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Old 21-09-2006, 07:10   #1
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How to make your Diesel last a long time.

Relatively new here so I hope nobody minds if I chirp in. While looking over some of the posts I noticed quite a few questions on the expected longevity of diesel engines. While I don't claim to be the lord-of-diesel... many useful points have been picked up as a diesel mechanic in another life.
Do as you want with these suggestions, this is from personal experience and various diesel courses from different manufacturers.

Synthetic Oil - doesn't need to be said does it? Use synthetic, not a blend (there are 5 grades). In the US, the oil companies got the labeling changed so they could add as little as one drop of synthetic to their Dino oil and put synthetic or synthetic blend on the label. The container must say "fully" or to that effect synthetic. Oil change intervals can usually go beyond what the oil companies state, use the engine makers oil change recommendation.

Don't idle a diesel engine for long periods. Of course you must give it a chance to warm up the piston(s). Diesels were made to work, when they loaf the rings don't fully seal causing cylinder glazing and excessive blow-by diluting the oil.
Idling causes undue wear on the connecting rod bearings (refered to as the lower end).

If the engine is not working, instead of idle have it rev at approx 1/3 of redline.

When working your diesel rev it up, again this can hurt the bottom end if it's run too slow.

Spinning big alternators is "work" don't do this at or barely above idle.

The color of exhaust smoke generated by diesels is very indicative of it's health... learn to recognize the teltale signs (white vs. dark) there is many sources of info on this online. For instance leaky injectors have a certain color, vs. bad rings etc.

As we all know it's the high compression that makes diesels what they are. High torque, fuel economy, clean burning - most of what comes out the exhaust is pure soot (harmless carbon), hardly any monoxides and tiny amounts of hydrocarbon.

What to watchout for - Diesels, because of their compression have a very low exhaust temp. On some truck engines the exhaust manifolds are a light-weight tin stamping and the paint doesn't even burn off. Try that on a gas engine. So if you suspect a high exaust temp, (yes it's hard to tell with water in there) something is wrong with compression

Cheers Duckhead
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Old 21-09-2006, 15:10   #2
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"Spinning big alternators is "work" don't do this at or barely above idle."
Only if they are under load, doing charging. Most alternators will hardly put out any power (and consequently develop next to no load) at idle RPMs.

On the bright side...you can solve the problem of not putting a load on your engine AT idle speed, if your alternator system is set up so it DOES put on that heavy load.<G> And you won't be able to run at that low idle speed if the load really is "heavy".<G>

I've literally seen a small (80A rated) alternator buck and kick the belt off the pulley when it was running at low speed, charging one battery, and the battery switch was thrown to "BOTH" bringing the load of the second discharged battery online. (Both the alternator & the battery switch on that boat are safe for switching while in use, not all are.)
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Old 21-09-2006, 16:50   #3
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Best RPM for Yanmar 3GM30?

I have a Yanmar 3GM30, the nameplate on engine says "RPM 3400". Is this the red line?

I usually run engine around 2200-2500 RPM which moves the boat at about 5.5-6+ knots. If I push it to 3000+, I can make 7 knots, but with a lot of noise and churning of water aft of transom like it might be cavitating.

Is 2200 RPM too low? I even run it at 1800 when channel rules limit speed to 5.

TIA
Forrest
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Old 21-09-2006, 17:21   #4
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I am curious about the top RPM of my engine.. a Volvo MD17D... Is full throttle exceeding the "redline"? or is the redline at full throttle?

Is it harmful to rev a diesel with no load to the top RPM? Is it less harmful rev it in gear?

Is running at high RPMs wasting fuel and or harming the engine?

My own experience is that the higher the revs the faster the boat moves...right on up to max RPMs which these days is around 2600 RPM.... and that seems like it should be higher. But in flat seas at max RPM the boat is moving hull speed and then some.

This engine is 21 yrs old and only recently had the top end rebuilt... which made it run a hell of a lot better. I want it to last until I die... hahaha

Jef
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Anyone with experience please comment.
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Old 21-09-2006, 18:47   #5
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I'm too burnt tonight to answer. Look for commentary tommorow, sorry.
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Old 21-09-2006, 18:53   #6
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What I'm saying is extended Idle time is not good for diesels, you have to warm up your engine of course (at idle) once warmed up you are doing your motor no favors by idling for extended times.

Manufacturer says rpm 3400 then yes that's redline.

Generally 3/4 of redline is a good max "run all day" engine speed, tho nothing in stone that you MUST stay at 3/4...slow down and go 1/2 or 1/3 if you want.

Some engines will reach redline with full throttle, some won't it depends on your prop pitch/size.

Don't rev your engine to redline with no load.

Funny but it's my experience too that the more I rev the engine the faster my boat goes? who'd a thunk it?

Want your engine to last...then don't let it sit for months between start-ups, change your oil, keep a fresh impellor in it.

Duckhead
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Old 21-09-2006, 19:17   #7
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Also, speaking to redlines, I have an ancidotal comment:

I was once told that the proper RPM for a diesel engine is also where it is in harmony. You can find these sweet spots by feeling the vibration your engine makes. No matter if you are trying for 3/4 of redline, 1/2 of redline, or 1/4 of redline, your engine will have a few very special spots where the vibration and chatter will abate completely. The engine will "hum" rather than rev and rattle. I was taught that these RPMs are also ideal for long-term motoring since you wont rattle anything loose, and the components are all in a sort of vibrating harmony, vibrating at the same frequency.
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Old 22-09-2006, 01:29   #8
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Diesels don't have a "redline" as such. They are speed Governed. The redline point is usually much higher than the governed speed. "Redlining" is of course, a term taken from a Rev counter on a Petrol performance engine. The "Redline" being a red marker that was set to a upper RPM limit of the engine. Above that limit usually meant detruction of the engine. As a Petrol engine can rev easily much high than it's safe operating RPM, "redlining" is easily achieved.
A Diesel should be able to be reved to it's max RPM and sit there governed by the limiter in the IP. The danger with the Diesel engine is not being able to reach close enough to max RPM when under load. A rule of thumb is usually a difference of approx 200RPM between full and no loads. The continuose and Max ratings are relevant to heat production and are very different to "Redline" terms. By the way, a Diesel can indeed run very hot. Infact, in some circumstances, they can output much more heat than Petrol. I have seen large engines running their manifolds a very cherry Red. In most circumstances, the heat output of Diesel engines require more cooling than Petrol engines.

Yes, the big killer of a Diesel is idle, especially when cold. We have had some great discusions on this subject and a lot of info is available with a search. But in a nut shell, get the engine under load as soon as you can.
An Alternator will not put much of a load on most engines. An 80A alternator takes ruffly 2Hp from an engine, so even a 20Hp engine will find that fairly easy work. But also, most alternators will not start charging till they reach 1000RPM and good charge power is not untill 1500RPM. But what speed the alternator is actually spinning at is determined by the gearing of pulleys driving it. So Engine RPM may or may not be indicative of what the Alternator is doing.

Sorry Duckhead, I'm not meaning top bust you here, so please don't take it that way. But it is interesting that the Carbon soot from Diesel emmision is now considered to be possibly the most carsonagenic substance known. But it is also true that many more of the noxciouse emmisions are not present that are in Petrol exhaust.

Another good discusion we have in the archivs is on oils. A search wil bring up some good info on that. But also in a nutshell, the way to check oil for quality is within the specs on the back of the container. You will see a number of manufacturers specifications that the oil must meet to obtain that rating No. the manufacturers have required. The oil MUST meet that rating as a minimum requirement. So don't read the front lable, it may tell you nothing more than it's a syntheic blend, but those numbers on the back tell you what the blend is required to meet.
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Old 25-05-2007, 12:04   #9
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Ive searched the internet and cannot find much on diesel smoke diagnostics. Can you point me to such information?
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Old 25-05-2007, 13:20   #10
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Free Advice for Diesel Owners.

Second hit on google search for diesel smoke

Diesel Smoke

diesel smoke - Google Search

United Diesel UK &ndash; Diesel Engine Smoke Explained
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Old 25-05-2007, 13:22   #11
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SMOKE COLOR AND ITS CAUSES:
Diesel Smoke
BLACK SMOKE - Restricted air flow ( dirty / obstructed air filter; plugged exhaust; restrictions in exhaust system; defective turbo / supercharger); Overload; Improper injection (poor atomization, injector dribble, late injection)

BLUE SMOKE - Worn or stuck piston rings; worn valve guides and stems; high crankcase pressure; worn / supercharger oil seals.

WHITE SMOKE - Misfiring cylinders; water in fuel; air in fuel; water in cylinders (blown head gasket, cracked head or liner); lack of compression.

More Info Goto:
Free Advice for Diesel Owners.
The colour of diesel engine exhaust smoke and when it occurs can tell you a lot about the internal condition of an engine.
Automotive Systems
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Old 25-05-2007, 16:11   #12
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My manual for my Yanmar 3GM30F states that the max continuous rpm is 3400. Max intermittant is 3600 rpm. I'll have to go back to the manual to make sure, but if I remember right, intermittant means no more than an hour or so at max intermittant. The manual also states not to run the engine for long periods under 80% throttle (or power? I don't remember). If you are going to run under 80% throttle an extended time, rev the engine to higher rpms every hour or so. I believe the manual says to operate it this way to not accumulate carbon in the engine and to not glaze the cylinder walls. I've been running mine at minimum 2900 rpm for cruising speed.



John

Quote:
Originally Posted by WindDancer
I have a Yanmar 3GM30, the nameplate on engine says "RPM 3400". Is this the red line?

I usually run engine around 2200-2500 RPM which moves the boat at about 5.5-6+ knots. If I push it to 3000+, I can make 7 knots, but with a lot of noise and churning of water aft of transom like it might be cavitating.

Is 2200 RPM too low? I even run it at 1800 when channel rules limit speed to 5.

TIA
Forrest
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Old 25-05-2007, 19:36   #13
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Quote:
Originally Posted by cal40john
My manual for my Yanmar 3GM30F states that the max continuous rpm is 3400. Max intermittant is 3600 rpm. I'll have to go back to the manual to make sure, but if I remember right, intermittant means no more than an hour or so at max intermittant. The manual also states not to run the engine for long periods under 80% throttle (or power? I don't remember). If you are going to run under 80% throttle an extended time, rev the engine to higher rpms every hour or so. I believe the manual says to operate it this way to not accumulate carbon in the engine and to not glaze the cylinder walls. I've been running mine at minimum 2900 rpm for cruising speed.



John
80%, Is that where the maximum torque is?

I was told that we would be fine running our Cummin's B3.3 65hp motors at max torque, which put's out max torque of 50hp @ 1500rpm and 65hp @ 2600rpm.

I hope that is right, 'cause that was our plan.

Dave
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Old 25-05-2007, 19:59   #14
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Im not positive but max torque on a diesel happens much lower on the curve.Gas engines reach maximum torque and horsepower the more revs you achieve.

The more you run a diesel under load the happier it will be and the longer she will last.Allan already mentioned the pollution realities from a diesel so I won't.
The more she is run the better lubricated she will be.
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Old 25-05-2007, 20:08   #15
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Quote:
Originally Posted by cat man do
80%, Is that where the maximum torque is?

I was told that we would be fine running our Cummin's B3.3 65hp motors at max torque, which put's out max torque of 50hp @ 1500rpm and 65hp @ 2600rpm.

I hope that is right, 'cause that was our plan.

Dave
Torque is pretty flat on the 3GM30's. If I remember the manual right, Yanmar doesn't care if you run higher rpms, they just imply that if you run lower, you can eventually damage your engine. I don't know what Cummins recommends.

Let's see if the picture attached.
John
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