Overheating after changing thermostat

[CJS-90]

So I've had the temp gauge indicating about 80degrees for a while now whilst driving normally, but that would go up to 90 degrees in traffic, or on a spirited drive.

Obviously, the two culprits are temp sensor, and thermostat.

I changed the temp sensor two weeks ago, and although I received increased MPG, the problem still persisted.

So yesterday I changed the thermostat...

All went OK (apart from it being a bit of a PITA due to it's location).

I ran the car with the coolant cap off, and topped up as necessary...I then went for a small drive (about 1 mile), stopped, and topped up again. I then drove home, but as I was parking up, the temperature was nearing 105degrees on the gauge...obviously I immediately shut the car off, opened the bonnet, put the ignition back on to allow the "fast fans" to cool the car down.

I left the car to cool down completely, and checked the coolant level...it's where it should be. so I ran the car up to temp for about 15minutes with the cap off again to try and alleviate any air locks it might have...nothing changed, and the temp sat at 90...

Drove to my friends house (3miles away) and half way there, the temp exceeded 90 again...so I put the fans on hot, which brought the temp down and I was able to carry on driving, with the temp sitting at 90, whilst the fans were on hot.

Same again this morning. Driving to work, I get about 3/4 miles into my 7 mile commute, and the temp goes higher than 90 again (despite it being sat at 90 for about 2.5miles without any issues).

So again, to combat this I put my fans on to bring the temp down which it did, so I could carry on my commute.

I'm a bit baffled really. I know the CTS is fine because I ran it for two weeks without issue, giving correct temp readings.

Could there just be an air lock somewhere? Or am I looking at a dodgy thermostat? I bought the thermostat from AVS car parts, so it's not a genuine part, but it's supposed to be to OEM spec (I don't have a VAG dealer particularly close to my house)


Sorry for the essay...any help appreciated!?

 

[Crhome]

Hi mate, am having the same issue at the moment. I replaced thermostat and engine coolant temp like yourself and still no joy. I also got my radiator replaced for a brand new 1 recently cause of a leak. I am lost as to what I could do next to eliminate the problem. Is your fans kicking in how they supposed to? Your slow speed fans work? I also done slow speed fan mod done to my car a while ago. B4 I replaced my rad car was running perfect, but now its not. And since my slow speed fans work correctly, I never had my fast speed fans kick in. I am baffled.

 

[David McMahon]

Is the bleeding on these difficult? Where are the bleed points? Does it need vacuum or something to bleed?

 

[leegreenaway]

Self bleeding system IIRC

 

[sockpuppet]

Did you use the correct coolant adative G12 G12+ or G13? I read on here that any other additive/anti freeze can react with the G12 and turn it solid.

There are 2 plastic pins/prongs in the Thermostat housing which if they don't snap off will be very out of shape. If the Prongs are both snapped off then the thermostat could be in the horizontal position rather than vertical.

http://www.seatcupra.net/forums/showthread.php?t=210977&highlight=thermostat

 

[CJS-90]

Yeah I used VW spec stuff, G12+.

I didn't realise it had to be completely vertical. Maybe that's my issue then, and that's why it seems to be so random?

Bit annoying I'll have to take everything off again just to check it's vertical

 

[sockpuppet]

If you still have the two prongs in the housing you have to twist the thermostat into the prongs and the thermostat bar can only be vertical. If you are going to take it off, it might be worth getting new housing and the genuine thermostat for piece of mind.

 

[CJS-90]

I'll just twist it round for now and see if that fixes it. The car is still driveable (just about) so that's all I'm bothered about.

I think I've got a decent knack for getting the thermostat housing off so should be able to get it done pretty swiftly.

 

[Adam4D]

probably more likely that the water pump impeller blade is spinning on the shaft

 

[w1ll0711]

If you turn the fans on hot inside the car and you only get cold air then you're mire than likely looking at a new water pump, had the same problem on a mondeo where it wouldn't heat up at all, I changed the thermostat and coolent then the missus drove it to work and it just started overheating, every mile or so it would go into limp mode and id have to stop, cool it down and carry on (took me 2 hours to travel the 15 miles home >.< ) got the water pump off and the splines on the shaft were completely polished! Not sure how the job is on a SEAT but thanks to fords great design I had to change the water pump, steering pump and oil cooler thermostat housing as they were all dead hope its a easier fix for you!

 

[CJS-90]

Hot air is definitely hot, and the temperature of it goes up in relation to the coolant temp. My situation is definitely thermostat related.

 

[w1ll0711]

Id try ordering a genuine thermostat from dave at sere motors or a seat dealership. Thermostats can be a right pain in the arse if they arent genuine parts, but first pull it out, stick it in a pan of cold water and put it on to boil, if it opens up then its fine if not then you know what your problem is... although if its fine it could be causing flow restiction to the system preventing it getting cooled efficiently.

 

[Adam4D]

Have you even checked the water pump?

Take out the thermostat and put your fingers in the whole and try to turn the impeller, if it cannot be turned happy days, if I can then you need to change it!

 

[traumapat]

Does it start overheating when pushing on or at a standstill in traffic?

 

[ibizacupra]

checked rad bottom hose for getting hot (indicating stat is opening and flows occuring)

 

[CJS-90]

Have you even checked the water pump?

Take out the thermostat and put your fingers in the whole and try to turn the impeller, if it cannot be turned happy days, if I can then you need to change it!

I'll check that when I adjust the stat...today hopefully if the weather breaks!

Does it start overheating when pushing on or at a standstill in traffic?

When pushing on it does, I can't really put my foot down at all otherwise the temp starts rising. When sat in traffic it doesn't seem to move, just sits at 90 which is very confusing.

checked rad bottom hose for getting hot (indicating stat is opening and flows occuring)

I'll check that after I've adjusted the stat and gone for a drive

 

[CJS-90]

So to update this, I've bought another thermostat and whilst it isn't quite as bad as the other one, the car still over heats when I put my foot down.

Any ideas? I put the thermostat in boiling water, and it opened as it should do, so I'm guessing the thermostat is fine...it has 88degrees written on it which would be an acceptable level for it to open at?

I'm a bit stumped to be honest, since with the old thermostat the temperature was sitting a little too low, now these new ones it's getting far too high.

 

[David McMahon]

Perhaps have a garage check for Head gasket fail by checking the coolant (I hope it's not)

 

[Adam4D]

Did you check the water pump impeller?

 

[CJS-90]

Did you check the water pump impeller?

Totally forgot both times when changing the stat. Whoops!

Perhaps have a garage check for Head gasket fail by checking the coolant (I hope it's not)

I don't think the head gasket has gone - even if it had I don't think it would cause such dramatic overheating anyway?