Checking Lower Unit? How to pressure test?

[enginesilo]

What is the procedure to test a lower unit? After checking the current oil to see if it has any water mixed in, is whitish or creamy, the next step would be to pressure test the Lower End.

Can a typical gauge pump or carburetor pop off tester sufficiently test the pressure of a lower unit?

What is the procedure and what is the pump or tool needed. Could the pump be built?

How long does the unit need to hold pressure for, and at what psi?

 

[iwombat]

Re: Checking Lower Unit? How to pressure test?

You can use a LU lube pump fitting (the one that goes into the fill plug) and hose-clamp a bicycle pump or other small pump to it.

It should hold about 10psi.

Submerge the whole thing in a big tub of water, pump it up and see where the bubbles come out.

Is this the same LU that had the melted impeller and has the possible "bad bearing"? If so I'd be surprised if it didn't melt all the rubber seals when the bearing overheated.

 

[enginesilo]

Re: Checking Lower Unit? How to pressure test?

Hi iwombat,
nope, not the one with a bad bearing, I am the guy who is buying the 2000 four winns with the 115.

So does the LU need to be drained completely to do this test? Is the tub of water test common or do I need to also do that if I see that it holds the 10psi of pressure ok?

Was also thinking, if this boat was winterized last season it probably has fresh oil in the crank so I won't find water in there. Would water get in by hooking it to the hose, or will it only get through once the engine is in the water for a good while? Think water would get into the oil during a 1 hour test drive?

 

[iwombat]

Re: Checking Lower Unit? How to pressure test?

Ah, sorry about the confusion.

"So does the LU need to be drained completely to do this test? Is the tub of water test common or do I need to also do that if I see that it holds the 10psi of pressure ok?"

Yes, it does need to be drained to do that properly. I'm assuming it won't pass the 10psi test since it's got water in the LU. However, a very common source of water intrusion is not replacing the drain/fill plug washers after EVERY fluid change. Could be that's the entirety of the issue.

Regardless . . .

Drain the LU and pressure test it by seeing if it'll hold 10psi. If not, submerge and look for the bubbles.

 

[enginesilo]

Re: Checking Lower Unit? How to pressure test?

Yes, it does need to be drained to do that properly. I'm assuming it won't pass the 10psi test since it's got water in the LU.

This one doesn't have water in it....or I don't think it does. Not sure because I didn't check yet, and the boat was winterized and got new oil last season. Are you confusing me with another guy maybe that has a problem with his LU already?

Thanks again for the tips.

Ok, so i'll be planning on draining and then testing for 10psi to hold. If it doesn't hold and I do the water test and see bubbles, what is involved in replacing these seals?

 

[iwombat]

Re: Checking Lower Unit? How to pressure test?

"After checking the current oil to see if it has any water mixed in, is whitish or creamy"

I assumed that meant you'd already checked and found it.


Give it a look to see if it's got water. Then, put it in the water and run it and check again. No need to pressure test unless you just have to.


Edit: And yes I was confusing you with another thread on testing LUs. I understand that you want to keep all the separate issues in separate threads. I think this would be a lot easier to keep in all one thread though. Something like "Checking out a new motor". It's getting a bit confusing at this point.

 

[enginesilo]

Re: Checking Lower Unit? How to pressure test?

Thanks iwombat,
I didn't check it yet, but am going too. If I don't see any water and I run it and test again and still no water i'll assume it is ok. If I can put together a makeshift tester I might go at it.

The reason why I kept the topics separate is so someone else could later search and find these details helpful in the archives without a bunch of mixed up topics and responses.

 

[wilde1j]

Re: Checking Lower Unit? How to pressure test?

Most LU's can be pressurized to ~ 15 psig ... no higher, though. Most should hold some pressure for about 45 minutes. A shop manual will provide more detail, however. Prop shaft seals are typically two seals back to back, one for prerssure and one for vacuum. To do a complete test, test with the highest vacuum you can produce (a brake bleeder does fine for vacuum).

 

[enginesilo]

Re: Checking Lower Unit? How to pressure test?

Most LU's can be pressurized to ~ 15 psig ... no higher, though. Most should hold some pressure for about 45 minutes. A shop manual will provide more detail, however. Prop shaft seals are typically two seals back to back, one for prerssure and one for vacuum. To do a complete test, test with the highest vacuum you can produce (a brake bleeder does fine for vacuum).

A member has suggested acquiring a MityVac break bleeder model 4050 that can do both a pressure test and a vacuum test. Anyone ever do the procedure with one of these? I might try to get one of these, or make a pressure one.

 

[wilde1j]

Re: Checking Lower Unit? How to pressure test?

I've used one of those deals (don't know the model, but it shouldn't make any difference) and you don't even have to use a gauge, since the best vacuum you could possibly achieve (-15 psig) wouldn't jeopardize the seals. Any vacuum source is fine. As in the pressure test, submerge the LU to find where the leaks are.