Thanks for the replies :)
It is a Zetec engine, 1.24.
Is there a way to test the valve/thermo?
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The best way is to bridge the valve out of the circuit completely with a suitable length of copper tube. If that cures the problem; then replace the valve.
Other possible causes are low coolant level and a failing water pump.
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An update.
We decided to try changing the thermostat, since the heater valve was replaced by the garage relatively recently. We looked under the bonnet and the alternator is in the way, but on inspection it would seem that the alternator is rather attached to the engine support brackets... the whole top of the alternator seems to be bolted in from the side with 2 long bolts, one of which has a kind of "mini" bolt... so hard to explain.
This is a 1.25 Zetec-S 2001 Fiesta, if anyone knows what that looks like.
Anyway, we decided not to try it in the end, and bled the coolant to see if there was an airlock. After refilling with water we ran the car and the engine got up to mid-temp, but still no hot air. We gave it some gas, up tp 2k rpm and the hot air started to blow. Went for a short drive and the engine temp moved just into the red and the car still blew hot air.
So... do these extra symptoms point to the thermostat do you think?
The horizontal bracket attached to the top of the alternator can be seen here, kinda... to the right of the lowest yellow cap. www.britishblogs.co.uk/images/275110.JPG
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I did all that first as well - thinking that a brand-new valve wouldn't be faulty.....
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Does any of this new information support your suspicions of the valve affecting the thermo? or is it not any more helpful?
"The heater valve can have an effect on the thermostat as - on some models - the return from the heater opens the stat.
I suspect the valve is stuck halfway and is the cause of the problem. "
Also, is this valve just behind the dash area, where the two hottest pipes are going in at the moment? We felt it while we changed the dash control between hot and cold and it was definitely "thumping" when we hit cold, but no feeling when moving to hot... does any of this help identify the problem? Is the valve easier to change than the ridiculously placed thermo? :)
Thanks so much for all your help thus far, I've learnt a lot.
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I can only repeat my earlier advice....
"The best way is to bridge the valve out of the circuit completely with a suitable length of copper tube. If that cures the problem; then replace the valve."
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I would... but I just wanted to check if we are talking about the same valve :)
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Yes; the plastic two-pipe valve under the cover on the bulkhead.
Just take off the two hoses from the engine and join them together with a bit of plumbing tube.
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Thanks I'll give that a go :)
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Hi again,
Right I think I should have time to do this tonight, if I am lucky.
So, I join the two hoses that feed into the valve, and this will close the circuit bypassing the in-car heating, right? So my engine wont overheat but I wont have heating in my car until i replace the valve.
So long as my understanding is correct, then I shall do this tonight, but please correct me otherwise :)
As you can tell I am sure, I dont usually do this kind of stuff, but I simply cant afford a mechanic right now!
Edited by matt_b on 04/11/2008 at 08:56
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Do I need to block the ends that I remove the hoses from?
www.fordpartsuk.com/shop/fiesta_heater_control_val...m
Is the part number any good on that item?
"
Engineering number on unit is 7N21-18495-AB
This number replaces all the engineering numbers shown below
96FW-18495-BD
98FU-18495-AA
98FU-18495-AB
98FU-18495-AC
"
Many thanks everyone :)
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The heater matrix will be full of coolant, so you'll get some spillage as the car moves about. If you can block them easily, it's probably worth doing as much to avoid crud getting in as anything else.
I had countless, endless problems with this on SWMBO's old 1.4 Zetec Fiesta, which actually almost drove me to sell the car. Then I noticed in the service history that the heater valve had been replaced two months before the previous owner sold the car. I changed the valve (after replacing the thermostat, radiator and water pump), and all the overheating problems ceased overnight.
This also happened to loads of people on the Zetec-S owners club after replacing heater valves. Cars that previously ran bang on temperature started boiling over and blowing head gaskets.
Anecdotal evidence, including a strip down of an "old" 96FU valve, and the "new" 98FU valve that had succeeded it, with a photo comparison that a friend of mine did revealed a marked reduction in size of the coolant bypass channel in the new valve compared to the old one. The conclusion we drew was that this "design change" choked the coolant flow whenever the heater was turned off, and the coolant could not flow through the heater matrix.
Our car would run happily all day with the heater on, but as soon as the temperature control was set to cold, would overheat within two miles, accompanied by a cold radiator, and constantly buzzing cooling fan. To me this didn't make any sense at all.
Screwloose's bypass test will confirm if the valve is causing your overheating problem. I very strongly suspect that it will be the cause.
This is a shocking problem, which to my knowledge, Ford have never publicly acknowledged, and which the forum I was a member of at the time had evidence was caused by a change in manufacturer of this valve (at the time the part number changed from 96FW to 98FU). This would also appear to be borne out by a few people with badly overheating cars fitted with replacement 98FU valves fitting 96FW valves liberated from scrapped cars, and having the overheating problems disappear overnight. Later 98FUs were also OK, as were pattern parts from non-Ford sources (the route I took in the end to a satisfactory conclusion).
Good luck
Cheers
DP
Edited by DP on 04/11/2008 at 10:21
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Thats very informative, thank you.
Do you know if a valve with part number "7N21-18495-AB" displays the same serious design flaws as the previous "new" ones?
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Hi Matt,
This is going back about 2 years, and only what I and some rather irritated members of another forum deduced. How true it is I don't know, because according to Ford dealers, and Ford themselves at the time, there was no problem with any of these valves. My understanding was that only the early 98FU valves were affected, and certainly from speaking to other owners, mine had been changed within a month of the part number changing.
My father has changed these valves on the two Ka's he looks after for current part number 98FU valves from Ebay in the last six months and had no problems with either of them, for what that's worth.
The bypass trick suggested by Screwloose will confirm the cause beyond any doubt. I can also tell you which Ebay item I (and my dad) used if that helps. I will need to trawl through my records though.
I would be very surprised if the current valves from Ford weren't perfectly OK, given these things fail regularly, and the number of stricken, overheating Fiestas and Kas would have made headlines if they'd been problematic for two years.
Maybe we were barking up the wrong tree, but the evidence I saw, and the reports of hundreds of fellow owners were quite convincing to me personally.
Cheers
DP
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Good morning all.
Last night I nicked my dads tools (then nicked my dad to help :p) and we set about dismantling my car. We removed the valve which turns out to be one of the newer part numbers, 7N21, and bridged both sides (its too cold to be without heat!).
Driving around town there was no problem, and this morning I got all the way to work without incident :)
Thank you all very much for your help and advice. I will replace the valve, although if the 2007 part is still dodgy I guess I'll see this problem again before long!
Cheers again :)
-Matt
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