I just finished some major work on my '81. Heads (60909), cam (2102), and intake (2101). All Edelbrock. Re-cored the radiator, new heater core, and rebuilt water pump. New 180 degree thermostat. Timing @ 12 degrees. Running 50/50 mix of coolant.

What I'm noticing is that on initial startup (just letting the car idle), the temp gauge rises to about the 240 degree mark before dropping to about 180 - 190. I'm only going by the stock temp gauge, which doesn't seem to be calibrated linearly and doesn't have values at every mark. Using the marks, it rises to the second one past the 200 mark on startup and then drops back to the one before the 200 mark once the thermostat opens.

Once this initial situation passes, the engine temp remains between 180 and 200. I've put about 500 miles on the engine in temps around 80 degrees and several traffic jams without overheating. It never goes above the 200 mark after this startup occurrence.

I used all Edelbrock gaskets, including the 7310 head gasket. I did notice that those gaskets have significant restrictor holes to impede the flow of coolant in some of the water jackets. I did not change the location of the engine temperature sensor (front side of left head). The electric fan does not come on during this behavior (I believe it is supposed to engage at about 240 degrees). That sensor is on the rear side of the right head.

Is this behavior normal/expected for replacement aluminum heads? I don't remember the old cast iron heads doing this. Any comments most appreciated.

 

Sounds like there might be a little air in the system, or that the thermostat is not opening as soon as it shoule on initial warm up. To make sure, replace the thermostat with a new one, stock 180* and drill a 1/8" hole in it. That will allow the air to escape and make sure you have a good thermostat.

 

Had the same problem. Here's some good info.

http://forums.corvetteforum.com/show...2&goto=newpost

 

Had the same problem after draining the coolant to replace the heater control valve. Not a big believer in coincidence since the thermostat has been in for 2 years with no problem. I'll try drilling the hole in the thermostat as well.

 

Corvettes never cease to amaze me. I had a slight coolant drip from one of the temp sensors (on the passenger side, for the electric fan). In addition to snugging up that sensor, I also decided to snug up the one on the driver's side (the one used for the engine temp). Bingo. I've started the car cold several times since then and the problem is gone. Never had to touch the (new and previously tested) thermostat.

The best I can guess is that I had a bad ground or a bad wire connection. I did disconnect the wire from the sensor to snug it up, so I can't say for sure what fixed it. It was either tightening the sensor in its plug, tightening the plug (on these heads, you have to use an adapter to match the boss in the head with the sensor's size), or disconnecting and then reconnecting the wire lead. Live and learn.

Thanks to all who replied.