Coolant Flow

Grubbworm · April 2

At the risk of sounding like a noob (which I am not), I am going to do a complete flush and change of the coolant system in my 2004 GMC 2500HD, 6.0 gasser. My question is: which way does the coolant flow in this engine, bottom to top? I have heard that the LS engines flow backwards.

Edited April 2 by Grubbworm

newdude · April 2

Bottom to top.

Water pump pulls from the lower rad hose (rad outlet hose), pumps coolant through the block and water jackets, then the head and passages then out the upper hose back to the radiator (radiator inlet hose). So the radiator flows top to bottom, but coolant flows the engine bottom to top.

Grubbworm · April 2

7 minutes ago, newdude said:

Bottom to top.

Water pump pulls from the lower rad hose (rad outlet hose), pumps coolant through the block and water jackets, then the head and passages then out the upper hose back to the radiator (radiator inlet hose). So the radiator flows top to bottom, but coolant flows the engine bottom to top.

So, I can remove the rad hose from the top of the radiator and let the used water flow out while filling the overflow tank with fresh water.

newdude · April 2

31 minutes ago, Grubbworm said:

So, I can remove the rad hose from the top of the radiator and let the used water flow out while filling the overflow tank with fresh water.

I believe so, yes. Should be able to.

CamGTP · April 2

Probably won't be a ton of flow though if the thermostat is still installed. Cold fresh water will just keep it closed.

On many cars I'll yank the belt off and hoses off, then stick a garden hose in the water pump and back flush the block. Same with the heater core, do the radiator next and hook it all back up.

Grubbworm · April 20

Last week / weekend I replaced the water pump in my GMC. Had a little leak, could not find it. Thought it was leaking from a pinhole in the Coolant overflow tank. Replaced it. Saw it leaking from a hose, new clamp solved that. Still had a leak. Finally found it and replaced the water pump. Did the Thermostat while I was in there. No leaks now and the truck runs great.