This happened to me this recently and just like above, i too have replaced the coolant temp sensor, but it makes no difference. i still have to spray hot water over the sensor for about 10 seconds or so to warm it up and then the car fires up instantly. This ONLY happens when the outside temp is below freezing. Has anyone actually overcome this problem ?

Well I’ve just had the same problem, car wouldn’t start, suspected glow plugs but warming this sensor did the trick....any ideas for a permanent fix? Many thanks to Marsh 23 for getting me out of trouble 👍

Just a guess, but could you not insulate the sensor with bubble wrap or a bit of tube lagging you put over water pipes. May save you pulling off the engine cover. I don't have this model so may be talking a load of rubbish but worth a try

Not a bad idea maybe, I'll give it a try. I do wonder though, why would the temp reading from this sensor prevent the car from starting. With my very limited mechanical knowledge I'm assuming that the sensor is reporting a cold coolant temperature, which maybe requires something else to take place in order for the engine to fire up? i.e. additional warming from the glow plugs? Warming the sensor with hot water fools the sensor to report 'normal' temperatures and the car starts up but is that having a negative impact on something else?

Few extra points:
Never had a problem starting previously, fired straight up, even in snow after standing unused for months
Battery is strong and only a few months old
Once started the car runs like a dream
When turning over trying to start there are clouds of white fumes from the exhaust

Initially thought it would be the glow plugs but now not so sure.........Any clever people out there??

So I've been digging into this problem on the D3 site, it seems the sensor I was referring to is known as the ECT (Engine Coolant Temperature) sensor, and feeds temperature information to the ECU that controls the glow plugs. The glow plugs have three modes of operation, pre-cranking, cranking and afterglow (I think!). By warming the ECT sensor, the ECU operates the glowplugs differently (I'm assuming eliminating the pre-cranking stage?), as it thinks the ambient temperature is higher than it actually is.

Is anyone able to throw some light onto whether this can cause any damage to the vehicle and also why the car will start without the pre-heat, but not with?

With previous cars I'd have just replaced the glow plugs, but it seems that's one hell of a job on the D3/RRS, so would like to avoid unless absolutely necessary.

The clouds of white smoke will be vapourised diesal fuel and is a sympton of a car that hasn’t fired up. Rather than concentrating on glow plugs, you may want to broaden your thought process unless you have fault codes pointing to glow plugs. I was thinking it may be an air issue, if the coolant sensor is warmed, does it tell the ECU to allow more air in at start rather than perhaps nothing (when it should be choked). 2019 5.0 SC SVA (Current)
2012 5.0 SC AB. Sadly written off by a campervan
23 plate Focus ST (Current)
1942 VEP Ford GPW Jeep (Willys) (Current)
1943 Whites M16 Halftrack (Current)
16 plate Eurofighter Typhoon, 2 x Eurojet engines with 20,000lbs thrust each. 1380mph

Quote from another thread.

‘ECU coolant temp sensor does effect the fuelling, timing and glow plug operation. When it detects the engine cold the signal from it tells the ECU to retard injection, sets rich fuel for start and fast tickover, lets the glow plugs function. When the engine reaches a certain temperature the ECU switches off the cold start functions according to the signal from the temp sensor’

Perhaps ECU is getting the cold settings wrong. 2019 5.0 SC SVA (Current)
2012 5.0 SC AB. Sadly written off by a campervan
23 plate Focus ST (Current)
1942 VEP Ford GPW Jeep (Willys) (Current)
1943 Whites M16 Halftrack (Current)
16 plate Eurofighter Typhoon, 2 x Eurojet engines with 20,000lbs thrust each. 1380mph

Cheers, useful stuff. I think the first thing I'll do is check the current draw on each glow plug, as this seems to be a relatively straight forward test, and take it from there......

And where is this sensor on a tdv8? Cant find mine...