Corvair Forum

I have a 66 Monza and one of the thermostats failed in open position. I have a non running engine with a a good thermostat. How difficult is it to swap out the thermostats? Any tips would be appreciated.

Just covered here --- probably more information than you need and folks use different methods so you decide.

See viewtopic.php?p=147367&hilit=thermostat#p147367

Do try to avoid stretching a good thermostat open (elongate). As with most things thermostat replacement is simple if you know what to do, otherwise it can seem complicated. If you have skills then you'll figure it out. If no skills, then have someone who knows how show you.

Stretching a good thermostat will not hurt it at all. The method to hook up and adjust the thermostats in the shop manual shows pulling the thermostat out to full travel to adjust the doors. Been doing the shop manual method for 54 years and never had an issue damaging a thermostat.

corvairsince70 wrote: ↑Wed Nov 20, 2024 4:42 pm Stretching a good thermostat will not hurt it at all. The method to hook up and adjust the thermostats in the shop manual shows pulling the thermostat out to full travel to adjust the doors. Been doing the shop manual method for 54 years and never had an issue damaging a thermostat.

Guess you are lucky, as others have reported stretching them can ruin them.

They have to be able to stretch to the stop to work properly and I'm not sure how you would hook them up without stretching them.

That is the main reason I put Riv-nuts (blind nut, Rivet nuts, Grip-Sert nuts) to hold thermostat bracket and shield onto the lower shroud. I can setup the lower shroud, cooling box, thermostat and adjust the door rod while on the bench as an assembly. Then remove the thermostat mount from lower shroud to install cooling box with door, rod and thermostat as an assembly. I then put lower shroud up to thermostat to loosely bolt it on. The lower shroud is then positioned to engine case and bolted on. Thermostat bracket bolts are tightened and job is done. I have done this mod twice on 2 rebuilt engines and once on a resealed engine. But Mod can be done anytime lower shroud is removed.

Since then, I have removed lower shrouds and left thermostat and bracket on engine, while I fix an exhaust leak, an oil leak, or to clean head air passages. I really say more than that it is much easier to do work under shrouds with the removable thermostat bracket.

Excellent idea! Thanks!

joelsplace wrote: ↑Thu Nov 21, 2024 7:03 pm They have to be able to stretch to the stop to work properly and I'm not sure how you would hook them up without stretching them.

They EXPAND when hot due to internal pressure. When cold and you stretch them it increases the vacuum force inside, and apparently that can damage them. At least that is what I saw in a couple posts.

Yes you have to stretch them a little during install, but A LITTLE. I gave up on a few different methods and found it was just easier to pull the pin out of the door and you can slide the door in so you can easily access the rod to the door to disconnect, adjust, or connect without yanking on the thermostat. I had two NEW style thermostats (yes they have a bad reputation) fail in short order after stretching them to get the rod on the door (which was a huge PITA). That is when I started removing the door pin to let the door slide in. Really not big a deal and it made hooking up the thermostat rod to the door much easier. Yes you have to get the door back up and the pin in it, but again it is not a big deal. Just me.

I guess it is like the temptation to just drop the engine vs. the whole drivetrain, but dropping the whole drivetrain avoids problems that can make the "short cut' no bargain.

I have always just pulled the door pin to remove the lower shrouds. Just looking at that "Jesus" clip and trying to install it with the rear air grille in place just looks hard. Yes, the bendable pin holder does snap after a few times, but a well placed sheet metal screw/washer takes care of that.

I squeeze the clip where the hole is a little so it will stay on the arm in the open position and then use a bent coat hanger that grips the rod ahead of the swivel to pull the rod and thermostat back and get it through the holes. It's tricky when the swivel turns too easily. You can't really do it with the rear air grille installed.

Sometimes instead I'll angle the lower shroud down in the front to gain access to the clip. I need to get a better arrangement for getting light in there, I just thought of a magnet on the oil pan.

The 61s with the rear air duct welded to the lower shroud are a piece of work, especially with the oil tube on a FC.

I'd rather practice up in dealing with them as is than modify every car that comes through here.

By the by I use #10 x 1/2" stainless pan head phillips sheet metal screws along the top of the rear air grille and #10 x 1/2" flanged 5/16 hex head sheet metal screws on the ends.
I bought like 2000 of the hex heads with no screwdriver slot a few years ago and I'm surprised to see an end in sight. I guess it takes a lot for engine shrouding and belly pans. I'm a bit of a fastener snob and the screwdriver slot seems so hardware store.

Don't tell anyone but I've used two failed thermostats on cars that just get driven in the Summer so at least they match. It's hard to explain $150 for a pair of thermostats to some people.

a guy has really great one ' s better then the factory junk

turbodan70 wrote: ↑Tue May 06, 2025 2:43 pm a guy has really great one ' s better then the factory junk

Actually the factory thermostats are reasonably reliable. I have bought old original ones out of high mileage cars that STILL WORK!

The problem was with the aftermarket units made in the 70's after GM quite making them. The replacements had a high initial failure rate since they were made different. Clark's sells the aftermarket style, and replace the ones that fail within a year. Of the four I bought, two failed within the year and Clark's replaced them. The other two are still working.

The original thermostats have "rounded" accordion edges, the aftermarket units have "pointed" accordion edges.

For a car that's only driven in the Summer, two failed thermostats with the doors open all the time isn't so bad.