Bit of advice needed.. Odd temp readings

[Syvee]

Hi Guys

Getting some odd temp readings.. After driving the car for about 7-10 miles (at about 50-60mph) the temp gauge is only showing about 65 degrees... It will then go up to normal running temp (90ish) .. Then after a couple of mins drop back down to 60-... I was thinking thermostat at first but now thinking it may just be the sender unit?

Car is under warranty so it goes back to the garage next week.. Just wondered what your thoughts were on this.. Oil temp is as it should be.. Do you think I should lay off the boost and drive it like my gran till next week or do you think I'll should be ok to give it a little after 15-20 mins?

Hope somebody can advise on this

[adsgreen]

Could be a few things...
- duff sensor is always a reasonable chance.
- Sticking thermostat.

What you need to do is actually see what temperature the coolant is.
If it takes forever to warm up the coolant then it's the thermostat. If it warms up ok and coolant temp stable but dash readings all over the place then sensor.

Oil temp could be a red herring depending on the workings of the oil cooling system. if it's got it's own thermostat then the coolant temp being lower won't affect it much if at all.

[Syvee]

Good call... The reason I think it's the sender is that it can go from 60 to 90 then back to 60 again in about 30 seconds.. I recon if it was a sticking stat wouldn't it just stay open or closed .. Rather than staying open for 10 miles then closing and immediately opening again...

To give you an idea... I drive 10 miles to work and the reading stays at 60... Last mile or so it sometimes then goes up to 90 but within a minute or so drops back down to 60 again

Thanks for your input tho...

[Syvee]

Got an idea.... If I use the onboard diagnostic control (on the climate control) I should be able to monitor the engine coolant temp.. If this goes up to and stays at a steady 90 degrees I should be able to rule out the thermostat .. Thus pointing a accusing finger at the sender unit ... Well that's my theory anyway

[adsgreen]

Depends - if that uses the same sensor....

[adsgreen]

One idea...
If you can get an accurate coolant reading displayed in the screen...
Then with the car warm sit on the motorway for a few miles at 60 in top gear. The coolant should be a stable temp (slow rpm so relatively open stat) so if you drop say to second or third and hold the same speed you should have a large amount of cold coolant hit the stat before it can react. If the temp drops by a large amount straight away then it's the stat... If the temp is relatively constant (temp will naturally drop a little) then likely to be sender.

I have seen other thermostats do far weirder things than that - the ones I've used have been pressure and temp based and can get issues with either part. Would put any kind if failure past them!

[Syvee]

Temp is staying at a steady 90 degrees (when viewed on the climate control) guess it must be sender unit so nice easy fix for the guys at the garage next week ...

[Syvee]

Temp sender ... Easy peasy sorted