Lower Unit Lube-Replacing Synthetic with non-synthetic fluid

[Doncc]

I have a question regarding synthetic vrs. non-synthetic lower unit lube for an older 1961 5.5 HP Johnson. My local marina recommended the Merc High Performance (Synthetic) lube for my small engine. After reading the label on the back it says "don't use with a non-synthetic lube". I assume that it means don't add "make up" lube that is non-synthetic when levels in the lower unit need some more fluid. My question is: Could I go back to a more traditional lube (non-synthetic) if desired on the next or subsequent changes or is it better to continue to use the synthetic fluid? I ask this because I have used the non synthetic fluid in my larger MercCruiser without issues and have plenty of that fluid available to me as well as being half the price for future changes.
I would appreciate any/all comments regarding same. Thanks much.

 

[R.Johnson]

Re: Lower Unit Lube-Replacing Synthetic with non-synthetic fluid

As I recall, when that engine was built, GX-90 hyphoid oil was used. On that small engine, heavy gear pressure is not going to be an issue. That gearcase uses bushing's throughout, there are no ball, or roller bearings. Any of the newer gear lube's should be fine, it does'nt need a synthetic lube.

 

[Doncc]

Re: Lower Unit Lube-Replacing Synthetic with non-synthetic fluid

Thank you for your reply. Do you think I harmed the "seals" by using the synthetic for a short period? Someone suggested that the synthetic might cause leaks as it has a "cleansing" effect that would interact with dirt/water in the lower case and could cause seals to leak.

 

[R.Johnson]

Re: Lower Unit Lube-Replacing Synthetic with non-synthetic fluid

No! I think someone is trying to scare themselves.