My therastat seemed to stick closed on me during an acceleration WOT uphill. It didn't start cooling down right away and I pulled over to check under the hood. After a minuite the thermastat opened and the ect dropped to the normal 190*F. It did it to me again climbing a hill on the way home but it seemed to open up faster this time as the ECT dropped faster. Anyone experienced this with a thermastat on a cold morning?

If you suspect the thermostat the best thing to do is remove it and check it in water as you bring the water to a boil. A candy thermotor is a great help but just watching the first bubbles forming in the water is a good indication the water is approaching the boiling point. The stat should start to open about 15 to 20 degrees before it's set point and be fully opened by the set point. If you get the water to boil before the stat is fully open you have a bad stat. If removed from the heat spurce and any cool water added to the pot you should see the stat close quite fast as water is added.

I'm wondering if maybe that's a "cold" thing you have going on there. Stat maybe staying closed moreso than on a warmer day. You rush the hill, build up heat, (at least a reading at the sensor) and it takes a little bit for the stat to react further up the line. If the stat is closed down more than usual, the flow moving through it and to it is much slower, and make take longer for it to open up.

We have a similar problem with refrigeration equipment that is water cooled this time of year. City water supply water temps drop, and over-rated regulating valves open, and shut very quickly making a machine gun sound with a bad water hammer. Warm water temps don't do it, because, it's regulating a flow, and not stopping the flow.

Just a thought.

Hm, I've had a broken thermostat on another car many years ago and one on my truck. Both just stayed open. I'd expect those thermostats to be designed in some way so that they stay open when they fail, but I don't know if they actually make them so.

Just put a new one in, that's cheap insurance.

Well, it was the waterpump. I was 50 of 70 miles into the commute to work monday morning and the ECT pegged red. I guess you can say I got the HO waterpump the hardway. I had a generator and aircompressor and was lucky enough to exit the freeway where an autoparts was. I took a pic of the gears with the pump off.

Lee, The t.stat's are not designed to break in the open position. I just read a whole article how team Hummer destroyed thier entire 6.5 when their t.stat's failed-Closed.

Yes, the designed failure mode for a thermostate is Closedand and that is the case for 99+% of stats. But so mush for design. If you want to see 6.5 failed thermostates take a look on my web page. Both of those stats came out of the same truck a 98 6.5 Sub.

Howie, they look scary ...

MDT, was the article on some webpage?