Hi, I initially thought I had a coolant temp sensor problem but am now thinking it's the thermostat...

* Driving normally (gently) the temp gauge stays between about 70-80 degrees, even when stationary in traffic

* Motorway 70mph - about the same temps

* Driving quicker round town etc (20-40mph) it reaches about 90oC.

* When left idling for several minutes when it was being MOT'd it stayed rock solid at 90 degrees but as I drove it home it dropped back to 75 ish.

It has the green colour temp sensor though I don't know how old this is.

I've ignored it so far but with winters colder temperatures coming I thought I should get it looked at. Anyone know how much a replacement will cost? And would running cool like this mean my mpg is lower than it should be? Even driving gently I'm only getting low 30s MPG.

Thanks very much!

Edited 21 November, 201114 yr by OU51

so long as you have eliminated any other factors like air locks or leaks in the cooling system id say its a fair bet that a new thermostat will fix it

it should be 90 oC at all times - if moving around and no coolant leaks definately replace thermostat

mpg being lower is a tell tale symptom

For the price they cost I'd do both at the same time, the thermostat is a fiddly bleeder tho

Thanks guys. It's hard for me to tell because I've only had the car 6 months and it's always been like it.

There are no puddles under the car and the coolant level hasn't gone down in 2500 miles so I don't think there are any leaks.

I've been looking at a couple of how-to guides and I'll be paying someone else to do it for me I think! I'll post back if changing it fixes the problem or not.

mines doing this let me know if a stat fixes it

Will do - I hope to get it done in the next couple of weeks.

Sounds like the stat is stuck open to me.

Buy a genuine one too. I fitted a topran GSF one which failed after a few months.

I've just this minute ordered the official parts from the nearest Seat dealer (they're closest to where I live)

thermostat £23.59

seal £2.41

On second thoughts I'm going to have a go at doing this myself but can get a mobile mechanic in if I get stuck.

Edited 22 November, 201114 yr by OU51

mines doing this let me know if a stat fixes it

I've good news and bad news...

Good news, had the new thermostat fitted today and this has fixed the problem. Temps got up to 90 degrees within about 2 minutes of driving and stayed there just like they should. The old thermostat was closed when it was removed so I wasn't sure if the new one was going to make any difference but it fortunately has.

Very strangely, the car also drives much better now. On cold starts the secondary air pump thing used to make quite a loud noise for 90 seconds or so and if I tried driving off while it was still running it was quite jerky and definitely not right. This has now stopped. I'm not sure if the air pump is running on startup but I can't hear anything - but there are no error codes or anything. I was able to drive straight off and it was all very smooth. In the past it sounded like the air pump would sometimes come on whilst driving too. I did clean the throttle body out yesterday so this may explain the new smoothness but not the quieter cold startup.

Bad news is that the alternator seems to have died and I'm going to have to get that replaced now as well!

Edited 2 December, 201114 yr by OU51

Good news on the stat. In regard of the SAI I always used to let it stop doing it's thing before driving off. If the SAI sounds like a Dyson on start up the rivets on the pump housing have probably failed. It's a common problem that is pretty easy to fix by drilling out the rivets & fitting nut's & bolts in their place.

make sure you haven't disturbed the wiring on the back of the alternator when you did the stat.