flyrotary@lancaironline.net Mailing List Archive

I agree with Lynn (on the restriction) and Al on the swirl pot (not necessary).

Note that there is a built in restriction in the Mazda water pump housing. Its just barely big enough to squeeze a couple of fingers through. A restriction does restrict the maximum flow but the pressure in the block (and back pressure on the pump) does 2 good things. Reduces the chance of bulk or film boiling in the block by raising boiling point and more importantly, the pressure reduces the likelihood of pump cavitation which would reduce flow much more than the restriction does and eliminate the pump damage that cavitation does.
In other words, the engineers were willing to give up a little maximum flow in order to insure a higher minimum flow.

This won't end the age old debate on this subject but that's my story and I'm stick'n to it : )

Tracy

On Tue, Aug 18, 2009 at 2:00 AM, Al Gietzen <ALVentures@cox.net> wrote:

I respectfully disagree with the idea of the putting a flow restriction at the exit of the engine. True, it does increase the coolant pressure in the block, and that’s good. But it reduces flow, and that’s bad. Reduced flow increases the delta T around the loop and reduces the cooling capacity of the radiator, and in an aircraft application we don’t like to add additional radiator size. As far as increasing the pressure in the block, you can get about the same affect by plumbing the filler/pressure cap to the inlet side of the pump rather than the outlet, so the pressure drop around the loop is not seen by the cap.

A swirl pot works, but is not necessary. You need an air bleed from the high point of the engine (usually the outlet of the pump, and from other places that the air may get trapped, like the rad tank. A small bleed line (3/16” o.d. aluminum is good) from the point the air gets trapped back to the filler neck/bottle. Since the filler neck is plumbed to the low pressure side of the loop, any air gets drawn back there.

I connected the turbo coolant port on the rear iron of my 20B back to the port on the pump outlet to bleed air from the rear iron, and a manual bleed plug at the pump outlet to vent air during fillup. I have small bleed lines from each of two custom radiator tanks back to the filler neck (which is connected to the line just before the pump inlet). After fillup, one run cycle purges all the air back to the filler neck.

BTW; the cold to hot expansion for my 20B system is about 2/3 of a quart.

Works for me, but of course each installation is different; but the concept is the same.

Al G