Mailing List Message #67407
From: Stephen Izett <>
Subject: Re: [FlyRotary] Coolant barbs
Date: Wed, 15 Mar 2023 21:22:10 +0800
To: Rotary motors in aircraft <>
Hi Andrew

You were right. I mistakenly called my outlet the inlet.
The restrictor is in the outlet where the thermostat has been removed and flow much less restrictive than the OEM thermostat path.
And yes a smaller outlet would have achieved the same thing I suppose while reducing weight.

Did you put the Re-medy pump in from the beginning? Would be interested in a comparison of the pumps if anyone has that experience.

I thought rightly or wrongly that the restrictor provides a slightly higher pressure at the inlet of the pump and so reducing cavitation.


Steve Izett

On 15 Mar 2023, at 8:00 pm, Andrew Martin <> wrote:

I blocked all unnessesary coolant leaks. Installed Remedy pump on standard pulleys, 25mm hoses no restrictor, 1.3 bar cap, double stacked crossflow heat exchanger under belly, can maintain full power max Rate of climb without coolant issues, so it overcools and could possibly do with cowl flap on heat exchanger air outlet.

The argument for restrictors in the coolant line dont really make sense to me, better to use smaller hoses to restrict flow and save weight. restricting the inlet of any pump is one sure way of ensuring cavitation so if it must be done, restrict the pump outlet or in our case engine outlet.  Install 2 temp sensors, inlet & outlet to check deltaT to check if “mods/improvements” are real.

Oil cooling was whole nother issue in my setup, mazda oil heat exchangers are crap and should never be considered, a good racing exchanger that can flow max rpm oil flow is a must and 5/8 oil lines also otherwise oil will open the pump safety valve and dump straight back into sump causing immediate overtemp.

On Wed, 15 Mar 2023 at 10:39 am, Stephen Izett <> wrote:
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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