Radiator cap

[Doug&Deb]

What pressure cap should be on a 52 Coronet? I’m thinking 4 pounds. Someone put a 7 pound on mine and I’m having problems.

[Plymouthy Adams]

50 - 52 is 4 lbs                               53 - 54 is 7 lb...… my book stops with the 54 for a quick check...

[Doug&Deb]

Thanks, that explains a lot. I’ve resealed just about every freeze plug on this thing. It had a 4 pound cap that apparently got changed during the engine rebuild. I’ll get the correct one and see if that works.

[Plymouthy Adams]

sometimes setting these freeze plugs folks are a bit apprehensive about giving them a good smack, but with the right tools, you can get a good dimple in them and that is the effective sealing action as they expand their outer dimension...I also suggest a bit of Permatex on the sealing surface...

[Doug&Deb]

I agree. Hopefully the correct cap fixes things. I’ve had more problems since the rebuild than you could believe. I just want to drive this car.

[kencombs]

JMHO, but I seriously doubt that the radiator cap pressure has any bearing on a welch plug issue.  The same type plugs are used in unpressurized and pressurized systems up to 14PSI or more.  A properly fitted plug will hold a lot more that 8 PSI.

 

However, my core block from a 56 plymouth had been rebuilt at some time in the past, .010 crank, .040 overbore etc, and had the plugs all just smeared with gasket maker!  Obviously the earlier mechanic either had no confidence in his work, or had to fix some leaks after the fact.

 

A nice clean bore and a little Permatex in the seating area and installed correctly, they shouldn't ever leak.

 

I plan to use a new aluminum radiator and up mine to 12 or so since it will eventually have AC installed and may need the higher boiling point. 

Edited June 11, 2019 by kencombs

[Doug&Deb]

It’s that whole “installed correctly “ part that worries me. I’ve never seen coolant come out of the overflow on the radiator no matter the engine temperature. This car has been a nightmare since the rebuild.

[Plymouthy Adams]

have you properly tested for a bad head gasket or one improperly installed/damaged during install.....an exhaust gas tester for the cooling system is reportedly priced about 35.00 at most big box store.....this is usually your best test...

[kencombs]

1 hour ago, Doug&Deb said:

It’s that whole “installed correctly “ part that worries me. I’ve never seen coolant come out of the overflow on the radiator no matter the engine temperature. This car has been a nightmare since the rebuild.

 

I must have missed the problem description.  Is is leaking, where?  or overheating?

[Doug&Deb]

Not overheating. The freeze plug on the head above number 6 was being pushed up. This is the 3rd plug that’s leaked. There seems to be too much pressure in the block and I’m stumped as to why.

[Jerry Roberts]

Did you retighten your head gasket after the initial warm up after the rebuilding ? If the head gasket is leaking you might see bubbles when you look into the top of the radiator when the vehicle is running . 

[kencombs]

2 hours ago, Doug&Deb said:

Not overheating. The freeze plug on the head above number 6 was being pushed up. This is the 3rd plug that’s leaked. There seems to be too much pressure in the block and I’m stumped as to why.

Since you have no other symptoms I think it is safe to say that too much pressure is not the problem.

 

How about a pic of the plug location, with the plug out?  and the replacement plug.

 

edit to add:  OK that plug is so small that there will be very little expansion if just dimpled in the middle.   The whole dome needs to be flattened in order to get maximum size change when flattened.  Be sure the recess has nothing in it, put some sealer in the corner of the recess and try again, with a new plug.

Edited June 11, 2019 by kencombs

[Doug&Deb]

The mechanic said he re-torqued the head after the first warm up but I will check again. If I remember correctly the engine should be warm not operating temperature.