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Author Topic:   Mercury Oil System: Plastic Gear Failure
BILL LOTT posted 09-14-2007 12:00 PM ET (US)   Profile for BILL LOTT   Send Email to BILL LOTT  
I got into weeds so bad that no water got to engine. The temperature reached 200° and shut down engine. Next day plastic oil gear on my Mercury 175-HP failed. Did heat cause the plastic gear in the oil system to fail?
sosmerc posted 09-14-2007 08:20 PM ET (US)     Profile for sosmerc  Send Email to sosmerc     
I have no evidence to prove it, but I do believe that overheating the powerhead can lead to this failure. The boats that I service on a regular basis and get water pumps, thermostats and proper annual service just don't seem to have these problems.
lurkynot posted 09-15-2007 05:38 AM ET (US)     Profile for lurkynot  Send Email to lurkynot     
One of my biggest complaints with Mercury is all the plastic the use under the cowling. Plastic this and plastic that and all those plastic threads - stripped, darn!

Just this year alone I broke the threads on the tilt/trim fluid level cap, overtightened the oil reservoir cap - under the cowling, overtightened the temp probe in the port head. Not made of plastic but I cross threaded #6 plug hole on my Optimax.

jimh posted 09-17-2007 08:49 AM ET (US)     Profile for jimh  Send Email to jimh     
It sounds quite reasonable that the high temperature of the engine may have contributed to the failure of the plastic gear in your Mercury outboard oil system. The assumption is that the plastic gear that is used to drive the oil mixing pump may have been softened by the high temperature, and since it meshes with a metal gear, it may have been deformed or damaged when it became heated and softened.

The unfortunate news is that repair of the plastic gear in the Mercury oil system is very expensive, and it is common that because of this high cost the plastic gear is not replaced. There are two alternatives: you abandon the automatic oil system entirely and use a fuel which has been premixed with the proper amount of oil, or you replace the mechanical oil pump with an electrical one.

I am curious what your plans are for the motor? Are you going to repair it?

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