Funny lower unit situation

[DougyB]

Puzzling question here guys...

When I had drained my lower gear unit, the first few seconds consisted of all water draining out of the lower screw. What was left was only a few ounces of gear oil, but the oil was still greenish black, as if no water immulsion had occured. I just hooked up a leak tester to the lower unit, and it held 15 psi perfectly, completely surprising me. Is it safe to chalk the problem up to a poorly seated fill screw? Or do I have to look further into this? The reason Im confused is that the oil that did drain out seemed very clean still.

 

[HighTrim]

Re: Funny lower unit situation

That is because when sitting still, it will separate, water is heavier than oil, and will sit in the bottom of the gearcase. Totally normal.

Could be the crush washers as mentioned, try to change them then inspect the oil after a few runs.

Also, test the case with lower psi, like 6 or 7 psi. Too high will actually cheat and help seal. Be sure to submerge it in water, and shift the shift rod, spin the drive shaft, etc... while under pressure.

 

[boobie]

Re: Funny lower unit situation

You may want to also want to do a vacuum test on it.

 

[DougyB]

Re: Funny lower unit situation

Boobie, What is the difference between a pressure leak down test (filling the LU with air and waiting for a leak) compared to a vacuum test?

High trim, Im guessing you dont take your lower unit off of the motor to pressure test your LU? Leave it on and submerge i would assume?

 

[HighTrim]

Re: Funny lower unit situation

I prefer to have the lu off the motor, so I can see where it is leaking from. Fill 6 to 8 psi, submerge in bucket, then spin drive shaft, shift the shift rod up and down, spin prop, etc... and see if you see any bubbles. Then, a little more, to about 10 to 12 psi and do again.

The difference between pressure and vacuum is the forces exerted on the seal from opposite sides. Pressure testing is pushing the seal out, vacuum sucking the lips in. Might pass a pressure, but fail a vacuum.

I actually just do a full reseal if I suspect a leak. I would never open up a gearcase to change only 1 seal. Then pressurize it to test my work.

The crush washers are one of the most common spots for water intrusion. Might want to change them, then check the oil after a couple outings. They are a 1 time use. Trouble starts when boaters get cheap and try to re use them.

 

[DougyB]

Re: Funny lower unit situation

Very Informative High Trim, thank you. I will do as you say and then revert back to the pressure/vacuum tests if need be

 

[boobie]

Re: Funny lower unit situation

The vacuum test is mainly for double seal lower units.

 

[DougyB]

Re: Funny lower unit situation

would a 1986 johnson 25 hp.. J25TeCDC in fact be a double sealed lower unit?

 

[jimmbo]

Re: Funny lower unit situation

A vacuum test sort of simulates water pressure from a water pump which is usually right above the upper gearcase seal. Water is pushed into the gearcase and oil is pushed out wherever it can get past a seal

Propshafts usually have double seals

 

[boobie]

Re: Funny lower unit situation

Yes.......

 

[DougyB]

Re: Funny lower unit situation

Duely noted. I think I might have found the issue today. While putting new seals in and preparing to refill, I realized that the boatyard who did last years tuneup for me must have doubled up the washers for each drain screw. I could be wrong, but the only thing seperating the LU and the drain plug screw should be ONE crush washer... is this correct? there were the old washers on the plug and also a washer pressed against the Lu pilot hole

 

[boobie]

Re: Funny lower unit situation

Only one washer required.....

 

[jimmbo]

Re: Funny lower unit situation

Give it a try with just one washer. If the oil stays clear you should be ok. It was good to see the boatyard used , I assume new washers, too bad they didn't pay enough attention to remove the old ones.

 

[DougyB]

Re: Funny lower unit situation

View attachment 226846

https://www.youtube.com/watch?v=WwpJfxw0wBQ&feature=youtu.be

Hey guys, when i press on the shift rod, a bit of air bubbles or gear liquid seems to push up from the inside of the shaft hole. Could this be a type of seal leak? or is that just some likely spilled oil stuck in a crevice

 

[DougyB]

Re: Funny lower unit situation

any ideas guys?

 

[HighTrim]

Re: Funny lower unit situation

Could be, hard to tell from that.

As stated, change the washers, then check again after few outings.

If leaking still substantially, just reseal.

Just my 2 cents.