Two bad thermostats?

I bought a 1967 Coronet with a 440 in it about six months ago. Last summer I reached temps of 205 degrees. I had been running a 20' fixed fan, no clutch. I had read that adding a shroud should help keep temperatures down. I also read that a 180 degree thermostat is recommended for the motor. I changed the thermostat about 6 weeks ago to a Mr. Gasket 180 degree.

About three weeks ago I found and bought an original seven blade fan, used clutch and metal two piece metal shroud. The guy I bought it from told me that if the clutch was not good that he would swap it out for me. It seemed to run cooler with no problems, but then again the weather has been cooler. Last weekend I was out and the temperature reached 225 degrees. I pulled over to let the engine cool off. I started the car about 45 minutes later, the temp was 180, and the temp climbed back to 225 in about a minute. I called the guy I bought the fan, shroud and clutch from and got another clutch. I changed the clutch in a parking lot and when I started the engine the temps climbed as before. When I got home and the engine had cooled some I started the car with the radiator cap off to see if I had any flow from the upper hose. There was no flow and the temp climbed again. As i walked back to turn off the ignition I saw the temp was 230 degrees. Right before I turned off the key I had a geyser erupt from the radiator opening. That led me to believe the thermostat was defective and opening really late. I put the thermostat in water and it did not open even at 200. I bought another thermostat and installed it this week, let the car idle and it got to 180 and stayed there.

I took the car out this morning and the temp reached 203 but went no higher. This is a cool 52 degree day. I thought that was too high. We went to go somewhere this afternoon and by the time it had been running four minutes the temp was at 220. By the time I got it back home the temp was aroundy 240-250 and the radiator was boiling over. Both times when this happened the upper hose was very hard to squeeze.

Now the question, did I have two bad thermostats or am I missing something?

What brand stats are you using? I've had 3 bad ones in a row before. These days, I try to find Stants....

Cranky said:

What brand stats are you using? I've had 3 bad ones in a row before. These days, I try to find Stants....

Click to expand...

Same here, bought a stant from Napa, no more problems.

Yep, 180 Stant Superstat with green coolant. Could be something else going on though. Is it a new thermal clutch? Mine was slipping at idle and they can be difficult to diagnose. New one and problem solved.

Both of the replacements have been Mr. Gasket. I bought those because they most resembled the original. May have been a mistake. I did the boil test and the thermostat did not open, even when the temp showed over 212. I tried the 160 that was in the car when I bought it and it opened. I think for diagnostic reasons I may reinstall the 160 and see if I have any more problems. By the way, the 160 I removed looks identical to the Mr. Gasket but I don't see a brand name.I am also going to get a Stant to install after I confirm that it is the thermostat. Did y'all run 180 or 160?

180.

It is not a new clutch. When the motor was hot I could spin the blades about 1/4 of a turn if I spun it hard. Isn't that about what I should expect when the clutch is hot?

180 here too.....

One more thing on the thermostat, make sure it has a bleeder hole to let the air out.

I hate Stant Superstats and have also had sticky Mr. Gasket thermostats as well. I'd get a normal Stant and drill an 1/8" hole in it to help bleed air out of the system when you service it. My machine shop will not warranty and engine with a Superstat in it. They are usually sticky out of the box in my experience.

I've had really good luck with Stant Superstats ! The last Mr. Gasket failsafe high flow thermostat I had failed in the closed position and ended up blowing the original water pump on our car.

Just for grins, take the thermostat completely out for a TEST run. Still run hot? Water moving?

If it were me I'd be looking at the radiator. Have you checked Temps across the entire radiator ? Might have a flow issue

I did a couple of things last night. I put the second thermostat in water on the stove. It never opened, even at 215. I did notice a lot of gold flecks in the water. When I dumped the water out there was also gold material stuck on the sides of the pot. I believe that I got two bad thermostats in a row. I checked the original 160 again last night and it opened and closed as it should.
I ordered a stant superstat and will pick it up tomorrow. I am going to test it before I install it even though the other two didn't fail on the initial drive. The original (when I got it) 160 degree is back in it for today. I don't know what would cause two thermostats to fail other than them being defective. Thanks to Car Nut and Jeremiah, I did drill a hole in the thermostat before I reinstalled it. If this doesn't work I may take out the thermostat as Hemi 354 suggested.

Don't want my family to lose confidence in the car as we are planning our first trip to Cruising the Coast this year. Wife is really excited, even though the car doesn't have air.

I bought a Stant Superstat and will install this weekend. I have been looking for a replacement clutch in case I still have problems. Trying to find a Heavy Duty or Severe duty. I have read about the Jag clutch 2765 that is standard duty. I have found some sites that claim the Hayden 2747 will fit. From what I looked up, it won't. Has anyone found a heavy duty clutch that will fit on a 1967 Coronet with a 440?

I think the standard replacement clutch manufacturer is Hayden. Not sure of application . Also use a laser temp gun to be sure of temperatures on specific components.

Does the box that the t-stats came in say where they were made?

[video=youtube;aa1yG-fntRk]https://www.youtube.com/watch?v=aa1yG-fntRk[/video]

Like 65 - 440 posted I would look at the radiator, for sure your T stat should open at the correct temp when tested, but is it possible you have the smaller 318 radiator in the car ?

My 383 ran hot years back but I had a small radiator, I went with a 26" aluminum rad , shroud , and 7 blade fixed fan. I have a 180 stant in it & 50/50 mix of antifreeze & water and on a 100 degree day in traffic the most I ever see is 200 degrees, it runs aprox 190 most all the time. I know the fixed fan costs a couple horse's but I don't care as long as its running cool.

Make sure to take a heat gun and shoot that rad. Many of these old radiators have plugged tubes. In the old days before a temp gun a hand on the core would tell lots too. You could also take one of those defective thermostats and jam it in the open position, reinstall it and see what that does for you.