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?

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I moved my gearbox vent outlet (from underneath the firewall) to a location towards the top of the firewall. I used a modified motorcycle brake fluid reservior as a "catch can" (first picture, below).  The "modification" is drilling a small hole under the cap so air can escape.  Also, ignore the "upper" and "lower" level marks on it, as they are not relevant in this case.

I'd noticed some oil on the bottom of the fuselage, just aft of my old vent location. Rather than venting oil overboard, and thus losing it, I thought it would be better to allow that oil to drain back into the big aluminum gearbox oil reservior.

Seems to be working fine. Not losing anymore gear oil overboard. Haven't even noticed any reaching the level of the new "catch can".

The way I routed the vent lines on my airplane is shown in the 2nd picture below.

We now have a no-external-vent bottle system perfected.  It was demonstrated at our 2018 engine course but we did not get video of it.  Maybe someone else did?  If not we will post it here.  Basically it works like this:


That seems like a good improvement on the gearbox venting.     With this new design, will there still be a way to have a sight tube just to make sure we can see that there is sufficient oil in the gearbox?  

Hey Charlie:

Any external hoses can not be relied upon as sight tubes. The gear oil is way to sticky even after shutdown to show an accurate oil level referencing inside to outside of the gearbox. Since you decided to upgrade to the heavy duty turbo engine version, it includes a sight glass on the side you will be able to have an accurate reference.


I know what you are staying about the tubes being a poor choice to determine how much oil in the gearbox on shutdown.  I was thinking more about pre-flight when it is cold.

Glad to hear about the sight glass on the HD gearbox.

Thanks for continuing to work on improvements, we all benefit from that approach. 



We just emailed Alissa today to get our new vent, a question I have is about a possible sight glass in our 130 gearbox. Would you say there is any option to install a possible thread-in sight glass to the bottom gearbox hole so that way you could at least see if there is sufficient oil in the system.  I'm not sure it is necessary, we just want to make sure we have enough oil in the system and not too little or too much. thanks for your time. 


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