Are there any GM Techs out there?

[Billy Nees]

Can someone please explain just how the coolant flows through a 2003 2.2 Ecotech? Just when I think that I've got it figured out, I realize that I don't.

[jamie2370]

Timing chain driven water pump. Thermostat is on trans end of engine. PM me if you need to or you can text me at 4789194280

[Billy Nees]

Hi Jamie, I can find cooling system diagrams but I haven't been able to find anything that gives me the direction of the flow through the engine, the thermostat and all of the hoses.

[pmrphil]

Billy, I would think that the thermostat has to be at the end of the water flow to control temp, so it should be water through the block front to back.

[jamie2370]

Correct, pump is on side of block, it pushes thru the block, into radiator, out radiator to thermostat, then thru the pipe from t stat to back of pump. If you are having an overheating problem, remove the plate on the front cover( has 4 small bolts) and make sure gear will NOT spin by hand. I have seen the balance shaft chain break(spins pump) and not make any noises or cause any problems other than it will run hot.

[jamie2370]

Originally Posted by Billy Nees

Hi Jamie, I can find cooling system diagrams but I haven't been able to find anything that gives me the direction of the flow through the engine, the thermostat and all of the hoses.

Heater core hoses are after the thermostat assy. So between housing at trans end and the larger pipe that goes to back of water pump. Coolant goes in pump side of block, flows around thru to other side of block(cylinders are siamesed, no coolant between them) and then out the front of block to the radiator

[Billy Nees]

One heater hose is behind the thermostat (hot side), the other hose goes into the rear of the block (?).

[jamie2370]

Straight from GM service manual that makes it as clear as mud lol.

The cooling system's function is to maintain an efficient engine operating temperature during all engine speeds and operating conditions. The cooling system is designed to remove approximately one-third of the heat produced by the burning of the air-fuel mixture. When the engine is cold, the coolant does not flow to the radiator until the thermostat opens. This allows the engine to warm quickly.

Cooling Cycle

Coolant flows from the radiator outlet and into the water pump inlet. Some coolant flows from the water pump, to the heater core, then back to the water pump. This provides the passenger compartment with heat and defrost capability as the coolant warms up.


Coolant also flows from the water pump outlet and into theengine block. In the engine block, the coolant circulates through the water jackets surrounding the cylinders where it absorbs heat.

The coolant then flows through the cylinder head gasket openings and into the cylinder heads. In the cylinder heads, the coolant flows through the water jackets surrounding the combustion chambers and valve seats, where it absorbs additional heat.

From the cylinder heads, the coolant flows to the thermostat.The flow of coolant will either be stopped at the thermostat until the engine reaches normal operating temperature, or it will flow through the thermostat and into the radiator where it is cooled. At this point, the coolant flow cycle is completed.

[Billy Nees]

Alright, I am pretty sure that I've got it. With the thermostat closed, coolant goes through the heater core and into the rear of the block and is circulated through the block and head by the water pump. When the thermostat opens, water goes into the LOWER radiator hose AND through the block and head. It goes through the radiator and into the UPPER radiator hose where it is circulated through the block and head until the thermostat closes . Clear as mud....

[jamie2370]

Billy, sometimes I think even GM doesn't know how it works lol. I have followed some of their diagnostic trouble trees for certain trouble codes that say , Step 1... replace this part Step 2... does code reset Step 3.... if yes replace this part Step 4...Does code reset, if yes, refer to Step 1