I know this issue has come up before, but the previous thread(s) didn't really help me...
My 65 Skylark is overheating when cruising or idling. Engine is a stock 300 2-barrel with the fan shroud in place. No AC. A friend of mine has a 65 that never gets hot, even though he has a stock radiator and a 4-blade fan. I, on the other hand has tried every trick in the book to keep cool.

1. Radiator has been rebuild. Thickest element that could fit the original tanks was installed. He even had to expand the lover tank. This stopped the radiator from boiling, but still made my idle unstable when cruising.

2. Added 16" electric fan in push mode. Helped some, but not enough.

3. Removed electric fan and original 4-blade fan, and installed an 18" 6-blade flexifan. This sucker (sorry) really moves some air, and the lower radiator tank is quite cool to the touch. Still didn't solve the problem.

4. Attached a thermometer instead of the stock switch in order to se whats going on, and the temperature goes to 250 °F (max reading) very fast on startup and stays there. Seems it's not the radiator/fan that's the problem. How can I troubleshoot any other internal problems, without tearing the engine apart.

I'm building a buick 350 engine that'll replace the 300 so I can rebuild the 300. Maybe I should speed up the work on the 350, and not worry about the 300 now since I'll rebuild it later on (matching numbers).

Regards
Peter Ettrup
webmaster:at:coolcruisers.dk (webmaster@coolcruisers.dk)

You didn't mention replacing the thermostat, did you? After that, I would try a bunch of flushing to clean the block a bit. If you get a lot, I would then pull the rad and wash it out seperatly.:thumbsup:

If you haven't checked the thermostat and the block isn't really plugged, then there has to be a blown head gasket or a cracked head or something...250+ is pretty hot...maybe have a radiator shop do a pressure test on the system to see if there is any leakage to start...

Replaced the thermostat and checked it first, together with the old one. they opened at the exact same time.
Coolant is superclean. I flushed it completely and used radiator cleaner a few years back, and I change the coolant every 2'end year since that. It doesn't loose coolant unless it's really warm, there's no mayonaise in the oil and it doesn't smoke.
I checked the thermometer in boiling water (showed 205 °F, allmost right). Pressure testing the system is my next move. That should show if the head gasket is blown, but a compresion test should show this as well?
Other Ideas: cavitations in the waterpump/front cover? :confused: