Overheating Problem

[66PolaraRag]

I'm having a problem with my Polara overheating on the highway. I can drive it around town with no issue and even on State Routes at 55-60, but on the interstate running at 70+ it will overheat every time. It's a 383 4 barrel without air. I have replaced the temperature sensor, radiator, fan & hoses. The water pump is less than a year old. The heads have been checked. I've even tried an auxiliary electric fan. I'm not sure what else to look for. Any suggestions?

 

[detmatt]

Does the lower hose have a spring in it to keep it from collapsing?

 

[saforwardlook]

When was the last time you rodded out your radiator, and does the coolant look rusty at all? Sludge will collect at the bottom of your radiator over time and block coolant flow especially at freeway speeds.

 

[Xenon]

Where the above are good places to look also look at the thermostat...
One to make sure there is one in there and that it is not too cold of one..
A 190 degree would be a good start ...

 

[Polaraco]

Seems to me there was a filler pan between the bumper and the rad support on the bottom. If it's not there, you may be losing the air to under the car. Is there a front valance? They could be just as important.

What doesn't make sense is it's OK at 60 but not at 70. True there is some dynamic air flow changes at 10 MPH faster. That's what made me think of the valance.

I had a 70 Newpie that did that. The rubber filler between the rad core and the front bumper was missing. Replaced it and off we went.

 

[cbarge]

Do you have Fan shroud?

 

[Polaraco]

Do you have Fan shroud?
View attachment 194323

Good point. But they didn't always have one

 

[cbarge]

My car did not come factory with one but made sure I installed one

 

[cbarge]

Seems to me there was a filler pan between the bumper and the rad support on the bottom. If it's not there, you may be losing the air to under the car. Is there a front valance? They could be just as important.

What doesn't make sense is it's OK at 60 but not at 70. True there is some dynamic air flow changes at 10 MPH faster. That's what made me think of the valance.

I had a 70 Newpie that did that. The rubber filler between the rad core and the front bumper was missing. Replaced it and off we went.

Again,my car did not have a filler pan but I installed one..

 

[Polaraco]

My car did not come factory with one but made sure I installed one

Cheater. LOL

 

[72Fury]

Good point. But they didn't always have one

Or overflow tank. Still a good idea.

 

[mr. fix it]

What about the water pump? was it replaced when you did the project?
if so did you compare the old pump to the new pump fins?
Was the radiator inspected when you had it out of the car?
Perhaps it is undersized for the car.
It could be again as suggested a stuck or slight stuck thermostat.
Lastly, which way is the fan blades facing? if you install it backwards it will not draw air correctly (but this would be an in the city driving not highway issue...)

Lastly lastly, what about the ignition timing? an engine with bad timing will cause heating issues as well

 

[cbarge]

Retarded timing can cause overheating. I agree.

 

[mr. fix it]

Retarded timing can cause overheating. I agree.

Dealing with the latest snowflake R-Tards causes me to overheat too!

 

[azblackhemi]

You said you replaced the radiator. With a new one or at least known to be good?

 

[livininharrow]

Do you have Fan shroud?
View attachment 194323

I would think a fan shroud would be more important at lower city driving speeds. he mentions overheating at highway speeds where you should have all kinds of air through the rad. I don't think its an air movement problem. maybe the rad cap is not allowing the cooling system to be pressurized enough. just a thought.

 

[Mudeblue]

I'm having a problem with my Polara overheating on the highway. I can drive it around town with no issue and even on State Routes at 55-60, but on the interstate running at 70+ it will overheat every time. It's a 383 4 barrel without air. I have replaced the temperature sensor, radiator, fan & hoses. The water pump is less than a year old. The heads have been checked. I've even tried an auxiliary electric fan. I'm not sure what else to look for. Any suggestions?

Are you sure it is overheating or is it just the reading on your heat gauge? I had the same issue but was the heat gauge with the voltage limiter in the gas gauge. Changed it out, end problem. Just a question?

 

[cbarge]

Are you sure it is overheating or is it just the reading on your heat gauge? I had the same issue but was the heat gauge with the voltage limiter in the gas gauge. Changed it out, end problem. Just a question?

Another good suggestion,,,but think....If the temp gauge was pegged,so would the fuel gauge.

 

[cbarge]

You ask three people,you get three answers...
My recommendation would be...
Using a hand held laser temp gauge,when it gets hot open the hood and point it to the thermostat housing.
Does it match the temp gauge in the car??
No?? change out the gauge since you have a new sender.
Yes? Dig deeper.
Pressure test the system and rad cap.Should hold at 16 pounds.
If rad cap does not hold,replace it.

Has the engine sat for a long time? Lack of preventative maintenance from previous owners??
I had seen big blocks have water jackets full of crud that causes overheating.
Knocking out freeze plugs and flush out the block never hurts.Also reverse flow flush the heater core.

Another possibility is the system is cooling TOO FAST
As mentioned,the water pump came in different flavors. Too many impellers and it can push the coolant to the point it cannot get a chance to run through the rad to cool.
With the laser check the difference in the lower rad hose and water pump housing,etc.
Adding a fan shroud,a 5 or 8 blade clutch fan helps,too.
Check the timing/fuel mixture and adjust if needed. Today's gas runs leaner and adding a few degrees/fattening u the mixture does not hurt--just keep it from pinging.

 

[66PolaraRag]

Thank you all for the suggestions! I really do appreciate the help!
The thermostat has been replaced, the filler pan/front valance is there and the lower hose is new with the spring in it. The radiator is a new all aluminum replacement that was supposedly sized for the car. It has a new cap with a temp gauge in it. When the gauge in the car says it's hot, so does the gauge on the cap. I've also installed a overflow reservoir to keep it from puking all over the place when I stop. I thought about trying a high flow water pump next. I'm pretty convinced that it's a water flow problem and not an air flow issue.