65' Overheating

[Ron Luchene]

It's been great getting the Riv back on the road but it is amazing how many things that worked perfectly fine when I parked the car a year ago just don't seem to work properly today. I have plenty to keep me busy for the next few nights.

The car is flirting with overheating at highway speeds. I can drive it at 60mph-65mph for miles with no issues. If I take it up to 70mph-75mph the "Hot" light begins to flicker after 10 miles or so. If I push it, it will eventually come on steady. If I back off to 60-65 she cools back down.

The radiator was boiled about 15K miles ago. The sending unit was replaced last year. I put some octane booster in the last tank of gas just to see if it would make a difference. I have 3.07 rear end and it is running at approximately 3000 RPM at 70mph. If I try to spin the fan manually it will only rotate 1.5 - 2 times so I think the fan clutch is okay but maybe not. I'm running a 50/50 mix of water and antifreeze.

Not sure what more I can add. Has anyone experienced this with their car? Let me know your thoughts!

Thanks - Ron

[Paul K.]

Sounds like a flow problem like the radiator is clogged, but since you boiled it out 15k miles ago, I would replace the thermostat. It may not be opening all the way.

[Jim Cannon]

When the engine is hot, if the fan does not ROAR, the clutch is bad. Spinning it is not a test. Unless you know how old the clutch is, replace it. You must use a fan clutch with the little coil spring in front, no the economy model with the smooth font face.

[JZRIV]

Ron,

Over heating at highways speeds I tend to think its a coolant flow problem. When they boiled the rad, were they confident it was back to like-new performance or just a little better than before? I prefer to have a new rad or new core installed. That way you know for sure what you have.

Why did you have it cleaned? Were you having problems with overheating prior to that?

Have you replaced the water pump recently? There are 3 blade and 5 blade impeller pumps and some autoparts only sell the 3 blade impeller for some reason. If you're not running A/C the 3 or 5 blade impeller shouldn't make much difference but....... a 5 blade can make up for small inefficiencies elsewhere in the cooling system.

These problems can be tough to diagnose and sometimes its a trial and error process. As someone mentioned start with the T-stat. Its cheap and easy to rule that out.

Lastly, make sure your timing is set properly and the vacuum and mechanical advance is working in the distributor. If you aren't getting the proper amount of advance and it is running retarded, it will run hotter than normal.

Edited September 6, 2010 by JZRIV (see edit history)

[Ron Luchene]

Thanks for the responses guys! The engine was rebuilt and the radiator boiled by the previous owner. All I have is the receipts so not sure why the work was done other than the obvious reason i.e. old and needing to be freshened up. Prior to this year I have not had any issues with overheating.

I guess I will start with the thermostat and go from there. I have not checked the timing, vacuum and mechanical advance but the car runs strong so if these are off it would be a slight adjustment.

Todays project was the center support for the drive shaft. Wow...was it worn out! Turns out the bearing is bad as well so a trip to NAPA is in order.

Thanks for the advice and I will let you know how I make out.

Ron

[RivNut]

If the previous owner replaced the water pump at the same time he had the radiator boiled out, he might have replaced it with a remanufacturered pump. As mentioned before, it could have been replaced with a 3 impeller pump instead of a 5 impeller pump. One other trick used by rebuilders to make a pump "look good" is to grind off some of the corroded blades so they look clean, even, and new. This will cause a clearance problem between the pump and the housing. At high speeds, the impeller will cavitate inside the water and not move it.

Boiling out a radiator is okay, but unless the tanks were removed and the tubes rodded out, there may still be a lot of blockage in there. You also want to make sure that the fins on your tubes aren't bent over and not allowing air to pass between them. Alignment of the a/c condenser in front of the radiator is important to allow air flow through the condenser to reach the radiator and pass through it too.

Ed