C5 X7 Coolant Temperature

[Cit fan 151]

When driving our 2012 C5 3.0 HDI down long hills, sometimes the coolant temperature reduces from normal operating temperature to much cooler. Could this be caused by anything other than a faulty thermostat? It doesn’t appear to be a common problem with this model?

[GiveMeABreak]

If you're coasting down a a long hill for some time, then fuel injection is reduced so there is less heat produced from the engine as it has less work to do, but even with air intake possibly providing more cooling, I can't really see how this would reduce your engine temperature significantly enough to notice once it reaches normal operating temperature.

So I would be looking at checking the thermostat / checking for air in the system. Has the coolant be changed recently and was it properly bled? Are you getting hot and cold air from left and right sides of the interior vents? If not that can be a symptom of a blockage in the coolant system.

[Peter.N.]

I had this problem with one of mine, the temperature would go to zero down a long hill in cold weather. Unfortunately it was the thermostat, I say 'unfortunately' because its a pig to change, its enclosed in a plastic housing on the side of the engine - ah, I have just noticed yours is a 3 litre, mine is a two, maybe yours is easier to get at - or more difficult although I wouldn't think that was possible.

I have done a guide to changing the 2.0. on here somewhere, have a look at that and see it it helps.

Peter

[Gibbo2286]

Temperature sensors can be faulty, that would be my first thing to look at.

[Cit fan 151]

Thanks for the feedback.

The coolant was changed about a year ago, but I have only noticed problem with coolant temperature recently.

I did think a sensor might be a problem, but the fact that it only fluctuates from normal down a long hill made me doubt this was the problem?

Will have the mechanic do it, but will also have a look at the guide on the 2.0 thermostat.

[GiveMeABreak]

The coolant draining and bleeding procedure is here in the Members' section, It's the same for your 3.0 HDi, just ignore the first diagram with the cooling hoses intended for the specific 2.0 engine in the guide, but the procedure is identical:

viewtopic.php?t=64036

[Peter.N.]

If the temperature drops a lot on descending a long hill but is normally OK that would indicate that the thermostat is not fully closing.

Peter