Overheats on the freeway but not when cruising around town?

[Kern Dog]

With the original 23 year old hose back on, I started pouring in anti-freeze.
Why? I should have just put straight water in since I was going to need to replace that lower hose soon. Sometimes my logic fails when I’m pissed or frustrated.
I started it up after dribbling fuel in the carburetor vent. It fired right up and ran fine but there is a water leak. I can’t tell where because of the limited light. A flashlight barely helped. It might be from the water pump. F**k it….
I left out of there in a bad mood, pissed that there wasn’t any obvious problem to solve. I called and ordered a 26” radiator from ECP/ Speed Cooling. I have that radiator in Ginger. It bolts in like stock, uses the stock shroud and hoses too. The radiator may not be the problem in this case but I don’t like the fact that hoses are difficult to find and mounting a shroud means some custom fabricated deal.
At home, I put the thermostat in a pan with water and set it to boil.

It is a 180. It sure looks open to me.

After ordering the radiator, I started feeling better about it all.
I’ll have to change to a 1970 correct water pump housing with the LH lower hose nipple. No problem, I have a few to use.
Which water pump would you use?
It seems to me that the one on the right (GMB) would move water better.

 

[Photon440]

With the original 23 year old hose back on, I started pouring in anti-freeze.
Why? I should have just put straight water in since I was going to need to replace that lower hose soon. Sometimes my logic fails when I’m pissed or frustrated.
I started it up after dribbling fuel in the carburetor vent. It fired right up and ran fine but there is a water leak. I can’t tell where because of the limited light. A flashlight barely helped. It might be from the water pump. F**k it….
I left out of there in a bad mood, pissed that there wasn’t any obvious problem to solve. I called and ordered a 26” radiator from ECP/ Speed Cooling. I have that radiator in Ginger. It bolts in like stock, uses the stock shroud and hoses too. The radiator may not be the problem in this case but I don’t like the fact that hoses are difficult to find and mounting a shroud means some custom fabricated deal.
At home, I put the thermostat in a pan with water and set it to boil.

View attachment 1456762

It is a 180. It sure looks open to me.

View attachment 1456763

After ordering the radiator, I started feeling better about it all.
I’ll have to change to a 1970 correct water pump housing with the LH lower hose nipple. No problem, I have a few to use.
Which water pump would you use?
It seems to me that the one on the right (GMB) would move water better.

View attachment 1456764

It's hard to tell which would be better. Standard engines usually had the eight vane pump while A/C engines had the six vane pump but with a different pulley so it spun faster.

 

[Kern Dog]

I’d love to hear an explanation from someone about the engineering behind that.
Non A/C using more blades but a larger pulley versus A/C using fewer blades and a smaller pulley.
My bonehead logic tells me they would balance out in terms of flow.

 

[Photon440]

I think you're right and they would be close in flow. The pulley change was likely to increase fan speed for the A/C condenser, the different pump put the coolant flow back to where it was meant to be.

 

[Don Frelier]

From the pictures it looks like a ton of rust?
Try flushing out the radiator and see what comes out.

 

[Geoff 2]

As I said earlier in this thread, there can be a myriad of reasons for an engine that overheats. It is also an engine that is 50+ yrs old......
It should have shroud. Because Betsy didn't have a shroud does not mean that this engine will run just as cool without one.

While the water pump has a plate behind the blades, what is MORE critical is the gap between the rear of the blades & the housing. Obviously this gap needs to be minimal; too big, & there is an escape route for the coolant; the coolant just gets churned up, instead of being captured & pumped through the engine. I have reduced coolant temps on many Pontiac engines which have a large gap. I weld a plate on the blades & in every case the temps dropped, about 15* on one car.

The cause of the hot running may never be found. It should not be overheating...but it is.
The choice then is to address the over-temps: bigger rad, more efficient rad, fan shroud, smaller pump pulley etc.

I talked about the bypass in post #20. You can reduce the size but it MUST be left open for reasons in post #20. I have found that reducing the size does get the engine cooler. I would plug the hole with a pipe plug or similar & then drill a 5/16" hole in it.

 

[70 GTX-R]

overheating at highway speeds but not in city usually relates to air flow through the radiator. In first pic, I don’t see a chin spoiler. Second pic car has one. I have dealt with this a few times on a few cars. Like the late 80’s camaro. It must have that or it will overheat on highway, may not be answer but something to look at.

 

[Kern Dog]

overheating at highway speeds but not in city usually relates to air flow through the radiator.

Sorry but that makes no sense to me. The grille and radiator are unobstructed.

At 65 mph, air is rammed through the radiator at a rate that I suspect is much greater than any fan can pull in.
I could see your point if this were a Daytona or Superbird but this car gets plenty of air flow.
The deep gearing had the engine at 3300-3500 at 65. That rpm might have dislodged some crud in the block that may have been wedged in place. When I rebuilt this engine in 2020, I pressure washed into the water jackets and the machinist hot yanked it after machine work was done.
I agree, the drain water isn’t clear like tap water but I have not had adequate anti freeze in the engine. I got this car together and went on to other things, coming back to tinker on it a bit more every few months. I forgot that it had no anti freeze.
Regarding the lack of shroud….
I agree that it should have one and it will. All the short trips around the nearby area had me thinking that there was no problem. Lots of classic cars were built and sold without shrouds and not all of them were in cold climates.
I’m going to flush the system out before I install the new radiator. If there are any flakes or crud, I sure don’t want it in the new radiator.

 

[dadsbee]

Lower air dam in place..??

I can cruise around town all day long with the Superbird with zero issues. Hit the highway and the temperature actually rises because the air goes around the nose and not through it.

 

[bm02tj]

The air dam will create negative pressure under car and draw more air through the rad

 

[Mackman]

I believe overheating at highway speed is more about coolant circulation. Fans and shrouds don’t mean anything at highway speeds.

 

[Kern Dog]

That is my thought too. To me, it is basic logic at play.
This car didn't run hot while I was out doing burnouts, hauling *** down the back roads, sitting in traffic and just messing around.

 

[Mackman]

If I were to replace a water pump, I think I would try to find a turbine style impeller as apposed to the paddle type blades. Just me running off.

 

[Sixpactogo]

I too suspect the thermostat to be the culprit. I've had a couple of them fail at Highway speeds in my 78 440 truck over the years. I have no idea how one could close up after being on the road for an hour but I had it happen a couple times. I always ran 180 degree stats and when they failed, I always replaced them not giving them a second chance.

 

[Don Frelier]

I too suspect the thermostat to be the culprit. I've had a couple of them fail at Highway speeds in my 78 440 truck over the years. I have no idea how one could close up after being on the road for an hour but I had it happen a couple times. I always ran 180 degree stats and when they failed, I always replaced them not giving them a second chance.

I suppose it's possible that the stat could close while driving?
I've seen my coolant temp drop down to 176 deg. F coasting in nuetral down the long hills for a couple miles in PA on the way to Carlisle.
Dropping a full 10 degrees from steady state highway operation.
That's the only situation I could think of otherwise it shouldn't if your'e constantly adding heat to the system.

 

[4speed68rt]

My thought was that the thermostat was not closing at all, therefore not allowing the coolant to stay in the radiator long enough to cool. With constant flow on a long run, the coolant will eventually get hot and stay hot if it doesn't stay in the radiator long enough to cool. The thermostat should open and closes constantly.

 

[Don Frelier]

My thought was that the thermostat was not closing at all, therefore not allowing the coolant to stay in the radiator long enough to cool. With constant flow on a long run, the coolant will eventually get hot and stay hot if it doesn't stay in the radiator long enough to cool. The thermostat should open and closes constantly.

I ran my plymouth probably 4 or 5 times with no thermostat and just water.
I don't think it got much over 150-160 degrees even after 1/2 hour running.

 

[eldubb440]

Lower air dam in place..??

I can cruise around town all day long with the Superbird with zero issues. Hit the highway and the temperature actually rises because the air goes around the nose and not through it.

I had a ratty 68 vette that did the same thing

*** you guys would have cut the vette a little slack, it was a fast, ratty convertible with chrome header/ side pipes..... I beat the crap out of it!

 

[Don Frelier]

Lower air dam in place..??

I can cruise around town all day long with the Superbird with zero issues. Hit the highway and the temperature actually rises because the air goes around the nose and not through it.

If you are missing the air dam you could make something ugly pretty easily just as a temporary test.
Flashing and gorilla tape maybe?

 

[eldubb440]

I also had an issue where a higher temp thermostat held the coolant in the radiator longer and cooled better than a lower temp thermostat or no thermostat at all

in support of post 56......it happens

I suppose every situation is unique