Hello, so I just did a 350 tbi (from a silverado) swap into a 89 firebird that was originally a 305 tbi. I have everything in and I got the car running great with good idle and decent power. It doesn't overheat at idle and will sit around 190 ish with a 190 thermostat. The truck ran and had no overheating problems when pulled. But now in the car it will overheat if driving it around. I tried with a 160 thermostat and I even bypassed the heater core and control valve and ran right to the back of the engine. The truck had only the upper and lower radiator hoses and had a hose from the top of the water pump to the heater core and then out of the heater core to the back of the engine. So I even pulled the plug out that I put in and ran a line from that to replicate the same cooling system as the truck. I takes a little bit longer to overheat but still overheats within 5-10 miles or so. Running stock radiator with 3 aftermarket electric fans. two pulling on the side towards the engine a 1 push air through on the other side of the condensor. Looking for any help available. Thank you.

 

What does it do when it over heats? Puke out? Gauge run high?
You may have air in the system, best to get it running with the rad cap off & see the coolant flow. Rev it up & hold it till the level drops, fill up the rad, put the cap back on, & let it idle.
Verify the gauge is accurate.
Air dam in place?

 

Yes, the gauge starts creeping above the 220 mark and if I let it go farther it starts to boil over. I had to rebuild the entire front end. I don't think it has an air dam. and gauge is accurate. already tested.

 

this isnt the right way to fix the problem but you could try drilling a 1/4 in hold in the thermostat and see if that helps any. you might have crap running through all the coolant passages and plugging up a port. sometimes rusty heads (especially on boat engines) can have a piece of rust break loose and plug a passage. another possibility is a head gasket is about to blow or even a cracked head.

 

"I don't think it has an air dam"

There's your problem. Fans don't do much good over 35-40 MPH. Air dam is needed for highway speeds.

 

Thanks, built an air dam and it fixed it.