Maybe that part of my theory was wrong. Couldn't it be drawing in air while the system is runing (and under pressure) too though? If the top tube is open to the air in the tank isn't there a possiblity that that air can be forced into the system?
If that's true that would confirm my suspicion. I don't know why it never occured to me before but it makes logical sense. BTW I also cleaned and sealed my tank last year and there was no tube inside.
Are you sure you are bleeding off air and not steam? When you open the bleeder valve with the system at operating temperature you release the pressure in the system which will cause the coolant to boil and release steam. If you are very far above sea level the coolant will boil and turn to steam at temperatures below the normal 212F (100C) when the system pressure is released.
you say you are bleeding air out when the engine is hot/very hot I would say after a fifty mile run.Now you release the pressure cap which is meant to raise the boiling point of coolant.Internal heat from the engine now starts heating up the surrounding coolant, This high coolant temperature with no cap fitted will create an aeration effect.Look at a jug before it starts to boil.I dont recommend taking radiator caps off when the car has been turned off for a minute or more.I like the w/pump idea but more likely to be the cap .if coolant water is recirculating through that tank is it aerating the coolant as it fdrops back into the tank l.Pitting around waterpump impellor area can cause aeration/insufficient antifreeze /inhibitor/sharp rough edges or bends in piping.I have seen hoses sucked flat and coolant cant be suppled fast enough around the impellor . if nothing appears obvious try switching the heater pipes over if thats possible (hondas/subarus suffer this prob)and i would try using a Wurth product called radiator system sealer(used in new vehicles)have used it with amazing results. Tony
Good point!! I don't know. What I can do is to run the car for a few miles then, when from past experience I know there is some "gas" (air or steam) in the radiator, switch of the engine. Wait until the radiator cools down and then open the bleed valve. If it was steam it should have condensed then no gas coming out; if it was air I should get the usual quantity of "gas" out from the radiator. But... thinking better about your sentence "...release the pressure in the system which will cause the coolant to boil and release steam..." I see a problem. When I open the bleed valve the coolant can't boil instantaneously because the pressure will not drop in zero time and therefore I shouldn't find a lot of "gas": I should, rather, get a stream of boiling coolant. But, anyway, your theory if very worth of a deeper investigation! Ciao and many tanks for this new point of view. Franco
Yes, the bit about being able to bleed the thing when the engine was hot was in response to the idea that the air was being drawn in as the thing cooled. The air is in the radiator straight after switch off (i.e. disproving the theory about air being drawn in as it cools) and it's still there once it's cooled off - so it isn't steam either. I.
You can't do this - boiling hot coolant will fly everywhere. You can however open the bleed screw on the radiator whereupon (in my case) air will come out to start with followed by coolant Unfortunately so do I. I really doubt this problem has anything to do with the expansion tank cap. Fundamentally the expansion tank seems to be under pressure when the thing is running & so any movement of air around the cap is likely to be outwards, not inwards. I wondered about this but I don't believe the coolant is foaming too much. I.
Ian i was explaining your approach to a hot engine.Read again it will explain itself .The pressurecap and coolant raise the boiling point /dont release cap it could then start to boil. Does it look foamy. Tony
Another thought, if the system is pressurizing normally, air cannot possibly enter the system while it is pressurized unless the air is at a pressure above system pressure.
It seems as if air, to a large degree, is being redistributed from the expansion tank to the radiator upper header tank. I don't understand the plumbing to the expansion tank on a carb GTS/B. One would assume the larger, lower hose from the thermostat housing would be principally a coolant carrier and that the smaller upper hose, also connected to the thermostat housing, would convey air or a mixture of air and coolant. Can anybody post with authority/knowledge on how this is supposed to work? Bill
Right, so if air was being drawn in it would have to be at a point of negative pressure in the system. Someone has suggested via the impellor shaft on the water pump - right behind the blades in the pump should be a point of negative pressure. I.
That's one option - but the system can't possibly have been designed to work like that.......can it? I.
The water pump will be pressurized to system pressure also. There will be a pressure differential between inlet and outlet, but both will be above ambient air pressure when the system is at normal temperature and pressure.
Not quite sure (in theory). The system has its minimum pressure at the pump inlet, its maximum at the pump outlet and we only know that the pressure in the expansion tank can't be higher than 0.9 bar. A centrifuge pump of this kind is likely to have a differential pressure of 2 or more bars therefore, if the pressure drop from the pump outlet to the expansion tank is not greater than 1.1 bar, the pump shaft pressure is less or equal the ambient pressure. As I said, all this is just theory: a better knowledge of the hydraulic circuit is needed before arriving to a conclusion. Ciao and to the next. Franco
