Mailing List Message #67404
From: Jeff Whaley <>
Subject: Re: [FlyRotary] Coolant barbs
Date: Wed, 15 Mar 2023 11:59:41 +0000
To: Rotary motors in aircraft <>
Think you guys have it covered pretty good.
I would add that if your radiator is mounted high it should have a purge line to a recovery tank; if it's mounted low it should have a purge line to the bottom of expansion tank.
My airplane is slow (100 mph) so needed the heater core outlet to feed a secondary radiator that Tee's back to engine at the water pump inlet.
No thermostat but I also have a 5/8" restrictor plate over the original thermostat port.

Hi Mark.

Thats what I have done re throttle body and heater with my Renesis.
Do you have a line from the top of rear iron(front in the aeroplane) to purge air from the top of the motor back to a highest point in the system?

I tapped and plugged the hole between the pump in and out circuits below to OEM thermostat, but I didn't put a hole in the plug for air to escape from the inlet side.
Is that recommended by the experts? Perhaps I missed that advice.
When I remove a screw on cap where the original thermostat used to lived, and my highest point in the system there is never any air trapped.

For clearance with cowl I cut off the Renesis thermostat housing and welded a screw on cap on top and an inlet barb onto the side so the flow is pretty much directly inline with the pump entry in the front housing.
I have from memory a 5/8" restrictor in the inlet to the pump.
Basically a piece of 1" aluminium tube that fits through the cap entry I welded on, that blocks the inlet except for 5/8" holes drilled through both sides of the tube inline with the flow.

I removed that restrictor recently and the temps went up considerably, which I put down to the pump cavitating well below my take off RPM limit to 7500.

My Renesis is Series 1 and I understand the pumps are known to cavitate at higher rpm.
I'm thinking, by removing the thermostat and smoothing the flow path I've lowered the rpm of the pump cavitating.

I'm presently considering changing the pump to an NZ pump many racers use (The impeller looks similar to the US Re-medy pump).
Basically an improved impeller designed to reduce cavitation at high rpm.
I might then be able to reduce the restriction and perhaps increase the flow rate, which will perhaps increase cooling.

Has anyone else changed pump, used a larger pulley to slow the pump, and has data to share?


Steve Izett
Flying - Glasair Super IIRG Genesis 4 Port RD1-C EC2 EM3

> On 15 Mar 2023, at 9:37 am, Mark McClure <> wrote:
> Planning my coolant flow for my engine setup on test stand only. Want to minimize unnecessary water lines. In searching the list/rx-8 forums I couldn't find any reason I cannot just block the in and out spots for the throttle body and heater cores.
> Will be bypassing the thermostat with center plug and hole tapped for air bubble. Only other line will be from radiator to expansion tank.
> Am I mis understanding something?
> Regards,
> Mark
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