is it a must to flush lower unit oil for new synthetic?

[vesselgreenhead]

I;m changing my lower unit oil for the first time on a new 150 mercury. I don't believe the oil in the lower unit is synthetic from the factory. I am opting to use a fully synthetic oil and will stick with it. can i just drop this oil and replace with synthetic or must i flush it some way before pumping synthetic. some folks tell me that non synthetic oil and synthetic should not mix, not even a drop?? secondly, what is the best synthetic lower unit oil on the market for this application for normal run abouts, (Normal Cruising) all replys welcome.. THANKS

 

[corm]

Re: is it a must to flush lower unit oil for new synthetic?

Hi,<br />THe reg oil will dilute the synth enough so it wont be any better than what you have.<br />Merc maks a synthetic for your motor. So you can run it and change it out again and be ok.<br />I only use syn for pontoon boats and Fast boats with nosecones. The syn oil seems to transfer heat better. I've used several brands and have stabil or staoil(I think) 90-140 offroad raceing oil for truck rearends. in my boat now.Th Merc syn works good in IO's so will work good it your 150. I don't feel it is necessary to run it under normal usage.<br />...have fun...corm

 

[BayStLouis]

Re: is it a must to flush lower unit oil for new synthetic?

As long as you let the gearcase drain as dry as possible, the little bit of conventional gear oil remaining shouldn't cause any problems when you refill with the synthetic stuff. I think you'll be okay, but if you want an extra bit of insurance, do a second drain & fill after the first time you run the boat. The synthetic lube is more expensive, but that should remove just about all of the lingering dinosaur juice.<br /><br />On another topic, I recognize your "handle" from the old Woodenboats forum. Did that forum shut down or just move to a new URL?<br /><br />Thanks...

 

[ODDD1]

Re: is it a must to flush lower unit oil for new synthetic?

change the lube and dont give it a second thought....merc puts regular lube in their cases from the factory for breakin purposes...a synthetic would be what you should use now, mercs hp lube is good stuff..as far as not mixin this stuff..BALONEY..

 

[OBMD]

Re: is it a must to flush lower unit oil for new synthetic?

You will have such a small amount of regular gear oil left in the lu that filling it with synthetic and mixing will not effect the syn oil. What brand are you going to use. I suggest Merc High performance.