Just got done doing the LT4 conversion on my 1994 z28 motor and i went in to drive it and the temperature just keeps rising. At idle the car wont go over 190 degrees but once I get in it to drive it the temp goes up very quickly. It will be at around 220 within a mile. The water pump works, The radiator is new and works, The fans are turning on at 180, There is enough coolant, it is flowing water, the thermostat works, i have bleed the system several times and there is no air, also the line that is hooked up to the back of the heads is flowing water. I have checked almost all of what makes up the cooling system and everything works. I dont know why it is overheating. From what i have tested, it shouldnt over heat, there would be no reason to.. I thought it might be a bad temp sensor sending the wrong temp to to gague so i hooked up a different sending unit and temp gague and there was no change. Is there possibly anything else that i could be missing here?

 

Stock pump? Did you check sensors on the water pump and in the head my bet is its one of those. I had same problem is was the ECT. Its one of those just buy to new ones for 8bucks. It also sounds like a stuck thermostat, If its new it does not mean it works, and that would explain why it gets hot when moving.

 

radiator cap maybe

 

Definatley not the radiator cap.... I was thinking, maybe the head gaskets may be different and may be blocking some of the water passages. I was pretty sure they fit right when i put them on but i really dont want to pull the heads of to check it.

 

have an exhaust gas teast done in the radiator it usually costs like 5 bucks or so it will tell you if you have a head asket leak

 

I am not worried about the head gaskets leaking, i am worried that they may not have the same hole patterns in them, therefore blocking water passages for the cooling system. The motor is not in a 94 z28 but a 68 lt1 and many of the elctronics have been deleted from the system. I am pretty sure its not one of the sensors (i could be wrong), because everything is flowing water and the temp still raises. Im not sure what the ECT is that Slug was talking about. The thermostat does work, i heated it in some water and watched it open to make sure. I think i am going to go down and look at some of the head gaskets i just put on and compare them to the stock ones and make sure they match up...if that fails i guess i'll have a lot of work ahead of me. But if they do match up i am lost.

 

well typically lt1 runs around 220 in semi warm climate that is well within operating temps for an lt1 what kinda cooling system do you have

 

AFCO aluminum radiator, electric fans, stock water pump, 60 thermostat....never used to run over 200, it hardly ever ran over 190

 

Coolant temp sensor the brass one in waterpump and in the head, they dont always trip a code.

You would have noticed in two seconds if they where the wrong gaskets. Replace the sensors before spending 2 hours to pull of the heads or head.