Hi all,

I'm fairly new to the Mopar world and have my grandfather's 64 Slant Six Valiant completely restored to original. Problem is, I cannot overcome an overheating issue. To date, I've had the rad recored, new thermostat, all new hoses, filters, fluids, block professionally flushed, carb rebuilt and the timing's spot-on. But am still having a meltdown. Any suggestions? Fingers now are pointing at the water pump.

Thank you!
Tom

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Tomz Val

It is unlikely your pump is the problem unless it is leaking or the impellor is loose or eaten away. Changing the water pump on a slant6 is easier than any other engine I've ever done.

Before you do that, first do an (air) pressure test and see if you've a leak somewhere in the cooling system. If it doesn't leak then, fill it with water, & repeat. If it still doesn't leak, warm it up and repeat the test.

Even a fairly small leak can cause big problems. I had the thermostat housing flange warp and cause terrible problems, even though it didn't leak much when I tested it cold - but leaked pressure (but not noticable coolant) hot.

If you've no leak, and your cooling system is in great shape, you may be generating excess heat. If an exhaust valve isn't opening sufficiently due to a warn cam, lifter, etc. you could be depositing much more heat that it was designed form.

You could also have low airflow over the radiator; a missing shroud
would do that.

IR thermometers are very cheap now; you might get one and look for hot spots if all else fails.

Go ahead and pull that valve cover to check the valve timing. I suppose the impeller of the coolant pump could be broken, or junk blocking the passage- it would be quick to pull it and check. The stock '64 didn't have a shroud, but the model with AC did, and a 7-blade fan too. If all else fails, the added cooling of that setup might do the trick. Also, exactly how high is the temp going? The guage could be off and maybe it is not that hot.

Is the rad cap old? if it doesn't seal properly the rad wont pressurize and boil over. Ive done it so has alot of guys, its sometimes overlooked even though its right in front of us also the thermostat, was it correctly installed with the spring facing down into the engine? youll know if your car heats up but your upper hose stays cold (another common mistake) worst case senario, your rad might be plugged. Recoring a rad makes no gaurantees, I had one fall out in less than a year

Thanks to all for your quick replies. I also did add a new rad cap along with the myriad of other goodies. I have not had the valve cover off however. Hopefully the radiator's been recored correctly and that's not the issue, but who knows.

I will see about an external temp testing to be sure the gauge is correct as well as check for leaks around the pump (just in case).

Thanks!

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Tomz Val

It's easy for sure, but a big block Mopar is even easier.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

Let's try and narrow-in on the problem a little.

Does your overheating occur at low speeds (idle, stuck in traffic) or at high speeds (say, over 45 mph)? Or both?

What indication of overheating do you have, aside from the dashboard gauge reading high?

If you've got a new/recored radiator and the gauge is going "H!", then the first thing to do is check whether the gauge is telling lies. Run the engine with the radiator cap on the half-stop (cap is on, but not locked down) until the temperature gauge gives its too-high reading. Use a kitchen candy thermometer to check the top tank temperature with the engine idling. The result will tell you whether your engine is actually overheating, or if the gauge system simply needs attention—such as a new sender or a rubbed-off piece of sender wire insulation repaired.

If you are actually experiencing overheating, we need to narrow it down to an airflow vs. water flow problem. If it runs cool at road speeds, but heats up when standing still or in very slow traffic, that's usually an airflow problem, either physical blockage of airflow through the radiator or improper installation of the radiator fan (...backwards...?). At higher road speeds, you usually have plenty of air going through the radiator from the car's forward motion, so overheating under those conditions is generally a water flow problem (clogged or gunked-up system, failure to include the coiled support spring in the lower hose, etc.)

Should also ask about your new thermostat. What is its temperature rating? A lot of the catalogs incorrectly list a 195° thermostat as correct (it isn't, 180° is) for your application.

What kind of radiator cap (pressure rating, brand and type) is installed?

Lean mixtures, vacuum leaks, retarded ignition timing and restricted exhaust system can also cause hot running, but let's make sure the cooling system is all the way debugged, first.

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