I drove my 1957 Mercury Monterey for the first time in 25 years. When I got back after driving a block or two it was way too hot. The thermostat works because I replaced it(160 degrees). The only major thing I have done to it was rebuild the carburetor; I don't have the carb settings right yet but I don't think it that would cause it to run this hot. Would it? Why would it run way hot after only a block or two? What should I do?

Is the car overheating? Boiling the coolant out of the radiator?

After the car is fully warmed up, touch the radiator in various spots to see if you have any cool or cold spots. This will tell you that there is blockage in the radiator.

Have you tried reverse flushing the radiator? Ot the flushing the block? You may have a lot of rust build up in the block.

Ron, that is brilliant troubleshooting. Most mechanics fail to use all their senses, and they miss a lot of clues.

Is your exhaust pipe heat riser stuck shut? If it is, exhaust gasses are constantly flowing through your intake manifold.

Make sure you have a tight cooling system that can hold 7-lbs of pressure. Each pound raises the boiling point 3-degrees F, or (3X7=) 21 + 212 degrees = 233F.

50/50 antifreeze helps a lot, too. Be careful not to mix the new orange stuff with the old green antifreeze, or it will turn to mud. (Your water pump will still try to churn it.)

Running a lean carb will raise your temp and cause detonation. It's always better to run a little rich. The real question is "does your cooling system have the capacity to cool your engine's heat output?" Under normal circumstances it should, all the way across the Mohave in Sept. If need good coolant flow, and a clear radiator.

I never knew about the heat riser. How do I check the heat riser? And if it does not work how do I fix it or where do I get a new one? It probably is running too lean and the cooling system is corroded but I don't even think that would make it run so hot so fast which is why I now suspect the heat riser is the problem.

All your V-8 cars have a heat riser 'valve' in one manifold. The purpose is to send hot exhaust gas through your intake manifold, to speed up the 'warm-up' time. There is a bi-metal coiled spring on the outside, and usually a counterweight. It acts like an exhaust butterfly, closing off the path towards the muffler. When the heat riser gets hot, it opens the butterfly inside your exhaust, allowing flow to go out through the muffler.
With the exhaust COLD, see if you can turn the counterweight with your hand. The butterfly is on the inside, with a shaft going through both sides of the iron flange. It should turn very freely. If it is stuck, don't force it. Hit it with penetrating oil. Keep blasting and trying for a few days. Eventually, it will free-up. Again, a stuck-shut heat riser will send all the exhaust gasses from half of your engine, through the intake manifold, all the time. Any radiator would have a hard time keeping up with that kind of heat.
Hope this helps - Dave Dare

Well? Did you find it? Was it frozen?
I forgot to mention that the valve turns 90 degrees for full-open. Just because it moves a little means nothing.

As your engine cools, the counterweight & bi-metal spring returns the valve to the closed position, and that's usually where it sticks. It is a good practice to manually check it periodically.

If you decide to elliminate the valve, your exhaust will flow more freely, but the engine will take a little longer to heat-up. (Some guys permanently wire it open, because the bi-metal spring rusted away.)

I have been spraying WD-40 all over the heat riser for a couple days now. It didn't move at all, not even a wiggle. So I lightly tapped the counter weight back and forth with a hammer. It still won't move freely but at least it is stuck in the open position. Now I feel exhaust coming out of the passenger side tailpipe. And the motor sounds alot better too. I would have never knew to check that intill you said it. I could have put a whole new radiator in and it and that still would not have fixed the problem. I need to replace the heat riser. Where do you suggest I get a new one and what do I need to do to replace it? Thank You!

I took it out again on the same short drive. It is still hot but certainly not as hot as it was.

Ok, you nearly had me stumped. I've been searching all over for a heat riser for you. I don't know what engine you have, but I know it's a '57 and it must be a V-8 (272, 292, 323, Y-block?).

Good news and bad news...

GOOD: You really don't need a heat riser (six-cyl engines don't have one, and as you saw, it restricts flow). Some places offer a spacer to take the place of a heat riser for around $25 or so.

BAD: Some places sell heat risers for $80-100.

EUREKA-SUCCESS: Ellis at t-bird.com has one, in stock, for $79.95. (800) 423-3723 T-bird Products (in PA). Tell him Dave Dare sent you.

As the picture above shows, your valve is bolted between the exhaust manifold and the exhaust pipe. Take the nuts loose, tap with a hammer, and the heat riser should drop right out. My '55 272 has the heat riser inside the RH manifold casting, and I cannot replace it. (Consider your situation somewhat lucky.)

Exhaust bolts are always nasty to work on. Sometimes, they are nearly gone from years of rust. Those need a torch, either to loosten the rusty nut, or to burn off the bolt/stud. I suggest, if you have any problem getting the old one off, bring your car to a good muffler shop. Those guys have all the equipment, and they run into this every day. It won't take them 15 minutes to have you back on the road.

I went through all this because it tickles me when someone like you discovers a problem and actually works on it to solve their issues. You are most certainly welcome, and Thank You for allowing me to help. That is what this forum is all about; restorers helping restorers.

By contrast, here's T.H.'s answer to fix his heater core problem:
So, what did you decide? Will you install a spacer or the replacement heat riser?

Well since it is stuck in the open position I will probably keep the existing heat riser on untill I replace the broken exhaust pipe. So once I get enough money to replace the exhaust pipe I will replace the heat riser with a spacer. I just got a set of TOYO tires from a junkyard for $125 with good tread so that I can drive it around without the tires deflating. My Mercury has not been driven for 25 years since my Grandpa had it. Thanks for the resource for heat risers and spacers.