4 stroke fully synthetic engine oil - auto or marine?

[eze]

Somehow I feel you guys have done this one before, So for the benefit of us folk with less knowledge can we open the debate once again.

It is possible to obtain 20 Litres of a fully synthetic 5w/40 for circa £50-60 that is auto grade. However, if we want Marine grade oil the price is seemingly double or treble the above price.

Question;

Is it okay to use a fully synthetic 5w/40 auto engine oil in a Marine outboard and if not then why not?

thanks
eze

[Pikey Dave]

Suzuki "recommend" their own oil, but concede that you can use any good quality oil as long as it meets or exceeds the api/sae rating of theirs.

[Xk59D]

There are a handful of differences I'm aware of.

1. If you are in warranty you better use their oil.
2. Foam inhibitors due to higher sustained rpm.
3. Corrosion inhibitors.
4. Price obviously.

Lots of people run correct spec car oil in their outboards though. in 25 years of boating I've never put car oil in my outboards or inboards so no first hand experience.

[eze]

[QUOTE=Xk59D;762346]There are a handful of differences I'm aware of.

1. If you are in warranty you better use their oil.
2. Foam inhibitors due to higher sustained rpm.
3. Corrosion inhibitors.
4. Price obviously.

QUOTE]


1 - agreed, best use their oil.

2 - Sounds reasonable tbh, but 4s motorbikes will run 3-4 k rpm on cruise and also go up to 12k rpm full chat. but I get your point.

3 - Is there any difference here between auto & marine as both are by design internally sealed?

4 - agreed.


Thanks for the replies chaps.

[mick]

Give millers oils a ring they will tell you all you need to know.

[Xk59D]

The difference is probably down to moisture build up, normally cars won't build up much unless you take them into the lake!

The reason the marine oil costs more is simply down to the market size and the extra additives so volume discounting is way less than road vehicles....plus boat doesn't stand for Break Out Another Thousand for nothing. That doesn't mean car oil won't work of course, that is upto the owner to decide.

[beamishken]

If the spec matches then just use it I doubt the oil knows wether it's in a boat or car bike or truck
I've run standard 15 40 in my inboards for years and wouldn't even consider buying branded marine oil
Obviously the manufacturers want you to believe it's different but they would there making a tidy profit on their own brand oil

[Fenlander]

As Xk59D says in post #3... there are big differences in the operating conditions of an outboard at sea to a car and marine oil is different with particular regard to constant high revs, vibration from the OB, movement from sea state, sometimes infrequent use and corrosion from sea air.

With the small amount of oil used in the OBs I've owned up to 20hp the extra cost of marine spec oil is insignificant... but even with a larger OB I'd still treat it.

Which brand of marine oil used is a different choice and a personal thing.

Inboard marine diesels may be a different matter. I only have experience of these from the 1960/70s when we used car oil.

[Searider]

Engine Oil & Lube » Yamaha Maintenance Matters

[beamishken]

Originally Posted by Fenlander

As Xk59D says in post #3... there are big differences in the operating conditions of an outboard at sea to a car and marine oil is different with particular regard to constant high revs, vibration from the OB, movement from sea state, sometimes infrequent use and corrosion from sea air.

With the small amount of oil used in the OBs I've owned up to 20hp the extra cost of marine spec oil is insignificant... but even with a larger OB I'd still treat it.

Which brand of marine oil used is a different choice and a personal thing.

Inboard marine diesels may be a different matter. I only have experience of these from the 1960/70s when we used car oil.

Maybe a 20hp uses only a small amount but it takes close on 30l to do my two yanmars
With regards to the differences between automotive and marine, a 4 stroke outboard is working virtually like a dry sump engine which all but does away with the oil splash or boat roll problem, all the oil is delivered by the pump then migrates back to the sump which is well below where the crank will contact the oil. A bike engine works far harder than an outboard,the hp per cc is way higher so stress isn't as high on an outboard as a bike engine,boat engines also do way less hours than their on road counterparts
As for corrosion the sump system is fully sealed with complex breather systems so corrosion shouldn't be an issue in normal use
The only benefit in using branded oil in my opinion is the placebo effect that you've used the 'correct oil' however in my opinion any oil within spec is fine.
If anyone can provide indisputable proof that marine branded oils provide any benefit over alternative same spec oils I'm all ears

[Fenlander]

>>>only benefit in using branded oil in my opinion is the placebo effect that you've used the 'correct oil' however in my opinion any oil within spec is fine.

Fully agree... the spec for my Suzuki 20hp being 10-40 (or 10-30) marine grade oil. I don't buy Suzuki branded oil... well I sort of do but it says something different on the container.

I would say the jury is out re outboard vs motorbike in terms of working hard. An outboard motor is often trolling bogged down by an over high gear (prop) for the speed... or working at a high percentage of its maximum revs with virtually unchanged throttle openings for longer periods than you'd see in road use car or bike.

Re corrosion of course the intake air is frequently salt laden as is the air that can enter the engine at rest through open inlet/exhaust valves.

[beamishken]

Originally Posted by Fenlander

I would say the jury is out re outboard vs motorbike in terms of working hard. An outboard motor is often trolling bogged down by an over high gear (prop) for the speed... or working at a high percentage of its maximum revs with virtually unchanged throttle openings for longer periods than you'd see in road use car or bike.

I don't think the jury is out at all with regard to bike engine v outboard a yamaha R1 is 1000cc & 200hp
Yamaha 200 is 2785cc
No doubt in my mind which is higher stressed

Engine shouldn't be bogged if it's propped correctly engine oil won't compensate for poor setup or misuse
Accept the throttle settings will be more constant but that should be a plus in that correct operating temp should be maintained

Re corrosion of course the intake air is frequently salt laden as is the air that can enter the engine at rest through open inlet/exhaust valves.

The oil will make no difference to the intake tract as it's not oil lubricated the engine oil never sees these areas
Only danger of corrosion is from moisture ingress into breather system but assuming breather filters are used this should be minimal

[A1an]

its all about the specs, labelled 'marine' or not.

[Pikey Dave]

Originally Posted by A1an

its all about the specs, labelled 'marine' or not.

Yup, the Suzi workshop manual says as much[emoji106]

[otilly]

The difference has to do with engine temperature. A car/motorcycle engine reaches far higher temps than an outboard. This is because of the cooling water; in a car the water can reach temps of higher than 110 c, in an outboard its less than 20 or 30 c.

Thus other kind of oil is needed, despite the specs.

[beamishken]

Originally Posted by otilly

The difference has to do with engine temperature. A car/motorcycle engine reaches far higher temps than an outboard. This is because of the cooling water; in a car the water can reach temps of higher than 110 c, in an outboard its less than 20 or 30 c.

Thus other kind of oil is needed, despite the specs.

Outboards have thermostats to limit the cooling effect of the colder water, manufacturers set the temperature limits appropriately for their engines via the stat
Therefore engine temperature has no special oil requirement
Unlike comparing aircooled 2 strokes to water cooled which do require different oils

[Fenlander]

>>>The oil will make no difference to the intake tract as it's not oil lubricated the engine oil never sees these areas

Not worried about the inlet tract... but every gulp of air an outboard takes moves past its valve stems and into the cylinder bore and over piston & rings. This salted moisture laden air therefore ends up in areas where corrosion isn't ideal.

>>>Outboards have thermostats to limit the cooling effect of the colder water, manufacturers set the temperature limits appropriately for their engines via the stat

Absolutely and a typical outboard stat might be 60 deg C (usually between 50 & 70) compared with a car around 90deg C. Oil spec needs to account for this.

>>>a yamaha R1 is 1000cc & 200hp Yamaha 200 is 2785cc No doubt in my mind which is higher stressed

Operating stress is not all about bhp vs capacity but how much of the duty cycle is at a high percentage of available revs and a high percentage of maximum throttle opening. The use of a typical outboard if applied to your (I assume) Yamaha bike would be to constantly travel at a fixed 165mph or for my car of modest power to be run constantly at 120mph.

An analogy to consider that I've read is an outboard compared to a car or bike is like the road vehicles being stuck in first gear.... perhaps not exactly right but broadly so.

>>>If anyone can provide indisputable proof that marine branded oils provide any benefit over alternative same spec oils I'm all ears

You say "same spec". Marine oil is not just a label... it is a spec of its own (FC-W) ... a different spec to auto oil.

Making the Grade: Earning NMMA FC-W Oil Certification : The Fishing Wire

**I refer to everything above purely in the context of outboard motors... and in particular those used at sea.