lower unit cooling

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trapper

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Morning guys, I seem to always have more questions than answers, may be one day that will change. Anyway, Is it possible to have the lower unit on my Yamaha f 200 run hot because of trimming the outboard up too high? My optimum speed without cavitation is on the fourth bar from the bottom, or one from the top on the trim gauge. I guess I am still trying to discover the reason for the drained black gear lube in my last post. As mentioned before I have changed the gear lube to Mercury high performance, so doing my best to cover all the bases. Cheers, trapper
 
How many trips are you getting out of it before it turns black? The lower unit gets cooled for the most part by being submerged in water. If your lower unit is in good shape (pressure test ok , not losing oil, vaccuum test ok, not taking in water) you should be able to get a season out of it without any change in the looks of the oil.

The main reason its getting black is because its getting too hot. Either youre losing oil and its getting cooked, or an internal component (bearing, gear, shaft etc) is causing excessive heat.
 
do you have a water pressure gauge? is your engine running hot? does the engine pee ok?

i know the v6 yamaha has dual water pickups, but not sure about the 4. the lower unit is cooled by the lower pickup that also cools the motor. so usually the lower unit would be the last thing to overheat if you went too high. you will normally lose the high pickup first. this would result in water pressure issues and overheating of the motor before a problem with the lower unit.
 
Thanks guys, Yes I have a water pressure gauge that shows 20 psi when running a my normal rpm 3800 t0 4000 rpm. Engine temp has never risen over normal. Running with my trim at the fourth bar gives best speed for the rpm. I agree that if the motor was too high the lack of water to cooling intake would be the first sign indicating that the engine was overheating due to lack of water flow to the engine. Not sure what you mean by dual water intakes susukidave, Mine has one on each side of the lower unit (one that is joined to both sides?) On draining the lube I have never seen any sign of water intrusion or lube leak. Ok I will keep and eye on things closely and check the gear lube after a few hours of running.
 
susukidave, The F200i4 only has the single pick just centre and above the gear housing. Thanks trapper
 
trapper said:
Morning guys, I seem to always have more questions than answers, may be one day that will change. Anyway, Is it possible to have the lower unit on my Yamaha f 200 run hot because of trimming the outboard up too high? My optimum speed without cavitation is on the fourth bar from the bottom, or one from the top on the trim gauge. I guess I am still trying to discover the reason for the drained black gear lube in my last post. As mentioned before I have changed the gear lube to Mercury high performance, so doing my best to cover all the bases. Cheers, trapper
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I seem to remember several responses to this issue that mentioned that some gear oils will turn black under certain conditions. My suggestion would be to run the oil that Yamaha recommends. Black oil doesn't mean it is overheating. In fact all your other measurements are fine. The LU would have to get really hot to burn the oil and if it got that hot you would know it. In addition, burnt oil has a different smell than just plain dirty oil.
 
I very much doubt your trim angle has anything to do with this. If you were trimming it up that high that it was overheating, I would also think you'd be experiencing ventilation of the prop.

What spec is required for the gear oil of your engine? Check your manual, but for now I'll assume it's GL4. The Merc Hi-Perf stuff is excellent gear oil and as long as your drive doesn't require GL5 gear oil, it's not the issue. A suggestion would be to do some oil sampling. That way you can find out if there's anything major going on. You can send it away to a place like Blackstone Labs, or find a local CAT dealer. Typically, it'll run about $20 which is pretty cheap considering the amount of information you'll get back.

Here's what I'd do (always noting the amount of hours on the oil):
-- Take a current sample of the blackened oil
-- Drain the oil and then flush it. Waste a good two quarts worth by filling from the vent hole. Change the trim level of the engine to be sure and flush all areas out. I would even go as far as to artificially heat the gear housing with a small heater. Heat it up for a couple hours to get everything nice and warm inside so the oil flows better.
-- Fill the gearcase and then take another sample after about 5 hours (or whatever you feel is necessary based on prior experience of how long it takes to get black.
-- Do another sample.

Ask the oil sampling company if they'd need a clean sample of gear oil, for reference.

I would also pressure test the gearcase for good measure.

This is just a wild thought, but I wonder if maybe some exhaust gases are getting in there. You would think that exhaust water would then be getting in there, too, though. The Merc stuff would turn light green with water (only), but maybe there's only gasses getting in there somehow. You could collect the gear oil in a jar and see if water separates out from it, though (easy and free test, if for nothing else than to eliminate variables).
 
Thanks DenisGO1 and seasick for your input to my concern. I will follow through with running a few hours on the new lube, drain, flush and fill again and see the results. If things haven't cleared up I will forward a sample to the oil gurus for a diagnosis. Great site and great guys with much knowledge and so willing to share. Thanks, trapper
 
On the off chance that you need to sample the oil, keep any oil that you drain out. Put it in a clean jar and label it. Most sample companies only require about 6 or 8 ounces (at the most), so just keep at least that much. Meaning, you don't have to keep everything.
 
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