Outboard Gear Oil: Emulsion of Water into Oil

[Oldslowandugly]

I have always used OMC Hi-Vis oil in my old outboard engines, but that product is obsolete.

BRP has XPS HPF Pro gear oil that is recommended for all models 1973 and later.

E-TEC engines probably came from the factory with EXP HPF Pro gear oil.

Other synthetic oils are available.

Water in a gear case tend to emulsify into solution the organic oils; a long time is needed for the oil and water to separate.

Recently I drained a gear case that had water in it. The oil was synthetic. The water was distinctly separated from the oil. The water came out first followed by oil with no water emulsified at all.

Q1: do all synthetic oils always resist mixing water into the oil as an emulsion?

If you have used synthetic gear oil, reply with your experience [with the behavior regarding finding complete separation of water and oil when draining a gear case].

[MarkCz]

I have been using Mercury Quicksilver gear oil. I do not notice water separating from the oil. My engine gear case has a small leak. Even after the engine sat undisturbed for two months no water drained out; just milky gear oil drained out.

[jimh]

I am not sure which characteristic of outboard engine gear case lubricant is being viewed as desirable:

Q2: is an outboard engine lubricant that DOES NOT mix water into an emulsion with the oil to be viewed as a better lubricant than one that DOES allow mixing of oil and water into an emulsion?

[jimh]

Q1: do all synthetic oils always resist mixing water into solution with the oil in a emulsion?

While not in any regard being an expert, my limited understanding is that the characteristic of an oil lubricant to resist water mixing is a natural behavior, and for an emulsion to be formed usually requires additives designed to allow the emulsion to occur.

Some background science is available at:

https://www.unionkitchen.com/resources/2021/2/2/emulsifiers-the-science-of-mixing-oil-and-water

[jimh]

BRP has XPS HPF Pro gear oil that is recommended for all models 1973 and later.

Q3: Why wouldn't XPS HPF Pro gear oil be suitable for your use?

I doubt there is a basis to know why 1973 was chosen as the start of the use range epoch. Perhaps there is a correlation with a particular component like a shaft seal, which may have been changed in 1973. But that is just a guess.

[Oldslowandugly]

From 1968 [I think] to 1972 OMC used an electric shift gearcase on a lot of models. It used a much different gear lube. They went back to the mechanical shift from 1973 on and then the HI-Vis oil was recommended. I could use the BRP XPS since it is the equivalent of the Hi-Vis. I was just wondering which would be better, organic or synthetic. As Jim mentioned, one emulsifies water with oil and one does not. Or, at least it separates quickly. What is strange is that neither type oil seemed to allow rust on any of the parts inside the gearcase. You would think that a water and oil emulsion would expose all the metals to the water and cause damage.

[jimh]

As Jim mentioned, one emulsifies water with oil and one does not.

Huh? You lost me. You are the source of information that one oil inhibits formation of emulsion with water, and another oil did not. I just asked which behavior is desired.

[Oldslowandugly]

As Jim mentioned, one emulsifies water with oil and one does not.

Huh? You lost me. You are the source of information that one oil inhibits formation of emulsion with water, and another oil did not. I just asked which behavior is desired.

Sorry.
That is what I meant. The question of which attribute is desirable.

I have been reading a lot about lower unit oil. On most forums it lead to all kinds of arguments. That is not my intention. I only ask for real world experience. Many argue about the use of automotive gear oil in a lower unit. I did learn something interesting. True marine gear oil has additives that make the oil cling to metal surfaces. Then even if water gets in the metals are protected. This protection is good to around 10% water intrusion.

Some oils claim high emulsifiers. Some claim high demulsifiers. None explain why either is better.

Only one article claimed that conventional oil draws heat away from metal better than synthetic oil.

I also found that OMC makes a synthetic blend called HPF XR-Pro that extends the oil change interval from one-year or 100-hours to three-years or 300 hours. That oils looks to be hard to find for sale.

I have to be honest that the more I read about these oils, the more confused I get.

[jimh]

As my earlier question posits, I don't know which behavior is preferred, either.

I am skeptical that natural oil lubricates better than synthetic oil. In automobile engines synthetic oil is now widely used, and the service life is good for 10,000 miles. Petroleum oil was usually only recommended for 3,000-miles.

Regarding lubricating oils for engines or gear cases, there certainly are many opinions. I know some automobile engine owners are fanatics about changing oil. I have read accounts of people who change the oil twice in rapid success. The first change to remove the used oil. Then fresh oil added to dilute any remnants of the used oil. Then all that new oil is quickly changed after just a few hours of engine run time, and replaced with more fresh oil. Then they run the engine for 3,000-miles and repeat that whole process. I think that is a bit obsessive. However one fellow I met who was following that oil change regime was driving a GMC truck with 350,000-miles on the V8 engine.

On my 2010-model-year Evinrude outboard engine, I am not changing the gear oil every year. I don't remember the exact lubricant I have been using. It was originally a Evinrude product. I think BRP re-branded all the Evinrude oil products under the XPS branding a few years ago. I think the reason for that was BRP was also promoting those oils for use in their E-TEC snowmobile engines, their personal watercraft engines, and their off-road vehicle engines, so they created a common brand name between all those product groups using the XPS branding instead of an individual brand for each product group.

[Oldslowandugly]

As for organic oil, it was not that it lubricated better [than synthetic oil], but that it removed heat better.

The additives that they use to make the oil cling to metal sounds very similar to the additive they use in limited slip differentials on automobiles. Originally Whale oil was used, as it had the peculiar characteristic of causing oil to cling to hot metal rather than repelling it. Thankfully they synthesized that substance and stopped using the Whale oil.

There are many reasons that synthetic oils are now standard in automobile engines: it flows at very low temperatures, and it does not break down from heat as easily as regular oil.

But what is the benefit of using synthetic oil if it gets drained every year?

Perhaps if you leave it in for several seasons it would make sense.

But that assumes no water has gotten in.

I know someone that merely opens the drain, and if no water or emulsified oil comes out, he just tops off the oil and leaves the old oil in. He says that the oil getting dark is not an indication of failure and you are wasting oil by replacing it.

In my case if I had not drained my oil I would have had three motors with water in the gears.

ASIDE: didn't Evinrude advertise the E-TEC engnes as "no maintenance" for three years when new? I seem to remember that. If so then the three-year oil change interval of the HPF-XR pro would factor into that.

[jimh]

ASIDE: didn't Evinrude advertise the E-TEC engines as "no maintenance" for three years when new? I seem to remember that. If so then the three-year oil change interval of the HPF-XR pro would factor into that.

The E-TEC engines were sold with a warranty that did not require scheduled maintenance of certain items like filters, spark plugs, and gear case lubricant for three years or 300-hours if the engine was used in normal recreational service. There was no claim that there would not be some unscheduled maintenance that might occur in a three year or 300-hour interval; unscheduled maintenance happens with all engines at some time or another. Engines used in abnormal recreational service or commercial service needed more frequent scheduled maintenance to meet the warranty requirements.

[jimh]

As for organic oil, it was not that it lubricated better [than synthetic oil], but that it removed heat better.

The ability of a material to conduct heat is measured by the material's thermal conductivity.

Another heat related property of a lubricant oil is the heat capacity. Heat capacty measures how much the temperature of the oil will increase per unit of heat applied. The higher the specific heat of the oil, the more energy it takes to increase the temperature of the oil. This gives a measure of the the ability of the oil to absorb heat.

Do you have any data about the heat capcity or the thermal conductivity of various petroleum oils to compare with various synthetic lubricants?

Maintaining the lubricant oil at a lower temperature in operation is certainly to be an advantage. The cooler the oil stays, the less the oil will break down. The less the oil breaks down, the longer the service life.

In the particular application of an outboard engine gear case, I don't think that heat is a big problem. The gear case is made from aluminum, a good heat conductor. The gear case is surrounded by cold water. The nearly infinite amount of cold water and the very high heat capacity of water tend to result in the gear case getting extraordinarily good cooling. So I don't see that heat is a big problem in the gear case.

[Oldslowandugly]

gear case lubricant for three years or 300-hours

So that would indicate they used the synthetic blend gearcase oil [XPF-HR] from the factory. I have no data on oil heat capacity. I think it was something I read on the "Bob the oil guy" site. I do agree that an outboard lower unit that is operated in cool water should have no problems with heat. However the factory manual says that if the drained oil is very dark or black- then it has gotten over-heated. I have found that most of the time my drained oil IS very dark. That is why I regularly change the oil every season.

[dtmackey]

I find the heat topic interesting. How hot does water need to get before oil cooling becomes and concern? My guess is it's not a concern at all since the Navy operates outboards in the Middle East and is not using synthetic fluid.

My understanding of the Evinrude synthetic lower unit oil is it's ability to deal with minor water intrusion and still provide adequate lubrication to prevent damage and allow for multi year service. I bought the stuff in bulk some years ago when it was inexpensive, but prices have risen significantly since then. I run the stuff in 4 of my outboard motors (1-Evinrude, 2- Yamaha and 1-Tohatsu) and replace every 3 years or so since they get minumal usage 10-50 hours per year depending on the motor. But, I always check the fluid before winterizing the outboard and if I detected water, I'd drain the lower, do seals and fill with new fluid, but that's never happened and the motors are 16, 20, 22 and 28 years old. The 2 things that damaged seals are corrosion and fishing line.

I also buy and sell motors as a hobby and find that most of the motors with bad seals and water in the lower units were poorly maintained or have fishing line wrapped around the prop shaft. I inherited an old outboard that was over 50 years old and the orginal seals were still good.

Personally I think this thread is overthinking things.

D-

[Oldslowandugly]

Personally I think this thread is overthinking things.

D-

Ha ha. Agreed. I do tend to overthink stuff. Let's make it simple. What is better- regular oil or synthetic oil in the lower unit?

[dtmackey]

Personally I think this thread is overthinking things.

D-

Ha ha. Agreed. I do tend to overthink stuff. Let's make it simple. What is better- regular oil or synthetic oil in the lower unit?

Sythetic is better, but you need to decide what is better for your use and maintenance habits.

Synthetic Advantages
Resistant to oxidation and chemical degradation - Protects gears when water is present in the lower unit
Withstands temperature extremes better (cold and hot) - Not really a problem in an outboard lower unit
Flows better at cold temperatures - When used in winter, not many boaters do this
May produce less sludge and surface deposits - Not really relevent to a lower unit
Longer oil change intervals Yes
More robust film thickness at higher temperature and higher loads - High load capability is superior to conventional oils.

Disadvantages
More expensive
Slightly lower fuel economy at highway speed - negligable in a lower unit
Possible additive precipitation/separation

D-

[Oldslowandugly]

- Protects gears when water is present in the lower unit

D-

I read that the OMC/BRP regular oils did also protect metals against water. That was why I mentioned the Whale oil additive above. It causes oil to cling to hot metal. They add that to hypoid gear oil so the limited slip clutches don't chatter when turning. I guessed that property was also beneficial to lower unit oil that may see water intrusion. So I figure that if you have a newer motor that one can expect the seals to be in great condition, then synthetic oil is probably a smart choice since you can leave it in for several seasons with no concerns. An older motor with questionable seals would more likely get some water so a less expensive conventional oil would be better. Yearly draining is wise and not so expensive.