Diesel Engine Wear

[martynwhiteley]

Whilst 'running-in' my new baby Merc 1.7, and getting used to revs required to get on and off the plane, it got me thinking about what's best to minimise engine wear, and as a spin off, get the best economy (not that the 1.7 could ever be accused of being thirsty - last week I completed 25 hours, 242 miles on the GPS, moving average 11.1, and it only used 41 gallons of diesel!)

For much of its running in time, I was in the 2000-3000 rpm region, but its not planing at these revs and needs to get up to about 3600-3800 to lift up. Once up, I can throttle back to about 3300 and it will continue to plane (in calm waters).

My question is that, would it be better for the engine to be running at say 3800 as a 'cruising speed', than 2800 where it would be in semi-displacement mode? (The engine will rev to 4200 with the current 15" prop, about right, since the max is 4400, and the manual states WOT 4000-4400).

Or would it just be a case of better economy, but the higher revs would mean more engine wear? (it does run hotter at the higher revs).

<hr width=100% size=1><font color=blue> Real boaters do it on the Humber </font color=blue>

 

[oldharry]

Diesels dont like being run too slow, and in the longer term you could get problems from running it too slow. The ideal speed for a diesel is around 3/4 of its full revs. Speed (unless you permanently thrash the thing flat out) does not make a huge difference as at lower speeds more soot and carbon gets formed which goes into the oil and increases wear rates anyway. Thats why you see the Sea anglers roaring home at full throttle at the end of a days low speed trolling - they are not just trying to get back to the pub a bit quicker, but are blowing the carbon and muck out of their engines.

The best way to preserve the engine is to change the oil and filter if anything before the due service interval. If the oil should be changed every 100 hours - do it every 80, and I will guarantee your engine will last longer. Taxi drivers can quite often get 500,000 miles out of their diesels simply by doing more frequent oil changes. And use good quality oil - not cheap car shop rubbish.

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[Deleted User YDKXO]

Firstly what are the running-in instructions given by the manufacturer? Secondly, it does no engine any good to run continuously just off the plane - the engine is loaded but not running at its most efficient rpm. I would say that you should avoid running at max rpm but run at planing speed varying the rpm on a regular basis as running at constant rpm will also not help to bed the engine in

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[Dave_Snelson]

My response is not that technical - you buy an engine to get enjoyment from your boat and the engine will run within the range of planing speeds.

However...once you have run the motor in thoroughly (and I mean thoroughly) you may want to try a one-off oil additive called "Slick-50". This coates the engine interior with Teflon which greatly reduces friction, and so inhibits engine wear and excess heat. It will also stop your engine from running in , if you haven't run it in fully.

It is added at oil change time and remains in the oil until the next change. Then you can probably get two to three seasons before another addition.

Hope this helps.

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[martynwhiteley]

Thanks Harry (and Mike and Dave),

It's good to see that there's still plenty of prompt and very helpful advice on the forum, despite all the trivia and fun!

I have completed the 20 hour running-in period as best as I could in accordance with the recommendations, although there did seem a bit of conflicting advice regarding setting off from cold, where on the one hand the usual few minutes of warm up was recommended, but also it stated that when running in, one should start and set off, getting to at least 1500 rpm very quickly. I took a sort of compromise route, letting it idle for a couple of minutes. However I did note that the otherwise smoke free engine, would start to smoke a bit when at idle for more than a few minutes.

It looks like it's good news then, although 75% max would be 3300, and this is just perhaps a bit too close to the dropping off point to cruise at. I'll work between this and 3800, and keep changing after a while. (Not forgetting the odd blast at 4200!).

I noticed the little 1.7 got a mention in MBY this month. Albiet in an article about the new V***o D3. It'll have to be good to better (or match) the little Merc. /forums/images/icons/smile.gif

<hr width=100% size=1><font color=blue> Real boaters do it on the Humber </font color=blue>

 

[MickJ]

Volvo AD31 manual simply says "max fast cruise should be 200 r/min below max revs". I did just that recently (well, 300 r/min below max) on an 80 mile trip. No smoke, no heat rise, not a drop of oil burnt, and it purred like a kitten all the way!!

It's difficult to accept when you are used to petrol engines, and I dont think normal considerations apply, cos this would be considered giving them a good thrashing if they were petrol. I'm told labouring a diesel is much worse.

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[Dave_Snelson]

Martin, you have chosen a good engine. I would recommend (if you go down the Slick-50 route) not to use the additive until you have notched up about 50 hours.

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[Jerbro]

Volvo give the same advice on the TAMD63P (cruise is 200 rpm below max obtained RPM - could be below max designed RPM if dirty bum I guess). The Volvo engineer I use says they are designed to run at maximum RPM for 1 hour continuously. So could the same apply to a mercruiser?

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[duncan]

Yanmar also rate most of theirs as 1 hours max output from WOT and 200 less for cruise.
I would have to suggest that somewhere between 3600 - 3900 seems to be the range at which martyn's rig will be running comfortably - and that his choice within that range should be driven by boat speed/conditions and closing time (not necessarily in that order!)

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[andy_wilson]

Real boaters do it on the Humber

They didn't call it Grimsby for nothing you know.

Running in.

The manufacturers guidance is usually best but a couple of thoughts.

Firstly prolonged idling or v. slow running is not too good for a diesel motor, and neither is a heavy load whilst still cold.

Particularly when running in therefore (and thereafter whenever possible) it is a good idea to prepare to slip the berth, start the engine, and warm up for no longer than required for smooth, reliable running. Bear in mind that new motors can be tight, or need idle adjustments and could be prone to stalling when cold.

A couple of minutes on tickover before casting off should be fine, and don't give it the gas until the temp. needle is close to or on 'normal'.

For cruising whilst running in, never has a marginaly powered rig been such a bind. With plenty of power in hand you can bring her onto the plane and then throttle back to within or at least close to the running in RPM range. If the power is too marginal you may have to remain at displacement speeds, which may even be below the stated running in RPM.

Judicious use of power trim or trim tabs can help in this regard.

For normal cruising once run in, use your ears (does it sound comfortable or strained), the trim devices, the log and rev. counter.

Best economy on the plane will usually be when trimmed to the angle of least resistance, and throttled back, but not so slow that the conditions will knock her off the plane.

For any required speed, trim for the angle of least resistance, which usually means you can throttle back some more.

Accelerating, head seas and following seas all require trim adjustments.

Heavy seas often need to be tackled by constantly adjusting the throttle.

Another general point, engines wear to the RPM (we are talking 10 maybe 20 years leisure use here so don't get too hung up on this). Use at different settings WILL prolong engine life so don't fall into the habit of conducting all long passages at the same, constant RPM setting.

Feed the cooling system Humber gravy and she is bound to run hot. As long as it remains stable but hotter at high sppeds, that's OK. It's a problem if the needle continues to rise off the scale unless you slow down.

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[martynwhiteley]

Re: Real boaters do it on the Humber

Thanks for your comprehensive summary Andy.

I like the bit about 'Humber Gravy', It does worry me a bit, the raw water system must be undergoing a constant 'sand blasting'.

Getting comfortable with no internal raw water pump (It's in the leg on the Merc drive), not being able to check the impellor, not having real need to fit or check a strainer and the usual see through pipes. But earlier posts on the forum gave me some confidence that all should be ok, as long as I change the pump unit every three years. Not sure they knew about the Humber Gravy though /forums/images/icons/smile.gif .

<hr width=100% size=1><font color=blue> Real boaters do it on the Humber </font color=blue>