Lower Unit Milkshake....

[Darrell W.]

I needed a different lower unit (Johnson 88 special) and I found one nearby. I drained the oil from it (looked okay) and pulled a vacuum of 15 inches/mercury for 10 minutes and it held okay. So I bought the unit and installed it. After running it on the lake, I cracked the drain plug to check the oil and out came a "vanilla milshake" thick liquid. I drained the stuff and pulled another vacuum. Again it held 15 inches/mercury for 10 minutes. So I reloaded the oil in the unit and tried it again. Yep - you guessed it - "vanilla milkshake" came out again. Frustrated, I checked the lower unit for any visible signs of leakage and found none (seals looked good and no oily residue visible). It looks great! Here's my question: Is it possible for water to get into the lower unit without any oil coming out?

 

[ezeke]

Re: Lower Unit Milkshake....

Sure, and the pressure test is usually more revealing than the vacuum test.

Be careful that you don't put too much pressure on, but I like to see 12 to 15 psi hold for around 45 minutes.

Check your prop shaft, if it is bent, it will leak while running,even though the tests show good.

Most of the time the leaks that I have had are from the shift rod seals and the driveshaft seals unless it is the fill and vent plug seals.

 

[HybridMX6]

Re: Lower Unit Milkshake....

I would definitely replace the drain and fill seals on the screws, look like nylon washers. If the unit is holding pressure, but still becoming a milkshake, you may want to let it stay open for a doy or two, could be some residual water in there not getting out with the oil change. If the fill/drain seals don't end up the problem, suspect ezeke's suggestion above.

 

[mikesea]

Re: Lower Unit Milkshake....

knowing you have a problem,at this point,you may want to operate the unit to best of ability while pressurized or vaccuumed.The leak may only happen during mmovement,I like pressure and soap test.I will bet on the propshaft seals there are 2 back to back,one keeps in one keeps out,you may want to reseal at this point for piece of mind,there are many possible places,oring on bering carrier,the 4 carrier bolts,shiftshaft drove/propshaft

 

[Darrell W.]

Re: Lower Unit Milkshake....

Thanks for all the replies! I've replaced drive shaft seals, bearing carrier o-ring, shift shaft o-rings and gaskets under water pump and shift shaft housing. If this doesn't fix the problem, I'll replace prop shaft seals and housing o-ring. I'll keep you informed - thanks again...

 

[Darrell W.]

Re: Lower Unit Milkshake....

Latest update: replaced driveshaft bearing housing seal and o-ring, shift shaft o-rings and gasket and still got the "vanilla milkshake". I took the lower unit off and submerged it in a tank of water and applied compressed air. I didn't see any bubbles at all! Without any bubbles around the prop shaft seals or bearing carrier housing, I'm assuming they are okay! I've tried wiggling and turning the prop and drive shafts to create bubbles, but to no avail. Any suggestions?

 

[petryshyn]

Re: Lower Unit Milkshake....

did you install NEW "vent" and "fill" gaskets?

 

[Darrell W.]

Re: Lower Unit Milkshake....

Yep - new nylon washers on both plugs...

 

[petryshyn]

Re: Lower Unit Milkshake....

what volume of lube are you getting out when you drain it? Are you sure you are getting it full and doing a final top up when the bottom plug is installed?

 

[Darrell W.]

Re: Lower Unit Milkshake....

I put in about 7/8ths of a quart and I get about the same amount of milky white fluid out. I use a fluid pump to put the oil in through the lower port until it comes out the top. I then close the top plug and remove the pump from the lower hole and put the bottom plug in. I've had boats for decades and this is the worst I have ever seen the lower unit fluid! A whole bunch of water has to be getting in some how...

 

[petryshyn]

Re: Lower Unit Milkshake....

Well Darrell
Its sounds like you did everything right. Its time to take it down and replace all seals and gaskets. You have no alternative. I have to admit, I have done some vacuum/pressure tests that checked OK, but when I removed the leg and replaced the water pump, I could see the driveshaft seal full of cracks.
Therefore the vac/press test is not infallible.

Cheers....

 

[bhughes]

Re: Lower Unit Milkshake....

How bad is it to just change the lower unit oil more frequently instead of going through all that trouble to fix the leak?

 

[robert graham]

Re: Lower Unit Milkshake....

I believe you really need to find this leak and fix it, especially if you're running in salt water. I have a little 3HP air cooled motor that leaked all the time and it turned out to be a worn and bent prop shaft...Replaced it and now it's fine. Is your prop shaft worn or pitted where the seal rides on it?..might be the seal has worn a groove in prop shaft, allowing for water entrance. Good Luck!

 

[Darrell W.]

Re: Lower Unit Milkshake....

I found the problem! I took off the prop and pulled out the bearing housing with seals. Although the outer seal looked good, the inner seal looked "melted". I replaced the seals and o-rings, refilled the unit and ran it. No leaks! Even though the unit passed vacuum and pressure tests, it did have a bad seal on the prop shaft!

Thanks to everyone who replied to this problem...