1955 Exhaust Manifold Thermostat Purpose

[Hilde]

What is the purpose of the exhaust manifold thermostat on the passenger side? My '55 is a 292 cid, with dual exhaust. There is not one on the driver's side. If it's working properly, it starts out with the exhaust pipe closed, and slowly opens up as the manifold heats up, so you're driving around with reduced performance, and building up carbon inside the exhaust manifold (and probably the head & the tops of the cylinders) until the manifold gets hot! This doesn't make any mechanical sense to me. Mine happened to be stuck closed (stuck in rust), so I'm wondering if I should just replace it with a spacer or replace it with a new one. The thermostat costs around $85.00, and the spacer is around $12.00, so if I knew why Ford put it there, it would help me make a decision.

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[biddle]

You will get more responses with a brief subject that summarizes your post. "1955 Exhaust Manifold Thermostat" could be anything. I've revised it.

 

[55blacktie]

It's part of the choke system. It's not uncommon for it to stick. If you have converted to electric/manual choke, Casco sells a spacer that's used in its place.

 

[Ward 57]

It's pretty simple. I fact I've been helping another fellow with what I think is the same issue. First of all, you may be able to just smack it loose and getting it to rotate again.
It's purpose is to send exhaust gas up through the intake manifold to heat it up for better vaporization of the fuel in the manifold and heat to open the choke. It's closed at idle but as soon as you accelerate the valve opens up by the force of the exhaust and sends the exhaust out through the exhaust pipe.
If you live in a hot climate don't need the choke or have an electric choke you may be able to get by with the spacer but will take a little longer to warm up the manifold. If it's stuck shut you are sending ALL that exhaust up through the intake manifold, overheating it and the carb. adding to the possibility of vapor lock.

 

[zeroroadkill]

If it’s the heat riser on the exhaust pipe just below the exhaust manifold with the weight and spring, just unhook the spring and it will stay open. If that’s what you’re referring to?

 

[Hilde]

It's pretty simple. I fact I've been helping another fellow with what I think is the same issue. First of all, you may be able to just smack it loose and getting it to rotate again.
It's purpose is to send exhaust gas up through the intake manifold to heat it up for better vaporization of the fuel in the manifold and heat to open the choke. It's closed at idle but as soon as you accelerate the valve opens up by the force of the exhaust and sends the exhaust out through the exhaust pipe.
If you live in a hot climate don't need the choke or have an electric choke you may be able to get by with the spacer but will take a little longer to warm up the manifold. If it's stuck shut you are sending ALL that exhaust up through the intake manifold, overheating it and the carb. adding to the possibility of vapor lock.

Thanks Ward 57. Looks like I should definitely replace it with a new one. Albuquerque has hot, dry summers, but it gets pretty cold in the winter. Mine was so stuck in rust that once I freed it, so it would swing easily, it would still get stuck closed when I let it close. I removed the exhaust manifold, and the t'stat was rusted solid to the manifold. I had to beat on it for a good 30 minutes before I could pry it off. The bimetal coil was so rusty that it probably doesn't work properly, or at all. So, I've ordered a new one. Thanks again for the good info.

 

[paul5456]

I don't think that acceleration opens the valve. Heat makes it open. It is just like a carb choke. When the spring (bi-metal coil) heats up, it opens the valve inside

 

[Ward 57]

I don't think that acceleration opens the valve. Heat makes it open. It is just like a carb choke. When the spring (bi-metal coil) heats up, it opens the valve inside

That could be very true. It would make sense as once the engine is warm there would be no reason for it to close. Hilde, Just noted that the spring was bi-metal also. I have never read a description that it was and just assumed it was a standard spring. Now that I think about, when I rev it up a little when warming up, I can hear it flapping but once warm it never does.
The day is not wasted, I learned something new.

 

[Hilde]

That could be very true. It would make sense as once the engine is warm there would be no reason for it to close. Hilde, Just noted that the spring was bi-metal also. I have never read a description that it was and just assumed it was a standard spring. Now that I think about, when I rev it up a little when warming up, I can hear it flapping but once warm it never does.
The day is not wasted, I learned something new.

Thanks, me too.

 

[jack-in-sac]

What is the purpose of the exhaust manifold thermostat on the passenger side? My '55 is a 292 cid, with dual exhaust. There is not one on the driver's side. If it's working properly, it starts out with the exhaust pipe closed, and slowly opens up as the manifold heats up, so you're driving around with reduced performance, and building up carbon inside the exhaust manifold (and probably the head & the tops of the cylinders) until the manifold gets hot! This doesn't make any mechanical sense to me. Mine happened to be stuck closed (stuck in rust), so I'm wondering if I should just replace it with a spacer or replace it with a new one. The thermostat costs around $85.00, and the spacer is around $12.00, so if I knew why Ford put it there, it would help me make a decision.

Others have posted the information you seek as to purpose. whether you replace it may depend on where you live and when you drive the car. I lve n Sacramento California. this is not cold country. I replace my heat riser with the spacer because I do have the cold weather of more northen climes and altitudes.

 

[Ward 57]

I don't think that acceleration opens the valve. Heat makes it open. It is just like a carb choke. When the spring (bi-metal coil) heats up, it opens the valve inside

I guess I missed interpreted the part description as thermostatic control. Not noticing it controlled how the valve worked.

 

[jack-in-sac]

Correction to my previous reply made in haste:
Others have posted the information you seek as to purpose. whether you replace it may depend on where you live and when you drive the car. I live n Sacramento California. this is not cold country. Even though i found my heat riser to be stuck open, I replaced it with the spacer because I do not have the cold weather of more northern climes and altitudes.