank and lots of steam) and it seemed that there was very little flow to the radiator, despite me fitting a new thermostat which was fine when tested. I suspected a head gasket at first, but further investigation changed my mind.

Turning the heater to hot immediately brought the temp down (ok, so it gets a flow of cold water immediately from the heater matrix so that makes sense) BUT it did not require the heater fan to keep the engine cool.

To investigate further, I removed the pipes from the heater valve (engine side) and shorted them together with a copper pipe. In other words, hot water now runs up to the baulkhead, through my copper pipe, and straight back down to the engine again. The engine now never overheats and the gauge quickly reaches Normal and stays there.

So my question is, should the heater valve be allowing this type of flow anyway when the heater is set to Cold? Or should the water not be flowing in these vertical pipes unless the heater is on? And if so, what could be wrong lower down which now requires this flow in order to keep the engine cool? Thanks for thinking about this one for me!

Reply to
jfuller105
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wrote

I removed the pipes from the heater valve

This suggests that your heater matrix is blocked which in turn suggests that the coolant has not been replaced at the correct interval.

You could try back-flushing it- connecting a hosepipe to the exit spigot and blasting it through with water at mains pressure.

Reply to
Knight Of The Road

With the heater set to cold the valve effectively short-circuits the heater matrix and hence, yes, the coolant continues to flow. I can't remember the exact layout of the Fiesta's cooling system however given continuous coolant flow is therefore expected to/from the heater matrix at all times I'd guess that there's probably nothing else actually wrong (other than the blocked heater matrix as suggested by Vince).

Having said that, does the heater still kick out plenty of controllable hot air? If so, can it really be blocked? Hmm....

Mathew

Reply to
Mathew Newton

The heater matrix definitely does not appear to be blocked - when connected up the heater gives a great blast of hot air. The overheating only happened when the heater was turned OFF, hence me suspecting that the valve is not allowing the bypass flow in the way that it should.

Think a new valve is the only way to be sure.

Reply to
jfuller105

Try getiing the airlock out first.

Reply to
Duncan Wood

This is a message that came directly to my email from Ernesto, put here for anyone else's benefit:

Hy to all the newsgroup I write from Italy, my wife's fiesta 1.25 started to have a similar problerm after changing the heater valve (plastic body with 2+2 pipes) The problem was that the cooling fan was always on. Shortly, the problem is that the new heater valve, when internal heating is in cold position, does not allow the correct coolant flow; moreover seems that there is a defective lot of these valves at local Ford dealer, so I solved modifiy the internal parts of the new heater valve to exactly match the old.

Regards

This seems to make sense - since the colder weather began I have reconnected the heater and it has been working fine, although during a long run yesterday I turned the control to cold, and after a few minutes the gauge went into the red. Again, it needed no assistance from the heater fan to bring the temp back down once I adjusted the control. Since the position of the valve is a high point in the system it seems that any airlocks are going to float up to this position, and they are not easy to clear. I went down a steep hill in 1st gear so that the high revs and zero combustion gave the circulation a chance to blast it clear, which seemed to help. Looks like I need to dismantle it again to open up the valve - thanks for the tip Ernesto!

Reply to
jfuller105

Did you fit a new valve? If not, why not? They're a very common failure point on the Fiesta as discussed...

Mathew

Reply to
Mathew Newton

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