Thermostat test?

[andrew96]

I've been reading my Haines manual and just want an opinion from other experienced audiziners. It tells me if I want to test it to pull it out and first check to see if it's open. If open, then it's faulty. If not then to try this. Suspended the T-stat from a price of wire and put in a pot of cold water. Begin to boil the water and before the water is fully boiling, the Tstat should open. Can anyone confirm or deny this method before I go to the trouble of taking it out?

Thanks!

[USAF Long]

Yep that's how you test it. If it's stuck open you know right away. If it's stuck closed you will know by boiling it. Just put it in a pot of water.

Are you overheating? What is your cause to believe you have a faulty thermostat?

[andrew96]

Yup, over heating. Replaced rear coolant flange, water pump, turbo coolant feed line and thermostat all within 6months. Getting plenty of flow and heat so water pump seems good. Can't find any external leaks and oil consistency is normal as well as coolant consistency. also not blowing off coolant so head gasket seems fine so far. Top radiator hose gets hot while bottom hose to the radiator and Tstat stays cold. Also coolant reservoir seems to fill up and drain every time I turn on and off the car. Leads me to believe it's stuck closed.

[USAF Long]

Hopefully not a head gasket. I'd do a compression test to be sure. The fluctuating coolant levels means there's a lot of vacuum on the cooling system. Not a good sign.

[andrew96]

I'll have to do one soon. Now, the oil and coolant consistency are just fine and I'm not getting any blow off either. Engine also runs just fine. Are there any other signs I should look for besides a compression test?

[USAF Long]

Well if your oil isn't milky and your coolant isn't looking contaminated I'd test the t-stat to rule it out. If you overheated it too bad you might have popped the head gasket. Even a small tear in the gasket can cause it to overheat. Hopefully if that's the case your head didn't warp or crack, but I'd get it inspected to be sure if it turns out to need a head gasket job.

[andrew96]

Thanks for the input. I'll check the Tstat tomorrow. If a head gasket blows or you have a warped or cracked head, would any CEL come on or would the engine run any differently?

[customa4]

Here's some good info on testing the thermostat.
Click
Click

[andrew96]

Thanks customa4, those links were super helpful. I'm boiling it now and just want to make sure, the sensor does not have to be plugged in right? That sensor only reads the temperature and does not tell the thermostat to open? The door is not opening so I believe the Tstat is defective

[old guy]

That isn't a sensor on the thermostat it is a heater. The ECM uses the heater to force the thermostat to open sooner under specific conditions.

[andrew96]

sounds like the thermostat is defective. I just called ECS and they are sending me a new one. Could you explain under what conditions the heater would be activated to speed up the thermostat? I've been having so many issues with the coolant system so it's definitely interesting to learn more about it.
Thanks old guy!

[old guy]

The thermostat heater is in constant use. Here is an excellent tutorial on how an electronically mapped cooling system functions. The tutorial is for a different engine but the function is the same for the 1.8T.

Clicky click®

[diagnosticator]

I'll have to do one soon. Now, the oil and coolant consistency are just fine and I'm not getting any blow off either. Engine also runs just fine. Are there any other signs I should look for besides a compression test?

You can have a sample of coolant examined by an oil test lab like Blackstone or Caterpillar, for the presence of combustion gasses dissolved in the coolant. If there are dissolved combustion products and gasses in the coolant, then the head gasket is leaking.

[diagnosticator]

I'll have to do one soon. Now, the oil and coolant consistency are just fine and I'm not getting any blow off either. Engine also runs just fine. Are there any other signs I should look for besides a compression test?

You can have a sample of coolant examined by an oil test lab like Blackstone or Caterpillar, for the presence of combustion gasses dissolved in the coolant. If there are dissolved combustion products and gasses in the coolant, then the head gasket is leaking.