Screwloose that's brilliant! Will test it and see what's what.
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I can't find a J7R 636; but a [UK-spec] J7R 768 is c.290 Ohms @20c and 390 Ohms @ 80C.
Thank you to Screwloose and Maceman for this thread. My Espace (another J7R 636) has started running less-than-happily until it warms up, and you have inspired me to check the coolant temperature sensor. Mine reads 4.05 kilohms at 5 degrees C, so I'll be asking the local Renault dealer for a price for a new sensor. If I remember, I'll check the resistance at room temperature before I fit it.
For what it's worth: my symptoms are that the engine starts all right, but the idle speed hunts up and down (between about 700 and 1200 RPM) every few seconds until the temperature gauge gets off its end-stop. Changing gear while the engine is cold sometimes provokes a sudden loss of power for a second or so. Once it's warmed up, I get smooth idling and what seems to be the usual amount of power and fuel economy for this vehicle.
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Replying to my own note, and showing off more ignorance than useful knowledge.
My first attempt to identify the temperature sensor got the wrong one. On my 94 2.0i (J636, J7R engine) there are two temperature sensors screwed into the thermostat housing. The one on top has one wire, and feeds only the dial on the instrument panel. The one hiding just under the heater hose, with two wires, part 77 00 737 571, connects to the engine management electronics. On my second attempt I got the right bit from my local Renault dealer.
Car certainly now [1] runs more smoothly. The bad news is that my resistance measurements aren't very different for old and new parts, and I don't think I have a good measure of the temperature. The new part measured
5.23 kilohms at 13 C
4.05 kilohms at 15 C
3.43 kilohms at about 20 C
750 ohms at about 60 C
In case anyone else needs this - it went on with a 21 mm spark plug socket and cost £15 including VAT and a new seal.
Notes:
[1] Actually, until this morning. At the moment it doesn't work at all, because I've been trying to replace the heater matrix: don't trust Haynes for this if you have a right-hand-drive model! With any luck it will work again by the end of tomorrow morning.
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