I would like to hear from people who have tried different ways to vent their gearbox.  I know Jan has used a few different designs in recent years and it would be helpful to hear from people which ones worked best for them.  

I see the new gearboxes have an oil separator ports on them and that may work well.   

Also, do most find that 8oz of 75w mobil one full synthetic is working well?    Any issues with foaming at high RPM?

Views: 908

Reply to This

Replies to This Discussion

Add as much oil as the system will accept.  Usually 12oz is good.  Drain and replace often to keep a close view of the condition.  

Tie an old sock around the vent until everything has settled down and you are familiar with the venting.  


Thanks.   I have  noticed over recent years of different venting routes on the gear boxes.    Can  you share what you have learned.   How important is it to vent both of the holes on the upper face of the GB?   Is is always best to vent the one at the top, or will one or two of the ones on upper face suffice?    

I only have a few hours on mine and I have experience some slight overflowing of the 75w mobile one synthetic, but I think this will be manageable with a few minor changes in the vent line routing.

P.S.   Are you OK with clear polyurathane tubing?   (Not PVC).

I hope other builders jump in here and comment too.  We are here to share ideas and experiences and help each other out...


(move to bottom of page.)

We have only done a few short test runs. With that in mind, here's some photos showing what we have observed.

This photo shows how our system is set up.

Here's a photo after adding 16 fluid ounces of 75W-90.
Here are three photos of what appears to be some aeration after a short test run:
Contacted Jan and he said it's not a problem.

More photos here ––> https://www.facebook.com/Experimental750ES/posts/501307906916339

Sam, I appreciate you posting the info and pics. I only have a few hours on my gearbox too.

Is your oil level about 2" above the bottom Port while cold and at rest? Jan's been very helpful.

I'll try to post a pic of my current vent set up. I may have to switch to a larger reservoir. The small one in my pics is actually a Yamaha mater brake reservoir I had, and at high RPM it gets filled. And I do not think I have too much oil in the GB...Charlie

Picture of my gearbox and current venting solution....

The best system so far on the 130 is the new aluminum catch can but with a hose from the top of the can, above the engine and down the firewall for an exit.  The vent cap supplied with the unit can leak oil.  

Here's a picture of the Gearbox Oil Reservoir I installed yesterday (still need to secure some lines/wires, but no leaks).

I cleaned out the old plastic gearbox reservoir and swapped it out with the old coolant reservoir.  Here's a picture of the old one and the new one that I've got on my plane.  When I originally installed the larger old one, I had to shape it with a heat gun to make it fit.  New one is smaller, fits higher up on the firewall, and doesn't entail carrying around a pound of excess coolant all the time (have not seen any change in coolant level during operation).

- Pat


Thanks for sharing.    So the top line goes to that white resevoir on the firewall, in addition to the black tank you have up near the gearbox?   If so, why did you choose to use two tanks?  Just curious.

Also, the black colored tank up front is that something you made or is it an off the shelf product?  

Last, the temp probe.  Interesting, have you run it long enough to get a feel for average temps, and if so, is that in flight or ground testing?


Hey Charlie, the hose coming off the top of the black tank is the vent line for the gearbox.  This line goes up, over the engine, and down the firewall.  I bought the black tank from Viking.

The white tanks are different.  They are for the coolant overflow.  The big tank is the old one that I removed.  The smaller tank is the new one (which was my old gearbox overflow tank, but I cleaned it out and re-used it for this.  Hope that makes sense). 

I haven't taken any special note of the gearbox temperatures during flight testing, other than not seeing any temperatures (indicated on the Viking View display) that were any cause for concern.   A lot of that kind of data also gets separately logged to a Data Logger, but I'm still learning a lot about that).

- Pat


Yes, that does make sense thanks for clarifying that.   Good flying to you!


I have both the aluminum canister installed, and I received an email from viking recently suggesting the canister be vented out the top and down the firewall.  i then debated running from the top of the canister into the clear tank (which i had, but was never installed).  this way it would catch anything that was frothed/pushed out.  more for inspecting the oil if it were being pushed out, and then perhaps it would settle back into the gearbox.

Also, I'm interested in the data logger you have as well.

Thank you all for the photos!



New from Zenith:

Zenith Planes For Sale 

Classified listing for buying or selling your Zenith building or flying related stuff...

Custom Instrument Panels
for your Zenith

Custom instrument panels are now available directly from Zenith Aircraft Company exclusively for Zenith builders and owners. Pre-cut panel, Dynon and Garmin avionics, and more.

Custom Upholstery Kits for your Zenith Aircraft:

Zenith Vinyl Upholstery Kits

Zenith Apparel from EAA:

Zenair Floats

Flying On Your Own Wings:
A Complete Guide to Understanding Light Airplane Design, by Chris Heintz

Builder & Pilot Supplies:

How to videos from HomebuiltHELP.com

Developed specifically for Zenith builders (by a builder) these videos on DVD are a great help in building your own kit plane by providing practical hands-on construction information. Visit HomebuiltHelp.com for the latest DVD titles.

Aircraft Insurance:


West Coast USA:

Pro Builder Assistance:


Transition training:

Golden Eagle Aviation

Pianosa Flying Farm

Aircraft Spruce & Specialty for all your building and pilot supplies!

© 2022   Created by Zenith.Aero.   Powered by

Badges  |  Report an Issue  |  Terms of Service