its been like 80* or so here lately and my truck is over heating like crazy what gives. i've got the 160 stat in and it still runs at 210 going 70mph down the interstate. usually going down the interstate it keeps the coolest. i don't think it my fans because at 70mph there not even on. now sitting at a red light yeah it just creaps up from there. i still have stock radiator the smaller one. i don't get it last summer during august in arkansas in 100* plus weather it never ran hot and i had one eletric fan from a grandam with a v6. got it for $5 ata junk yard. that was with the 4.8. now i have a ls1 in it a dual eletric fans and it will not keep cool if its over 70* out side. what gives?????????

 

Mine did the same thing, and I called the dealer, he said to check the fliud. On GM, it has to be on the line or it won't run right. Use only Dex. and make sure it's 50/50

 

Sounds like an airflow issue... if I read your post correctly, it is running hotter than normal while driving at freeway speeds and overheating while at idle? I learned a lot about this issue after having this problem in a 383 powered RX7.

As far as overheating at speed:
Has anything in front of the radiator been changed/removed- plastic ducting, shields, etc.? Are there flaps in the LS1 shroud to let air thorugh at speed when the fans are off (I know the LT1 models had this)?

As far as at idle:
Are the LS1 fans sealed to the radiator? I don't know the core size of a truck radiator, but if the fan shroud is sticking out over the edges or much smaller than the core, you are not getting max cooling from them. I'm looking at this issue now with my Supra motor swap.

EDIT
If your "dual electric fans" are Perma Cools or similar, this could be your problem- I modified a set of 12" Perma Cool fans in the stock shroud behind a huge Be Cool radiator when I had a Procharger on my Trans Am, and it overheated (240) at idle. I went back to the stock fans w/o blower and the problem went away. This was what led me to the rear mounted turbo.

 

I you have air in the system it will also make the engine run hotter.

 

when i added water i rev the eng to about 3000 rpm and it helps to bubble any air out of it and i cap it before letting it idle back down which pressurizes it. i'll check for any blokages and all and try my other fan but with a 160 stat shouldn't i get like 170 going down the interstate because fans are off at that speed.

 

oh yeah the fans are not ls1 fans just the engine. there some kind of after market fan i got them from snake eater for my clutch fan. i didn't have this problem with my grandam fan and it was just one. but it did pull some hella air. they need to be wired in parallel to be in "high mode" right? i'll put in the other fan at lunch and try that i guess.

 

I also like to run the heater when Im putting new coolant in. It makes sure the water circulates through that heater core.

 

The fans shouldn't be an issue at highway speed unless they are blocking airflow through the radiator. If you can attach a pic of them, this would be helpful. The key thing here to me is that you didn't have this problem until you switched the fans.

By parallel, you mean each fan is seeing +12V, right, and one is not wired to the other, i.e. positive to negative (series)?

I run a single 16" Lincoln MK 8 fan on my LT1 280 and it will suck the paint off the wall/small animals from roadside at high speed. It is also a close match to the radiator core, so all air is going through it.

As for air in the coolant, I'm not that familiar w/ the Gen 3. I know the LT1 has two air bleeds in the cooling system.

 

make sure they are pulling air and not pushing. Cause if they are pushing air on the highway I coudl see that causeing overheating.

 

So your running some kind of aftermarket mechanical fan bolted to the waterpump pulley correct?
If thats the case, I would ditch that and at least go back to the stock clutch fan. I had one of those cheap flex fans before on an older vehicle (not this one) and it was a piece of ****.

Get yourself a LS1 fan setup and call it a day.

I ran my LT1 fans on my LS1 without problems using a 180* thermostat. I'm still using the same fans on my 11.5:1 LQ9 without problems.