Exhaust fumes in the Highlander-Help!

[marl59]

Well I took my better half for her first flight in my new to me Highlander, Rotax 912ULS, yesterday. She liked it a lot but the exhaust fumes in the cabin got to both of us. We got relief when I opened my window. I know its like swiss cheeze in these planes so I will seal every possible opening at the firewall. My straight cut exhaust stack only sticks down below the cowling opening about 2" or so. I have to assume that I am not the only one who has faced this problem. Anybody ever extended the exhaust pipe to get the outlet further down in the slipstream? I read after searching "fumes" on this forum that it was suggested it may be coming in around the tail wheel. Id love to hear of someone who had the same issue and was able to solve it! Thanks in advance for your help!

[donRNO]

I check mine with a very sensitive meter from time to time. The result is always the same: 0.0 ppm of CO. Same thing with the exhaust-muff heater open fully. Extending the exhaust stack could help your situation.

[marl59]

Thanks donRNO, I'm glad you're not having this issue. Are you running the Rotax? Is your firewall really well sealed around the perimeter and the penetrations? Mine is not, yet.

[scubarider2]

I run a Rotax 912uls with Toucan double exhaust and have never had an issue. They stick out below the bottom cowling at least 6inches if not more. My firewall is well sealed with no issues there.
All I can recommend is to make sure you do not have any leaks inside the engine compartment and seal your firewall as well as you can. If you still have issues then extending your pipes might have to be your next step.
Dennis

[marl59]

Thanks scubarider, wilco. I'll post my results.

[marl59]

So I dismantled the entire skin of the a/c back to the front of the seats. This plane has sheet metal between that point and the front cowling. I used high quality glazing tape, (it's double stick but I left the protective layer on the one side so I can easily remove the part later), 1/16" x 1/4" and 1/8" x 1/4" as needed. Sealed all of the cable/wiring firewall penetrations with acrylic latex caulk with silicone. Test flight results were about an 80 to 90% reduction in perceived exhaust smells. I'm going to extend the exhaust stack down and to the starboard side with an automotive 45 degree extension pipe and a balony cut just to try to make the goofy thing look halfway cool. FWIW.

[alan]

I've never had exhaust fumes in the cabin of our Highlander. I started with a Toucan system and then went with a 4 into 1 system. My firewall is not particularly sealed with the throttle cables just sliding through a couple of modified bulkhead fittings. The top isn't sealed at all with a flexible rubber strip folded over against the boot cowl.

All the airflow should move down and out the bottom. Since you have fumes you should carefully inspect your exhaust system for leaks. Leaks will show up as stains around the joints. I don't have to tell you how serious a problem this can be.

Good luck.

Alan

[marl59]

Thanks Alan, its comforting to know that this isn't an inherent problem with the Highlander. I'll do a thorough inspection of the exhaust system as you said and post my results.

[marl59]

Well I inspected my exhaust system and found no evidence of leaks. I replaced the springs holding the system together as well. Then as I said previously, I extended the single exhaust outlet with an automotive stainless steel, 45 degree extension pointed back and out the starbord side a bit. Problem solved. No more hints of exhaust smells in the cabin. Thanks for all of your input!