1971 LS5 Cooling System Capacity

[Christian]

This is about a 1971 LS5 (454 ci) cooling system.
The owner manual says the capacity is 23 qts.
I have flushed the system several times, through the lowest point I could find: The fitting just below the lower connection point of the radiator (bottom right).
The most I get out of the system, and therefore the most I could get back into it was approximatley 3 gallons (12 qts).
Any idea about this ? Any experience with a similar engine ?

 

[Culprit]

Draining the system from the radiator drain doesn't get all the coolant out of the engine block or the heater core. Sticking a hose into the top of the radiator and letting it run out the bottom drain valve only flushes the radiator itself. If you want a thorough system flush to change all the fluid, you'll have to use one of those back-flush kits they sell at the auto stores and Wal-Mart etc. You have to cut one of your hoses and install a hose fitting that lets you connect a garden hose to flush water through the entire system.

Semper Fidelis,
Culprit

 

[JohnZ]

There are several quarts trapped on each side around the bottom of the cylinder walls that can only be drained by removing the block drain plug on each side, just above the pan rail. Hardly anyone ever does this, so there's LOTS of corrosion, scale, and crud built up down there. You have to drain each side, as they're not cross-connected. You'll be amazed at the crud that comes out of there - you'll probably have to probe through the crud blocking the hole after you remove the plugs to get any flow, then it'll POUR out - have a pan ready!

 

[72VETTE454]

Fyi

Maybe you already know this . Especially after draining the entire cooling system, Chevrolet recommended this procedure to ensure there is no trapped air in the system: Disconnect the upper radiator hose form the thermostat housing, hold the hose straight up and fill it with antifreze until antifreeze comes out of the thermostat housing. This is slightly messy, but well worth it considering an air pocket can cause your engine to overheat. I don't know if this is just for big blocks, or small blocks too. But this definately worked on my LS5 when I refilled my system after an air pocket caused overheating ad . Good luck.

 

[JohnZ]

It works even better if you fill the (dry) system through the thermostat opening in the intake until the coolant rises to the top of the opening; then install the thermostat and bolt down the thermostat housing (already attached to the upper radiator hose), and continue filling through the radiator fill opening (on BB's) or the expansion tank (on SB's). If the thermostat and housing are already in place, and you flll through the upper radiator hose, the thermostat will be closed, and won't allow all the air in the block to be displaced by the coolant being added.