Mercury motor lower unit very hot

[CHRISBRITTAIN1]

What would cause lower unit to become very hot on 00 mercury 2 stroke 8hp? 1/2 a mile and steam coming off the lower unit from bottom of the motor to propeller, brand new LU Lucas gear oil. Mixed gas to 50:1.

 

[ondarvr]

That's not the lower unit, it's the mid section, the exhaust travels through it.

When was the last time you changed the water pump impeller?

In very cold weather you may see some steam, but there are othe reasons it can become hot.

 

[SeaDooSam]

Was there water coming out somewhere near the power head?

 

[CHRISBRITTAIN1]

Yes the water was coming out in a very nice stream, the water was warm but not as hot as the mid section. Could I have have spun a shaft bearing? not sure on the last time the impellar was changed i just got the boat...should it be so hot that you can only hold you finger on for about 2-3 seconds...56 degree water evaporates in 2 seconds when splashed up on it... I've just never noticed this being this hot before. This motor looks brand new and previous owner used it for 5 hours and let it set around for 10 years. I've put 4 hours on it..

 

[Texasmark]

Well you answered your own question......."sat around for 10 years".....water pump needs a new impeller. The impeller is supposed to look like the spokes of a wagon wheel. When they sit for a long time the side in compression (inside the water pump chamber is eccentric) dogears so when it goes by the wide portion it can't expand and pickup water to compress in the compression section adequately.

 

[achris]

Unlike the 15, the (2 stroke) 8 does not have an internal exhaust tube, so the whole of the drive shaft housing IS the exhaust tube. If you are running that engine without have a full service (which includes an impeller replacement) after sitting for 10 years, lack of cooling water is the problem. That said, even with a new water pump, that housing is going to run quite warm anyway....

Chris.........

 

[CHRISBRITTAIN1]

Inspecting the water pump and replaced and the mid section at exhaust port and bottom case of the motor is still hot as all, after running 40 secs out of the water. I think I have spun a crank bearing the heat is coming from the bottom cylinder and warming the upper mid section that quickly.... it has to be a bearing or something to get that hot that quick...

 

[achris]

.... I think I have spun a crank bearing the heat is coming from the bottom cylinder and warming the upper mid section that quickly.... it has to be a bearing or something to get that hot that quick...

Outboard engine bearings are not like Nacar engine bearings. Outboard engine bearings are rollers or needles... They are designed to spin. And that's why we have to put oil in the petrol, to lubricate those bearings (and a few cylinder walls)....

Exhaust gases are, by nature, very hot. 40 seconds running without water is well more than enough to heat up the driveshaft housing too hot to touch (and cook an impeller). How hot do your Nascar header pipes get after 40 seconds? Because the driveshaft housing IS the outboard equivalent of your headers, it's the exhaust manifold. When you are running the boat in the water, do you get a good stream of water from the tell-tale hole? If so, don't worry about the drive shaft housing.....

Chris............

 

[racerone]

No------Not likely a bearing.-------Roller bearings / ball bearings do not produce that much heat.---------Are you running this motor out of the water ??---------Are you providing cooling water to the impeller??