Need help troubleshooting a temp issue.

[Darby]

I think you have a couple problems. The car is old enough that its had a couple water pumps installed and probably some other engine work; each time some gasket material finding it's way into the cooling system. This will easily clog some passages in the radiator and heater core. Add rust into the mix and like so many here have mentioned, the flow is restricted. The rust is also hard on the water pump seal.
A cooling system is a closed system (as you know) and when there's a leak anywhere it's no longer "closed" and the pressure is lost. As mentioned here, you need the pressure. For every pound of pressure the boiling point is raised 3 degrees so if you have a 15 pound cap, the boiling point will be 45 degrees higher and you probably need that on the hills/mountains with a compromised cooling system any time of the year. The gauge jumping around is probably the fact the sending unit WILL NOT MEASURE AIR TEMPERATURE!! The air introduced into the system from a leak (drawn in every time the engine cools) and the boiling coolant will not show the engine temp on the gauge. The worst thing you could have happen is your gauge go from real hot to real cool, the cool reading says the coolant is gone and you're now destroying the engine. The gauge jumping around is probably air bubbles moving through the system and showing a reading when some coolant touches the sending unit. The gauge will not move real fast at any time with a properly functioning cooling system.
Just my 2 cents - good luck!!

 

[saylor]

open the rad and run the water hose thru it.

unhook the top and bottom rad hoses from the block and run the water hose thru it.

button it all back up.

fill it with 50/50 radiator juice and water.

crack 1 raw egg and put it in.

get 5 packets of pepper from whatabruger and open them and pour them in.

go drive the **** out of it for like an hour.

try not to die -

- saylor

 

[stubs300]

freeze plugs are something I should replace while I'm going through it all right?

It certainly wouldn't hurt just to CYA, but here's the kicker. Unless you pull the engine, your going to have one hell of a frustrating time doing it. Are you up for that? Otherwise cross your fingers and hope that one doesn't blow at a later date. Your choice of radiator is good as long as you ordered the correct one. Question for you, don't you hate buying/having a car with a neglected cooling system? LOL We've all been there at one time!

 

[Big_John]

Shes a cold one today

View attachment 434901

Don't know how cold it is, but be careful of just leaving water in the block. I lost a race prepped 440 block because I didn't drain the block after a night of fall racing. Temp dropped in the high twenties over night and even though I had drained the radiator, the block cracked in the lifter galley. Yea, I didn't believe it would happen, but the cracked block said it all.

 

[demonhead]

How's it going all. I really need some help with a cooling issue I have and I would really appreciate any and all help. A few weeks ago I was driving home from work and noticed my temp gauge alittle higher than normal. This is a 1973 plymouth fury with a 360 btw. So I noticed my gauge alittle bit high and kept an eye on it, the scary part was after a few minutes I had a very sharp and sudden temp spike. My gauge went through the roof and slowly dropped back down. So I thought the worst (blown headgasket even though I wasnt driving it hard) and pulled over. Checked my coolant level, it was alittle bit low and alot of air escaped when I released pressure from my cooling system. Topped it off and checked my oil. I didn't have coolant or oil mixing. So I babied the car home (keep in mind I daily drive my fury 180 miles every day) I noticed my temps would drop when going down hill and would randomly spike and then go back to normal. So anyways long story short I replaced the thermostat and the car was fine for a few weeks. Tonight on my drive home the car did the same thing again. I live in northern nevada its winter right now, we have snow, we are lucky to get above 40 degrees Fahrenheit right now. I've been driving this car daily for over a year now and never had an issue with it even in the hot nevada summer. So why am I having cooling issues now when its colder than hell. I havent changed much recently besides the belts and an alternator and changed the oil. Idk what my issue is, another thermostat? Should I run no thermostat? The first time I had this issue I put in a 160 degree fail safe thermostat and it did fine until tonight. I'm so bummed right now

I had same issues on my 66 Monaco 500. Factory 440 engine and professionally rebuilt. I tried everything: new thermostat, rodded out the radiator (had great flow), rebuilt heater box, new circuit board,etc. It turned out to be the gauge.