enough solid particulates that running the engine until hot is better for changing out the cooling fluid? Under "running temperature" conditions how much liquid does the system flow per minute? Mostly curious and will probably just drain the cooling systems on two T's until I get around to "waking" them up in early Summer.
Not much help to pre-warm the radiator.
Unlike an oil change where its helpful to get the oil sloshed around with a slightly warmed up running engine, the radiator doesn't need to be warm. Unless its real cold out and the coolant is about to freeze
Just drain, and then, most importantly, flush the system with running water. Best of all is to use slight pressurized method, or even better, remove the radiator, flush by itself. Then flush the block from reverse, flowing water into the upper outlet, and out the inlet at the side.
If older block, rust chunks will flow out the block from the head and cylinder passages. But if its really old block, likely the steam passages in the head are blocked too. Pull the head and clean it separately.
Don't know that you have "flow per minute" with thermo-syphon, the coolant gets up to an elevated temp causing then a rapid flow, more in a bolus or barf of coolant into the upper radiator tank. Falling cooler water from the radiator then is pulled or flowed back into the block. The process isn't continual, just occurs from the physics of the hot fluid moving to the highest level. Flow rate depending on engine heat generated, RPM, higher speed, or load in climbing uphill for example, slow going in low pedal at slow speed pull, less air passing thru the radiator preventing best heat-to-air dissipation.
I have to get my self a FLIR -
They are in the building next to us in N Billerica MA- maybe one will fall off the truck!
I would contend that the flow IS continual, once up to temperature. While it may flow at different rates depending on conditions, I believe it does pretty much flow continuously. When you actually hear the repeated 'barfs', I believe this is an indicator of overheating and what you are hearing is repeated bubbles of steam coming up through the water.
In an older radiator I once had that was missing the baffle, you could actually remove the cap and see the current of water flowing into the upper tank.
I don't really think it has to be "up to temperature" to be flowing. There only has to be a temperature differential between the head and lower radiator. Hold your hand on the head after starting. Once it starts to feel warm, it should be flowing. It only takes a few degrees delta but the higher the differential, the faster it flows.
According to the late brass-car guru, Harold Sharon, thermosiphon only works when the level of the coolant is higher than the tops of the tubes in the radiator—and intuitively, that makes sense. _Now, I've heard a lot of talk about how far up one should fill the radiator (halfway up the tank, 3/4 of the way up the tank, etc.), but it seems to me the simplest way of getting it right is to intentionally over-fill the thing and then let the excess blow out the overflow tube.
But okay, more to the point; the Model T Ford's 20-horsepower engine, let's face it, is weak and operates at very low RPMs in comparison to just about anything else, so the little mill doesn't generate a whole lot of heat. _That's why the languid, relaxed circulation of thermosiphon is enough to absorb and radiate away what little calefaction is generated.
Ken, you are right. I should have been more clear.