Thermostat

[2002MK4]

Got a few questions on the thermostat.

Is this something that either works or doesn't work or does it degrade gradually over time?

Did the meat thermometer test today after 10 mins [city] car was at 75 degree. Jumped on the highway at 120km/H for about 20 mins...car got up to 80 degrees. Question is a) shouldn't the ALH engine run at 90 degrees and b) is this why my MPGs are low? Or to say it differently...how much would a 10 degree variance in temp reduce my MPGs by?

I guess the last question is if the meat thermometer reads 80...why does the dashboard say 90???

 

[RacerTodd]

Thermostats can fail completely by jamming shut (car overheats) or jamming open (car runs way too cold). They can also fail partially, where they open too soon (car runs a little cool) or too late (car runs a little hot).

I gained 2 mpg when replacing my thermostat, car was running maybe 10-20deg cool.

Here is a thread I made, showing a log of coolant temp with a new, 87C VW thermostat: http://forums.tdiclub.com/showthread.php?t=391412

With a stock 87C thermostat, the coolant should run right around 90C once warmed up.

The dash gauge is useless - it displays 90C when the coolant is actually between 70-110C or so.

If you have VCDS or Vag-Com you can access the coolant sensor and see what the real coolant temp is.

 

[Cogen Man]

The dash temp. gauge will show 90*C (190*F) anywhere between about 165*F and 210*F. It's purposely buffered this way by the manufacturer. If not everyone would be freaking out seeing their temp. swinging so much. When was the last time the thermostat was changed ? If you don't remember I'd just go with a new one. I use a Scangauge II. Plugged into the OBDII port and gives me real time coolant temp and many other readings that the dash doesn't show.

 

[2002MK4]

Thanks RacerTodd. Very helpful.

 

[2002MK4]

Ya thanks Cogenman, will grab one tomorrow. Believe they are like $24. For 2 may-be 3 MPGs more why wouldn't I. I'll get this money back in the next 2-3 weeks.

 

[Cogen Man]

Ya thanks Cogenman, will grab one tomorrow. Believe they are like $24. For 2 may-be 3 MPGs more why wouldn't I. I'll get this money back in the next 2-3 weeks.

http://www.giffordautomotive.com/SGC/index.php

Above is a link where you can get a SGII if you've a mind to.

.

 

[FlyTDI Guy]

Make sure you pick up a new housing and o-ring as well. You'll most likely break the old one getting the it out. Also, don't get a local A/P tstat. Use OEM or you'll be doing it again. Behr is good. Here's the best deal I've found... www.autohausaz.com

 

[2002MK4]

Thanks.
So may-be I'm not understanding something. The Wahler is the OEM but is only rated for 80 degree celcius? My coolant was at 80 degree celcius after the meat thermometer test anyways. Why should I replace?

 

[FlyTDI Guy]

You may want to read THIS for more info. Not sure where you're getting your info but it should be 87ºC.

 

[phaser]

Thermostats can fail completely by jamming shut (car overheats) or jamming open (car runs way too cold). They can also fail partially, where they open too soon (car runs a little cool) or too late (car runs a little hot).

My original t-stat had 290k miles on it, and failed in the closed position.

Now it will get changed out with every timing belt.