Hi. So this is probably very simple but I cannot work this out from googling around and I am getting myself pretty confused.

I want to change the engine oil and the marine gear oil myself for the first time and need to buy some oil. The engine is a new 2YM15 with about 70 hours on it only.

Marine Gear - The manual says the marine gear oil should be "API Service Categories: CD or higher, SAE Viscosity: #20 or #30".

Engine OIl - The manual says the engine oil should be "API Service Categories: CD or higherTBN value: 9 or more. Recommended SAE Viscosity: 10W30,15W40. Engine oil 10W30 and 15W40 can be used throughout the year., NEVER use API Service Category CG-4 or CH-4 oils.

My questions are:
- Can I use the same oil for both the engine and the marine gear?
- Is something like this suitable? - www.whitworths.com.au/castrol-rx-super-diesel-engin-oil-5lt
- When it says use SAE Viscosity of #20 or #30, is this refering to the 30 in the 10W30?
- Mineral, semi-synthetic, fully-synthetic? Should I be choosing one or the other for the marine gear?

jbarnes85 said..
Hi. So this is probably very simple but I cannot work this out from googling around and I am getting myself pretty confused.

I want to change the engine oil and the marine gear oil myself for the first time and need to buy some oil. The engine is a new 2YM15 with about 70 hours on it only.

Marine Gear - The manual says the marine gear oil should be "API Service Categories: CD or higher, SAE Viscosity: #20 or #30".

Engine OIl - The manual says the engine oil should be "API Service Categories: CD or higher TBN value: 9 or more. Recommended SAE Viscosity: 10W30,15W40. Engine oil 10W30 and 15W40 can be used throughout the year., NEVER use API Service Category CG-4 or CH-4 oils.

My questions are:
- Can I use the same oil for both the engine and the marine gear?
- Is something like this suitable? - www.whitworths.com.au/castrol-rx-super-diesel-engin-oil-5lt
- When it says use SAE Viscosity of #20 or #30, is this refering to the 30 in the 10W30?
- Mineral, semi-synthetic, fully-synthetic? Should I be choosing one or the other for the marine gear?

For the gearbox where it states "SAE Viscosity: #20 or #30" it is referring to a single weight oil, that is either 20 or 30 weight. not a multi grade oil like 10W30. I'm not sure why they specify a CD grade for the gearbox as C grade indicates it's for diesel engines but using it will do no harm to the gearbox.

The Castrol RX Super would be suitable as it falls within the recommended specifications.

jbarnes85 said..

LooseChange said..

For the gearbox where it states "SAE Viscosity: #20 or #30" it is referring to a single weight oil, that is either 20 or 30 weight. not a multi grade oil like 10W30. I'm not sure why they specify a CD grade for the gearbox as C grade indicates it's for diesel engines but using it will do no harm to the gearbox.

The Castrol RX Super would be suitable as it falls within the recommended specifications.

Thanks for that. How do I tell that Castro's RX Super is suitable for the gear box? Or is it just that a multi grade can be used instead of the single grade?

The Castrol RX Super is not suitable for the gearbox as it is a multigrade oil, it is an engine oil.

The gearbox requires a single weight oil as stated, either 20 or 30 weight.

Hi Jolene, I'm slightly confused... why do manufacturers specify a multigrade oil for engines when it seems a mono grade will do the job? Can this be done with other makes as well? (Curious to know, I'm up for an oil and filters change soon). Thanks.

AzureF305 said..
Hi Jolene, I'm slightly confused... why do manufacturers specify a multigrade oil for engines when it seems a mono grade will do the job? Can this be done with other makes as well? (Curious to know, I'm up for an oil and filters change soon). Thanks.

it's to do with extremes of environmental temperatures. in cold climates, the reduced viscosity is important when the engine is cold. in warmer climates you can sometimes use monograde instead.

for example (note 40 degrees F is about 5 degrees C, and 60 degrees F is about 16 degrees C):

www.castrol.com/en_us/united-states/home/motor-oil-and-fluids/engine-oils/motor-engine-oil-types/monograde.html

fishmonkey said..
in cold climates, the reduced viscosity is important when the engine is cold. in warmer climates you can sometimes use monograde instead.

I don't think that is quite right when talking about viscosity.
During my Navy apprenticeship in marine engineering we were taught that viscosity is a measure of the flowability of a fluid or gas, i.e. the more a fluid or gas flows, the higher is it's viscosity.
Therefore a 90 grade oil that one would put in the differential of a vehicle is less viscous than a 30 grade oil that one would put in the engine of a vehicle. logically the 90 grade oil has a higher film resistance to pressure than the 30 grade.

Heat will reduce film resistance so therefore if one was operating an engine in the Antarctic it would be wise to use a thinner grade of oil such as 10 grade and vice verca at the equator maybe a thicker 50 grade oil for the same engine.

However, upon consulting my Concise Oxford English Dictionary, the definition of viscosity is "stickiness".

Now I am really confused because super glue is as runny as hell but when you have it on your forefinger and thumb and you put them together, It don't flow at all.

cisco said..

fishmonkey said..
in cold climates, the reduced viscosity is important when the engine is cold. in warmer climates you can sometimes use monograde instead.

I don't think that is quite right when talking about viscosity.
During my Navy apprenticeship in marine engineering we were taught that viscosity is a measure of the flowability of a fluid or gas, i.e. the more a fluid or gas flows, the higher is it's viscosity.
Therefore a 90 grade oil that one would put in the differential of a vehicle is less viscous than a 30 grade oil that one would put in the engine of a vehicle. logically the 90 grade oil has a higher film resistance to pressure than the 30 grade.

Heat will reduce film resistance so therefore if one was operating an engine in the Antarctic it would be wise to use a thinner grade of oil such as 10 grade and vice verca at the equator maybe a thicker 50 grade oil for the same engine.

However, upon consulting my Concise Oxford English Dictionary, the definition of viscosity is "stickiness".

Now I am really confused because super glue is as runny as hell but when you have it on your forefinger and thumb and you put them together, It don't flow at all.

Your ass about Cisco,,,, Water = less viscosity ,,,Maple syrup = more viscosity

Hi. I have no intention of using anything other than what the manufacturer recommends. It's deciphering the oil specification recommendation I am doing. First time buying oil.
They don't actually specify to use a Yanmar oil. They just give the specs of the oil.

2ym/15,, 3ym/20,, and 3ym/30 oil chart



According to the chart the 10w-30 or a mono SAE 30
15w-40 very acceptable as well probably a better choice north of the 26 parallel or you have a very hot engine room.
Boat motors don't tend to have a high ambient temperature environment due to the fact they use plenty of sea water to remove heat. unlike a car or truck

looks good to me