So I had a post in here like a week ago or so about my vapor lock, traced it back to my thermostat as the root cause of the trouble. I had installed it on the motor fresh at the rebuild, 160 degree. I figure I paid $15 for a HiPo thermostat, it should perform, I got about 8000 miles out of the first one (the one I removed a week ago) it started opening at 185 instead of the advertised 160. So I pop in a spare Mr. Gasket 160* that I had and I had gone for a drive....its evening, about 65 degrees, and the temp starts climbing to 220 (never had that happen before) I got her home as quick as I could and I hit 240 pulling into the driveway....I shut her off and put cooling fans on the front of the car and she pegged to 280/290 and I could hear the coolant boiling inside the block, I am ever so happy the freeze plugs didnt blow. I released the pressure from the cap and she came down to 220 agaion and then I just left her alone for a week. I blamed an air pocket in the coolant passageways.

I pop out the thermostat today to verify that its working. Mind you this is a 160* and I had a thermocouple reading 225 and the thermostat was still sealed shut. Just because its new doesnt mean its going to work. I already know this from other parts but come on....its a 30+ yr old design, cant I get 10k miles out of a part like this at least?

I am going back to the cheapo $2 Stant's and drilling the 1/8" holes in the body like I used to with the slant that had one thermostat in her for 45k miles..

Yep, went through the same thing with a so called hi flow, hi performance thermostat no too long ago. After installing it my temp in the Coronet would climb up and beyond 200 degrees, when before it would run at 180 to 195, depending on the temp outside. Pulled it out, got a stock type thermostat at NAPA, installed it and all was well.

How long was the MR.G stat sitting around? New or used before?

The reason I asked is that sometimes they stick from sitting around a long time and just need to be unstuck to work correctly from then on.

If you hit 240 I think you are going to find more problems.

cheapo Stant? Stant used to be a very good brand

The sticking closed thing could happen with any brand thermostat, mass production makes it a crap shoot. AFAIK, all of the high-flow thermostats are made by Robertshaw and repackaged by the various vendors.

There are cases where the high-flow thermostat makes the engine run hotter even when the thermostat is working perfectly, some systems simply can't use the higher flow.

I am going back to the cheapo $2 Stant's and drilling the 1/8" holes in the body like I used to with the slant that had one thermostat in her for 45k miles..

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Thats what i still do..

In case you haven't checked, make sure your lower rad hose isn't collapsing shut on acceleration.

It can drive you insane since it usually won't show any sign while at idle.

There's usually a large coiled spring in the hose to prevent this but some auto suppliers magically loose parts from time to time during the trip between the manufacturer and the store shelf.

Just my

I've run the Mr. Gasket 180 high flows in a pair of 440's for 5 years + and never had a problem. Maybe newer ones are bad for some reason. I know from experience having stats test fine in a pan of water then fail in the cooling system under pressure.

I had a mr gasket 180* in my big block, worked great for 2500 miles.

then the water temps started hovering around 190 and in the city would creep up to 210-215 and really made me nervous!

I discovered my heater core was leaking so I simply bypassed it since it's a warm weather vehicle now anyway.

then started thinking about it...leaking coolant out would typically run cooler until the coolant got too low and would THEN overheat.

changed the thermostat too, and now it's back to maintaining 185-190 (it was a 185 stat)

Have them in 3 motors.No problems at all.Mine has been in for 10 years.Untouched 65 rad and still runs at 180 or less.Rocky

Pretty much all stats are made by Stant or Shaw.Ive bought a ton and they all were made bo one or the other.At the shop we used Stants in almost everything.Rocky

Milodon still carries the good ones for our older cars.