Highway heat

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Gartho

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1967 dart GTS 440 car . 727 3500 stall 410 gears, alu rad dual cooling fans ( both pullers ) , engine temp runs 190-195 in town / get on highway ( 90-95 kph ) temp starts to rise after about 15 min, goes to 200-205 as soon as i get off highway temp starts to drop back again / 180 t stat in it. Had a tranny cooler hanging in front of rad ( i know tranny gets warm cause its not locking up ) re-located under car with a fan cooled unit. Doesnt matter on out side temp could be 30 c or 15 c. Any thoughts
 
When you're on the highway, sometimes the fans can actually interfere with air coming through the radiator. Have you closed off all the paths that air can get around the radiator when at high speeds. Too much advance can cause the engine to overheat at higher RPMs. Do you have a temp gun (they are pretty cheap nowadays) to check heat at the upper hose and heat at the outlet to see if the radiator is cooling enough for that big block??
 
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i had a 68 with a 440 ,did the same as your car, ended up switching to a 195 thermostat and driveing down highway it would stay 195
so for a quick switch of a thermostat i would try that first, it fixed my problems,
if you think about it the thermostat stays closed til temp gets 195 then opens so coolant stays in radiator longer to cool , 180 opens 15 degrees sooner,and cant cool radiator down.
atleast thats how i look at it..
 
May be a rad problem, coolant flow, etc

OldManMopar pointed out an odd thing which I am convinced happened to me He claims old radiators after years and hundreds of cool/hot thermal cycling, and crack loose the bonds between fins and tubes. This of course continues to allow coolant to flow freely, but doesn't radiate much heat.
 
I can roll thru a packed parking lot with no air flow once so ever, and temp never goes up. Dual fans in a shroud, sealed to rad. Rpm on highway is 2400-2600 @ 90kph. is it possible cyl temp goes up cause walls r on the thin side? . I don't know what the bore is
 
Typically if cooling at idle is good, but not good at speed it is an air flow issue (or a pulley speed issue). If you have a shroud it can be blocking airflow at speed.

One member had a shroud that was blocking almost 50% of the airflow through the radiator.
 
Got any pictures of your set up? Are you sure the fans are pulling air? My dad has a set of pulling fans built into a shroud and aluminum radiator (Champion set up) on a 440 and it would overheat. He removed just the fans and shroud and it cooled better with no fans or shroud. He went mechanical fan and it never overheated. A lot of folks have found that the shrouds are restrictive and the fans simply can not pull enough air and it is difficult to fit an electric fan large enough to pull enough CFM to cool.
 
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Well, with 4:10's and cruising at 60mph your turning what, 33 to 3500 RPM's?

A 10* rise in temp doesn't seem out of the realm of possibility with the engine working a little harder. Do you have the hood to core support seal in place?
 
4.10 gears & hi stall c'ter doesn't make for a cool running engine. Also, the engine produces twice as many heat producing power strokes at 60 mph than it does at 30 mph......but the same amount of coolant has to dissipate the extra heat.
Your elec fans are probably acting as baffles at higher speeds, & temp goes up.
There was nothing wrong with the factory clutch fan & a good shroud.....
 
Gartho said:
Doesnt matter on out side temp could be 30 c or 15 c. Any thoughts
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From the info you posted, I think this is a key piece of information, and speaks to the cooling fins not sucking heat out of the coolant, or the coolant not transferring the heat in the first place. or your coolant sensor is stuck in a pocket of stagnant coolant.
 
70duste said:
if you think about it the thermostat stays closed til temp gets 195 then opens so coolant stays in radiator longer to cool , 180 opens 15 degrees sooner,and cant cool radiator down.
atleast thats how i look at it..
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If you think about it, that is not how thermodynamics of fluids work. That's not how any of this works. Period. Less time in the radiator is offset by more fluid passing through in a given time.

This urban legend/myth has been popping up for the 40+ years I've been turning my own wrenches and I just can't understand why it keeps coming back. Forget "doesn't have enough time to cool".

Flowkooler has an article that can explain it better than I can:
Doesn't coolant need more time in the radiator to cool?
 
Gartho said:
1967 dart GTS 440 car . 727 3500 stall 410 gears, alu rad dual cooling fans ( both pullers ) , engine temp runs 190-195 in town / get on highway ( 90-95 kph ) temp starts to rise after about 15 min, goes to 200-205 as soon as i get off highway temp starts to drop back again / 180 t stat in it. Had a tranny cooler hanging in front of rad ( i know tranny gets warm cause its not locking up ) re-located under car with a fan cooled unit. Doesnt matter on out side temp could be 30 c or 15 c. Any thoughts
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No pics of the car in question: I knew a guy that had an unsealed hood scoop on his 505 crate motored chevy pick up that did the same thing. His scoop was bringing in enough air to combate the radiator air flow ------------
 
Interesting. My Dart also runs a little warmer on the highway than at idle/slow speed... wonder if the six-pack scoop (unsealed to the single four barrel beneath it) is causing radiator airflow issues too.
Easiest way to test that theory is probably just to duct-tape over the scoop opening and go for a ride :)
 
DrCharles said:
Interesting. My Dart also runs a little warmer on the highway than at idle/slow speed... wonder if the six-pack scoop (unsealed to the single four barrel beneath it) is causing radiator airflow issues too.
Easiest way to test that theory is probably just to duct-tape over the scoop opening and go for a ride :)
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sounds good .
chevy engine was a 502 , not a 505 =my bad .
my friend was always , my stuff is better than ur stuf , kinda guy . Hurt his feelings when I waxed his hi dollar crate motored pick up , w/ my home built 406 sbc / 92 gmc .
Miss him tho , passed at 61 yrs old .
 
I figure there will always be someone with a faster car...but damn few of them built it themselves! Any fool can write a check to the Hellcat dealer...
 
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