The old brass/copper radiator that came with the FFW for our S7, back before John & Debra had the company, started getting some moist spots around the tubes where they entered the end tanks.

Anyone who works with cars knows that it nearly impossible to find a genuine radiator shop that can competently repair or recore a radiator can guess I might be looking at a replacement rather than a repair.

Anyway, the radiators that John Mcbean makes for the current Kitfoxes equipped with the rotax are: 1) All aluminum, 2) have a thicker core, 3) Dimensions similar but not identical to the old tech brass radiators - after communicating with John & Debra I became convinced the new radiator was the way to go.

I wanted to make this report so others are aware of the minor modifications needed to adapt the current aluminum radiator to Kitfoxes that had the old brass radiator and I am happy to report the mofifications are minor and straightforward. No need to fear the change.

1) The new radiator is about 3/8" thicker; and, the center ends up being about the same dimension lower in the cowl due to the fact that the bottom is flat all the way across whereas the old one has the end supply tanks protruding down a bit resulting in the center where the strap goes being a little higher. Due to these minor differences in dimensions, I found the old center strap had to be replaced with a new one to allow for the thicker core and slightly lower bottom - easy enough to measure up the differences and fabricate a new center strap.

2) New longer end straps (about 7/8" longer) which run vertically to each side of the engine mount from the radiator had to be fabricated to account for the lower position of the two holes in the mounting tabs on the ends of the radiator compared to the old radiator.

3) The back edge of the NACA vent which delivers air to the radiator had to be trimmed about 5/8" (on this installation) to account for thickness of the new core and slight dimensional differences regarding how the radiator suspends from the end straps. I do have the air filter in the back of the NACA vent and by some confluence of circumstance - The filter location was not a factor with the trimming of the back edge of the NACA vent.

Referring to the original build manual for the FFW - I followed the same order of business in locating the radiator in the lower cowl, accounted for the slight forward location of the front of the new radiator and maintaining the bottom clearance with the cowl & trimming the NACA vent with a small wheel. Next determined the correct length of the end straps and hung the radiator, then determined the correct length and bends for the center strap. Decided to use 1/8" X 3/4" aluminum strap rather than SS strap. When drilling up through the bottom for the three rivets, I used a drill stop - although there is plenty of room - one "oh tinky poo" due to a slip of the wrist would cost too much in terms of $ and unnecessary work.

All in all I have to say the amount of work was not bad at all, the installation and modifications needed are straightforward and I am happy with the end result.

For extra points, the new radiator weighs a bit over a pound less than the old one. I also went from the Evans waterless coolant to 60% Dex Cool which should give a boiling point of 270 degrees F. with the pressure the system operates; and, under standard conditions.

Did a pressure test of the new radiator prior to installation as well as a flush & reverse flush with detergent/solvent/fresh water flush drained and sucked dry with the shop vac. No leaks and very little crud flushed out - just a few flakes due to the welding. Also worth noting the end tanks and core support are fairly heavy gauge aluminum and the welding is solid.

So how did it perform??? My initial test was 90 degrees OAT , 75 F dewpoint, altimeter 29.90 - Full power climbout and the CHT stayed at 220F where I would normally see 240F. No idea how much of that was due to new radiator and how much was due to the coolant change since both were changed at the same time; but, In my opinion, the combination hits the sweet spot. ......Plus I don't have those incriminating damp spots on the radiator now

Sincerely,

Dave S
KF7 TRigear
912ULS Warp Drive
St Paul, MN