Yanmar Questions

[Dockhead]

I recently received the following PM from Phoenician, which I am posting here with his permission:


"Yanmar engine
Dockhead, I realized from your recent post that we both have the exact same Yanmar engine, with approximately the same number of hours - mine has 1700. In addition, we both have similar sized boats.

I haven't experienced your problem at high revs yet, (I actually never rev it this high), so i'll keep an eye for that and let you know if it happens with me.

However, I thought it might be interesting to benchmark our respective engines and compare experiences: (hence the PM)

I have a three blade MaxProp, pitched at 20 degrees, and when motoring on flat sea at 2300-2400 rpm, my SOG is around 7 to 7.5 knots, which someone observed seemed on the low side. I wonder what is your own experience?

On another topic -probably "post worthy":-), a very good mechanic, while servicing my engine last month, recommended that I switch to 20W50 oil- His reasoning was that at 1700 hours on the engine, with oil droplets starting to appear on the exhaust side of the airfilter, it would be reasonable to switch to a more viscous oil, particularly considering the warm summer waters in the Easter Med. Any thoughts?

Kind regards, Jean"


It will be interesting to hear what other think about this. My thoughts:

1. It's hard to compare speeds and RPM. On my boat, the speed achieved for a given RPM varies very widely depending on cleanliness of the bottom and sea state. Moreover, my boat has a variable pitch prop -- a Brunton Autoprop. So a constant RPM will give an even wider range of speed depending on the resistance -- the prop will pitch up and move the boat faster and faster if there's no resistance or if there is, for example, a following wind.

2300 RPM, these days, is my fastish cruising speed. If I'm not in a hurry, and especially in very calm weather and/or with a favorable tide, I mostly use about 2000 RPM, taking advantage of my self-pitching prop. In a dead calm and glassy smooth water and clean bottom, I guess I get about 8.5 knots out of 2300 RPM, but falls rapidly with a headwind or any bottom fouling.

I don't think there's anything wrong with 7 or 7.5 knots with a fixed pitch prop like the Max Prop. I don't know your waterline length, but if its like mine (47 feet) I am guessing that you will easily reach 9 knots without stressing the engine -- is that correct? Even 9.5 to 10 if you open it up? If all this is true, then that's just the way your prop is pitched, and probably it's pitched right since you will need that somewhat lower gearing for tougher conditions.


2. I would never mess around with oil viscosity of a marine engine. They run much cooler than terrestrial engines. Our engines have direct sea water to lube oil heat exchangers, so the oil is never going to get very warm (in fact I wonder if it is simply too cool) -- nothing like the 120 degrees C plus which lube oil can reach in a car engine. I can't imagine that the recommended oil is going to be too thin under any possible circumstances.

Now that's my amateurish guess - maybe some real prop with actual knowledge could say something on the subject?

[gonesail]

i was using 30W oil and noticed the engine was loosing more than i thought it should while running. mechanic suggested i switch to 10W-40 and it definitely reduced the amount of oil used by the 3GM.

[HappyMdRSailor]

DH,

I don't think there's anything wrong with oil experimentation... I see and understand/relatively agree with your running temperature differences between cars and boats too...

It's relatively cheap... Easy to do... and excessive oil changes are never a bad thing...

I use Castrol GTX 15-40 in the boats, haven't found a reason to go with harder one's to find...

Cars I'm passionate about and massaged particular oils for each one... 944 turbo castrol 20-50, jag XK8 Mobil 1 10-40, TR8 Valvoline 50 racing... Maybe I'm weird...

[Loredo]

My boat is a SO 49 with a LWL of 42' 3''.
The engine is the 4Jh3-TE ( 100 Hp ). With the Maxprop set @ 20° pitch the boat speeds were as follows:

2500 R's = 7.5 K ( 5 litres hour )
2800 R's = 8.0 K ( 7.5 litres hour )
2900 R's = 8,1-2 K ( 8.0 litres hour )

I have now switched to an Autoprop but don't have any reliable data yet. All I know for now that I've got 8.7K @ 2500 Rpm thus far. I had never seen that high of a speed under engine only with the Maxprop.

"I would never mess around with oil viscosity of a marine engine."
AMEN!

[Phoenician]

@Loredo: Interesting speed data for your SO49, it would seem to confirm the feeling that the speed my 54DS (LWL of 48'4''), with same engine and prop is on a slow side (obviously, so many other factors at play, but your data and DH's feedback warrant further investigation on my part). Btw, how did you measure the fuel consumption?

On switching to a different oil grade, we have 2 diametrically opposed experiences: DH and Loredo seem to think that it is a big no no, whereas gonesail and Happy are more relaxed about it...

(I for one vaguely remember reading in Calder's book that switching to a more viscous oil is acceptable in some cases).

To those in the "don't do it" camp, can you elaborate why it would be such a bad idea to switch oil grade in a marine diesel?

Thanks

Jean

[d design]

Nothing wrong with changing oil grade. As the engine gets older and more worn out, the clearances get larger and thinner oils cant maintain a film properly.

[a64pilot]

If your going to change viscosity of your oil I think you need to be able to monitor oil pressure. Look for low oil pressure at idle after just coming off of a high power run.
I think for most of us straight 30W is hard to beat, but admit I tend toward multi-vis oil myself

[Dockhead]

Originally Posted by Phoenician

@Loredo: Interesting speed data for your SO49, it would seem to confirm the feeling that the speed my 54DS (LWL of 48'4''), with same engine and prop is on a slow side (obviously, so many other factors at play, but your data and DH's feedback warrant further investigation on my part). . . . .

But his speed was spot on with yours, when he was using a Maxprop. I think what you've got is normal.

The much higher speed he quoted was after he switched to the self-pitching Autoprop, like what I have. And interestingly, his speed is now spot on with mine.

The Maxprop is geared down (it's a one-speed transmission) to deal with harder conditions. I think this is correct and your results sound normal to me.

[Dockhead]

Originally Posted by d design

Nothing wrong with changing oil grade. As the engine gets older and more worn out, the clearances get larger and thinner oils cant maintain a film properly.

Viscosity varies by temperature, and terrestrial motor oils are meant to deal with oil temperatures of 120 degrees C and more (my 1970 Porsche 911S will get the oil temperature up to 140C if you drive over 200km/h for a long period of time, despite the massive oil cooler under the right front fender -- I use Castrol 20W50 in that). In marine engines with low oil temperatures, on the other hand, we simply don't need the high temperature viscosity that these oils provide. And a too-high API grade can be deadly for a marine engine. See: Oil for yacht engines

If our oil pressure is way down, then by all means, go up a viscosity grade. Otherwise, I would not mess with it, personally.

[reefhunter]

Our vessels probably have more hours on engines than just about anyone on this forum. We have used Rotella-T 15W40 dino oil from the very beginning (1982) till today. We did do a few years of testing of C*****l synthetic oil on one vessel.

[d design]

Originally Posted by Dockhead

Viscosity varies by temperature, and terrestrial motor oils are meant to deal with oil temperatures of 120 degrees C and more (my 1970 Porsche 911S will get the oil temperature up to 140C if you drive over 200km/h for a long period of time, despite the massive oil cooler under the right front fender -- I use Castrol 20W50 in that). In marine engines with low oil temperatures, on the other hand, we simply don't need the high temperature viscosity that these oils provide. And a too-high API grade can be deadly for a marine engine. See: Oil for yacht engines

If our oil pressure is way down, then by all means, go up a viscosity grade. Otherwise, I would not mess with it, personally.

Agreed

[oceannavigator]

How about the synthetics?

I have been putting the same Mobil 1 Synthetic 0w-40 from my Mercedes diesel into even my small Honda engine with great results. Quiets the engine right down and has much longer service intervals.

[d design]

Originally Posted by oceannavigator

How about the synthetics?

I have been putting the same Mobil 1 Synthetic 0w-40 from my Mercedes diesel into even my small Honda engine with great results. Quiets the engine right down and has much longer service intervals.

Great! everyone should use Mobil 1!

[Loredo]

Phoenician,
I always fill up to the neck so that I can see the fuel in the hose. Then I
keep a very close eye on the Rpm's kept and the engine hours. You know, cruising in the summer in the Med one has to motor very often if he want's to get anywhere. On the next fill up I do the math. That's how I get my fuel consumption. Do that time after time after time and see the trend.

Oh, yeah, before I take the boat to any lengthy motoring, I always dive and clean the prop and hull. Any growth on the prop / hull substracts a lot of speed and increases the fuel consumption BIG time.

This is my third boat with a Maxprop. I always felt that the efficeny of that prop is a bit limited. What I mean to say is then closer one get's to hull speed then less efficient that prop becomes. In fact, I've NEVER been able to get any of the boats to the expected hull speed with a Maxprop.

That's one reason I mentioned the speed with the Autoprop. The 8.7K max speed I've seen thus far places me right at the hull speed for the LWL 42'.3". To boot, I got to that speed @ 2500 Rpm.
With the Maxprop, no matter how hard I'd beat on the engine 8.2K @ 2900 Rpm has been the highest speed ever recorded. Anything above 2900 would only increase the noise and the fuel consumption.

I'm not saying that a Autoprop is the solution for everything. In fact for me the overall verdict is still out since I've been able to test it only a couple hours thus far. From the little I've seen it sure looks promising. I'll know more and better by the end of this year...

Engine oil.
One needs to realise that the tecnology in building engines have changed dramatically over the past 50 years. Tollerances have become smaller and steel / bearings quality has gone up.
Try to use a synthetic oil in a Perkins 4.108 and see how that goes. It'll start to burn oil at the same rate of diesel. Well kinda, been there done that and changed back to dyno oil after 20 hours or so. The tollerances... the thin syntethic oil just does not match the old engine design.

At the same pace, use too viscous of an oil in a more modern engine design and you're getting likely the opposite result. Especially with a cold "tight tollerance" engine can that thicker oil get to where it has to go???
Try it and report back! No matter what people say, I'm not going to do that kind of test.

[Phoenician]

Thanks to all for your very interesting feedback. On the oil viscosity switch, I'm going to have to quizz again my mechanic to really be convinced by his recommendation, since the jury is out on go/no go..

Loredo, great post, thanks. It is true that unfortunately we do a lot of motoring in the Med... Regarding the efficiency of the MaxProp, can we say it is a trade-off, ie, less efficient while motoring but more efficient under sail?