LS3 coolant filling question

**Gobs** · 01-06-2013, 12:33 PM

Hi All,
I am new to site and in the middle of a LS3 engine transplant into a 55 Chevy.

I need advise on the best way to fill the engine with coolant. I was told the filling procedure is unlike most Chevy earlier engines.
Thank you.

**pajeff02** · 01-06-2013, 04:48 PM

The LS engine seems more prone to airlock than a SBC -- at least that has been my experience. Make sure the thermostat has an air bleed -- most all do these days. Fill the radiator slowly and jounce the car on its suspension to work out any air pockets. Once you get it running, blip the throttle several times to again work out any air. Pay attention to your upper hose and make sure it starts to get warm as the engine comes up to temp. If it doesn't, shut her down and let her cool off a bit before you try again.

**Gobs** · 01-07-2013, 07:40 AM

Thank you the information. it is greatly appreciated.
My Thermostat is the stock version that came with the new LS3 motor from the dealer. Will it have an air bleed or will I have to replace the stock unit with an aftermarket one with an air bleed?

Someone also recommended raising the front of the car while filling the coolant. They claim the air will then move to the highest point which will be the rad instead of the block. Does this make sense?

**pajeff02** · 01-07-2013, 06:17 PM

That thermostat should have an air bleed in it already. Yes, raising the front of the vehicle can sometimes help, had a '90s Lumina that used to fight me when I serviced the cooling system. Never did this with an LS equipped vehicle though.

**cammed goat** · 01-13-2013, 09:53 AM

I don't have an LS3, but when I had to refill my coolant from a trip I took, my coworker told me to "backfill" the system by filling the coolant through the upper radiator hose.

**2002ssslp** · 01-13-2013, 02:04 PM

You can work air out of the system by putting a pressure tester on the radiator while it is running, open the bleeder and slowly apply pressure. Note: do not go over 16 psi. once you get a steady stream out of the bleeder you should be ok. This method is just like running the car with a cap on but it keeps the pressure high so air bubbles to not have time to hide.