I am having some trouble with my car over heating. (64 Valiant with 225) I have rplaeced the radiator with a three row, new water pump, new stat, I ahve flushed the block, new hoses. The trouble is when I am on the Highway, the car will start to run hotter and continues to get hotter as long as I am on the Highway, when I drive it around town i have no trouble. Any thoughts??

Is the fan belt in good condition & tight?

A new radiator installed in front of an old, sludged-up engine, can quickly become clogged. Drain the coolent and inspect the top of the core tubes, if you see scale and junk stuck in the top of the tubes, the engine & radiator will need to be cleaned.

Note, I use a course stainless steel screen in the upper radiator hose to trap the large "chunks" before they get into the radiator. On older engine, I am always surprised on how much scale gets trapped in the screen.
DD

It sounds like you've covered the basics pretty well. The fact that it does well around town but not at highway speeds is an interesting clue. How fast do you normally drive?

My '64 with a two-row Aspen radiator holds steady at 70 MPH, just a little over halfway on the temp gauge. It did the same with the stock radiator.

Is your thermostat opening properly?
Does your lower hose have a spring in it to prevent collapse at higher engine speeds?

How is your timing set?

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"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

Don't forget to do a pressure test; even small leaks can cause big overheating problems. The radiator caps can get weak, especially after 1 good overheating.

I drive about 65-70 on the highway. As far as any leaks i do not see any and I just put on a new radiator cap. I also set the time to the specifications. I do not know if the bottom hose has a spring, it is a new pre formed hose. I did put a new fan belt and mad sure that it was tight and the car ran even hotter then before? Last month I checked the core tubes and did not see any thing. I drove the car yesterday on a 70 mile round trip and it was running about 200-210 on the highway, how ever it was only 94 degrees, today will be much hotter. Thanks for the help

Hey Saltydog.

I just got my '64 Valiant 3.7 slantsix back on the road after a year of looking at every overheating avenue. The culprit? A crack in the exhaust manifold right down the middle. The fissure was sending superheated gas up through and porting right under the carb and had also trashed the manifold gasket. Apparently, the break point on the pipes is a common weak spot for 60's slant six motors.

I had it successfully stick welded by a pro for about $150 (as compared to an OEM pipe for $500). The gauge is the usual Mopar gauge and is about as accurate as a scud missile, but despite it reading hot the car's hottest temp is now a cool 170 degrees.

Also beware the timing, sending unit, a 160 or 180 degree thermo, and the right pound pressure radiator cap. All these can cause you grief!

Good luck to you!

Thanks for all your help! I do believe that my exhaust manifold has a crack, which will be getting fixed soon. I hope that will fix the problem. Thanks

We're going through the overheating issue with my son's '81 D150 /6. Replaced the head in November, flushed the engine, new water pump, hoses. Inspected the mainifolds and everything looked ok. Went through the issue of vapor lock/fuel boil and replaced the fuel lines, and carb (1bbl) no more problems there.
He came home the other night and steam is coming out from under the hood, we let it settle down for a few hours and cool and found almost nothing in the radiator.

Didn't find anything on the dipstick or in the cap or breather, so I'm assuming it's not going into the head. Where did it go?!
Replacing the radiator today and we'll see what happens. I'd be interested to see if you find a crack in the manifold.

I'm really hoping it's just a gunked up radiator.

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If it ain't broke, you didn't have fun playin' with it.

'74 Duster
'74 Valiant

I like that idea. How do you attach the screen? any pics?


Thanks

TopHat

There are various ways to put a filter screen in the system. If you want clean & elegant, see the link in this post.

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

once again Dan you are the Man

Might just be me, but my thoughts are also going to a lower hose collapsing. Especially if it is at speed/rpm related. Thought perhaps supported by the new fan belt tightened correctly made it run hotter. Have someone rev and hold the rpm up for you while you check the hose for flex in. Also, make sure that the hose is the correct length. Don't know about your application or brand hose you purchased, but some are made to be "cut to fit" even though they are molded hoses. Could possibly be the case that the hose is the correct shape etc., but the hose needed to be trimmed a bit shorter to fit in a "relaxed" position. Perhaps it is on, but too long and is kinking the hose shut a bit or creating a flat spot instead of round. Under the draw of coolant at higher rpm the hose is then sucking flatter and reducing the coolant that can flow through the system.

I'd look for the hose squishing down, check the thermostat is opening, make sure you do not have an air pocket in the system, perhaps could be an issue with the water pump and cavitation (sp?).

The temp range you list is not that uncommon from a normal operating range. Perhaps a tad high, but many cars run a 190-195 thermostat for optimum running conditions. A thermostat in this range is going to put you into that general area for normal operation.

As an example, my '71 dart calls for the factory replacement thermostat to be a 190 degree. The 180 and 160 are listed as alternates.

Also, may have missed it, did you replace the radiator cap with a new OE pound one? I might be remembering this wrong from the old parts days and the Stant training, but seem to remember that for every pound the cap is rated that is worth three degrees. Caps loose pressure over time so keeping a good cap to OE pound is worth the few bucks.

Best of luck on it.

Cheers

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From Mopars to classic Minis and back to Mopars in 19 years flat!

Will work for roast chicken crisps!!

A higher-pressure radiator cap does not reduce the temperature at which the system runs. All it does is increase the temperature at which the coolant boils.

Changeover from 180° to 190° thermostats was in '69 on Clean Air Package cars. Changeover to 195° thermostats was in '72 (California), '73 (across the board).

A careful check of the radiator hoses for kinking and collapsing is a very good idea.

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