Rotax 912s intermitant high oil temp

[NYBOR]

Hello. I have a Searey amphib with the 912s engine. Oil temp was fine for a year, but last trip it ran very hot (260 F) and I had to nurse it to the airport. But, when topped off with Avgas, it ran cool the entire trip back home???? I had been putting no-lead mogas in it before this trip.

 

The only thing i have done differently was use Yamaha Racing Oil, instead of the Aero Shell for Rotax engines. I have just changed the oil filter and went back to the Aero Shell - haven't flown it yet.

 

Does ANYONE have any idea what is going on?

 

thanks in advance

 

dave

 

 

[NYBOR]

oops, regarding the previous post, I meant to say non-ethanol mogas.

 

 

[facthunter]

Was the mogas 98. Nev

 

 

[NYBOR]

No it was 89 octane - and some 93. mostly 89. is that too low????? it seems that it HAS to be fuel related, since that was the only thing i changed on the flight back when everything was in the green.

 

thanks

 

d

 

 

[Garfly]

The US and Canada use a different measure of Octane rating than most of the rest of the world so those numbers can't be directly compared.

 

http://en.wikipedia.org/wiki/Octane_rating

 

 

[NYBOR]

Hmm. just looked up the difference and read this?????

 

Both Canada and the US use the same system for Octane ratings (RON+MON)/2.

 

 

[Garfly]

Yes, that's right. North America uses the same measure but Australia uses a different one so when facthunter refers to mogas 98 you'd have to make the adjustment.

 

 

[facthunter]

The only change you made was to add Avgas. That would have raised the octane rating so there's your clue. The 100 hp engine runs the higher octane mogas normally and should not use the lower auto grades. You can't trust auto fuel all the time as it can be doctored at points along the delivery chain. Nev

 

 

[Guest Maj Millard]

Mybor, Minimum recommended octane for the 100 HP engine is 95 as it is a high compression engine. They will handle straight avgas or a mix just fine, but don't go below 95 octane.

 

Yamaha racing oil is not approve for use in that engine, so that may well be the problem. Aeroshell 4 is approved so stick to that in future, and your temps should be fine.

 

Also you Probabily need to familiarise yourself with Rotax Service bulletins so that you know what to use , instead of just what's available. Hopefully you haven't done any gearbox damage by using the unapproved lubricant................Maj....

 

 

[fly_tornado]

oil wouldn't cause intermittent increase in temp, bad fuel might

 

 

[Guest Maj Millard]

The wrong oil certainly would when it is also used to lubricate the gearbox !.....Rotax recommends certain oil types for a reason, it's only when operators ignore those recommendations that problems occur............Maj....

 

 

[fly_tornado]

we have to agree to disagree, Yamaha spend more on engine R&D in a year than what Bombadier give Rotax every decade. Rotax ended using Rockwell ECU in there new engine, so I don't think they are close to Yamaha in engine development.

 

 

[facthunter]

Regardless of good oils being about, in the case of the Rotax clutch/damper arrangement, I would stick to the maker's recommendation, more so than with most other motors , with reduced oil change period with use of avgas. In the short term I don't believe the oil would cause the significant temp change noticed. Was there an ambient effect or was a slower climb speed used?. I don't like to think about HOW a too low octane fuel would have raised the oil temp, but it is not to be ruled out but you would normally notice a power loss.

 

With most synthetics in these ROTAX applications 130 degrees C is still safe from damage, though out of the desired range. Nev

 

 

[Guest Maj Millard]

we have to agree to disagree, Yamaha spend more on engine R&D in a year than what Bombadier give Rotax every decade. Rotax ended using Rockwell ECU in there new engine, so I don't think they are close to Yamaha in engine development.

Regardless of wether you disagree or not, it is simply not an approved oil for the engine, and therefore should not be used...end of story........People like you had thought the same about MOTUL oils, but they ended up causing huge dramas with the sprague clutches because of some additives they contained.................Maj....

 

 

[cscotthendry]

I don't think it's related to the brand of oil, for the reason that Dave said that when he filled up with avgas he was able to make the trip home without further oil tem issues. He did not change the oil until he got back home and hasn't flown the aircraft yet. So the only difference between the two flights (as far as we know from his post) is the different fuel used.

 

I suspect bad fuel on the first run may have caused detonation in the engine which would have raised the temps.

 

Something I have noticed on my own aircraft is that if I do a long climb at cruise power, the oil temp rises without an attendant rise in coolant temp. Maybe something along those lines was at play here?

 

 

[Guest Maj Millard]

I don't think it's related to the brand of oil, for the reason that Dave said that when he filled up with avgas he was able to make the trip home without further oil tem issues. He did not change the oil until he got back home and hasn't flown the aircraft yet. So the only difference between the two flights (as far as we know from his post) is the different fuel used.I suspect bad fuel on the first run may have caused detonation in the engine which would have raised the temps.

Something I have noticed on my own aircraft is that if I do a long climb at cruise power, the oil temp rises without an attendant rise in coolant temp. Maybe something along those lines was at play here?

Quite possibly Scott, however as soon as he mentioned the unapproved oil, flags went up. Using straight avgas will bring the temps down a bit also in my experience, which is what he experienced on the way home. It is possible he was getting the high temps from sub-standard fuel, however had the engine been experiencing detonation, you would also expect a rise in cyl head coolant temps also, which he made no mention of......the Searay is a big heavy machine and may well cause the oil temps to rise if a protracted slow airspeed climb is carried out at high power............Maj....

 

 

[cscotthendry]

however had the engine been experiencing detonation, you would also expect a rise in cyl head coolant temps also, which he made no mention of..................Maj....

Good point

 

 

[fly_tornado]

Yahama racing oil is designed for motorcycle engines which like the 912s have integral gearboxes and clutches. Its not a car oil

 

 

[facthunter]

It might be a great oil. The 'clutch" is a torsion vibration damper in the case of the Rotax, set to a grip figure/range. If it (Yamaha oil) meets the specs I am sure Rotax will approve it, but why risk these things? Why would you expect Rotax to support you, if you won't use the oil(s) they recommend ? The damper is there to protect the crankshaft.( and the prop)...Nev

 

 

[Ultralights]

what about an air bubble in the system somewhere?

 

 

[Guest Maj Millard]

what about an air bubble in the system somewhere?

Well I'm wondering if the line to the fuel pressure gauge has been correctly bled, could be air caught in there.....Maj....

 

 

[geoffreywh]

The FIRST thing I would check would be the temp guage!