Pipe - expansion tank to heater circuit return

[The Great Pretender]

Mike, the way I see the difference between the Toyota patent and the Bongo is that the Toyota system is primarily designed to overcome latent heat problems when stationary in traffic or when switched off after a run with a 'mid' engine i.e. Luceda, Estima.
They have plenty of head problems to, they also fit the stat in the bottom hose.

Mazda chose to try a different route.
Did they succeed?
I think they hoped the bleed pipe would contain excess air, may be the reason for its length?
IMHO no, why, because the engine position from an engineer's perspective is a ba**s up.

As a package it is a brilliant use of space.

Fig. 2 In the patent shows a vapour pipe rising to the degassing tank, if in reality you could do that you would have a natural upward path from the engine to the radiator for the main coolant pipe allowing a natural convection path as per the 'old days' negating the need for the patent.

[mikexgough]

Mel, I tend to agree with your analysis on that and the Mazda set up does contain the fundementals of a degas set up and I would say that dictates the location and shape of the Header tank inc interior chambers... The Lucida owners I have dealt with have had head issues mainly due to skimping on coolant...

[Northern Bongolow]

Fig. 2 In the patent shows a vapour pipe rising to the degassing tank, if in reality you could do that you would have a natural upward path from the engine to the radiator for the main coolant pipe allowing a natural convection path as per the 'old days' negating the need for the patent. [/color]

so in answer to the original question from steve.
the small dia (and therfore low pressure) pipe from the exp tank to the heater circuit could be a low pressure path for the vapours/heat from the engine to escape through when engine is hot and switched off,direct to the exp tank,as it cannot go out of the top hose as it dives down and could cause a vapour/air lock.
this pipe is the nearest they can get to a direct vertical link from the stat to the expansion tank to safely degas the system.
this link pipe also stops the flow of coolant from reversing in the system,when the heat trys to escape and rise to the highest point after engine shutdown.

maybe

[Northern Bongolow]

as an add on to the above, and to take the theory to its limit
when the engine overheats the effect we know as kettling also must take this path in an attempt to dump the heat as its the fastest route to the saftey valve/pressure cap, but unfortunatly as the system is now near meltdown the violently escaping vapour takes with it the coolant as it super heats this on the way out.