Overheats on the freeway but not when cruising around town?

[cosgig]

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 mentioned this a couple pages ago, and it was met with a “airflow is it the problem at highway speeds” speech. The idea that highway speeds Ram air through the radiator is not completely correct. The radiator support is an air dam, and trapping the air in front of it by having the upper and lower seal in place is the first step, like I said, without them it’s like sucking through a straw with a hole in it. But even with that, the air dam needs to have a vacuum to suck the air through the radiator, the more vacuum, the more air follows air through the radiator. It’s like pouring liquid through a funnel, dump the liquid in all at once, it just overflows, swirl the funnel and liquid creates a vortex that draws more fluid down the hole.

Now, onto the flow, the pump is moving liquid, so that’s not the problem, the thermostat opens at a certain temp, but it also closes at that temp or less, allowing liquid to stay in the radiator longer. People think because they run a 160 thermostat that their car should run 160, but that’s not the case. The motor runs in a certain temperature range, and putting too low of a thermostat in will just keep it open all the time, counteracting the idea of cooling the liquid longer in the radiator. But you can’t tell people that, they just don’t understand. Not saying this is the OP, but I see this question all the time.

So, @Kern Dog, is the upper and lower seal in place? Do you have a shroud and clutch fan? Are you running a 190 or 195 thermostat as they came from the factory? Is the lower hose collapsing? Is your cap a 16lb cap, and is it working? Don’t discount any aspect of the system because you don’t “think” it’s the problem, it all works together. Confirm that all items are in working order, and in place, process of elimination.

 

[Rick62]

If the radiator doesn't have enough cooling capacity the car can overheat because the water doesn't stay in the radiator long enough to cool it and the thermostat stays open.

 

[Kern Dog]

So, @Kern Dog, is the upper and lower seal in place? Do you have a shroud and clutch fan? Are you running a 190 or 195 thermostat as they came from the factory? Is the lower hose collapsing? Is your cap a 16lb cap, and is it working? Don’t discount any aspect of the system because you don’t “think” it’s the problem, it all works together. Confirm that all items are in working order, and in place, process of elimination.

It does have a clutch fan....the famous Hayden 2747 stubby. I'm not familiar with what you're calling a "Lower Seal". My red car has the rubber seals on the hood but I'm not sure if Jigsaw does. It does have a 16 lb cap that seals. The thermostat was a 180. I tested it in boiling water and it did open and stay open.
What IF I left the house and the coolant level was simply low? There is no way to know now but wouldn't that be a kick to the crotch??
3.91 gears and freeway speeds could heat up an engine especially without the proper amount of coolant inside. An engine that is all iron sure takes longer to cool down than one with aluminum heads.
It would be nice to know if all of this came down to something so simple.

 

[streetwedg]

I was having the same problem with my GTX . I finally figured out the the water pump pulley was too small, causing it to flow too fast . I changed to a larger pulley and slowed the flow. Fixed.

 

[Mackman]

I think it’s always best to move the water as quickly as possible.

 

[Don Frelier]

I think it’s always best to move the water as quickly as possible.

Not necessarilly it takes time to cool off the hot stuff and make it cool before sending it back into the engine.

So taken to the extreme here is a hypothetical example:
Say it only took 1 second for the hot engine discharge to go back in the block there is no way you could take out 20 degrees of energy.

 

[Photon440]

Turbocharger after-coolers work extremely quickly, a radiator doesn't care what speed the fluid inside is moving. If it is hotter than the outside air, it will transfer heat. A slow moving coolant in a radiator means that by the time it leaves the cooling fins at the other end it is already cool enough to stop expending heat, while the coolant inside the block is still getting hotter.

Moving fast means that the coolant cools off a little less, but the actual volume of fluid losing heat is greater.

 

[cosgig]

It does have a clutch fan....the famous Hayden 2747 stubby. I'm not familiar with what you're calling a "Lower Seal". My red car has the rubber seals on the hood but I'm not sure if Jigsaw does. It does have a 16 lb cap that seals. The thermostat was a 180. I tested it in boiling water and it did open and stay open.
What IF I left the house and the coolant level was simply low? There is no way to know now but wouldn't that be a kick to the crotch??
3.91 gears and freeway speeds could heat up an engine especially without the proper amount of coolant inside. An engine that is all iron sure takes longer to cool down than one with aluminum heads.
It would be nice to know if all of this came down to something so simple.

It would be nice if it was just low coolant. I’m sure you know, but Mopars like to have a couple inches of air space below the filler neck, but I get nervous when I open the radiator and see no coolant at all.

 

[Kern Dog]

With a factory type down flow radiator, I understand that you are supposed to leave room for expansion. This radiator is a cross flow type.

 

[Sixpactogo]

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.

Yeah, I guess maybe that could be what happened to mine. I remember it filled the puke tank to overflowing and popped the cap on the puke tank. I never gave it a chance to do it again. I replaced it immediately.

 

[Joe Jacalone]

Definitely not and airflow problem, so has to be coolant flow. Either thermostat is not opening all the way or water pump is not turning enough due to slipping belt or passible a bad impeller.

 

[Butch Harley]

I bought a summit thermo DID NOT OPEN almost overheated a fresh motor!! Witch would have void the warranty! Bough a stant.

 

[Carcinogen]

Possible the piston clearance is not enough and when RPMs go up tight piston to wall friction is causing heat.

Dad had a fresh rebuilt SBC that would idle and run ok at lower revs but would heat up at higher RPM. Honing bores for more clearance fixed problem.

 

[Jeff Peterson]

I'm not familiar with what you're calling a "Lower Seal".

 

[Kern Dog]

Thank you. I don't have that on either car.

 

[1KoolBee]

Kern Dog, in general, low speed overheating is airflow and high speed (above 35 mph) is water flow , so I believe you are correct that it’s a water flow problem. So thermo, lower rad hose collapsing are likely suspects. Or maybe rotten impeller on pump or clogged radiator, but less likely since it’s newer aluminum. I had a stuck “hi performance” thermostat once on my truck and it caused heating problems all the time, plus big time puking out cap from pressure problems. Hopefully not an internal leak like crack or head gasket. Coolant will help with boil over if cap is good. Good luck!

 

[Purepony]

I’m not running a shroud on one of my mopars, and it doesn’t overheat. I really don’t suspect a shroud. I also don’t have a fan clutch in the car so it’s running at all times no issues there either.

If the water pump wasn’t leaking, I would’ve left it on. I would suspect two things they sound small but you would be surprised.

The first thing I would do is change the thermostat it’s cheap insurance anyway, I would get maybe some thing around 175-185 degrees

The second thing and everyone’s probably gonna laugh but the radiator cap .

If it’s an older That could be an issue since they have a valve and they’re rated.

Assuming of course, that your hoses are good, assuming that the water pump is flowing, assuming that your radiator works.

I’ve run the car with water when I’m doing checks like replacing a water pump or I had a leak and then once all the leaks or everything is running well I drain it and replace with antifreeze. I actually ran my Challenger for over a year with water, and I never had any overheating issues and I’ve driven the car on very hot days.

If those two items don’t make a difference my next move would be the radiator m.

Best of luck.

 

[Purepony]

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.

Same here. I ran water in my Plymouth I ran it in the challenger while I was diagnosing a few temperature issues or replacing some parts

You don’t wanna get a habit of doing that, though the water could rust It doesn’t have the capabilities and benefits of the antifreeze long term

 

[Orig69]

With a factory type down flow radiator, I understand that you are supposed to leave room for expansion. This radiator is a cross flow type.

I myself would make sure to remove as much air from the cooling system as possible before driving it again.

 

[6872n73]

Hot cooling pressure test on your cooling system? Head gaskets?
one of these might help see whats going on