3.0 oil

[TunaFish389]

What oil to run in 3.0 1984 engine. I think the manufacturer recommends thicker velocity oils. Wondering why? Like auto engines runs thinner velocity oils. Know this is like apples to oranges comparison. What do you run in your 3.0 and if you know why run a thicker velocity oil?

 

[Scott Danforth]

your motor would have been speced with SAE 30 or SAE 40 (depending on your location and the temp), or now days they run 20W50

I would personally run Rotella T4 15W-40 in your motor because its a flat tappet cam and that means you need zinc in the oil, and Rotella is about the last oil with zinc in it needed for flat tappet motors

to answer your question because a boat motor is always under 100% load and your car only takes 5hp to move it down the road. your boat is not a car. its not apples and oranges, its more like turnips and elephants.

it has to do with engine architecture (flat tappet vs roller) and thermal breakdown of oil viscosity in a loaded motor.

find a 3 liter motor in a car that runs on thin oil, hook a trailer up to it, fill that trailer with lots of stuff, now drive up hill in sand in 4th gear with your foot on the throttle holding it wide open. it wouldnt make it before the thin oil broke down on the crank and rod bearings and you tore the motor up.

 

[achris]

For the loads a boat engine is under, oil formulated for diesel engines is more apt than for petrol engines. Which is what Rotella is... I used to run Vanellus C6 Global, until BP stopped making it. I now run Mobil Delvac MX 15W-40, in both my boat and my car (Landcruiser 100 with a turbo-charged GM Optimizer 6.5 )...

Bottom line.... As long as the oil meets the viscosity and standard set by the book (the GENUINE Mercruiser manual for YOUR engine) then you run that oil without having to worry about it...

The 1984 manual for your engine calls out various viscosities depending on air temperature. But if you're running above freezing, use 20W-40 'SE' or 'SF' rated oil.... As you would be very hard pressed to find an SE or SF oil these days, the latest manual for a 3 litre engine (which is exactly the same as yours) calls out any MINERAL oil 25W-40, 20W-40 or 20W-50, SH... So yeah, any reasonable oil meeting those specs will do you just fine.... (I think API are up to SN for petrol engine oils now???)

Merc specifically recommends AGAINST using synthetics. Please don't argue with me on this. I have no idea why they say that, and I'm only quoting from the manual, I didn't write the manual or have any hand in that direction, so please don't shoot the messenger!

Ok, just re-read your post and I think I know where you're coming from...

... Like auto engines runs thinner velocity oils. .... What do you run in your 3.0 and if you know why run a thicker velocity oil?

Modern car engines run very 'thin' oils, like 0W30. Most of that is because modern engines are running much tighter tolerances than your 1950's design engine. Running 'thick' oil in a new car will starve most components of oil due to it being just too thick to run through the smaller clearances properly...

Chris.......

 

[TunaFish389]

Good info, I have started to read on the flat tapp

 

[TunaFish389]

Good info, I have started to read on the flat tappet lifters.. The tolerance is also a good subject.. BUT.. I have to think that a boat engine runs cooler then a vehicle.. I run normally about 140f .. Not sure if that is normal but the 30 or 40 weight is at 100 Celsius. If boats run cooler they why the extra pumping load on oil pump.

 

[achris]

Good info, I have started to read on the flat tappet lifters.. The tolerance is also a good subject.. BUT.. I have to think that a boat engine runs cooler then a vehicle.. I run normally about 140f .. Not sure if that is normal but the 30 or 40 weight is at 100 Celsius. If boats run cooler they why the extra pumping load on oil pump.

:facepalm: Why are you second-guessing the manufacturer? Mr GM says run 20W40, so have enough faith in their engineers to know what they are talking about!

 

[Scott Danforth]

Good info, I have started to read on the flat tappet lifters.. The tolerance is also a good subject.. BUT.. I have to think that a boat engine runs cooler then a vehicle.. I run normally about 140f .. Not sure if that is normal but the 30 or 40 weight is at 100 Celsius. If boats run cooler they why the extra pumping load on oil pump.

because a @#$%@#$%@#$ car only takes 5hp to push and a boat takes all 130hp from your motor.

oil temp in cars only run a few degrees warmer than the coolant temp. oil temperature in boat motors runs about 50 degrees higher than the motor due to loading

so in a car you dont need much of an oil film on the bearings because there is no load. where the loading in a boat is 100% of the motor will be needed for the holeshot alone and while on plane, never less than 50% load unless your in neutral or just idling along at 2mph

a boat motor is loaded more like a dump truck loaded with sand while driving uphill in sand in the highest gear they have.

dont believe me, run thin oil in your boat motor.

you will spit every crank and rod bearing out within a short period of time

believe the manual......you asked, we answered

or dont believe, run what you want and then when you kill your motor, you may then believe the manual.

 

[TunaFish389]

So I guess the question is what is a "short period of time". I been running 10w30 from the start of the season. Been out 16 times with an average of 2 hours running per time with towing but only twice. I am thinking by my logic I will be good till end of season, which will be another 30 hours.. And synthetic.. Thanks all, next year I will put in a 10w40.

 

[achris]

.... I been running 10w30 from the start of the season. ... Thanks all, next year I will put in a 10w40.

I have to ask, why have you put significantly thinner oil in than every book says?
And why do you plan on putting oil in next year, that still isn't correct? Do you hate your engine and are planning on killing to justify getting a new one? (Because, that's what you are doing!)

Book (written by people way smarter than you and I combine) says....
1. use 25W40 or 20W40...
2. DO NOT use synthetic oil.

Chris.......

 

[TunaFish389]

Well first in am planning on using the same oil as you said your books say.. If I have to explain this to you then why post on a subject you don't know.

Synthetic oil is proven better protection then convention with long life span higher, less heat breakdown and reduce friction which makes me question the validity of these books.

I also believe the book says that SAE 30 is acceptable which 10w30 meets those standards but I guess I don't need to explain that...

 

[achris]

....

I also believe the book says that SAE 30 is acceptable which 10w30 meets those standards but I guess I don't need to explain that...

You do need to explain why you keep ignoring both advice here, and the Merc service manual...

Again, from the manual. In the event of SAE30 not being available, use 25W40 or 20W40.... And the use of synthetic oils is NOT recommended..

So, DO NOT use 10W30. DO NOT use synthetic oils. But you're not listening....

You seem intent on doing all you can to NOT use the right oil, and appear to just be here looking for someone to say "yes, you're doing the right thing", despite the fact that you are not, so I'll leave you to it...

Use whatever you like, but if it's not the oil recommended by the engine supplier, don't complain when all the insides become outside...

Chris...