So I have a 2003 Jetta sedan 2.0 l (I think) that was overheating. I assumed the thermostat was stuck and replaced it. When I relaced the thermostat another guy was there and pulled the housing off that bolts in with two bolts and a sinple O ring. When I put the thermostat housing back on, I didn't see one of those conventional gaskets or even know if its sopposed to have on, other than the O ring? But now when I start the car it leaks pretty bad. So, my question is - is there another gasket that I didn't see to put on?

It looks like this.. I cannot tell easily where the leak is coming from either but it seems like its this plastic flange that covers the thermostat. The auto part place sold me the o ring. perhaps its too small? Thank you Dave

 

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What is that picture off?

 

sorry, that's the housing that connects to the enginer where the thermostat lives.... its a internet picture of that part... David

 

You sure that you got right size thermostat for that type plastic housing,
on your car,
and do not need the rubber seal on the thermostat,
[this rubber seal in the BOX is supplied for metal thermostat covers]

The rubber Seal on the cover is built in seal on unit,
Not replaceable,
,
The new thermostat is sitting in a RECESS
and plastic hose connector
should fit very squarely over. the top
of new thermostat and that makes the seal,
if your cant seal this unit,
I check for plastic housing seal is not damage, if is damage
soon use silicon mastic to seal it
or if you damage plastic housing by cracking it
by over tight in the bolts,
Your have to renew the thermostat plastic housing ,
YOU CANT GLUE IT TO SEAL CRACK ,
DONT WORK on this type hard plastic housing,
Know because I been trying to glue these kind of housing for yrs,
never last long ,