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They can open at to lower temperature without necessaraly sticking open.
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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
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Go get a genuine stat - it'll cost slightly more but be of known quality. Around £10.
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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.
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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.
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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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