2000 Mercury 90hp 4 stroke pro series

[mcduffeejm]

Hello everyone! I could use some help. I am currently experiencing water in my crankcase oil. It is milky brown. I am going to take the motor off and tear into it this winter. I am trying to find a gasket kit and carburetor kits for it. I am having trouble figuring out what to get. Any help would be appreciated! Model number 1F90412WN I have included pics of what my spark plugs look like and what my oil looks like.
Serial number 0T158752

 

[Yegboats]

Hello everyone! I could use some help. I am currently experiencing water in my crankcase oil. It is milky brown. I am going to take the motor off and tear into it this winter. I am trying to find a gasket kit and carburetor kits for it. I am having trouble figuring out what to get. Any help would be appreciated! Model number 1F90412WN I have included pics of what my spark plugs look like and what my oil looks like.
Serial number 0T158752

Mercury is making a lot of the parts for "their" early carbureted 4 strokes obsolete. These engines were a joint venture between Yamaha,and Mercury using Yamaha powerheads this lasted from mid 1995ish to around 2005ish. It ended in a lawsuit as I understand. You may have better luck,and pricing if you can source your parts through Yamaha.
Mercury no longer supplies the engine rebuild gasket kit for your engine. When they did the last price i can see was around 500 canadian for it. Another example of this would be (1) of your carburetors from Merc that is still available is around 800 canadian. Yamaha is around 250 USD
Also before you tear into your engine make sure you start with compression and make sure water in oil isnt from tstat stuck open,or extended trolling.

 

[mcduffeejm]

Mercury is making a lot of the parts for "their" early carbureted 4 strokes obsolete. These engines were a joint venture between Yamaha,and Mercury using Yamaha powerheads this lasted from mid 1995ish to around 2005ish. It ended in a lawsuit as I understand. You may have better luck,and pricing if you can source your parts through Yamaha.
Mercury no longer supplies the engine rebuild gasket kit for your engine. When they did the last price i can see was around 500 canadian for it. Another example of this would be (1) of your carburetors from Merc that is still available is around 800 canadian. Yamaha is around 250 USD
Also before you tear into your engine make sure you start with compression and make sure water in oil isnt from tstat stuck open,or extended trolling.

Thank you for your help. I plan on doing a compression test. I didn't think about the thermostat being stuck open. That would be a little easier check and replace. I did talk with mercury marine and they said the same thing about the gaskets and to check with yamaha. I called yamaha and the lady helping me said she had never heard of mercury and yamaha working together on parts. lol I did find a gasket kit through seawaymarine.com. My other problem is before I started getting water in the oil, it would run good and then when I would give it more gas it would spit and sputter and then take off. Now I can't give it gas without choking it off. Not sure if that is because of the water in the oil getting past the rings because of increased crank case pressure or my carbs are messed up. Thinking about rebuilding or replacing them also. Again, thank you for your input!!

 

[mcduffeejm]

Mercury is making a lot of the parts for "their" early carbureted 4 strokes obsolete. These engines were a joint venture between Yamaha,and Mercury using Yamaha powerheads this lasted from mid 1995ish to around 2005ish. It ended in a lawsuit as I understand. You may have better luck,and pricing if you can source your parts through Yamaha.
Mercury no longer supplies the engine rebuild gasket kit for your engine. When they did the last price i can see was around 500 canadian for it. Another example of this would be (1) of your carburetors from Merc that is still available is around 800 canadian. Yamaha is around 250 USD
Also before you tear into your engine make sure you start with compression and make sure water in oil isnt from tstat stuck open,or extended trolling.

Question: I haven't had a chance to do the compression test or check the thermostat yet. If the thermostat is stuck, how would water get into the oil in the crank case from that? Sorry, if this sounds stupid. Thank you for your help!!

Justin

 

[boscoe99]

Thank you for your help. I plan on doing a compression test. I didn't think about the thermostat being stuck open. That would be a little easier check and replace. I did talk with mercury marine and they said the same thing about the gaskets and to check with yamaha. I called yamaha and the lady helping me said she had never heard of mercury and yamaha working together on parts. lol I did find a gasket kit through seawaymarine.com. My other problem is before I started getting water in the oil, it would run good and then when I would give it more gas it would spit and sputter and then take off. Now I can't give it gas without choking it off. Not sure if that is because of the water in the oil getting past the rings because of increased crank case pressure or my carbs are messed up. Thinking about rebuilding or replacing them also. Again, thank you for your input!!

Completely normal. A lady working at Yamaha today would have nil reason(s) to know of any Yamaha/Mercury joint ventures from decades ago.

 

[Thirsty Endgrain]

Question: I haven't had a chance to do the compression test or check the thermostat yet. If the thermostat is stuck, how would water get into the oil in the crank case from that? Sorry, if this sounds stupid. Thank you for your help!!

Justin

I've not heard of water getting into the oil from an open thermostat. What I do know (which is not much compared to some here) is that a stuck open tstat/extended low rpm (trolling) can have these engines "making oil," where the oil is diluted by fuel passing the rings as in both cases the proper operating temp is never reached, and the rings don't expand enough to seal at the piston/cylinder interface.

If you have water in your oil it has to come from some part of the cooling system. Def do a compression or better a leakdown test. Sounds like you are tearing into that thing pretty deep this winter unfortunately.

 

[Dave1027]

Thank you for your help. I plan on doing a compression test. I didn't think about the thermostat being stuck open. That would be a little easier check and replace. I did talk with mercury marine and they said the same thing about the gaskets and to check with yamaha. I called yamaha and the lady helping me said she had never heard of mercury and yamaha working together on parts. lol I did find a gasket kit through seawaymarine.com. My other problem is before I started getting water in the oil, it would run good and then when I would give it more gas it would spit and sputter and then take off. Now I can't give it gas without choking it off. Not sure if that is because of the water in the oil getting past the rings because of increased crank case pressure or my carbs are messed up. Thinking about rebuilding or replacing them also. Again, thank you for your input!!

Normally, water in the oil is caused by a blown head gasket. As noted already, a compression/leakdown test will confirm it.

If you have a bad head gasket, water may be getting into the combustion chamber. Basically putting out the fire in that cylinder(s).

New carbs are super expensive. Rebuild them.

 

[flyingscott]

Question: I haven't had a chance to do the compression test or check the thermostat yet. If the thermostat is stuck, how would water get into the oil in the crank case from that? Sorry, if this sounds stupid. Thank you for your help!!

Justin

You will hear it called making oil. The motor runs to cold and can't burn off the condensation. All that excess ends up in the oil pan and Yamahas seem more prone to that. So before anything check your thermostats.

 

[mcduffeejm]

I've not heard of water getting into the oil from an open thermostat. What I do know (which is not much compared to some here) is that a stuck open tstat/extended low rpm (trolling) can have these engines "making oil," where the oil is diluted by fuel passing the rings as in both cases the proper operating temp is never reached, and the rings don't expand enough to seal at the piston/cylinder interface.

If you have water in your oil it has to come from some part of the cooling system. Def do a compression or better a leakdown test. Sounds like you are tearing into that thing pretty deep this winter unfortunately.

How do you do a leakdown test?