Water in Transmission Oil

I decided it was time to change the transmission oil in my new to me boat. The oil came out brown and sure looks like water is in it.

The engine is a Cummins 6CTA8.3 M3 - 450 HP with a Twin Disc MG 5075 transmission.

Any ideas where I should look for the problem? Thanks

Oil cooler, if it has one, may have failed.

Larry M said:

Oil cooler, if it has one, may have failed.

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+10

Agree, it should have an oil cooler and thats where you should expect to find the leak.

After you replace the oil cooler, I would suggest two more oil changes to get all the water out. I would do the first after maybe an hour, and the second after 3 to 5 hours perhaps.

While the suggestions above are probably correct, keep in mind that as ATF (if your transmission uses ATF) gets old, dirty and worn out it begins to turn brown.

Come to think of it that's the engine in our boat. It should have a zinc on the aftercooler and the heat exchanger, have you checked or replaced them?

I believe some after coolers had two zincs for some reason, but I could be mistaken. My wife claims I frequently am.

Maybe all this is obvious, but coming from the sailboat world, I was surprised to find zincs inside the boat.

Thanks all. Is there a chance I've done damage to the tranny? I don't know how long water has been in the oil. Shame on me, but I seldom check the tranny oil. When I did check the dip stick, before pumping out the oil, there was a lot of pressure as the brown liquid spit out the tube when I pulled out the dip stick. My first clue I was in trouble.

Marin said:

While the suggestions above are probably correct, keep in mind that as ATF (if your transmission uses ATF) gets old, dirty and worn out it begins to turn brown.

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I wish, but this Twin Disc uses regular 30 wt oil.

To Marins point, you can test to see if there is water in it or not. Of course you can have it analyzed, but you can try #2 in this link:

Poor Man's Oil Analysis - The Motor Oil Evaluator

I've done it with just a match before.

As I write this, if the boat is new to you, having the oil analyzed can be a good source of knowledge on the health of the power plant and trans.

Call Mike at Harbor Marine in Everett. He's probably the West Coasts most knowledgeable transmission guy plus he'll talk to you on the phone. (425) 259-3285

Has the oil just turned brown? If you checked the transmission oil level prior to the last time you ran the boat, was it a "normal" color?

Google water in engine oil and look at the images results. many pictures so you can compare what you're seeing.

If it is water it has a milky appearance. If it has a lot of water you can also have bubbles I think.

Sorry about your issue Windmist. As noted by Larry, you are in a good place to have some top notch help troubleshooting the transmission.

For any newbies out there this is an important post. Transmission coolers are relatively cheap and after a cleaning or two many consider them throw away items. Secondly, fluid checks should be done before the days's cruise begins so that changes or problems can be noted as early in the "failure" cycle as possible.

Good luck, you hopefully dodged a bullet. Flush the unit ASAP to get any salt water out that may be there.

Hopefully, it's coolant. You've had the catastrophic, now you need expert advice. Definitely flush it but get someone to look at it. Sunchaser is so correct about the coolers.

Why didn't the survey catch it? If it's salt water, it might have sat in there for a long time...

Might also get input from Boatdiesel.com. Lots of knowledge there as well

Thanks everybody. Looks like it was a flash alarm. I think I mistook foaming oil which I checked right after a 2 hour run, with water being in the oil. And then when I removed the oil using the built in pump, it looked like water was coming out at the end but it must of been just oil.


I poured the used oil into clear containers and let it sit for a couple of hours. I could find no evidence of water in that oil. I also removed the hose from the drain plug and just good oil drained out. Looks like I over reacted. Sorry. By the way, a new heat exchanger from Cummins is just $881 and they have one in Portland. Dodged that bullet.


Good thing is with all your help, I learned a lot. Thanks again.

Good deal Windmist.

For grins, you may want to check with Seaboard regarding the price of their HXs. I have two new ones on the shelf that I'm probably going to sell soon, but they are smaller than what you need, good for a transmission hooked up to a 250 HP or less engine.

Sunchaser, you are letting him off way too easy! We want a training session on how to properly identify water in oil please! Pictures and everything!!!

Cheap scotch and cigar would be considered in your sentencing.....

Glad you found it.....

Whoh! Tranny oil is not usually visibly dirty unless very high hours or something is wrong. Water in oil will not separate once it is mixed well. The color however is baby $hit brown, sort of dark mustard without any burnt smell.
It is not hard to remove the cooler on that engine and pressure test it.

Foamy oil sometimes happens, and it can look dirty or as it is containing water. Just let it sit an hour or so and check again.

If you are under way, drip some on a clean surface and let it settle there. Foam eventually vanishes leaving clean oil.

If your oil is not pure clean yellow, or pure clean atf if that is used, change it. Normal trans does not crap up oil, or not very fast. Some clutch facing material is shed, but that is over lots of hours. Bottom line, if does not look clean, change it. Water in it, likely gear cooler.

The spoon/flame trick is a very good test for water presence.

You should also follow your hoses to see if the cooler is cooed with salt water or coolant. On my TAMD41s, the gear cooler is salt water cooled, after the engine HX.

bayview said:

It is not hard to remove the cooler on that engine and pressure test it.

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Hopefully not thread highjack since discussing oil coolers. I often see references to pressure checking H/E, oil coolers, etc, as above. Is this testing by water hose on intake with outfall closed, at regular water pressure, such as municipal water pressure, or other method ? I am referring to DIY testing, not radiator shop. Thanks.

I pressure test coolers by using my well pump pressure which is about 40psig. Rig up garden hoses with adapters to give the cooler a constant supply of water to one water fitting, with the other capped off. Leave it for an hour or whatever with oil ports left open. Any water shows up in oil side means fail.

Some municipal water systems have very high pressure, and those I would be a bit hesitant to test some larger coolers. Little gear coolers should be a non issue due to their small size, small tubes and brazed on end caps.

Twin Disc recommends 40 wt. engine oil. There should be a lubricant plate detailing exactly the type and requirements of the lubricant. They do not use ATF Fluid and it voids any warranty on their Gear.

What they did with my heat exchanger was to submerge it in water with one of the oil ports caped off and with a compressor attached to the other port. pressurized it with 40 PSI and made sure it held pressure for one hour and no bubbles come up.

Today I removed about 2 cups of oil from my Twin Disc into a clear glass jar because I had over filled it initially. Again it looked like water was in the oil in the first amount of oil out of the tranny. However after letting it sit for an hour or so, the oil looks uniformly the same. I use a built in oil change pump that is used for the engine, generator and transmission. Is it possible that the oil change pump could foam up the oil until it gets good flow?


If water is in the oil, wouldn't it be very plain to see in the glass jar?


To answer one of the questions, my transmission plate says use 30 wt engine oil. The previous owner used Delo 100 30 wt. The gear cooler uses sea water for cooling.

windmist said:

Today I removed about 2 cups of oil from my Twin Disc into a clear glass jar because I had over filled it initially. Again it looked like water was in the oil in the first amount of oil out of the tranny. However after letting it sit for an hour or so, the oil looks uniformly the same. I use a built in oil change pump that is used for the engine, generator and transmission. Is it possible that the oil change pump could foam up the oil until it gets good flow?

If water is in the oil, wouldn't it be very plain to see in the glass jar?

To answer one of the questions, my transmission plate says use 30 wt engine oil. The previous owner used Delo 100 30 wt. The gear cooler uses sea water for cooling.

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If you haven't checked the condition of your transmission heat exchanger, you have not completed your due diligence, especially if your tranny oil has not ben changed. My tranny hx was nearly completely clogged. I had no water in the transmission, but it was not allowing good flow to the coolant hx. Btw waht engine is your transmission coupled to?

I had water in my Borg/Warner in Nov. Did the flush 5 times. 3 hours of cruising later and it was time for Towboat US. One day and $3500 later and the rebuilt unit was back in service.

Daddyo said:

I had water in my Borg/Warner in Nov. Did the flush 5 times. 3 hours of cruising later and it was time for Towboat US. One day and $3500 later and the rebuilt unit was back in service.

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One day? Wow.

Yep, that part was amazing!