93 1.4 Overcooling - thermostat problems? - Scotiawhiskers
Had this petrol car for about 3 years now. When I got it it was running cold all the time according to the gauge and heater output, top hose getting warm very quickly, so I replaced the thermostat. It improved markedly for just a few months and went downhill again gradually.

So about a year later I replaced the thermostat again. Same thing - improved for a few months then gradually running cold again.

I am currently running with 2 modified carpet tiles blanking off most of the radiator, meaning it warms up in about 3-8 miles (instead of never) and then runs at about the right temperature mostly, but it does run hot enough for the fan to cut in regularly if I get stuck in traffic or when coming to lower speeds off the motorway. This isn't ideal, or good for the engine or my wallet.

Has anyone had similar problems and found a cure? Both replacement thermostats have been QH branded ones purchased from a major high street motor accessory store, but I can't believe identical failure patterns and times in batches that must be from separate manufacturing runs.

Alternatively does anyone know of a different thermostat which fits the CVH housing and is more reliable? Or just try a motor factors instead of the high street?

Thanks.
93 1.4 Overcooling - thermostat problems? - L'escargot
If it was me, I would try to get a genuine replacement thermostat from a franchised Ford dealer.

Does the outer diameter of the thermostat have a seal to prevent leakage past the thermostat? (A new seal should be fitted when you fit a new thermostat.) Is the thermostat seating area clean and flat? Is the thermostat stuck open? Has the thermostat got an integral bleed valve which is stuck open? Any leakage whatsoever past the thermostat will result in overcooling. Have you got the heater on all the time? Does the heater valve have a bypass feature which is malfunctioning?

You can check the thermostat by suspending it in a saucepan of water, gradually heating the water and then checking the temperature at which the thermostat just starts to open. When I say just I mean just. During normal running, especially in winter, the thermostat shouldn't open more than a few thousands of an inch. For your car I would expect the rated start-to-open temperature to be in the region of 82°C to 85°C.
93 1.4 Overcooling - thermostat problems? - Scotiawhiskers
Thanks for a speedy reply.

Yes there is a heavy rubber seal which fits between the thermostat base and the housing, replaced that every time after cleaning any deposits out of the housing. Thermostat seats firmly against it - the spring clip to hold it in place is a sod to get in or out so definitely not leaking past that.
No integral bleed hole, but I compared all the thermostats in that section and all had a tiny sliver of light visible at some point on the circumference between the valve and the seat, I assumed that was to do the same job and just picked the one with the smallest amount of light. Sounds like shoddy manufacturing tolerances then? I'm used to aircooled bikes so thermostats aren't too familiar for me!
Heater is airblending, as far as I am aware there aren't any valves and the circuit is just open for flow round the exchanger all the time, certainly gives warm air sooner with the tiles than without and gets up to a decent output after a while.
Temperature stamped on the old thermostats is 86C, I didn't bother checking as I don't have a high enough heat range thermometer and as the part was only £4.50 - suppose that shows you get what you pay for.

I'll try to get a genuine one next week when I am back home and report back on what difference it makes. At least it isn't too bad a job to do and the weather is warmer now, not like doing it in December at around freezing temperatures!
93 1.4 Overcooling - thermostat problems? - L'escargot
Heater is airblending as far as I am aware there aren't any valves and the
circuit is just open for flow round the exchanger all the time ............


When you turn the heater to cold there must be a valve which stops the coolant flow. It may not be visible, but it's there.

For what it's worth, read JesseT's post in this website ...........
passionford.com/forum/showthread.php?p=3887196
........ regarding a plastic ball somewhere near the thermostat possibly being missing.
I'm not familiar with the item so I can't really tell you anything concrete about it. I imagine it's an air bleed valve which should close off when the water pump starts running.

Trawl the local charity shops to see if you can find a Haynes manual for your car.

Edited by L'escargot on 18/04/2009 at 11:45

93 1.4 Overcooling - thermostat problems? - L'escargot
I imagine it's an air bleed valve which should close off when the water
pump starts running ...............


......... and if it's missing it will allow coolant to bypass the thermostat even when the thermostat is closed.

93 1.4 Overcooling - thermostat problems? - jc2
These cars have a full-flow heater system where the matrix is hot ALL the time.Temperature is controlled by diverting the incoming air either thro' the matrix or by-passing it.Max heat is 100% air thro' the matrix-cold is 100% air by-passing the matrix.Plastic balls and jiggle pins have not been in common use on thermostats for many years now.Most will have either a small hole in or a "V" shaped nick in the opening part to bleed air out.
93 1.4 Overcooling - thermostat problems? - jc2
Haynes manuals will normally be available in your local library where they can borrowed or ordered if not kept in stock.
93 1.4 Overcooling - thermostat problems? - Peter.N.
Unless the water is bypassing the thermostat somehow, it must be a faulty thermostat. Did you get them all from the same place?
93 1.4 Overcooling - thermostat problems? - Simon
Now unless I have missed it the OP hasn't answered one fundamental question - Were the thermostats that were taken out stuck open?
93 1.4 Overcooling - thermostat problems? - Peter.N.
They can open at to lower temperature without necessaraly sticking open.
93 1.4 Overcooling - thermostat problems? - Scotiawhiskers
All thermostats that came out were shut - looked the same as the new ones, so I made sure to label them and not put an old one back in!

All were High Street bought (Halfords) but over a wide time period, so shouldn't be from the same batch.

Got a Haynes manual, used it when doing the thermostat job.

Never noticed a little plastic ball - from what I remember the thermostat blocks the entire connection to the radiator top hose. There is a small passage which comes off the mating face, but that is for the very top (air bleed / balance?) pipe which runs over to the header tank. That has coolant running through it whenever the engine is running.

Where the weather is warmer now I have been running this weekend with only 1 tile blocking half the rad - has been running at about the right temp and not over heating easily during the day but when the temp drops in the evening it runs down around the M of NORM now. Also takes noticeably longer to get up to temperature.

Edited by Dynamic Dave on 21/04/2009 at 01:26

93 1.4 Overcooling - thermostat problems? - mfarrow
Go get a genuine stat - it'll cost slightly more but be of known quality. Around £10.
93 1.4 Overcooling - thermostat problems? - L'escargot
There is a small passage which comes off
the mating face but that is for the very top (air bleed / balance?) pipe
which runs over to the header tank. That has coolant running through it whenever the
engine is running.


Any passageway which allows coolant to bypass the thermostat is liable to result in overcooling. Are you sure that this passageway shouldn't have a plastic ball to allow air to go past it during filling from scratch, but prevent coolant flow during normal running? Perhaps, at some time in the past it's got lost as JesseT suggests in his/her post in the passionford.com forum. I vaguely remember a plastic ball in my 1980 (or thereabouts) CVH Escort.
93 1.4 Overcooling - thermostat problems? - sierraman
On CVH engines used in Sierras there is a flow direction arrow stamped on the stat which must point to the pressure relief valve,this is a narrow tube with a ballbearing in it ,held in by a crimp,the tube bypasses the stat housing(not the hose running to the expansion tank).Don't know if this applies to Escorts.It cannot be a faulty unit unless it is stuck open so save your tenner.On some vehicles it is possible to fit the stat the wrong way round,but this would result in it not opening and thus overheating.
93 1.4 Overcooling - thermostat problems? - Scotiawhiskers
I'll check that at the weekend then, but as that hose goes from the top of the thermostat housing across to the header tank and is only about 5mm bore, I don't see how it would get the rad and the rad top hose hot from startup in just a couple of minutes. It's a separate loop of the circuit so it can't feed into the radiator loop. The radiator does get hot from the top hose side, not the headertank one, so it isn't as if that water is somehow backflowing with a closed thermostat.

I'm not sure how you'd replace a plastic ball there anyway, wouldn't it drop out of the thermostat housing into the block? Or is the hole in the thermostat housing big enough to put it in but the hole for the feed from the block is smaller so it doesn't drop through?
 

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