Can anyone tell me why my cutlass runs great for about an hour and then suddenly overheats. The 330 he been replaced with a 455. It h a new t-stat, water pump, and cap.

 

Is that standing still or driving? Define overheat in degrees F. Or is it just spitting water out the overflow?

 

Also tell us about the radiator size and age (i.e. is it clogged? ). And is it getting sufficient airflow? And how about the fan clutch (if equipped)? Assuming that the above is OK, and ign timing and fuel/air mix are good, then suspect a bad head gasket.

 

I'd start with this. If you are running the 455 with the original two-row radiator from the 330, that's your problem.

 

The original engine was the high compression 330. The 455, I don't know what it was originally in. Radiator is factory 2 row. New 16 lb cap, new pump, new 180 deg stat. The car didn't have an actual shroud when I got it. The header plate extends out over the fan. Overheats after about an hour at idle or 7 or 8 miles. Stays right about 180 forever then jumps VERY rapidly to 230. Gauge is one of Sun Pro's better models. Car is just a small bit rich with just a very slightly low advance. Carb is 750 quadrajet off 330. Can has a touch more duration than stock, but not radical. Valves are OEM. Compression as 9:1. Thanks for any ideas. Y'all have been a lot of help ever since I got the car.

 

This is still your problem. You don't say if it's a new radiator or not, but in any case, a 455 needs a three row and preferably a four row radiator.

 

The missing fan shroud isn't helping. I've seen cars that are completely stock overheat without the shroud.

 

I "burped" the system again and is doing better right now. I can see the thermostat opening and closing on the guage. It is really pretty close to its' rating. The radiator is original equipment, not new. It looks good inside where I can see, but I am going to go ahead and order a new one today. I am, also, changing the reservoir to make it a closed system today. I adjusted the timing and carb yesterday. I love the 330, but I have to admit that the 455 has much more torque. Does anyone know where I can find an OEM shroud? I can mold one, but like OE if I can get it.

 

We will have to guess I guess...64, 65, 66, 67 Cutlass?
John, 2blu442 or Larry, lemonoldsnut may have an oem unit.

 

Since you've burped the system, is it still overheating while at idle and at speed?

 

Joe and Macadoo have buttoned it down I'll bet.
A radiator designed for the engine and the car, with the correct shroud, = journeys untroubled by overheating worries.

Roger.

 

Sorry, I thought I had said the year. My bad. It is a 66 Cutlass convertible. My new radiator is suppose to be here by 1/15.