Will swaping a smaller water pump pully from a 81' slant help or hurt my large pully 68'? I already have a later style two core radiator with matching shroud and thermal clutch fan.

Dart68

You don't need to spin the water pump any faster, and there wouldn't be any advantage to doing so.

2 rows of tubes in the radiator isn't a lot. The factory HD radiators were 3-row.

Is your car overheating, or...?

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

It runs hot on the freeway after about 25 minutes at 65-75 mph speeds. I should probably check for timing chain slack since it has been hard to start lately. Could I have a small head gasket problem? Losing coolant, but no visible leaks until it over heats. Should I get a factory HD 3-row or an after market aluminum 2-row that duplicates the factory unit in appearance and fit?

Thanks-Dart68

"Hot on the freeway" does usually indicate a water flow problem, since the forward motion of the car will provide enough airflow (UNLESS the fan is installed wrong way round!). But, the standard-sized water pump pulley works just fine on a system in good condition. Timing chain slop/slip/stretch is a good thing to check. You may have crud built up in the block and need to pull the starter, remove the rearmost freeze plug, dig out the scunge with a long stiff wire, then flush it all out the bottom radiator hose with a high-pressure nozzle through the freeze plug hole. What's the status of your thermostat?

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

Thanks Dan. I'll check on the sludge build up. I'm going to check for timing chain slack now. I've heard of head gasket failures that didn't involve coolant and oil mixing or even that white smoke blowing out the tail pipe from water pouring into the combustion chamber. I'll try the obvious for now and go from there.

Thanks again SSDan-Dart68

Something else comes to mind. How old is your lower radiator hose, and does it happen to have a spring inside? Sometimes, as the lower hose get old, it gets soft, and can collapse at high water flow demands. (Hiway driving.)
If yours is old and soft, and doesn't have an internal spring, you might want to change it out.

Roger