'69 Cutlass S , 350 2bbl.... I just rebiult it a month ago , and while running it to break in the cam, I had problems with the rad cap, anyway it wasn't full enough I think, and it overheated, maybe cracked a head. So now, about 3 weeks later, I tryed to run some block sealer through it,, and while running it a fast idle (1000) after about 20 minutes it got hot again. Goes up to around 180 -- 190, holds for a while then gradually creeps up,,even with an added fan in front of the car. Now, a few years back, we used to do alot of parades, and it would get hot idleing in the parades, so I added a small fan in front of the rad. Also reving it up for a while seemed to help......now, I do have the fan shroud on ( I didn't the 1st time ), but I don't have the rubber air sheild, or air dam, on under the rad.( as I don't have the frnt bumper on yet ) water pump is only about 2 years old, I'm thinkin maybe the rad need cleaning.... Question ; is it normal for this car to be that delicate for overheating ????????thanks

 

How much overbore is it? What temp is the thermostat? How hot does it get? 2 core radiator? The radiator could need cleaning. I use distilled water and antifreeze in mine.

 

.030 over, flat top , 10.25 pistons, ''thumper'' cam, original radiator, and it gets hOT^ ! I think it was a new 180 thermostat, I'll check the WP again as soon as it cools down Seems like it just slowly creeps up the more you run it . Filled system with water today, got the air out, held at 180, whent up the road a 1/2 mile and back tenmp started going up again. called Mundello this evening, he said (Junior) to take thermostat out and put a restrictor in it instead....any thoughts on this ? I'll check seeif it's 2 or 3 row core.............

 

If thats the original radiator I think I would replace it anyway. That could very well be the problem. Also should always use distilled water as 455man said. This will cut down the electrolyte build up, the white chalky stuff.

 

I think a car should stay at operating temp with a thermostat in. I would not use a restrictor on the streets. I have a 2 core radiator in my 350 2bbl. You might want to upgrade to a 3 core if so. Or just get the original rebuilt. What gear you running?

 

it has a 3 core rad, been in there as long as we owned it , going on 20 years....timing is 5 degrees..Water pump 2 yrs old, maybe a 1000 miles on it,so,,,,,,,,,,,, why should it over heat now with the ''new'' motor ? Was O K , before ?????

 

New engines are sometime very "tight". Also your new engine probably has a lot more HPs than an old tired 350, which creates more heat. Just my guess, good luck.

 

Yeah they say bored out motors will get hotter. You have a bigger cam so more fuel is getting in. New motor is tighter, then the radiator has 20 yrs of water deposits in it. I'd think 3 core should cool it so you probably need it rebuilt.
Also make sure you are not running too lean of an air fuel mixture. Does it over heat sitting still or on the highway or both? Sitting still only means the fan is not pulling enough air. Maybe the clutch fan. If it overheats on the highway its the radiator.
Did you install an overflow tank? I'm getting ready to on mine. That would help with cooling.

 

overheats ALL the time , never thought about the fan clutch....also seems to have flat spot when you first accelerate......NO fan clutch, direct drive

 

another question;;what timing are you guys running ? my book said 6, mine right now is 5

 

I'd rebuild that radiator (at least have someone pull the tanks and boil and rod it out) and replace the fan clutch with a new thermal type. Do not use a restricter they do not work for street use the engine will continue to hotter and hotter the longer you drive.

 

I'm taking the rad in tommorrow , will see what the man says , will maybe be done monday