i recently built an ls1 iron block from an 08 5.3 block and fired it up today for the first test drive well filled the radiator and started it and before i got out of the driveway it got to almost 220. i opened the radiator cap and it and that water was still cool, could it be air trapped in the engine ? or a bad thermostat?

 

Bleed air out by temporarily removing the hose from the steam crossover tube.

 

Do you just remove the hose until coolant comes out of the tube?

 

I had a similar problem and had to crack open both bolts on the crossover tube then slowly added fluid to the radiator until air stopped bubbling out of the holes. I did this until I got a steady flow of coolant from both holes and after that, all was good. Its seems like that wouldnt be a big problem but it really is! Mind you this takes a little times and be sure all air is out. That coolant system traps alot of air and venting the crossover tube is a necessity. If that doesnt work, remove your thermostat and boil it to see if it opens.

 

thanks guys that got it cracked the crossover tubes and the radiator level shot down to empty. appreciate it

 

So did you guys actually take the crossover tube off and run the motor until coolant is flowing out?

 

You don't need to completely remove it - just loosen it so leaks air, steam and then coolant.

 

Sorry for my ignorance, but why would you have to loosen the bolts in the first place. Wouldn't the air and steam come out of the front crossover tube outlet?

 

Following a coolant change I usually just use the crossover tube connection to the radiator return tube to "burp" the system. Following a head swap however, I like to loosen all four crossover tube connection points (my LS6 actually only has one front crossover with plugs on the rear of both heads) to make sure I have no air pockets at either end of either head.

 

Yah thats what i thought but that tube is just to constricting, cracking open those bolts just makes it quicker and easier to vent

 

Place a length of clear tube on the crossover tube (where you removed the rubber hose), then you can watch the air coming out, eventually you will see coolant only.

The clear tube keeps you from spraying coolant on the pulleys/belt.

If the front of the car is jacked up, then trapped air will migrate to the front of the heads.

The crossover flows sufficiently, you shouldn't have to loosen the crossover bolts, if you do then that indicates a blockage.

 

you would think so but it didnt lol. i didnt even run it i just unbolted the cross over tube on the front after the car had warmed up and as soon as i unbolted it the level dropped and i began putting water into the radiator until water came out the holes.then bolted it back up topped off the radiator and ran it for a while. let it cool down and topped it back off now im good to go

 

Did you check the crossover tube for blockage, blow it out with compressed air...?

 

nah i didnt hmm now this is gonna make me wonder to the point i take it all back off lol