Upgrading to silicone hoses at 5 year rubber change?

The tank pad is rubber and when exposed to heat and in time it will deteriorate.  The recommendation to change it at 5 years is shown in the new list of 5 year time life items to be replaced.  Given that in the past some have failed this is a preventive measure to be sure that the tank is protected.  Facts are that some fail in a few years and others may last a decade.  The question is what changed.  Suppliers change, rubber composition changes and the installations change.  All these variables make it impossible to predict a failure point so the 5 year is felt, like with hoses, to be the best time to match when you going to remove the hoses anyway.  (except the silicon ones) 

If it is an experimental you are good to do what you want, treat it as a recommendation. 

Cheers

 Quote: "The tank pad is rubber and when exposed to heat and in time it will deteriorate."

I fully agree so why not do it on condition since it's  so visible. Plus I've seen them 15+ years old an not an issue. If it isn't  rubbing on the case and not cracking or falling apart then why not on condition. It's  just a contact barrier between the expansion tank and the case and most never touch the case. I've never had one in the shop that has been rubbed, only broken rings where they attach. Rotax uses "O" rings throughout the engine with heat for 12 -15 years under more stress.

Sorry I'm  a research science guy and do research and testing all the time.  

Sorry,  I'm  not trying to be argumentative I just do lots of testing on many products.

I love research. ❤️ 

Hi Roger

Interesting viewpoints.  The issue rests with the failure of a substantial number of said pads about 8 to 10 years ago with the introduction of the 912iS.  In a large number some were found with failed attach loops cracked while removing them from the shipping box.  The result is this, the recommendation to replace with the 5 year rubber exchange.  It is subject to heat and also UV.  The O-rings internally are not the same at all.  They receive no UV and do not have the same vibrations and are not under tension like the loops on the pad.  I agree this is visible and can be inspected however Rotax has not given us an inspection protocol.  Normally such a protocol is going to be called out, such as checking spark plug gap at intervals to determine wear.  Rotax felt it better to replace this at the 5 year.  (preventive maintenance is the term) Naturally you can ignore that and do your own visual and decide if you are doing this for yourself. If you wish to not do this at the 5 year and are doing this for hire then that is a call you have to make.  

If the aircraft is flying students I personally feel it better to change it. As a note the original pads from 30 years ago were "glued" on the bottom with no loops.  I used to find these all the time stuck between the cylinder heads or gone altogether.  The factory experience does not support simple glue or some type and this is partly why they went to a pad with loops to attach it to the hose nipples of the tank.

One last note.  The reference used for silicone hoses is from the 915iS.  The addition of the pad into the 5 year list is a relatively new addition.  This was added in the latest version of the 912/914 series MML at the same time.

Cheers

First i fully agree on all other rubber replacement  at the 5 year mark.

I pretty much follow all Rotax rules and publications, but I  love to research and test.

p.s. 

I love to debate and learn from all. Learning is what life is all about. We just pick different  areas to learn. ?

I understand why Rotax has it this way. Like you said I have seen a some pads  that have had broken attachment loops and had slid out of potisition as you mentioned, but i have never in 15+ years seen a siliconed one come off a tank and many pads never touch the case. Pads that have come completely off was missed by owners and mechanics due to poor detail observation in pre-flights or annuals. If siliconing things on was an issue then Tanis and Reif wouldn't  silicone the oil tank heating pads on the hotter oil tank and when applied properly don't  fall off. How does this pad have deteriation from UV (ultraviolet light) in a crate  or in a cowl? The "O" rings are subject to more heat and not open to any normal inspection. The under cowl temps in planes I tested with heat strips all over were around 145F ish. Yes some were higher due to poor air flow which is due to poor mfg testing and manufacturing. The metal temps in many places where "O" rings are can be are 210F ish to 245F ish. The silicone adhesive can actually add an extra layer of protection.

For me common sense and paying attention the researched detail help in making this particular decision. I do lots of testing beyond the norms. It helps understanding why some decisions are what they are from Mfg's. 

I just did one on metric vs US standard hose because some said there was a big difference. I tested US and metric hose from Gates at 10 - 20 times the pressure we use without any issues. So it boiled down to their poor installation techniques. Too many times things are all in the details.