Engine loading

[RichardM]

Ok so I'm thinking, if it's better to keep the oil at a certain operating temperature (which really does make sense), how about a thermostatically controlled oil bypass from the oil cooler for those older engines that don't have the engine coolant oil warmer? Similar to an engine coolant thermostat that controls the flow of coolant going to the heat exchanger. It's probably relatively easy to do it home made but does that sort of system actually exist off the shelf?

 

[LarryM]

Ok so I'm thinking, if it's better to keep the oil at a certain operating temperature (which really does make sense), how about a thermostatically controlled oil bypass from the oil cooler for those older engines that don't have the engine coolant oil warmer? Similar to an engine coolant thermostat that controls the flow of coolant going to the heat exchanger. It's probably relatively easy to do it home made but does that sort of system actually exist off the shelf?

Yes, they are fairly common on high performance racing and street engines. They are known as 'engine oil cooler thermostats' and are available from a number of manufacturers. If the engine has an easily accessible external oil cooler, the installation could be fairly straightforward. Some hydraulic hoses and brackets are all you would need. Here is just one example.

 

[OldDan1943]

I had a N46 with a 120hp Luggar. Bringing it down from Long Island, we ran it WOT 24hr/day without a problem, when outside the ICW. It had keel cooler. Once we got into warmer waters, we had to watch the engine temp. When it started to climb, we'd reduce the RPM until it started to drop. I had the keel cooler boiled out but never did boil out the engine. That no doubt would have helped.

 

[Nomad Willy]

The question remains, who has first hand details on the early demise of a 4 stroke newer marine propulsion engine due to being "lightly" loaded? Myth, fact, dock talk, rare exception, reality or what?

Don’t have paperwork or documents to prove it but I asked the guys at (then) Klassen Engines and they told me it’s not uncommon up north (Alaska) to have gensets glaze their cylinder walls. They sold both propulsion and generator units to the vast fishing fleet starting in the 60’s. Sometimes the gen engines would run at 1800rpm for long periods w no load. I think they said it didn’t happen to propulsion engines.

But I agree w you re oil temp. Cool oil leads to deposits behind partially stuck rings and things go downhill from there. Ideally oil should be over 180 degrees f. IMO. Sunchaser I think we had a discussion about this before whereas I was suggesting to remove the oil cooler on underloaded engines too get the oil temp up but you said no that the thermostatically controlled coolant heats the oil on an underloaded engine .. since the coolant would be 180-190 deg f and the oil on an underloaded engine about 140. Better IMO to just load the engine 50% to ideally about 65% load. Like an FL burning 6gph at WOT propped right burning over 3gph. An FL burning 3.5 gph will have no issues whereas those that report burn rates of 2.5 gph or less (most commonly reported on TF) will eventually have some degree of problems .. most often lots of smoking .. especially at startup.

As to the glazing I suspect it’s just polishing and not a deposit or a film. The rings must be harder than the cylinder wall and thus have the ability to polish the walls. Just my “notions”.

 

[Pack Mule]

I thought the cylinder walls on my little Westerbeke 7.5 kw were glazed over. It was using what I though was a lot of oil. Some of the guys here told me to load it as much as possible and run it for a while. I did that and also added a little Lucas oil treatment. It seemed to help. I try to load it as much as possible now but I just don’t have that much to load it with .

 

[Mako]

I fixed it using Nulon oil additive added at double strength as per it`s makers advice, and (stop that sniggering please!) it worked.

I always thought Marvel Mystery Oil was the magical elixir for all things mechanical, but now I have to learn more about this Nulon stuff

 

[Mako]

Not to be flippant, but one practical solution to running a generator too lightly loaded is to turn it off. On my previous boat I had an Onan and a Westerbeke, both rather old and no sound shields, and I absolutely hated them. So eight 8D's and a 3000w inverter helped alleviate the issue while cruising, and this was an all-electric yacht.

 

[Pack Mule]

Not to be flippant, but one practical solution to running a generator too lightly loaded is to turn it off. On my previous boat I had an Onan and a Westerbeke, both rather old and no sound shields, and I absolutely hated them. So eight 8D's and a 3000w inverter helped alleviate the issue while cruising, and this was an all-electric yacht.

Yes I agree . It’s my rooftop air on those hot muggy days while cruising that I’m having hard time giving up.

 

[Ski in NC]

I have seen two types of polished bores: First is where hone grooves are packed with carbon, that can be cleaned out with the heat of high load. Other type is where bore is actually worn, not much you can do with that other than hone/re-ring/liner replacement/etc.

A real problem with lightly loaded gennies. Fixed a bunch of those.

Only seen a couple of propulsion engines suffering from light load, and the only complaint was high oil use. On those, they were absolutely cured by hours of 50%-plus load running. Never took the heads off those to see what it looked like, no need, they were fine afterward. These were four strokes run at VERY light load, like under 10% for like 100hrs plus with no power up. Liner if worn would not be fixed, so it had to be grooves packed with carbon.

 

[Rufus]

The article in this link helps clarify (at least for me) the differences between "glazing"....a varnish type deposit....and cylinder polishing....mechanical wear of the honing pattern. These folks suggest that a light honing can at least partially restore an engine that suffers from either.

Bore glazing and polishing in diesel engines – Cox Engineering

 

[OldDan1943]

LOL on my N46 I had a 20kw and an 8kw gen. The only way to load up the 20kw was to supply power to a couple other boat at the same time. The original owner had big plans to run a dive compressor on it. No idea if he went beyond the planning stage.

 

[Simi 60]

Yes, it is tough to get oil temps up on some lightly loaded engines.

Might it have something to do with where I am getting readings from?
I have a sensor on an oil filter and shoot with laser thermometer at same spot.

 

[BruceK]

I always thought Marvel Mystery Oil was the magical elixir for all things mechanical, but now I have to learn more about this Nulon stuff

I share your skepticism. Wanting an easy way out that didn`t involve dismantling,I tried the " double dose" Nulon oil treatment that (funnily enough) Nulon was advocating online. Nulon/snake oil/ something else concurrent I don`t know about,reversed glazing which was reflected in ample blue oil burning exhaust smoke. A reality I(but no one else)have to accept, and share FWIW.

 

[MYTraveler]

Take an extreme case of the QSB 5.9 480 hp engine. 75% is 360 hp.

I don't think that is correct, although the term "loading" is so commonly misused, it may be what the author intended. If so, I agree with you that 75% loading is not necessary.

The better definition of loading is rpm specific and represents the horsepower being produced by an engine at a particular rpm, divided by the max possible rpm (ie, load). That is how Cummins defines the term for purposes of loading indicated by my QSM 11s' display.

As such, the engine you reference, which is capable of putting out 360 hp well below max rpm, could be 100% loaded if called upon to put out 360 hp at an rpm for which its max hp is 360. Of course, if the boat were propped such that at max rpm (assuming that is max hp) it is only being called upon to produce 360 hp, then it would be only 75% loaded at that rpm.

On my boat, 1050 rpm gives me 8.7 knots +/-, and the load is 40% +/-. But that is enough to get everything "hot". I have it on good authority that the engine could/should last well over 25,000 hours if predominantly used this way.

By the way, you might be wondering (as I did) how the engine determines the load it is under. Since the relationship between fuel burn and hp is fairly linear, Cummins relies on fuel consumption as a proxy for hp production.

 

[BandB]

On our diesels we've been involved with, 75% load is 87%, 88%, 86%, 86%, and 86% of Maximum RPM. Looking at it another way it is 325, 250, 325, 325, and 350 RPM Below Max. The one it's only 250 below is one with max RPM of 2150. The others have Max RPM of 2450, 2300, 2300, and 2400.

 

[Arc]

It appears most are over thinking this subject. Very simply try to run your engine at thermostat temperature and no harm will come. All of this 75% load is a bunch of nonsense.

 

[DavidM]

It appears most are over thinking this subject. Very simply try to run your engine at thermostat temperature and no harm will come. All of this 75% load is a bunch of nonsense.

+1

David

 

[mcarthur]

I don't think that is correct, although the term "loading" is so commonly misused, it may be what the author intended. If so, I agree with you that 75% loading is not necessary.

The better definition of loading is rpm specific and represents the horsepower being produced by an engine at a particular rpm, divided by the max possible rpm (ie, load). That is how Cummins defines the term for purposes of loading indicated by my QSM 11s' display.

That's not correct from what I've been able to find - "load" from manufacturers is about fuel use, which equates pretty linearly with HP created. The HP rating at RPM values is not linear (which you said - agreed).

So measure load by either fuel used or HP, but not RPM.

 

[BandB]

That's not correct from what I've been able to find - "load" from manufacturers is about fuel use, which equates pretty linearly with HP created. The HP rating at RPM values is not linear (which you said - agreed).

So measure load by either fuel used or HP, but not RPM.

You omitted the rest of his post. At no point does he say load is RPM. He says hp production. He states the underlying theory and then how it's typically measured in the real world, which is by fuel used. He states that clearly.

By the way, you might be wondering (as I did) how the engine determines the load it is under. Since the relationship between fuel burn and hp is fairly linear, Cummins relies on fuel consumption as a proxy for hp production.​

 

[AusCan]

I have seen two types of polished bores: First is where hone grooves are packed with carbon, that can be cleaned out with the heat of high load. Other type is where bore is actually worn, not much you can do with that other than hone/re-ring/liner replacement/etc.

A real problem with lightly loaded gennies. Fixed a bunch of those.

Only seen a couple of propulsion engines suffering from light load, and the only complaint was high oil use. On those, they were absolutely cured by hours of 50%-plus load running. Never took the heads off those to see what it looked like, no need, they were fine afterward. These were four strokes run at VERY light load, like under 10% for like 100hrs plus with no power up. Liner if worn would not be fixed, so it had to be grooves packed with carbon.

My findings have been the same.

Generators can and will glaze up from light loading at a constant rpm.

It's rare for any propulsion diesel engine to glaze up due to the normally varied engine speed.

 

[mcarthur]

You omitted the rest of his post. At no point does he say load is RPM. He says hp production. He states the underlying theory and then how it's typically measured in the real world, which is by fuel used. He states that clearly.

Doh - sorry MYTraveler, I mis-read the message. Thanks BandB.

 

[BandB]

Doh - sorry MYTraveler, I mis-read the message. Thanks BandB.

Thanks for your response. I don't thoroughly understand the theoretical calculations myself but understand the gauges and how to calculate from fuel.

 

[sunchaser]

Might it have something to do with where I am getting readings from?
I have a sensor on an oil filter and shoot with laser thermometer at same spot.

I shoot both the oil filter and oil pan. The filter runs about 5F more than pan. The coolant temperature, at 175F, is about 20F less than filter once everything hot.

 

[DavidM]

I shoot both the oil filter and oil pan. The filter runs about 5F more than pan. The coolant temperature, at 175F, is about 20F less than filter once everything hot.

A 20 degree or even more difference between coolant and oil is about what I would expect. How hard do you have to run your engine to get there?


David

 

[FF]

"Generators can and will glaze up from light loading at a constant rpm."

If only the boat noisemaker assemblers would leave the 1930's and copy the new inverter style of many portable gas units, the engine would run at variable RPM, with a proper load 100% of its service life.

And life aboard would be lots quieter , most of the time.

 

[JohnP]

"Generators can and will glaze up from light loading at a constant rpm."

If only the boat noisemaker assemblers would leave the 1930's and copy the new inverter style of many portable gas units, the engine would run at variable RPM, with a proper load 100% of its service life.

And life aboard would be lots quieter , most of the time.

Good point! Hope some marine genny manufactures catch on!

 

[DavidM]

Mastervolt used to offer an integrated generator, inverter/charger and battery bank which automatically cycled the genset off and on to keep up with the loads. Don't know how well sold and I will bet it was expensive.


David

 

[OldDan1943]

Mastervolt used to offer an integrated generator, inverter/charger and battery bank which automatically cycled the genset off and on to keep up with the loads. Don't know how well sold and I will bet it was expensive.

David

There was also a automatic parallel for boats with 2 generators. That did not work out well.

Personally, I am not in favor of combined units because if one feature goes down, the other feature must also be removed to get everything repaired.

 

[sunchaser]

A 20 degree or even more difference between coolant and oil is about what I would expect. How hard do you have to run your engine to get there? David

My engines have a coolant to oil heat exchanger. The fuel curves say max fuel burn per engine is 10 GPH at 2500 RPM.

At a 20% fuel burn or about 1550 RPM, the oil is around 185F with coolant at 175F. At 2000 RPM, or about a 60% fuel burn the oil will rise to about 195F with coolant up a bit, maybe to 178F.

Even with water temperatures close to 45F (spots in Glacier Bay) the coolant and oil temperatures are in the same ranges.

 

[FF]

"Even with water temperatures close to 45F (spots in Glacier Bay) the coolant and oil temperatures are in the same ranges."

This is probably good for the engine maintaining its machined shape,
But has is no help for an under loaded engine that may begin to slobber