Faulty Thermostat

[slynch23]

Looking for some advice. The temp gauge goes up to 90, but when I’m on the motorway or or cruising at 40+ the gauge starts dropping. The longer I’m at those speeds to lower it drops. Done a bit of reading and sounds like the main thermostat is stuck open. Took it to an indie dealer (family friend) and he said they couldn’t find anything wrong with it. Anyone have any ideas? Cheers

[Octoparrot]

You could try changing to 2 temp senders first to see if that makes any difference.

[Tazocin]

What exactly could they not find wrong?

If they went to the trouble of stripping down and removing the stat for testing then they might as well have put a new one on and changed the temp sensor for about 50 quid in parts given that its a horrible job to do. If they just let it sit at idle then yes it will get upto temp. There are also inline stats that tend to cause the car to be slow to warm up but the number fo these stats depends on what year of manufacture your car is and whether its DSG or manual

[Rigsby]

Main stat, had exact same problem.
I just changed it, didn’t even check the old one.
Sorted problem

[bobby_fodge]

my issue was the temp gauge wouldn't get up to 90, swapped coolant temp sensors but it turned out to be the main stat.

[slynch23]

Cheers for the info guys. I never explained properly, just said the thermostat had gone from what I’d read on the net. They took it out and didn’t see the gauge go below 90 as they just went round town. Only dips when you get up to cruising speed. Spoken to him and it’s being done next week now so hopefully that’ll fix it.