Temperature gauge wandering

[slime bomb]

Hi all, my 2018 420r temperature gauge has started to wander. From cold, it will get up to temp then start to fluctuate. A few miles later it will go down to cold then up to 90degs again and so on. Before I have the hassle booking it in is there anything I can look at first? I've recently sprayed the chassis and panels with ACF50 and wondered if this has had anything to do with the problem.

Thanks in anticipation.

[mike150]

I imagine a dodgy thermostat.

Nothing to do with ACF50...………..unless you damaged a sender wire in the process of reaching around stuff

[fergus]

When you know the car is warm (i.e. touch the top of the radiator), take off the lead for the water temp sender and ground it. You should see the gauge reading deflect one way or the other (I can't remember whether low resistance is a high temp, or vice versa). This should confirm either a duff sender or a wiring issue.

[anonymous-user]

if it’s falling all the way back to the bottom of the gauge that implies no signal. The stat wouldn’t cause that.

My R400D fluctuates. From start it steadily goes up to just over 80. If I’m in traffic, or just plodding along it’ll stay there but occasionally may go up a little, but never over 85.

If I boot it, the temperature will fall to maybe 75, as the water starts flowing quicker and the rad airflow increases. If I carry on booting it, it will steadily increase to 80 or so.

I did a track day at Snet on Saturday. Never saw it over 81/2 and only then after 4/5 fast laps. Leave pits on 80 or so, temp falls to 75 then comes back up.

The temperature sensors do vary. My original one gave similar figures but rose and fell much more quickly then my current one. (I replaced the original to get away from the silly mismatched connector, now have a ring on a post with a nut).

Edited by anonymous-user on Monday 19th November 13:35

Edited by anonymous-user on Wednesday 21st November 16:32

[slime bomb]

Thanks for that guys. I will have a look at the weekend.