Eddie Hansen

Just wanted to mention that sometimes unrestricted water flow has an adverse effect in that it doesn’t give time for the radiator to do its job and cool the fluids they pass through too quickly for heat to dissipate sufficiently that is also a Partial function of the thermostat.
I myself hate overheating issues or perceived issues I was under the misconception that we should be running at 180-190 when it seems that 200 -220 degrees isn’t unusual?

69HO43

Flowing too fast for the radiator to have time to do its job is kind of a misnomer if you ask any fluid dynamics engineer worth his/her salt. As long as you maintain laminar, or smooth, flow through the system, mass flow rate is king. The faster the better, to a point. This is why the older distributor systems with the TCV that the distributor advance routes to is normally ported vacuum, until the TCV senses the engine is too hot, then switches to full vacuum advance from the intake manifold. Then swapping back when the overheating event is over. And it's another reason that different impellers have less slip than other impellers in the water pump. Keep the mass flow rate up. Agreed the thermostat prevents flow to the radiator during warm-up, but once warmed up, it's really just another obstruction.

I'm not in any position of authority on it, but years ago when I worked at a nuclear power plant, myself and one of the older steam generator engineers were discussing this very topic and he explained why higher mass flow rates in both air flow and fluid flow are your friend in a radiator situation. As long as you're moving enough air across the tubes to carry away the heat from the tubes and enough coolant to carry the heat away from the heads and cylinder walls, you should, theoretically, never overheat. It's when there are imbalances in the system that make things mess up, like crud build up which affects the thermal transfer from the coolant through the tubing material to the air. Or if the flow departs from laminar flow and becomes turbulent. The turbulence prevents good heat transfer so too fast isn't really a function of exceeding the capacity of the radiator's abilities, but rather the contact area of the heated fluid to the tubing material is reduced. Contact patch for the fluid being reduced reduces cooling capacity, thus heat isn't transferred as readily. This is why good air flow across the radiator is just as important as the fluid flowing through the tubes. Air is terrible for a heat transfer medium unless it is moving, i.e. fan or differential pressures causing wind flow, or moving the radiator through the air like driving down the road.

Qdot = mdot x cp x deltaT where Qdot is heat transfer rate, mdot is mass flow rate, cp is specific heat capacity of the fluid (which is generally considered constant for all intents and purposes) and deltaT is the difference in temperatures between the two mediums. So you can see, the the heat transfer rate is directly linked with mass flow rate and the differential temperatures.

And that is your basic thermodynamics lesson for the day. I'm sure there are smarter people than I on this forum that can expound on this further should they choose. Be my guest.

Duh

You don't want laminate flow. You want turbulent flow. Higher velocity, the greater the Reynolds number. The greater Reynolds number the more turbulent. If you have laminate flow through a tube only the fluid at the boundary will cool. So yes slowing the flow down does not help.

69HO43

Thank you for the correction. I obviously misunderstood what he said and got it backwards on the laminar vs turbulent flow. Maybe I was thinking departure from nucleate boiling. I just recall he mentioned something about turbulence could be bad for the tubes if flow was too high, so maybe that's where I got that idea. This is why I don't design heat exchangers/radiators.