Lower unit gear lube for 40HP Yamaha

[Douglasdzaster]

I’m new here. Awesome forum. I’m looking forward to the help. I purchased a Yamaha 40 MSHQ 1992. Got it running and now replacing the impeller. Also changing the gear oil in the lower unit. I’ve always used sae90 . I was wondering if I can put a synthetic 80w90? Also should I check the thermostat on the engine if so how often? It’s been in fresh water.

 

[Scott Danforth]

put in marine gear lube

 

[Douglasdzaster]

These are marine lubes I’m looking at.

 

[racerone]

Gears / bearings / shafts are expensive.----A Yamaha dealer would know the best oil to save you some coins.

 

[Douglasdzaster]

Thanks for the input folks. I really appreciate y’all. Anyone know about my thermostat question?

 

[Sea Rider]

Buy the gear oil whichever SAE Yamaha sells. Will be gook to inspect the thermo condition, if still good can cleant it with a tooth brush, if removing it will probably need to buy a new thermo gasket as the current one may be already hardened.

Happy Boating