Pressure testing lower unit - question

[pdqford]

I would like to pressure test the lower unit on my '81 75HP Chrysler (and check the condiction of the impeller).

But it is starting to snow here in Central New York State! I'd like to remove the lower unit and put it in the basement for the winter in case it needs to be re-sealed, so:

Can I remove the lower unit and pressure test it while it is off the motor or does it have to be connected to the motor for it to hold pressure?

(I've had this motor for 25 years and it runs like the Energizer bunny. All I ever do is drain the carbs and fog it in the fall, change the lower unit lube every 5th year, and fuel it up and go in the spring. Then I found this site and now I get the feeling I should have been doing more preventitive maintenance each year.)

 

[Frank Acampora]

Re: Pressure testing lower unit - question

Most lower units are pressure tested OFF the engine after a seal replacement.

Ahhh! If you are changing the lower unit oil every five years and not seeing water in it, then you don't need to pressure test.

 

[capri1600]

Re: Pressure testing lower unit - question

I'm jealous. What does your oil look like after 5 years? how much runtime do you think it sees?

 

[pdqford]

Re: Pressure testing lower unit - question

Most lower units are pressure tested OFF the engine after a seal replacement.

Okay. Thank you for that information Frank. If I can get a halfway decent day I'll try and pull it off so I can check the impellar.

Ahhh! If you are changing the lower unit oil every five years and not seeing water in it, then you don't need to pressure test.

Well, I check the oil each spring and fall. Usually get about a tablespoon of water out of it in the spring (I figured that was proably from condensation over the winter) and a tablespoon out of it in the fall (figuring that it may have sucked a little water in while boating).

 

[pdqford]

Re: Pressure testing lower unit - question

I'm jealous. What does your oil look like after 5 years? how much runtime do you think it sees?

Other than a tablespoon of water, it looks like clean oil. (BTW, I also use AmsOil in this unit.)

But this year when I fogged it and drained the carbs I realized I forgot to check the LU oil before running the engine. (It usually sits for a couple of weeks before I check the lower unit.) When I lossened the drain plug, no water came out and the oil looked milky. So I'm not sure if that was a result of having just run the engine or if I have a water leak.

So, since its been five years since it has been changed, I drained it into a clear plastic container and let it sit for a few days. The oil cleared up and I don't see a water bubble in the bottom of the container, but there is a layer of gray paste (looks like liquid antiseeze) on the bottom of the container.

So I figured this might be a good year to inspect the impellar and pressure test the LU.

It doesn't get much run time. We just use it to go back and forth between our Island cottage and the main shore. We go through between 2 and 4 remote tanks of fuel each year.

 

[redfury]

Re: Pressure testing lower unit - question

Condensation would account fora minuscule amount of water. You shouldn't get ANY water out of the lower unit oil. You probably have a seal that is starting to go. The oil turned milky because the water got mixed in with it, otherwise it simply separated, and water is heavier than oil, so it sinks to the drain plug and accumulates, which is why you can visibly measure the amount.

 

[jerryjerry05]

Re: Pressure testing lower unit - question

There should NEVER be ANY amount of water in a sealed unit.EVER!!!
There is a problem with the drain on my 88/85's It's installed with pipe tape and it weeps slowly.
I have pressure tested and vacum tested this unit.It tests fine but after use it has a small amount of water in it,just a few drops.I had these motors for 22 years and they always did that.
Grey gunk is water.Milky is water.After all those years you probably need to pressure test it.Maybe a seal.The drain/fill plugs new gaskets everytime you change oil.The oil should be changed every year.
The impeller can last for 10 years if you want.I change mine every 2-3 years.I flush the salt out every time.
I live in Fl.My drive oil is changed 3-4 times a year.Like i said I check it every 3-4 times out.It keeps the screws loose and I don't have to fight to get them off.
AM Soil is a great lube.J

 

[pdqford]

Re: Pressure testing lower unit - question

The drain/fill plugs new gaskets everytime you change oil.The oil should be changed every year.

Ah-ha! There in may lie the problem. When I bought this boat/motor the LU drain plug hole was stripped and they had inserted an NPT pipe plug with no place for a gasket.

 

[Frank Acampora]

Re: Pressure testing lower unit - question

That may not necessarily be the problem. Chrysler used three different plugs and one was a 1/8 NPT pipe plug. NPT is by definition tapered and is designed to seal when tightened enough.

Initially, you did not say that you did see water internally, your reply stated the oil was good, so I replied that you did not need to pressure test. However as has been said above ANY amount of water in a sealed lower unit is cause for suspect. You need to check fill and drain plugs and the vent. You need to make certain that the shift pivot screw is tight and sealing--a gob of RTV silicone in the hole will ensure no leaks there and will remind you to never remove it unless you are rebuilding the lower unit.

Teflon tape around the pipe plug will help to prevent leaks and a pressure test will show if the prop shaft seal or the drive shaft seal under the water pump is leaking.

 

[pdqford]

Re: Pressure testing lower unit - question

Okay, I had a chance to do the pressure test of the LU this weekend. I pulled the prop off and fitted a large plastic barrel under the LU and filled it with water which just covered the fill and vent plugs...........

Pumped up a few pounds of pressure and saw bubbles at the fill plug. Gave the fill plug an extra twist and pumped it up to 10 punds. It seemed to hold fine and I didn't see any bubbles any place.

I came back 11 minutes later and it had lost ~1/2 pound. Watched it for about 5 more minutes and the gauge stayed right at 9.5 psi. Did it pass the pressure test?

 

[jason32038]

Re: Pressure testing lower unit - question

I'd say so.

 

[jerryjerry05]

Re: Pressure testing lower unit - question

You should change it more often.That old and the original seals.I check mine often.Just one time with water and you don't catch it and it's done.J

 

[pdqford]

Re: Pressure testing lower unit - question

I'd like to thank all that have replied. Now that I have the pressure pump and adapter to fit in the vent hole I'll be chacking it each spring and fall. And I will be changing the LU lube more often.

Thanks again for all the help . . . .