Low RPM dangerous for engine longevity?
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I have heard many people say that lower RPM is one factor in diesel car engines typically outlasting gasoline engines in the same car.
I wouldn't worry about engine RPM so long as it is within OEM specs.
I wouldn't worry about engine RPM so long as it is within OEM specs.
I have a VQ35 with the 5AT. It wont lug 5th gear no matter how hard I try.
It's a great question.
The hydrodynamic oil film is created primarily by surface speed difference (diameter and RPM), and viscosity, with bearing width and clearance playing a part as well...as well as providing the oil film, these things increase frictional drag.
Low RPM cruise is designed to reduce drag, and increase throttle opening to reduce pumping losses...which increases applied load on things like bearings.
So for a given cruise, the engine running at 3,000 RPM will have a significantly greater film thickness, lower pressure load (but higher inertial loads).
Low RPM cruising IS pushing bearings in an undesirable direction regarding lubrication, but the manufacturers are intimately aware of their designs, and it will still get the job done.
Couple of myths popped up in this thread.
* oil pressure does not, and lever has lubricated an engine. It is the delivery mechanism of the oil to the bearings, and nothing else...the oil pressure = lubrication myth is rampant on BITOG and needs to die.
* diesel low RPM is not pertinent to the discussion unless you also bring in the bearings diameters, widths, clearances, lubricant HTHS etc. all of which are markedly different.
The hydrodynamic oil film is created primarily by surface speed difference (diameter and RPM), and viscosity, with bearing width and clearance playing a part as well...as well as providing the oil film, these things increase frictional drag.
Low RPM cruise is designed to reduce drag, and increase throttle opening to reduce pumping losses...which increases applied load on things like bearings.
So for a given cruise, the engine running at 3,000 RPM will have a significantly greater film thickness, lower pressure load (but higher inertial loads).
Low RPM cruising IS pushing bearings in an undesirable direction regarding lubrication, but the manufacturers are intimately aware of their designs, and it will still get the job done.
Couple of myths popped up in this thread.
* oil pressure does not, and lever has lubricated an engine. It is the delivery mechanism of the oil to the bearings, and nothing else...the oil pressure = lubrication myth is rampant on BITOG and needs to die.
* diesel low RPM is not pertinent to the discussion unless you also bring in the bearings diameters, widths, clearances, lubricant HTHS etc. all of which are markedly different.
Shannow Couple of myths popped up in this thread. * oil pressure does not said:I'm glad you brought that up.
Car driven at constant revs is likely to end with glazed cylinder bores.
Should rev it out couple times a week through the range, of course after 20 mins or so to ensure the fluids are at operating temperature.
Should rev it out couple times a week through the range, of course after 20 mins or so to ensure the fluids are at operating temperature.
the semi's i used to drive allowed the driver to lug them down to 900 rpm per the owners manual. they lasted a milion or more
Hi,
Originally Posted By: Shannow
Low RPM cruising IS pushing bearings in an undesirable direction regarding lubrication, but the manufacturers are intimately aware of their designs, and it will still get the job done.
This is but ONE reason why a minimum HTHS viscosity is so important and why it was a keystone in ACEA's criteria from day one. It was designed in there of course by the Euro Manufacturers who make up ACEA
Originally Posted By: Shannow
Low RPM cruising IS pushing bearings in an undesirable direction regarding lubrication, but the manufacturers are intimately aware of their designs, and it will still get the job done.
This is but ONE reason why a minimum HTHS viscosity is so important and why it was a keystone in ACEA's criteria from day one. It was designed in there of course by the Euro Manufacturers who make up ACEA
Originally Posted By: Miller88
Those Nissans are awful with that. They lug the engine around and there just isn't enough balancing on the engine ... horrible vibrations into the cabin.
The VQ35DE is a sweet engine, the CVT sucks bad though, a real deal killer.
Those Nissans are awful with that. They lug the engine around and there just isn't enough balancing on the engine ... horrible vibrations into the cabin.
The VQ35DE is a sweet engine, the CVT sucks bad though, a real deal killer.
Originally Posted By: bullwinkle
Another reason to love manual transmissions & hate automatics-I'd rather do my own gear selection!
That is why I like newer autos that let me use a "manual" mode to select the gears myself. It just does the actual shifting.
Another reason to love manual transmissions & hate automatics-I'd rather do my own gear selection!
That is why I like newer autos that let me use a "manual" mode to select the gears myself. It just does the actual shifting.
Originally Posted By: Shannow
It's a great question.
The hydrodynamic oil film is created primarily by surface speed difference (diameter and RPM), and viscosity, with bearing width and clearance playing a part as well...as well as providing the oil film, these things increase frictional drag.
Low RPM cruise is designed to reduce drag, and increase throttle opening to reduce pumping losses...which increases applied load on things like bearings.
So for a given cruise, the engine running at 3,000 RPM will have a significantly greater film thickness, lower pressure load (but higher inertial loads).
Low RPM cruising IS pushing bearings in an undesirable direction regarding lubrication, but the manufacturers are intimately aware of their designs, and it will still get the job done.
Couple of myths popped up in this thread.
* oil pressure does not, and lever has lubricated an engine. It is the delivery mechanism of the oil to the bearings, and nothing else...the oil pressure = lubrication myth is rampant on BITOG and needs to die.
* diesel low RPM is not pertinent to the discussion unless you also bring in the bearings diameters, widths, clearances, lubricant HTHS etc. all of which are markedly different.
I thank you and others who have put my mind and right foot at ease, and to the suggestion that I should rev out the engine to prevent the cylinders from becoming glazed...not to worry, I have been faithfully exercising the tach needle as traffic and mood permits ;o)
It's a great question.
The hydrodynamic oil film is created primarily by surface speed difference (diameter and RPM), and viscosity, with bearing width and clearance playing a part as well...as well as providing the oil film, these things increase frictional drag.
Low RPM cruise is designed to reduce drag, and increase throttle opening to reduce pumping losses...which increases applied load on things like bearings.
So for a given cruise, the engine running at 3,000 RPM will have a significantly greater film thickness, lower pressure load (but higher inertial loads).
Low RPM cruising IS pushing bearings in an undesirable direction regarding lubrication, but the manufacturers are intimately aware of their designs, and it will still get the job done.
Couple of myths popped up in this thread.
* oil pressure does not, and lever has lubricated an engine. It is the delivery mechanism of the oil to the bearings, and nothing else...the oil pressure = lubrication myth is rampant on BITOG and needs to die.
* diesel low RPM is not pertinent to the discussion unless you also bring in the bearings diameters, widths, clearances, lubricant HTHS etc. all of which are markedly different.
I thank you and others who have put my mind and right foot at ease, and to the suggestion that I should rev out the engine to prevent the cylinders from becoming glazed...not to worry, I have been faithfully exercising the tach needle as traffic and mood permits ;o)
IMO, as long as the engine has decent oil pressure at low rpms and you're not lugging it, it'll be fine. The Jeep is smooth as butter down to ~800 rpm in any gear and will accelerate happily from that point under light throttle. However, if you drag it much under 800 rpm, it starts to get a little shaky, and I wouldn't ask it for much power under 1000 rpm or so (considering it doesn't exactly run a lot of oil pressure at low rpm when hot, ~15 psi at 650 rpm hot idle, 20 - 25 at 1000 rpm hot).
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Just to chime in my two cents. I just did a UOA for my 2014 Mazda 6 with a manual transmission. It has ~28K miles in it now and I regularly toodle around town at 1200 RPMs in 6th gear (around 35 mph), and I always do about 1000 rpms in parking lots and school zones in 2nd gear. Blackstone said my wear metals were excellent, below average in every catagory. I'll be posting the UOA up sometime today when I become less lazy.
So I really don't think there's any problem, though I never goose it at 1000 rpm, but I dont have a problem with accelerating from 1000 on a flat surface. I'll let it build slowly to 1500 rpm then goose it! I downshift to go up a hill, though, when the RPMs are that low.
I will add that the Skyactiv-G engine has a variable displacement oil pump, which certainly could factor into this whole thing.
So I really don't think there's any problem, though I never goose it at 1000 rpm, but I dont have a problem with accelerating from 1000 on a flat surface. I'll let it build slowly to 1500 rpm then goose it! I downshift to go up a hill, though, when the RPMs are that low.
I will add that the Skyactiv-G engine has a variable displacement oil pump, which certainly could factor into this whole thing.
Originally Posted By: NeoNoggie
Just to chime in my two cents. I just did a UOA for my 2014 Mazda 6 with a manual transmission. It has ~28K miles in it now and I regularly toodle around town at 1200 RPMs in 6th gear (around 35 mph), and I always do about 1000 rpms in parking lots and school zones in 2nd gear. Blackstone said my wear metals were excellent, below average in every catagory. I'll be posting the UOA up sometime today when I become less lazy.
So I really don't think there's any problem, though I never goose it at 1000 rpm, but I dont have a problem with accelerating from 1000 on a flat surface. I'll let it build slowly to 1500 rpm then goose it! I downshift to go up a hill, though, when the RPMs are that low.
I will add that the Skyactiv-G engine has a variable displacement oil pump, which certainly could factor into this whole thing.
NeoNoggie I agree with you.
Welcome aboard.
Just to chime in my two cents. I just did a UOA for my 2014 Mazda 6 with a manual transmission. It has ~28K miles in it now and I regularly toodle around town at 1200 RPMs in 6th gear (around 35 mph), and I always do about 1000 rpms in parking lots and school zones in 2nd gear. Blackstone said my wear metals were excellent, below average in every catagory. I'll be posting the UOA up sometime today when I become less lazy.
So I really don't think there's any problem, though I never goose it at 1000 rpm, but I dont have a problem with accelerating from 1000 on a flat surface. I'll let it build slowly to 1500 rpm then goose it! I downshift to go up a hill, though, when the RPMs are that low.
I will add that the Skyactiv-G engine has a variable displacement oil pump, which certainly could factor into this whole thing.
NeoNoggie I agree with you.
Welcome aboard.
Originally Posted By: CT8
That is shifting like a girl.
LOL. I can take that. After all, I shift a manual 18 speed non synchronized manual transmission in a commercial semi for an average 130,000 miles a year. for the last 32 years. I have no problem when I am in my pickup letting it shift for me. My time at home is time to relax, not try and play some macho game shifting a little 1/2 ton pickup.
That is shifting like a girl.
LOL. I can take that. After all, I shift a manual 18 speed non synchronized manual transmission in a commercial semi for an average 130,000 miles a year. for the last 32 years. I have no problem when I am in my pickup letting it shift for me. My time at home is time to relax, not try and play some macho game shifting a little 1/2 ton pickup.
Even with a 6400 rpm power peak my 6.1 will lug out from under 900 rpm in 4th gear around corners and do it super smoothly and quietly.
No reason to worry anymore with modern engine controls...
No reason to worry anymore with modern engine controls...
Big diesels turning under 1000 RPM and racking up millions of hours/miles would indicate that this is not a valid concern.
Originally Posted By: asand1
Big diesels turning under 1000 RPM and racking up millions of hours/miles would indicate that this is not a valid concern.
Vastly different designed engine! Plus, that engine might top out at 1,800rpm (idle at 500?). 1,000rpm might well be half its rated max engine speed. Akin to run at 3k for most gassers.
Big diesels turning under 1000 RPM and racking up millions of hours/miles would indicate that this is not a valid concern.
Vastly different designed engine! Plus, that engine might top out at 1,800rpm (idle at 500?). 1,000rpm might well be half its rated max engine speed. Akin to run at 3k for most gassers.
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