Some good news:

First the cylinder bodies were all fine. They measured in spec and had no scaring and no signs of warping.

The better news is the cylinder and heads all passed their hardness tests. The minimum hardness of the heads is 85HB and the Cylinders 90HB.


The heads measured between 102-134 and the cylinders 108-118. The lowest values were for #1 head and #2 cylinder.

As expected the bolts were all loose from the overheat. This probably caused a good amount of the compression loss.

The valves need to be reworked and heads trued up.

At the time of the landing we believe there was about a half pint of coolant left in the system.

The best news is that the insurance will do a pay-out under the clause the gives benefits if reasonable, unexpected expenses are made to protect the airplane from harm. The precautionary landing and teardown inspection fit this, so they will be covering most of those costs and most of the re-installation. Not covered is repair work to the engine.

Right now it is looking that the 7-Oh-Fun will be back in action around the end of January.

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Comment by John Marzulli on January 10, 2013 at 11:00am

Phil: I'm still not sure about the root cause. There are a few hypothesis's

  • Oil temps were a bit higher to start with, so the coolant may have been expanding and dumping out
  • Vacuum in the bottle causing the coolant to be pulled out
  • Large air bubble pushing the coolant out.

I'm open to other hypothesis's.

Comment by Raymond Paul on January 10, 2013 at 10:04am
just thinking if you havent already checked, when pistons over heat but dont sieze up they have a tenduncy to shrink in size, gives huge piston rattle when reassembled and running and starts consuming large amounts of engine oil.
Comment by Raymond Paul on January 10, 2013 at 9:47am

phew what great news John, seems the insurance guys have helped you out some what. Well that goes to prove if you act within the conditions of insurance it pays off, something maybe not all of us a fully aware of when hiccups happen.

Glad the motor is checking out ok thus far, looking forward to the final speculation as to how this happened, as was mentioned rotax's dont just do this sort of hiccup.

Comment by Bob McDonald on January 10, 2013 at 7:04am

For comparison purposes. My winter kit here in Canada consists of about 3 widths of Duct Tape across the bottom of my cowl opening for the oil cooler. I put nothing over the front of the radiator opening. My oil temps run 195 - 212F and cylinder temps 200 - 225F depending if the outside air temps are -20C to +10C.  I have a Rotax 912 oil thermostat but never installed it, and it requires 4 connections in the oil lines + the thermostat itself all of which could fail with "Bad Day" results. I prefer to idle the 10 - 15 minutes it takes to properly warm my engine (KISS). The other benifit of using EVANS NPT is the long life of the coolant. It was 6 yrs ago I filled my CH601HD Rotax 912A 80 hp (1400 hrs)... I check the level but never give it much more attention than that. The 50/50 anti-freeze mixtures go "sour" and the PH turns toward acid = corrosion issues.

Comment by Phil Smith on January 9, 2013 at 11:10pm


Thanks for the update - still curious to know what you come up with as the, as they all have asked, root cause.  The melted bottle has me scratching my head.  Seems even if the bottle had a hole that the coolant would have just vented what would have been a small amount that is used as the surge back and forth between hot and cool engine. Do you think that when the bottle failed that there was a negative pressure in that part of the cowl that "sucked" the coolant through the overflow circuit?? What pressure cap were you using at the time.

BTW check for a source of a more substantial bottle

All's well that ends sort of well - have a great year.


Comment by Rick George on January 9, 2013 at 9:06pm


Thanks for the update. I thought long and hard about using Evans, but decided against it due to the comparatively poor heat transfer rates. Since I also have a 912; I would sure like to understand the root cause of your lose of coolant.  

Comment by John Marzulli on January 9, 2013 at 7:43pm

Actually I am now rethinking Evans NPG with the "New Style" 701 Cowling:

Comment by John Marzulli on January 9, 2013 at 7:11pm

I'm still not sure why the blow out of coolant occurred. The oil cooler and radiator had some aluminum tape on them to keep the engine warm, otherwise I would not be able to get to 120F.

During the flight the oil temps were warmer than normal, but withing bounds. My theory is that maybe as the engine warmed up, the DexCool expanded, blowing out the overflow line. As more coolant blew out the engine got hotter causing more coolant to blow out...

There was about a half pint left in the engine.

My plan is to switch to NPG and a zero-pressure cap. I also plan on changing the bottle to be something other than the stock part, and hopefully not plastic.

Comment by Bob McDonald on January 9, 2013 at 7:00pm

What was the root cause of the over heat condition? Water pump failure, a bad coolant tank rad cap... what caused the over heat condition? Rotax 912's don't normally "blow" the coolant out of the engine, over heated they will as would any engine. It is good to hear your damage is limited, and the engine can be repaired. Using EVANS NPT waterless coolant with a zero pressure coolant tank rad cap is approved by ROTAX in this engine and you will never "blow" the EVANS into the coolant tank.. You have a good insurance agent / company perhaps you can offer their name as a recommendation to other pilots.

Comment by Joe Byrd on January 9, 2013 at 5:39pm


I'm glad to hear that there was no more damage than that to your engine.  Good luck and I hope you are back in the air soon.

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