First the issue.
This summer as I have been using my AC at idle the car is overheating, cools down at speed. During the winter fall and spring it did not, I don't drive it much though. I have replaced the water pump with a Stewart CCW rotation stage 2 pump. The radiator is recored from a local reputable shop. Both fans are working as they should, pulling not pushing, there is no radiator blockage, new 180 thermostat. New 180 coolant switch in the side of the block, fan programmed to come on at 180 and shut off at 170. There is good water movement in the system, no collapsing hoses and I'm using a 50/50 blend. Timing is spot on at the factory 6 degrees. The car is an 89 IROC with the 350.

Now my thoughts and the question.
I'm grasping at straws here, last fall I replaced my intake and runners with an Edelbrock manifold and AS&M runners. I had to do this twice since my center intake to head bolts stripped out during the install. I helicoiled them, I have no vacuum or oil leaks. I am wondering if I installed the correct intake gaskets. I didn't keep the stock ones or look them over (stupid move) but the first set I bought had the water passages open at both the front and the back. The second set only had the front open. The rear passages had a 1/4" hole drilled through a steel plug molded in the gasket. Seeing that this was the only differences in the two gasket sets I cut out the steel plugs so that the rear water jackets are not blocked. Should I have done this? Could this be creating the overheating problem?

 

Since there isn't any rear coolant passage on the manifold, what you do to the gasket opening back there doesn't make much difference.

 

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I sincerely appreciate your reply but this contradicts what I remember from back in December when I installed it. I think the Edelbrock base rear water cross over was there. I called Edelbrock to confirm this shortly after I read your reply and they too stated the rear passage is cast in. The GM gasket is 10159409 and according to my local dealer the passage is completley blocked in the gasket. So I guess I will be removing the intake again and installing new gaskets. Geez I get tired of doing the same thing over and over.

 

It still won't have anything to do with your cooling problems.

 

Well like I said I'm grasping at straws here. Everything in the system is new, except for the fan motors but they appear to be working. During my searches here I read somewhere that without the restricted rear passages the cylinders would not cool evenly. However that could be misinformation. I talked to a GM service mechanic shop foreman and he felt that the rear passages were blocked for emissions reasons. If I opened them I should be running cooler. When I originaly opened them up I thought so too. I guess I'll keep searching the other forumns as it is the car is not driveable, it heats up unless it's on the freeway.

 

You won't notice any difference.

 

Have you checked the temp sending unit to see if its actually reading accurately? Put a mechanical guage in the hole in the head and see if it does the same. I once had a guage (not sender, guage) go bad on my '83 and it read about 20* too hot all the time.

 

I think the sending unit and gauge are accurate on mine. I connected Tuner Pro RT and data logged. The water temp is very close to what the gauge reads. In addition when the engine boils into the catch tank the car is registering above 240. This aligns with what I have my coolant ratio set too now. I dropped it from 50/50 to about 40/60.
Recent update the car is now running under 240 all the time. I took out my new fan wiring harness and began to trouble shoot the wiring. I found one of the wires into the main connector nearly cut in two by whomever stripped the wiring. It worked but not all the time.
I replaced this terminal and the weather pack in hopes that I had some sort of vibration open in the circuit. Apparently I did and the car just spent an hour and a half driving in city stop an go without crossing 240. Came close but not crossing over. It mostly ran about 225-230. I'm going to continue with further investigation to see if there are other issues, need a good pressure flush to the block, check fan speeds.
Here is where I get frustrated. I had the radiator fixed, it was 20% blocked. To do a thorough job I replaced the fan harness with a new one because mine had some splicing and crappy terminals. So what happens is the flush helped the cooling but the bad wiring made it seem like it fixed nothing. Really tries my patience. Anyway signing off, thanks for all of your help and experience.
GW