65 El Camino running too hot

My husband, who is too stubborn to write, has been restoring a 65 El Camino. After he finally got it together, it would overheat when pulling a grade or going at highway speeds. It has a new radiator, new thermostat, hoses, a points eliminator kit. He did multiple block tests with good results. Radiator tests fine, tried differt radiator caps, 3 different thermostats, and even changed out the 327 for a 350 Vette engine. It is still overheating at high speeds and under loads.

Any ideas on what to do next? Thanks!!!

Is the fan shroud in place? Is the radiator sufficient for the bigger engine?

Is it carbureted? Don’t overlook the possibility that it may be running too lean.

To cool that engine you need lots of air; it takes A GOOD FAN, proper shroud and a big enough radiator, and a water pump that works. These should all be checked out. A friend of mine bought a car that had been repaired with a new radiator, which turned out to be too small (car overheated) as it was the size for an non-airconditioned model with a smaller engine. Sorry for the dumb suggestions, but these mistakes are easily made by car enthusiasts.

If the timing is too retarded, this could cause the engine to run hot under these conditions. I’m certain your husband would have set the timing, but it may be possible that the spark isn’t advancing properly.

As usual, some more info would greatly help.
Fan shroud in place? Has the fan clutch been checked?
What type of Vette engine; carbureted, injected, etc. and type of ignition (HEI, contact points, DIS?

If the fan shroud, fan clutch, etc, is known to be good and the vehicle is legitimately overheating then what about the ignition timing? How has he checked this?
Timing that is too far advanced will cause overheating but will also generally cause pinging.
Timing that is too far retarded is usually the cause of timing related overheating problems and this is often reflected in reduced fuel mileage and sluggish performance.

With all the modification what was retrofitted from the 327 to the 350? The 327 water pump turned clockwise while late model 350 engines with serpentine belts turned counterclockwise. And even if the water pump is turning correctly what about the fan?

If it’s overheating at high speed, the shroud isn’t going to make a difference. At 70 mph, the fan won’t be pulling in any air, it’ll all be forced through the radiator by the velocity of the car. If it was overheating at idle and low-speed cruise, then I would say for sure it could be the fan or shroud, because that’s when the fan is most effective.

Are you saying that it overheated when it had a 327, and it overheats now with a 350? Did he use any parts from the 327 on the 350?

Also; check the alignment. I bought a pickup truck that was badly out of alignment and it really made it hard to move. I got four more miles per gallon after the alignment. A worn idler arm could cause the problem. Make sure the thermostat is installed in the right direction. The temperature numbers usually go toward the engine. Check the oil in the rear axle. If the vibration dampener is from the wrong engine, the timing mark could be way off. The 305 was different than the 350 for example.

Plenty of good advice here. In addition:

1.) Make sure that the lower radiator hose isn’t sucking closed at higher engine speeds.

2.) Make sure, also, that there is adequate airflow through the radiator, meaning that the grill is not blocked or modified.

3.) If these are ok, the radiator may simply be too small to handle the engine’s heat load, or may be partially blocked.

Does anyone ever reply regarding the results of checking the advice given here? Not that I am missing anything important by reading and posting here but I am curious regarding my SWAGs.

Kind of a shame that we seldom get enough info to begin with and follow-up questions are never answered.
Your WAG about the water pump is a valid one and not off the mark. I’ve never seen the water pump fiasco on a Chevy but have seen it on a Ford.
The water pump on the V-belt cars turns in a different direction than the serpentine pumps. Since the pumps can be interchanged by swapping the pulleys only this means the pump impeller is spinning the wrong way.

Does he have a fan shroud? If he doesnt that would cause a lot of it. If he does try an electric fan and a bigger radiator.

Above 45 mph the engine will not overheat with the fan and shroud removed if the rest of the cooling system is in order.

yes, he is right, my dirtbike had the same problem, running lean is also very bad for your motor