Thread: Tstat housing upgrade for better flow, simple, cheap, and lots of pics to show why...

As the title states... Simple cheap easy upgrade to flow more coolant is as simple as getting an 04+ tstat housing and heres why...















The 04+ one is obviously the cleaner one with the bigger hole. I had a few laying around and was picking one out to attempt to polish and comparing them for surface flaws I noticed that the opening in the cleaner one was bigger. I had like 1 04+ and 4 97-03 and all the others were small too... The drill bit is a 31/64(metric equivelent for the bit needed to tap the f-body caliper brackets) for comparison. My motor is already an 06 so it won't be an upgrade for me when I put the polished one on but for any 97-03 guys this might help...

Both bottoms of each one are perfectly flat and measure the same opening width, so I'm sure there wont be any sealing issues... Was wondering if I should open it up even more? It still seems like a pretty big bottleneck on the cooling system. I took my coolant filter out cause I thought it was too restrictive. I guess so long as the motor stays in check temp wise none of this really matters anyway though huh?

Originally Posted by Kejross

I guess so long as the motor stays in check temp wise none of this really matters anyway though huh?

Yup, kinda what I was thinking.

Good info none the less, I guess if your in a new market for one for what ever reason...it wouldn't cost any more for a newer version with a bigger opening. In other words if you have to replace it, might as well go with this one. Couldn't hurt ya.

~F~

Does the thermostat housing opening on the 04+ match the 97-03 opening in the intake manifold?

Originally Posted by torq455

Does the thermostat housing opening on the 04+ match the 97-03 opening in the intake manifold?

They are identical as far as I can tell, aside from the hole inside being bigger on the 04+. The bolt holes in the piece are exactly identical too, one hole is slightly bigger on one side just like the older one.

Originally Posted by matt5112

What if i did this to my stock one?

There's oodles of material you could remove I guess... Would be kinda hard to get down in there with anything but a drill bit though and it would have to be a monster drill bit like 1" which the bit would probably cost more than a new housing. Maybe try a wood bit on a drill press, I would think it could handle a little bit of aluminum but don't be mad at me if it don't work.

Good find, but don't think it would help much. The thermostat itself I'd imagine would be more restrictive.

should you open up the opening on the lim on the series 2 to make the holes match up?..if that makes since

no because then the oring on teh t stat would not seal and you will make a mess.

Not sure if anyone has done this, but when i had a GTP project car (that ended up being parted out) i was on a porting spree... and i Ported the Tstat housing.

i smoothed that tight 90* bend and opened up that hole. i never tried it myself, but gave it to a friend who had a GTP.


im all for reducing restriction where ever possible. if you think about it ... any restriction in the flow of coolant will put more resistance on the water pump and reduce power. i know that the Tstat itself is a restriction. so how much this porting will help or not is unknown to me. but for 5-10 min of my time... i felt it was worth it

While it's a nice idea, and I like the way you are thinking. It's not likely to improve flow much. Between the T stat and the u bend under the TB, those will be your larger restrictions.

I did hot out the 90* bend and make it less on a stat housing. Didn't notice anything, but I figured less of a hard edge etc. And I think it was a matter of boredom/trail and error.

Aren't the t-stats for the 3800's the same? If so, why would GM go through the trouble to make the newer necks larger?

Less material? More $$ in pocket?

As far as I know the tstats are the same... I think I bought the 180* in my 06 motor for a 98. And Z34, sadly your probably right. I would like to think GM was fine tuning things and decided to open it up but its probably a materials thing. You gotta think an ounce or two less per part times like a billion of these motors that were made = more profit.

On a side note, you have to do an alternator or timing belt on that 3.4 DOHC yet? I really liked that motor and the redline it had but boy was it a PITA to mess with. I had a 95 z34 monte years ago...

If both housings have the same outer dimensions, I'm fairly certain they are, then the new ones are thinner. I