Cold start wear vs. hi/low viscosity

[MGBV8]

1911
If a thick oil requires more energy to flow the rpm drops, therefore the thin oil flows faster. This is most noticeable at cranking limits.

Mobil recommend on my type of car dropping from 20W to 15W at 0c

What are the reasons for this recommendation?
Easier to crank/pump (not at absolute limit)
Flow to bearings
Flow to Cam
Flow to Cylinder walls
Flow as tighter bearing clearance
Perhaps all or none of the above

Even above 0c the thinner oil obtains pressure quicker and less oil bypasses the engine.

I understand 0W oils are more expensive to produce but M1 OW40 (probably now surpassed by CG0W30) is the usual standard fill for European high performance cars, yet they are mostly not used in cold temperature extremes. However in summer a 15W40 would not be an issue for cold starts but why change from a 0W.

However, engine warm up speed and esters/aw additives may achieve more than flow.

For g forces baffles and dry sumps help avoid oil starvation. In the UK with traffic lights, roundabouts, and overtaking opportunities hard acceleration can be the norm, perhaps a reason for a 40 vis still being recommended.

My assumption is that a Cold or dry start is only when drainback has left insufficient oil to protect the surfaces. This would not be the case with a Hybrid constant start situation.

 

[1911]

quote:

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Originally posted by MGBV8:
1911
If a thick oil requires more energy to flow the rpm drops, therefore the thin oil flows faster. This is most noticeable at cranking limits.

Mobil recommend on my type of car dropping from 20W to 15W at 0c

What are the reasons for this recommendation?
Easier to crank/pump (not at absolute limit)
Flow to bearings
Flow to Cam
Flow to Cylinder walls
Flow as tighter bearing clearance
Perhaps all or none of the above

Even above 0c the thinner oil obtains pressure quicker and less oil bypasses the engine.

I understand 0W oils are more expensive to produce but M1 OW40 (probably now surpassed by CG0W30) is the usual standard fill for European high performance cars, yet they are mostly not used in cold temperature extremes. However in summer a 15W40 would not be an issue for cold starts but why change from a 0W.

However, engine warm up speed and esters/aw additives may achieve more than flow.

For g forces baffles and dry sumps help avoid oil starvation. In the UK with traffic lights, roundabouts, and overtaking opportunities hard acceleration can be the norm, perhaps a reason for a 40 vis still being recommended.

My assumption is that a Cold or dry start is only when drainback has left insufficient oil to protect the surfaces. This would not be the case with a Hybrid constant start situation.

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You quite literally could not possibly have things more backwards.

A) You said that thin oils obtain pressure quicker?..........what?????? The pressure is always higher at any RPM when the oil is thicker and that is why the bypass valve opens with thick oil...cause the pressure is too high.

B) And then you said the RPM drops with thicker oil???????????WHAT????????? When you start our cold motor, it goes from 0 rpm to idle speed and hits every RPM in the middle on the way up. Most engine computers set the cold idle at higher RPM. Basically, your right foot controls the RPM when your on it and your computer controls it when you are idling.......what on God's green earth ar eyou talking about here?

More importantly than this.......the system is designed to provide lower flow at lower RPM (that's how the ****ed pump works) and will provide plently of flow as long as the bypass valve is not way open.....what are you talking about? Are you saying that you are damaging your engine when you slow down from 60 mph to 45mph thus dropping RPM's and flow flux?

My point is that the RPM'S are not controlled by the oil viscosity and even if they were, why would you care since the pump size is designed to match flow to RPM. The flow will vary almost linearly with RPM whether the oil is cold or hot. And the designers rigged it such that there is plently of flow for each range of engine speed (and load condition).

 

[MolaKule]

http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=1;t=009487;p=2

 

[reyjay1]

quote:

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Originally posted by 1911:

A) You said that thin oils obtain pressure quicker?..........what?????? The pressure is always higher at any RPM when the oil is thicker and that is why the bypass valve opens with thick oil...cause the pressure is too high.

B) And then you said the RPM drops with thicker oil???????????WHAT????????? When you start our cold motor, it goes from 0 rpm to idle speed and hits every RPM in the middle on the way up. Most engine computers set the cold idle at higher RPM. Basically, your right foot controls the RPM when your on it and your computer controls it when you are idling.......what on God's green earth ar eyou talking about here?

[/QB]

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You are not understanding, in A) he has it exactly right, though you are both not wrong, but he might have said flow, but it will be true a thinner v flows faster at initial start, q.e.d will build a lower amount of pressure faster than the thick v.

B) he is talking about at turnover cranking, you know when you have a fixed amount of energy from the battery therefore the engine spins slower with higher vis because it takes more energy. You are talking about once it fires, he is talking about the very first cranking action and first second or two of start-up.

 

[1911]

quote:

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Originally posted by reyjay1:

quote:

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Originally posted by 1911:

A) You said that thin oils obtain pressure quicker?..........what?????? The pressure is always higher at any RPM when the oil is thicker and that is why the bypass valve opens with thick oil...cause the pressure is too high.

B) And then you said the RPM drops with thicker oil???????????WHAT????????? When you start our cold motor, it goes from 0 rpm to idle speed and hits every RPM in the middle on the way up. Most engine computers set the cold idle at higher RPM. Basically, your right foot controls the RPM when your on it and your computer controls it when you are idling.......what on God's green earth ar eyou talking about here?

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You are not understanding, in A) he has it exactly right, though you are both not wrong, but he might have said flow, but it will be true a thinner v flows faster at initial start, q.e.d will build a lower amount of pressure faster than the thick v.

B) he is talking about at turnover cranking, you know when you have a fixed amount of energy from the battery therefore the engine spins slower with higher vis because it takes more energy. You are talking about once it fires, he is talking about the very first cranking action and first second or two of start-up. [/QB]

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On A, I believe you are right.

On B, What do you mean the engine speeds slower? Every engine goes from 0 rpm to idle speed pretty ****ed quickly after ignition occurs. whether it's cold or not. Are you trying to say the engine like lingers at 25 rpm when it's cold?

One second after ignition, the engine will be around idle speed whether cold or not. If one engine is turning a little slower during the startup process (say 0.3 seconds into the startup or 600 rpm versus 800rpm), what difference would that make.........how would that be harmful? Please elaborate.

1911

 

[babydoggy]

It clings better and longer and the parts will have more space for flow in the cold.

 

[jorton]

"My assumption is that a Cold or dry start is only when drainback has left insufficient oil to protect the surfaces. This would not be the case with a Hybrid constant start situation."

I can hear start-up wear when a filter is not working.

Do you think oil grade is not a start-up wear factor as long as the oil filter is working?

 

[jorton]

"Wow, I would think that when the engine was at full operating temp (maybe 200F) the viscosity difference between 20W, 30W, and 40W is teeny tiny. I know that coming out of the sump at full temp I can tell very little difference, they all come out like water. Hard to beleive there would be much difference is the "cling" due to viscosity."

Even though the hot oil is thin, 40 wt still has more resistance to flow after you park your car, leaving a thicker film. A teeny tiny difference is represents a great benifit in tight spaces.

Joe

[ April 24, 2005, 09:52 AM: Message edited by: jorton ]

 

[Gary Allan]

quote:

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but it will be true a thinner v flows faster at initial start, q.e.d will build a lower amount of pressure faster than the thick v.

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Thinner oil flows EASIER when cold than thicker oils. The ONLY time it is faster is when the relief in the pump is open. It is only under that qualification is the term "faster" ever true.

 

[babydoggy]

anti-wear attitives will help protect at start up.

 

[LarryL]

Would using my oil pan heater in the summer help avoid startup wear?

 

[Ugly3]

quote:

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Originally posted by LarryL:
Would using my oil pan heater in the summer help avoid startup wear?

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Yes, however, the benefit would be smaller than the cost of electricty in my opinion. Winter is another case.

 

[Gary Allan]

quote:

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Would using my oil pan heater in the summer help avoid startup wear?

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No, and neither will a block heater. It will not warm the ill fitting pistons enough to make them not be out of shape and wear unevenly. It will shorten the full warm up event. It will simulate the resultant conditions of a fully warmed up engine ..not replace the cause of it ...which has to occur to put the elevated wear event at an end.

 

[LarryL]

I'm sorry if I was not clear. These gen-sets start up from dead cold and get up to 3.6k in 60 seconds and when the engine instrumentations says that it's running ok it gets loaded, quickly. Generally the load is 100% and they are sync'ed onto the bus loaded. If the load requirement expires before the oil is up to temp, a dummy load is applied (actuall rods that go into the ground) and the set is run until oil temp is up then shut down. And as someone stated, these engines are also test run on a schedule, just to make sure they are 'good-to-go'. In some applications, very few at that, they are run every day, but mostly once a week.

Now for the tear-down. We CAN NOT tell the difference between engines that run different weight oils. We look at and measure parts, including compairing weight of the same exact part new and worn, a couple of cases, but have not been able to tell which is which from observations. I know that does not jive with the theory of lighter vs heaver oils, but we have only been doing this since 1979 and it have only delt with 519 different gen-sets.

I think the real answer is that our experience does not lend itself to automotive applications which are much more complicated. Our engines just do the same think every time and have been modified for the job at hand, over the years.

We have used different brands of oil but the one constant we see is that synthetic is better in our application, how much better we can't tell anymore because we use it every where except on place. There the customer uses Delo 15w-40 with excellent results. And it's hard to tell how that relates because he's the customer that starts the engines every day, the only one. And he changes the oil so often it's hard to imagine he is every stressing it much. In fact he had the first engine that we acutally weighed bearings and pistions/rings before and after with the 15w-40 and 5w-30. We though we were really smart and would come up with something. Funny what you get when you look so carefully that you don't find what you're looking for.

 

[Gary Allan]

quote:

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Therefore, the cold gen-set engine probably sees less overall cold operation wear for the same amount of cold operation than an automobile does (excluding the 1970s mindset of 5 minute driveway warmups).

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I dunno

I reason that it would have much more wear per hour than an automotive application due to the full load in the warm up state. I would think that it would certainly make plotting an hour/refit curve easier since you can just (more or less) record the duration of the events (which appear to be somewhat at a fixed minimum ..anything longer is a steady state/full warm up as evidenced by the oil temp and can be ignored) and the number of events ..and you should be able to pretty much predict the overhaul schedule ...or so I would reason. Check that. Just count the number of events ..they're all the same.

quote:

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We have used different brands of oil but the one constant we see is that synthetic is better in our application, how much better we can't tell anymore because we use it every where except one place.

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It's a shame that you couldn't have used just one unit as a guinea pig with the rest being controls. Do you happen to use UOA with these engines? It would be interesting to see the results with synth versus dino. I mean you already actually measured the wear. This would have been an ideal opportunity to see if UOA wear metals have any direct correlation to measured wear.

 

[moribundman]

quote:

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Wow, I would think that when the engine was at full operating temp (maybe 200F) the viscosity difference between 20W, 30W, and 40W is teeny tiny. I know that coming out of the sump at full temp I can tell very little difference, they all come out like water. Hard to beleive there would be much difference is the "cling" due to viscosity. [I dont know]

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When I removed the valve covers on my Audi I got a good look camshafts and cam lobes. At the time I was using M1 0W-40 and the cam lobes felt almost dry to the touch. I'll be able to compare next time I replace a valve cover gasket.

I do believe that thicker oils leave a thicker oil film behind, because they don't run off as much as thin oils do. Whether or not the difference in film thickness is meaningful I don't know. Maybe boundary lubrication is all that matters during those couple hundred first revolutions. Engine design may matter, too. Do all engines keep oil in the heads after the engine is turned off? For example, my Audi has oil retention valves that prevent oil from flowing out of the heads.

 

[LarryL]

I am confused about our cold start problem. We have a bunch of gen-sets that sit around until called upon and then they get brought up to 3.6k and loaded, then run until not needed any more. If the load requirement drops off before oil gets up to temp they are run agains a dummy load and turned off when temp is reached, 80 to 90C. Some engines get 0w-30, some 5w-30 and some 15w-40. When an engine is torn down you can tell the difference, looking at the Hobbs meter and worn parts. We're not smart enough to go beyond looking and measuring and we're sure not smart enough to figure why the results are the same.

 

[Gary Allan]

quote:

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When an engine is torn down you can tell the difference, looking at the Hobbs meter and worn parts. We're not smart enough to go beyond looking and measuring and we're sure not smart enough to figure why the results are the same.

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Are you saying that they all wear about the same?

I would think that these gensets would show a rather high rate of wear since they rarely ever get up to any "steady state" condition ..ever. I imagine that they go to full load right off the bat. Some have "exercize cycles" where the engine just starts for no dam# good reason just to assure that the internals remain lubed and that moisture is purged from the system. Heaters would shorten the high wear event ..but nothing can eliminate it other than running your engine nearly 24/7, IMHO.

 

[bulwnkl]

I don't understand what you mean either. Are you saying you CAN or CANNOT tell the difference between the oil grades used. If you see a difference, what is it? Are the generators' engines all the same? What is the median run time for these engines?

 

[TallPaul]

I think the "CAN tell the difference" is a typo as his last statement,

quote:

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Originally posted by LarryL:
... and we're sure not smart enough to figure why the results are the same.

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, indicates there is no difference.

One thing that may help with a gen-set engine vs. an automobile engine is that the gen-set engine goes under full load pretty quickly after startup, but the load is pretty constant once it reaches full load; whereas the automobile has a lot of load variations from stop and go traffic, speed up and slow down for lights, etc. Therefore, the cold gen-set engine probably sees less overall cold operation wear for the same amount of cold operation than an automobile does (excluding the 1970s mindset of 5 minute driveway warmups).