SparTTan

My TT seems to be running on the cool side lately, so I figured I would try replacing the thermostat to see if that made any difference. (I am at 111,000 miles, so it likely could be going bad.) I still had the Wahler thermostat from my timing belt kit from a while back, which I never bothered to put in since the original was working fine at the time.

However, I have heard from various sources that the Wahler thermostats have been known to cause the car to run hot. So I decided to conduct a little experiment, since I had my old Wahler and had just picked up a new OEM thermostat.

Here are the two thermostats compared side by side. As you can see, they look like they would function about the same, but the Wahler is a little shorter. Same part number on the box.

<img src="http://www.msu.edu/~lytleric/IMG_1866.JPG">

<img src="http://www.msu.edu/~lytleric/IMG_1867.JPG">

<img src="http://www.msu.edu/~lytleric/IMG_1871.JPG">

<img src="http://www.msu.edu/~lytleric/IMG_1872.JPG">

<img src="http://www.msu.edu/~lytleric/IMG_1873.JPG">

Also note that they are both stamped "87 degrees." I assume that means they open up at 87 degrees celsius.

<img src="http://www.msu.edu/~lytleric/IMG_1869.JPG">

Here is the experiment. I put them both in a pot of water and turned on the heat, to see if they behaved any differently. If the Wahler is truly an OEM replacement, it should open up at the same temperature and open the same amount as the OEM, correct?

<img src="http://www.msu.edu/~lytleric/IMG_1880.JPG">

I started with lukewarm tap water. The bottom of the metal clip in this picture is right at 87 degrees C.

<img src="http://www.msu.edu/~lytleric/IMG_1886.JPG">

Nothing happened for a while (obviously):

<img src="http://www.msu.edu/~lytleric/IMG_1914.JPG">

But once the water reached about 91 degrees (according to my thermometer), both the Wahler and OEM started opening, at exactly the same time. You can see the metal disc at the bottom of the spring starting to open up:

<img src="http://www.msu.edu/~lytleric/IMG_1921.JPG">

As the temperature climbed, however, the OEM opened up at a faster rate than the Wahler. It is slight, but enough that I can see how a car driven hard in the heat of summer might run a little hot if that thing isn't allowing enough coolant to pass through. (The pictures are little blurry, but there was a ton of steam rolling off the water.)

<img src="http://www.msu.edu/~lytleric/IMG_1922.JPG">

<img src="http://www.msu.edu/~lytleric/IMG_1924.JPG">

<img src="http://www.msu.edu/~lytleric/IMG_1927.JPG">

<img src="http://www.msu.edu/~lytleric/IMG_1930.JPG">

So there you have it. Proof positive that the Wahler thermostat does not open as far as the OEM thermostat, and therefore, if you are replacing your thermostat, stick with the OEM. My dealer charged me $51.08 for this one.

BTTI

And you MUST share that recipe with me! Looks tasty!

Blue TTop

Thanks!

coasTTal

Some already did this. Still, good write-up.

AkRascal

Interesting, explains a lot, thanks for the info.

msauve

I've _never_ had a thermostat go bad. I'm currently maintaining 5 cars with &gt;100K (one with 240K), none has had the thermostat replaced and they all work fine.

SparTTan

Really? Oh well, further proof then.

SparTTan

My car is not heating up to proper operating temperature. Search reveals that the same thing has happened to others and the fix was a replacement thermostat. I figured I would give it a shot.

chicago_audi_dude

Wow! very cool.

Reggie

Excellent detailed write up - you could be an engineer