Thermostat fail?

**damianzmd** · 20-04-2011, 02:21 PM

So basically my MK4 Golf 1.8 (non Turbo), overheats while I drive it, and I have no warm A/C.

I would drive it out, on an 80 zone, and it would slowly increase it's temp, until the warning light would come on.

I opened the hood, noticed that the top radiator hose is quite warm, while the bottom is completely cold!

What does this mean? Is it a t-stat that's stuck open or stuck close? And is it still safe for me to drive? So that I can atleast drive it to a garage to get it checked out?

If it is the thermostat, how much am I looking at getting it fixed with parts and labour?

Thanks in advance!

EDIT: Could it be my water pump? The cabin is always cold, and car is overheating. Apparently if the cabin has heat and is overheating it's the thermo?

**dylan8** · 20-04-2011, 02:32 PM

thermostat arent to expensive, not a major part from memory.
I know mine was stuck open and not letting the car get up 90oC on the guage and making it run rich etc. It never logged a fault though...
The top hose you said was warm, how warm do you think? to warm to touch?

**dubbed** · 20-04-2011, 02:36 PM

Sounds like it could be the thermos have stopped working because of the internal resistors.

Turn your car on, turn AC completely off and make sure fans aren't running. Then turn on AC to the coldest setting and check if the fans are now running. If not, definitely your fans. Also check the fuses on top of your battery to see if the 30A for the fans has blown.

**damianzmd** · 20-04-2011, 02:37 PM

Well you could touch the top hose without being burnt, but it was significantly hot! As I said the bottom pipe was completely cold.

After reading all these various threads on forums, I'm so confused as to wether my thermo's open or closed!

EDIT:

I've checked the fans, both are working, I've also checked the 30A's on top of the battery, and they're all in check, no melting or anything as such!

I'm hoping its just the thermo

**craig_the_german** · 20-04-2011, 03:50 PM

Hi,

If the thermostat is stuck OPEN, it will not allow the engine to heat up (by allowing unrestricted coolant flow out of the engine and through the radiator)and therefore will not reach 90deg / operating temp.
If the thermostat is stuck CLOSED there will be little to no coolant flow out of the engine and through the radiator and therefore will get too hot.

If yours is overheating I would say it is stuck closed.

I put a thermostat in my 1.6 and the part cost ~$20 (non genuine but works just fine)

Hope this helps

Pete