Proper weight oil

DD's are a whole different ball game and I do not recall ever using a multi grade oil in them when doing my apprenticeship on heavy equipment in northern NZ.

I've never used multi weight oils in 2 strokes. SAE 40 only. For cooler climates perhaps SAE 30. But check with the manufacturer.

Hi,

I am pretty sure we used to use C 3 30 Vanellus by BP in them and everything else we worked on.

I just did in a 100' Hatteras with 1800 HP V 16 2000 Series Detroit MTU. To early to tell if it has had any effect. The owner has numerous construction machines and a fleet of trucks. He uses it on land and wanted it used on his boat. I treated 5000 gallons. Time will tell I guess.

Is it your position that CF4 40W is not suitable for DD 2 strokes ?

The technical reason for using only SAE 40 single viscosity, CF-2 rated oils in
Detroit Diesel two-strokes is because of the design of the piston oil control
rings, which are of the Napier style. Napier rings develop a very narrow and very thin oil film between the ring and cylinder liner, which in turn results in a phenomena known in the lubrication industry as excessive viscosity shear rate. Viscosity shear rate is defined as the maximum sliding speed between
two surfaces in inches per second, divided by the oil film thickness between the two surfaces in thousandths of an inch. Single viscosity oils are able to
operate at viscosity shear rates which are appropriate for Detroit Diesel two-stroke oil rings. Multi-viscosity oils are not capable of maintaining their proper viscosity at viscosity shear rates typical for Detroit Diesel two-stroke oil rings, which is why multi-viscosity oils are not suitable for use in Detroit Diesel two-stroke engines.

As a corollary, the same phenomena of viscosity shear rate limits is the reason most marine gearbox manufacturers require use of single viscosity oils only.

Yes, agreed, my query was perhaps not clear, are there any oils that are rated both, i.e. cf2/cf4.. I was informed once that Castrol assuron was labeled as such ?

If you have preheaters and pre oilers (pre heat and pressurize the engine oil system before start up) you can use straight 40w... or put gradually increasing light load on the engine as it warms up. The key is to warm up as soon as possible without building high combustion pressures.

Why is to gain adequate circulation and warm the engine to prevent startup wear where most of the wear takes place in the engine. Most of this startup wear is that the oil film at top dead center is very thin... and the cold metal lowers combustion temperatures and cause the condensation of corrosive combustion products with the water vapor from combustion on the cylinder walls. Typically, up to 60 degree C coolant temperatures this condensation takes place on the cylinder. Additionally, the startup produces wetting by diesel on the cylinder walls as the engine starts lowering the protective film of lubrication on the cylinder. Why is the oil film thin in the first place is that the differential speed of the piston and rings on the cylinder is low causing it to fall out of hydrodynamic lubrication into sliding with the high cylinder pressure near top dead center the lubrication is lowered and wear results. Replacing this oil film has to happen every cycle and with thick oil that happens less readily.

Engines subject to long periods of operation this is not an important issue. But engines subject to start cycles often this is a problem and thinner oil like 15-40w is better. Now why is not multi weigh oil the best is because viscosity improvers are not as lubricative as the oil and the 15-40 had part of the oil replaced by viscosity improver.

Now the issue of bearings and cams and the like is not really a huge problem as they always have a remaining oil film present. The issue with too thick of oil is the leakage rate from the bearing not being enough to cool the bearing as the oil film heat up but is slower to be replaced with cool lubrication. But a low power and pressure outputs the lube film heats up much slower so taking it easy as the engine warms up is a good idea with thick oil.

Hi,

Thank you for the very well written and explanatory post.

It is possible to order big gearboxes setup to run multi grade oils if you are getting them directly from the manufacturer as bespoke built units.

That said I was once on a boat that had gear oil low pressure alarms when manoeuvring.

It was using a Reintjes gearbox which was setup to run a straight 30wt oil, some clerical error had led to the Lube Spec for the vessel calling for Omala 150,( heavy gear oil) It had survived undamaged for around 4000 hrs and several oil changes, changing to a 30 wt oil magically cured the low oil pressure alarms.

Oil samples were sent correctly identifying the oil and nothing ever came back saying it was the wrong grade for a very common gearbox.

Couple more comments on oil.

These ratings of oil are either oil industry specific the CF-CG or "C" ratings for general use reference, or they are manufacturer spec. Why, is that manufactures use different components and design parameters in designing the engine. Even simple things like bearing clearance can effect things.
Example... Now just as important as bearing operating clearance is the side clearance to promote and control leakage of oil out of the bearing to allow the hot oil to be cooled by replenishing it with cooler oil.

Often one wonders if "S" type oils can be used in diesels. S rated oils are for gasoline, or gaseous fuel engines. Why is the additives. Gasoline engines have concerns about oil consumption and production of ash in the combustion process from burning oil and that creating deposits that increase the tendency to preignition or detonation. Diesels do not have this problem. However, diesels need valve lubrication for long lives they have. Therefore, a diesel or C rated oil is higher in ash than a gasoline oil. This ash and its makeup helps lubricate the valve seats... extending there life. The special additive lubricant chemicals to reduce rubbing wear in less than ideal situations like at the cam lobes and at the top of the cylinder... usually produce high ash. So gas engines use low ash additives and these usually are not as effective at this extreme case of lubrication (very high pressure and low surface speed)... diesel engines have higher loading on rings often and need long lives... so they use better but higher ash additives. But they don't mind the ash... and need it for valve seat lubrication. That is generically why diesels are not recommended to run on gas engine type oils.... it will reduce engine life. Now some manufactures (most now-a-days) get real picky about oils and warrantee so don't use the wrong oil if you want to get long life or warrantee repairs!

Whats worse on marine engines is they often set in port in moist or humid climates... these causes corrosion of surfaces... see my post on the rebuilding the Cat C18... "engine porno". If you notice the boat the engine came out of is a high speed type that likely doesn't get run much and does not have professional constant care or poor care... as is typical often. You will see some rust on the surfaces of the rods... from sitting in port. That means likely some of the critical surfaces may not be ideally kept from corrosion. But that is the hell of owning a speedy boat you got to run it often and even if it takes several hundred liters an hour consumption! Why was that engining being rebuilt... too much sitting around. Use it or lose it.

Note all my comments are not specific to a particular engine... but in general for all engines.

I was under the impression that LOW ash was the desired condition for 2 stroke diesels ? higher the ash content, less time between oil changes and indeed anything over 1% is basically unacceptable ?

Hi,

Mobil makes the oil that is found in buckets with a CAT logo on it.

But CAT might have their own additives or different additives blended into the oil than the Mobil branded oil. CAT oil is cheap enough to just buy it from them and that is why I use it in all CAT boats I manage. It's the Mobil synthetic for the MANS that really breaks the bank, but you have to use it in the common rails. I've seen that it doesn't break down though, at all. You pull the dipstick out with 150 hours and it still clings to it.

The big specification for the 2 cycle Detroits (other poster) was an anti-foaming agent, not necessarily low ash. I like the Chevron oil for DD's in those.

WOW ! All this from this: What weight oil is recommended in a Cat 3208 T marine engine with approx 2700 hours.
Gulf coast temperature

My friggin head hurts !!