my 65 dart 270 with the 225 and a 3 speed auto tends to overheat at highway speeds, it doesn't seem to do it at speeds below 50 or so, but anything more than that and it over heats within 5 or 10 minutes, i've checked my fluid levels and everything checks out, the thermostat was replaced not to long ago, and it is deinatly flowing because i can pull the radiator cap and watch the fluid moving. The car does not seem to overheat went driving at low speeds or went sitting in traffic. It only does it on the highway which is an issue, because i have a 20 mile trip to and from work each day 90% of which is 65-75mph traffic. any help ould be great.

How clean is your radiator? It might have debris in front of it blocking airflow!

the radiator is pretty clean from what i can tell, it doesn't look like there is a lot of anything in there, also i have 2 electric fans, on pushing and one pulling, could this be blocking the radiator or should it be ok?

Wow, two electric fans how is the polarity on the motors are they pushing and pulling in the right direction? Get an airhose and try blowing out the core from rear to front.

well i didn't install the fans, one is deinately going the right direction, the one that pulls, however the other is hard to tell, and it seems to run the same whether its connected or not, and i got a compressor at home so i'll blow out the rad and see what happens

I had similar problems before, too, and it turned out to be a blockage in the radiator. The coolant still flowed (could see it moving with the cap off like yours), but it was not being cooled effectively. I took the radiator to a good radiator shop to have it flushed. Forget about trying to flush it well at home. Since then I have been using premixed coolant always (to avoid minerals in city water) and I have not had a problem with it since. Make sure you always use distilled water with your coolant if you are not keen on buying the premixed stuff.

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'68 Dodge Dart 4dr Sedan

This is probably not an airflow problem. (Airflow problems tend to show up as overheating in low-speed/stuck-in-traffic situations). Pusher fans, depending on how they're sized and mounted, can block too much airflow through the radiator, though.

Just because water is flowing through the radiator does not necessarily mean it is being adequately cooled. How old is the radiator core?

How long since a careful tuneup with a check of all of the ignition timing parameters (basic timing, mechanical advance, vacuum advance)?

What's your gas mileage and power like at the higher speeds? Exhaust system restriction will cause high-speed overheating.

When did you start noticing this problem? Any changes immediately beforehand?

What kind of thermostat did you put in? 180° is the correct rating.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

the rad is fairly new, about 2 years or so
the car has not been tuned since i've had it ( about 2 months) no telling how long before that though
also power is good through out, so it can't be that far off, and i'll get back to you on milage cause i just got the speedo fixed last night
also the exhaust is all except the manifold

the rad is fairly new, about 2 years or so
the car has not been tuned since i've had it ( about 2 months) no telling how long before that though
also power is good through out, so it can't be that far off, and i'll get back to you on milage cause i just got the speedo fixed last night
also the exhaust is all new except the manifold

Y'never know. Check it all out.
Does the manifold heat control "heat riser" valve move freely, or is it stuck?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I have had radiators develop blockage in as little as 6 months to a year, so don't count out the possibility yet.

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'68 Dodge Dart 4dr Sedan

the riser does move freely, so im pretty sure thats not the issue
and i guess i can always get the rad re cored, or would you recommend a new rad all together, and do they make an oversized one that will work

Rare nowdays, but a collapsing bottom hose (which is why the bottom hose use to have the steel spring inside).

At high engine speeds, the suction on the outlet collapses the bottom hose, and flow is reduced.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

i think the hose is about 6 inches longer than it should be and if its soft enough to twist into a half circle than its probably soft enough to callapse

Good point! I forgot about that. I had that happen once and went as far as getting an NOS hose to take the spring out of. Now I have one of those universal hoses that has reinforced ribbing throughout.

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'68 Dodge Dart 4dr Sedan