1978 Evinrude 75hp....just blew the lower unit!

[BonairII]

Lower unit seized up solid today. Gear oil only had a few hour on it.

In hindsight, I should have known that there was a problem with the LU. Last week, I loosened the screw to drain the gear oil and the oil EXPLODED from the hole and covered me head to toe....and the oil smelled awful! Not realizing that it was a problem...I filled the gearcase and didn't think anything about it. LU seized up while we were running about 20mph.

I'm guessing that somehow the exhaust gases were getting into the gearcase somehow...pressurizing it.

​Anyone ever heard of this before?

 

[racerone]

Never heard of exhaust gas getting into a lower unit.!!!----Was it sitting out in the sun and getting pressure from that heat ?

 

[BonairII]

No...I store it in a garage. The fact that the new gear oil smells just like the other stuff that exploded out of the LU previously....all I can guess is that exhaust gases are what fouled it. I opened the LU tonight(after the seizure) and small amount of water(2 shot glasses full) came out first....then blackish oil oozed out. Normally, I would assume that the oil would've looked milky because of the water.....and a day or so later the water would've separated from the oil.

Somehow the oil and water didn't mix.

Between the "exploding" oil change and today's seizure....I put about an hour or so on the motor.

 

[Bosunsmate]

Did you fill it from the lower plug?
Pressure tested it?

 

[BonairII]

Yup...I always fill from the lower hole.

 

[BonairII]

Anyone ever heard of this problem? I don't want to replace the LU and have the same thing happen.

 

[racerone]

Exhaust is unrestricted to go out the lower unit.---Why would exhaust try to find it's way past seals in the lower unit ?---If seals were bad then lower unit would quickly fill with water !!!

 

[BonairII]

Exhaust is unrestricted to go out the lower unit.---Why would exhaust try to find it's way past seals in the lower unit ?---If seals were bad then lower unit would quickly fill with water !!!

I'm at a loss at to what would've caused the lower unit to pressurize then.

What the heck could cause new gear oil to go rancid(bad smell and clumpy) in an hour or so of running time?