A crystal clear, severe clear, blue ski day, with all kinds of fresh untracked powder just waiting to be tracked up, following a couple weeks of crap weather, so I of course blew off snowboarding and headed towards Afton for breakfast. A neighbor a 1/2 mile away had texted me earlier, wishing me Happy Happy, (I'm sick of hearing HNY) and he mentioned he had not noticed much activity by my place and just wondered if everything was AOK. Not sure what all he meant, same old same old here, but just to reassure him and his wife things were nominal, I decided to do a fly by. As the front part of the house is about 80% glass, I figured they couldn't miss me, so I did a brisk wing waggle, followed by a 2250 FPM zoom climb (all while follwing the FAA guidelines/laws etc) and then set course for the cafe 50 miles away. So now I'm 1,000' or more above my place, and about 3 miles away, and I did something I rarely do, I looked at the EIS and actually read the numbers. MY GRT EIS has a big red idiot light, if steady, all the parameters it is set for are being met, if it starts blinking, get your ass on the ground. So, my excuse for not doing a proper instrument scan like with steam gauges, but while the red light was steady, I noticed my CHT's were climbing in a way that didn't make sense. Throttling back, I thought things over, and then realized I'd have to make my own damn breakfast, Afton was not happening today. The Rotax heads are liquid cooled BTW, so an increase in head temps is as good as a increase in coolant temps.

With the engine at idle, I easily glided back to my strip (the first part of the perfect timing, to have an issue so close and high above home), in fact I had to slip off a bunch of altitude to make it in without making a goaround, no problem as I enjoy slips anyway. Now as I touched down, I was hoping that whatever was happening wouldn't result in an engine stoppage as I really didn't want to find out what happens if I lose power while on a 14% grade, I'm not sure my tail ski would be steerable in reverse, and I took my convex mirror out, for looking at what was going on behind me (usually a passenger's face) a couple years ago.

No problem, I made it up all the way to my level spot, where I can deploy the wheels and shutdown. Once back in the heated hangar, it was a 40 minute job to look for a bad coolant line (all good), and then I noticed a steady drip from the radiator......so I took it off, plugged the outlet, and supplied 3 lbs of shop air to the inlet while holding it underwater in the shop sink. The radiator had blown, the clear cause of the coolant leak, big fat air bubbles, mystery solved! Whether it was internal erosion (2350 hours TT), or something else, I at least had found the problem. The last part of the perfect timing thing: last night and today were the coldest of the winter, better to have this problem, this day, within gliding distance to the hangar and shop, then over the frank in July. I hope the rest of this new year stays this lucky for me. And for those flying behind air cooled legacy engines who are chortling about now, I get it! But then again I only burn 1/2 qt of oil every 50 hours, have zero oil leaks, don't have to worry about shock cooling, have an aux source of cabin heat, and generally enjoy the other benefits of a closer tolerance liquid cooled engine. But yeah, no free lunch, with all that comes another way to have a problem, if suffering a coolant loss.

Just now, I was googling "custom radiators", and making a list of them, (1 in Oregon, 2 in Arizona, time is of the essence....) and stumbled upon one heretofore unbeknownst (?!) to me, in Rexberg Idaho, my backdoor, 1 hour by Prius anyway. I had already planned to send it to whoever I chose to make a new one, just as an easier way to show how I wanted the mounting holes etc. Guess where I'll be at 8 sharp tomorrow morning. and they BETTER be open, (another bit of good timing, this didn't happen at the start of the holidays) I will hopefully jumpstart the process, and save UPS fees plus most important, time. I am hoping for total crap WX for the next few days, and being super busy at work.

I've always enjoyed your attitude and perceived (through the forums) outlook on life and this story reinforces that

I've always said that I don't begrudge a mechanical issue whilst still on the ground but a mechanical issue within gliding distance of your own heated hangar is a close second.

I'm glad that turned out the way it did.

Happy New Year, btwl-)

My custom radiator shop of choice has been very helpful, after I drove up there and walked that fine line between being a total PITA while at the same time stressing the fact that I need a new one fast tracked. I'll have the new one by the end of the week I'm now told (NEXT week), though I really wanted one 20 minutes after the old one failed, that will have to do.

He told me the old one split along one of the tubes that the fins are attached to (he had a different term) internally, leading to the rapid loss of coolant. He said he would get a better quality core, USA made, the old one being imported, from some country with a C and an A in it's name, and the quality left something to be desired. I bought it in Arizona. He said mechanical stresses can take a radiator out over time, so many cycles of expansion and contraction, kind of like an old airliner gets stressed everytime it pressurizes.

One thought I had along these lines: the radiator is solidly attached to the fire wall, the engine is on rubber mounts, and the two are attached of course by 1" hose. So maybe a bit of engine vibration/movement gets transmitted through the hose. I should mention the failed one was NOT the stock RANS one supplied with the kit, oh no, that wasn't good enough for me, but a larger aftermarket one. There is no epidemic of Rotax 912 radiators failing near as I can tell. I have had rads fail in cars and trucks, old ones with a lot of miles on them, it happens. A further item that may have precipitated this failure: is the diverter valve I installed that changes the fluid flow up into the under the panel HX in the cabin, in effect bypassing the radiator. This is extremely helpful in bring the engine up to temps, and keeping it there, during winter flying, the extra cabin heat (I have a muffler air heater also) is a side benefit. The way the diverter is installed, it made what should have been 8 or 9" of vibration absorbing hose, more solid, with only 3 or 4 inches of hose left to absorb vibrations. Not much I can do about this, if this is even a possible factor, not any spare room down there to change things, and I sure am not giving up the diverter, it's too handy. Fly enough and things wear out, better then the alternative, NOT flying.

I wouldn't stress too much about the MTBF on that radiator; 2350 hours of service for what it cost is well worth not having to re-engineer a more robust solution. I'd say it did its job.

Great to hear things falling into place , considering the alternatives. Another good time for crap to hit the fan [as if there is ever a good time] for me is WINTER. I agree with you on the radiator , 2200 hrs was a good run for it. Like you, I have been down for 1 1/2 months due to engine rebuild, Have had several neighbors call as you have wanting to know if all is well. I think some enjoy my flying as mush as I do!

Good luck on the radiators and may the Good Lord continue to provide you good options when needed.