How open is an open thermostat?

Just finished an engine-out HG job and did everything as documented using OEM HGs and seals, etc. Upon first start, we soon noticed engine was beginning to overheat and overflow bottle filling up. My suspicion would be air in system and/or faulty thermostat.

After bleeding system we couldn't fix it so quit for the night. Next day I extracted fluids for inspection and it all looked good. I decided to run without a thermostat. First test run car reached proper temp after a 15 minute warmup and I ran about 10 miles with perfect temp, coolant overflow bottle level, and no air bubbles. Conclusion: HG job is good and car is running great, must be bad t-stat. I then did a boil test with that t-stat and it appears to be OK, although I was hoping to find it bad.

My question is how open should a fully open t-stat be? Mine tested at about 1/4 inch between the mating plates when fully open. Is that enough or should it be more? T-stats sticking is just not something I ever think is real. I figure they are either good or bad. Thoughts? Thanks !!

is it a subaru t-stat?

if not , replace it.

after market t-stats can be crap.

and as you probably have experienced, can cause headaches right out of the box.

the only other possibility is ''air'' in the cooling system.

read this:

http://legacygt.com/forums/showthread.php/fill-and-burp-your-cooling-system-burpcoolingsystem-198487.html?t=198487&highlight=fill+burp

Well yes technically this is after-market. It's a NAPA OEM-compliant one that is described to be made exactly as OEM quality, and has served us well since a prior t-stat failure 18 months ago.

No doubt I will be picking up a Subaru brand t-stat and rad cap just to be sure.

I think I can feel confident with my HG job since running with no t-stat for a long period resulted in a steady temp gauge and zero reservoir bubbles.

Thanks for the burping thread link johnegg!

how did you seal the t-stat housing when you removed the t-stat?

that could be the sever leak you saw.

the gasket fits around the t-stat and is sandwiched in between the pump and t-stat housing.

this would be especially true if the leak did nor start until AFTER you removed the stat.

but no bubbles in the coolant is a good thing.

how high did the temp gauge go when running with out the tstat.?

i don't think they ever reach normal operating temp since the stat job is to both open when hot but close when cold.

the open pipe is so much larger with no stat.

i have not run on of these cars with no stat, so i don't really know where the gauge rides.

but when i did it in my 90 nissan pick-up, the gauge never moved past 1/4, no where near the halfway that was normal.

my problem ended up being the blades on the aftermarket water pump impeller.

they were steel and completely corroded, one was missing.

but that is a different car, story,forum.

and since you have the 2.2L engine (right?) it is lee likely that you have a head gasket problem.

i'm beginning to think clogged radiator.

assuming i got the facts right.