AW11 Coolant Flow

[MR22ZZ]

Hi folks

I have been shown this diagram showing the supposed coolant flow through an AW11 coolant system...







All logic suggest that flow through the radiator would be the OPPOSITE to that pictured.

Just trying to get people's thoughts?

if flow was the other way, the oil cooler would actually cool, the radiator would flow from bottom to top as is most efficient and you would not need to heat the entire 13L of coolant before the thermostat opened.

I would have thought the thermostat would open the other way and the filler point would be the final 'inspection point' in the flow before the block.

[Duk]

With a low enough coolant level you can watch the coolant flow in the direction of the arrow when the 'radiator cap' is off.
Also, most if not all radiators flow hot inlet at the top. I believe this prevents thermal siphoning (heat raising to the top). If the hottest liquid goes into the bottom, the heat will siphon towards the top and make the radiator less efficient at getting rid of heat.

[Hiro]

Actually it is the other way around - inlet at the top IS a thermo-siphoning system (which is a good thing). The coolant gets heated by the engine and rises to the top of the system (the inlet at the top of radiator) - as the fluid in the radiator cools it drops to the bottom of the tank through a combination of flow, gravity and change of density. If the water pump stopped working then the two remaining forces will still create some flow (early cars which didn't have water pumps worked entirely by thermosiphon, which requires a 100% full system otherwise the siphoning effect wouldn't work.

Practically all car radiators that I can think of work this way. The A-series was an example of Toyota bucking the trend and putting the thermostat on the outlet side of the radiator (ie the inlet to the engine) rather than the other way around, but they still used conventional flow through the radiator. Another easy way to tell is to trace the piping from the water pump - they are an impeller-style and thus push water in the radial direction (with an axial input, like a turbo).