| You guys are really confusing me! Granted all my rotary work so far is on my car. Once upon a time, my car had an AST (air separator tank). It was a small round job next to the radiator, maybe 3 inches OD, 3 or 4 inches tall. I’m thinking it served similar purposes to the swirl tank in your designs? Mazda made it of plastic and it had a nasty tendency to burst after aging in the heat soaked engine bay long enough. Most Rx-7 owners including myself, removed the AST system - others replaced it with aftermarket aluminum versions. As I recall it had a tube at the bottom that went downwards to an extra nipple on the bottom of the radiator, but I forget where the input came from. I am wondering how this system compares to the ones you are describing? Where is the pump in the last figure (Steve vs Jeff)? And where is the “airbleed hose” bleeding air from? Is the idea that it is just a high point in the system that continuously is drawing out any air bubbles that get created or trapped in the system?
I have to ask another related question - why not use Evans waterless coolant? I think we discussed it a bit before. It seems like the expansion/contraction is a lot smaller because it boils at a much higher temperature than standard coolant/water mix. I run this in my car now, but my car is a project car that hasn’t gotten enough serious abuse to have more opinions on the efficacy of Evans. But I believe that Rotax engines use it - so aircraft use is not beyond the pale. I am just wondering if all this (seeming) complexity in the cooling system arrangement would be needed if a waterless coolant were used.
— James
Hi Steve, I’ve attached a sketch of our two systems as I understand them. Your system is equivalent to a gas can turned upside down with a very small outlet hose and the air cap sealed tight – no, or at least very little flow out the bottom. I’m pretty sure if you de-pressurize your system, remove the expansion tank cap and come back 2-3 weeks later, the level in the expansion tank will have increased. You won’t see any change during a quick top-off in a couple minutes. If you open your Schrader valve it will overflow in a few seconds. I understand your systems’ equilibrium once it is topped-up and you are in maintenance-mode – but how do you fill your engine when bone-dry? I assume you close/pinch the lower hose and fill the block from the top as complete as possible; at this point you can seal the Schrader valve, add coolant to expansion tank, open lower hose, pressurize it and force it into bottom of engine while slowly opening Schrader valve. Jeff From: | | Subject: | Re: [FlyRotary] Re: swirl / expansion tank configuration | Date: | Thu, 29 Jan 2015 19:38:50 +0000 | To: | |
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| Jeff, In my system, the outlet of the water pump (high pressure and coolant high level) is connected to the expansion tank at a location a couple of inches from the bottom of the tank. The inlet of the water pump (low pressure and low coolant level) is connected to the bottom of the expansion tank. Both connections to the coolant tank are below the coolant level in the tank at all times. With the engine not running, the expansion tank does not back-fill with coolant even if the expansion tank filler cap is removed. In my system, the expansion tank cannot back-fill unless the volume of the coolant in the rest of the system is increased (by thermal expansion for example) or air is introduced into that part of the system. Steve |
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