How often do you change your gearbox oil?

My Twin Disc manual indicates the gearbox oil should be changed at 1000 hours or 6 months, whichever is earlier. In checking the oil levels it seems to me that the oil still looks like it went in yesterday, but its been there for 12 months and 320 hours. Now that is after a complete rebuild as well. Its only 5 quarts per gearbox so its not a big deal to change it reasonably frequently. But every 6 months seems a bit OTT.

How often do you change your gear oil?

I'll be interested in the thread on this question too. Similar experience - oil looks perfect after 12 months (though I know that is not the right test). My oil temp never gets over warm either...

Never changed ours in 25 years on our old boat that had Velvet Drives that used hydraulic oil. No problems ever.

Change it every 100 hours or annually on our new boat's ZF tranny that uses 30w engine oil, per the manual.

Insequent said:

How often do you change your gear oil?

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We try to remember to change it every five or six years. Whlle we use our boat year round, we don't put tons of time on it as the only time we can take a longer cruise is when I take vacation time for the purpose. So most of our trips are weekend or three-day trips, and they put only 6 to 8 hours on the engines each time.

I do inspect and smell the transmission fluid (Velvet Drives so it's ATF) before the start of every outing. Should I find it starting to get a bit brown or smell a bit burnt, I'd change it right away. So far, I've never encoutered those conditions.

But this does remind me that they are due for a fluid change.....

Insequent said:

My Twin Disc manual indicates the gearbox oil should be changed at 1000 hours or 6 months, whichever is earlier. In checking the oil levels it seems to me that the oil still looks like it went in yesterday, but its been there for 12 months and 320 hours. Now that is after a complete rebuild as well. Its only 5 quarts per gearbox so its not a big deal to change it reasonably frequently. But every 6 months seems a bit OTT.

How often do you change your gear oil?

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I have a Twin Disc 509 and change mine annually for drill. Clean the screens when you do so, especially for the first couple of changes. Twin disc makes a great gear, but they are notorious for leaving debris in the case during manufacturing - bits of metal, ham sandwiches - that sort of thing. The first time I cleaned mine it was like I had stripped a gear there was so much trash. Called the distributor and he said it was pretty common. Every change after that is clean, so I assume that is correct.

Delfin said:

I have a Twin Disc 509 and change mine annually for drill. Clean the screens when you do so, especially for the first couple of changes. Twin disc makes a great gear, but they are notorious for leaving debris in the case during manufacturing - bits of metal, ham sandwiches - that sort of thing. The first time I cleaned mine it was like I had stripped a gear there was so much trash. Called the distributor and he said it was pretty common. Every change after that is clean, so I assume that is correct.

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I will check the screens, but am hoping the guy that did the rebuild did not eat his lunch in the workshop. The screens were full of stuff when I was doing the refit, hence the gearbox rebuild was added to the list. The boxes were in bad condition, presumably from changing gear at elevated rpm and not pausing in neutral on the way through, so I don't regret the rebuild at all.

I change my gearbox oil once a year. This is probably too soon based on the condition of the oil (looks very good), but changing it on my boat is not expensive or time consuming--gives me satisfaction and peace of mind.

Insequent said:

My Twin Disc manual indicates the gearbox oil should be changed at 1000 hours or 6 months, whichever is earlier. ...............
How often do you change your gear oil?

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My transmission (Volvo) calls for an oil and filter change once a year or 100 hours. I usually do that but I skipped one this year because we put over 250 hours on it in two and a half months.

Comparing the cost of an oil change with the cost of the transmission I figure it's best to do what they say.

BTW: Like you, I find my transmission oil looking like new when I change it. There must be a reason for changing it though.

I change my transmission oil once a year, usually when I change the engine oil. Fortunately, it uses the same oil as the engine (Delo 15w-40) and is plumbed into the same oil change pump, so I don't even have to change buckets.

I am surprised to hear that some gear mfgs spec a change every 100 hours. That would get old fast. My TD's are every 500, and the mains (QSM11's) every 250. My biggest regret in the design of my boat was not to include old and new oil resevoirs. I am going to give some thought to retrofitting.

The Allison MH series calls for 500hr, 1 year. They use the same 40w oil as the Detroits. I got in the habit of taking an oil sample about every 150-300 hrs whenever I was doing the same as part of an oil change for the engines. This allowed me to stretch it out a month or two on the calendar if the boat wasn't getting used much, but I never exceed the hour limit. It's a big ticket piece of machinery, why mess around?

Every 400 hours on my TD 507's, but I check/clean the suction strainers annually. Even at 400-500 hours, oil looks as-new and strainers have been clean since the first time I did them. Local diesel mechanic told me he thinks changing every 400-500 hours is unnecessary, but I recall reading this as the recommended interval on BoatDiesel for these 'bomb-proof' (Tony Athens expression) trannies

caltexflanc said:

The Allison MH series calls for 500hr, 1 year. They use the same 40w oil as the Detroits. I got in the habit of taking an oil sample about every 150-300 hrs whenever I was doing the same as part of an oil change for the engines. This allowed me to stretch it out a month or two on the calendar if the boat wasn't getting used much, but I never exceed the hour limit. It's a big ticket piece of machinery, why mess around?

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I had to replace a pair of MH1's in a prior boat with 790 hp JT 892's. Those gears were marginal for that horsepower and the clutches slipped and burned. Apparently my gear oil pressure had been set a little too low by a mechanic who was concerned that higher pressure would cause an oil leak from the trans, past the rear main seal and into the crankcase. He made that executive decision without talking to me, but I wish I had been more sensitive to the need to keep the pressure up. A word to the wise.

MYTraveler said:

I had to replace a pair of MH1's in a prior boat with 790 hp JT 892's. Those gears were marginal for that horsepower and the clutches slipped and burned. Apparently my gear oil pressure had been set a little too low by a mechanic who was concerned that higher pressure would cause an oil leak from the trans, past the rear main seal and into the crankcase. He made that executive decision without talking to me, but I wish I had been more sensitive to the need to keep the pressure up. A word to the wise.

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Curious what boat that was. I take it you mean MH10 or MH11 (1.0 or 1.1 reduction, very unusual). the MH11 is rated for max shaft horsepower of 540. Those 892's were certainly way over juiced as well at 790hp. Even my MH20's were rated at 720 shaft. Yeah it sounds like that guy and whoever powered that boat didn't know their stuff. I make a habit of watching trans pressure like a hawk, including mechanical gauges right by them in the ERs. Pressure should be a min of 130psi at 1800 rpm in forward and 110 in reverse at 1500 (not that I ever went in reverse that fast!).

I change my 1989 7000 series Velvet drive tranny's every 250 hours when I change engine oil, which has been about once a year. They use Dexron ATF. Probably over kill but its easy to pump out and refill. It always looks perfect when changing the ATF.

caltexflanc said:

Curious what boat that was. I take it you mean MH10 or MH11 (1.0 or 1.1 reduction, very unusual). the MH11 is rated for max shaft horsepower of 540. Those 892's were certainly way over juiced as well at 790hp. Even my MH20's were rated at 720 shaft. Yeah it sounds like that guy and whoever powered that boat didn't know their stuff. I make a habit of watching trans pressure like a hawk, including mechanical gauges right by them in the ERs. Pressure should be a min of 130psi at 1800 rpm in forward and 110 in reverse at 1500 (not that I ever went in reverse that fast!).

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I probably got the model number wrong, I was doing it from memory and its been about 7 years. Definitely not 1 or even 1.1 reduction. Came from the factory with those gears and mains. Also from memory, my mechanic had reduced the pressure to 130 (the low end of the spec range), but after the new gears were put in we ran them right up to 160, the high end of the spec range.

Oil is different in your gear. It shouldn't turn black as there isn't carbon from combustion going into it. However, it does loose it's lubricity (yes that's a real word) which increases wear. Oil is cheap compared to everything else in boating. Annually or every 300 hours, whichever comes first.

Ted

WOW...I must have missed the boat on this one. We put new oil in when we rebuilt them 7 years ago. They didn't require rebuild it was just done as well as, while we were doing the mains. I haven't put 200 hours on them since but it still has me concerned. Hmmm

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I have Volvo MS3 gear box. Does anyone know if it has an oil drain plug or is it a pump out?

traderjohn,

There appears to be a drain in the lower bearing carrier flange. See here.

This gives you the added benefit of draining all the nasties through the bottom bearing elements and races. Meh, I guess it is sitting there all the time when shut down anyways...

Thanks!! Can't wait to see what comes out!!!!

traderjohn said:

I have Volvo MS3 gear box. Does anyone know if it has an oil drain plug or is it a pump out?

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I had the volvo MS3 gears in my last boat, it's been awhile so this may be wrong but I believe they had a drain on the side of the case.
My Hurth HBW-450s hold 1.9 quarts I change between 100 to 120 hours and use full synthetic.

dwhatty said:

Change it every 100 hours or annually on our new boat's ZF tranny that uses 30w engine oil, per the manual.

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Ditto.

We also have a magnetic filter on our gears; I've checked that, and it's always as clean as the oil.

-Chris

The output flange on my port engine broke loose as the center bolt give in of metal fatigue stress (misaligned shaft). When the flange was pulled out all oil in the gearbox emptied itself into the bilge. This happened on our way into a narrow tidal lock in Holland. Ouch! This was on the 1800 nm get-home run from southern Portugal to Scandinavia with our to us new boat.

Look at that color! This is supposedly straight 30 weight oil.

At the time the gearboxes had 1.000 hrs/15yrs on them. Could be the oil was never changed since they were installed?



Sourced a new bolt from a nearby yard, installed the flange, stretched the new bolt to the specified torque (we do not go on a cruise without a torque wrench, do we?) and filled NEW oil. We were on our way again after a 2 day delay. No trouble since.

Before rebuild my gear oil looked like that too. I have no idea the hours since the PO had changed the gearbox oil. I assume you fixed the shaft alignment when replacing the bolt? What engines and gearbox do you have in the Mk 1?