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Thicker oil better for engine start up? #4664787
02/13/18 01:53 PM
02/13/18 01:53 PM
Joined: Nov 2003
Posts: 1,114
Middle of Iowa
DriveHard Offline OP
DriveHard  Offline OP
Joined: Nov 2003
Posts: 1,114
Middle of Iowa
I see and read lots of people talk about how thinner oil is better for engine start up because it "gets to the bearings faster". I have not really put any thought effort into it, and generally considered it an acceptable argument. After some thought, I am not so certain this is a valid argument.

Assumptions:
the viscosity of the oil is not so high that it would cause oil pump cavitation
oil follows the same path for

Some quick points:
in general, Volumetric efficiency of a fixed displacement pump INCREASES as fluid viscosity increases

so, when an engine is first started, the pump starts pumping the exact same theoretical volume of oil (displacement * speed), but the volume of oil being pumped is actually a function of its volumetric efficiency (displacement * speed * Ve), where the efficiency decreases the volume of oil being pumped. If the volumetric efficiency for two identical pumps is the same, and the only difference is the viscosity of the fluid, then the pump pumping the fluid with the higher viscosity will be pumping more volume.

If the pump pumping MORE fluid due to the higher viscosity has the same oil passages to fill to get to all the parts of the engine, then how does it take longer for the oil to get to all the components when the oil has a higher viscosity? Not to mention that the volumetric losses through bearings/etc. are lower due to the higher viscosity, further increasing the volume of oil available to fill the oil passages, and get to the extents of the oil system even more quickly.

Another question...does bulk modulus also increase with increased viscosity? If so, that would also help this argument.

Looking forward to the discussion.


Smile, it increases your face value
2011 Silverado Crew Cab LT 6.2L/6spd
2017 Jeep Renegade Trailhawk (wife's)
2007 Nissan Xterra (trail toy)
2013 Fiat 500 Abarth (my DD)
Elio...?
Re: Thicker oil better for engine start up? [Re: DriveHard] #4664807
02/13/18 02:30 PM
02/13/18 02:30 PM
Joined: Jul 2005
Posts: 30,422
NY
demarpaint Offline
demarpaint  Offline
Joined: Jul 2005
Posts: 30,422
NY
Interesting topic. As Trav has stated earlier today, and several others have stated over the years, bearings already have enough residual oil to protect them from a cold start or from sitting for a long period of time. If I were inclined to worry, I'd worry more about cylinder walls than bearings during a cold start.


God Bless Our Troops

Re: Thicker oil better for engine start up? [Re: DriveHard] #4664811
02/13/18 02:34 PM
02/13/18 02:34 PM
Joined: Sep 2004
Posts: 7,518
Marshfield , MA
andyd Offline
andyd  Offline
Joined: Sep 2004
Posts: 7,518
Marshfield , MA
During a cold start, thin oil is good for about 30 seconds. After that it is a liability. 30 seconds is about how long it took for the thrust bearing in BIL's Datsun 510 to quiet down in a cold start. grin2


'16 Camry LE STP synth 0w20 and STP filter. the Fridge

1994 Ranger ,the Rat, 5w30 dino, STP filter

'16 Camry SE, Valvoline HM 0w20 and OEM filter
Thick oil is better grin2
Re: Thicker oil better for engine start up? [Re: DriveHard] #4664812
02/13/18 02:35 PM
02/13/18 02:35 PM
Joined: Dec 2006
Posts: 7,641
Toronto, Canada
KrisZ Offline
KrisZ  Offline
Joined: Dec 2006
Posts: 7,641
Toronto, Canada
This has been pointed out numerous times and there is a thread or two that explains the difference between fixed volume/variable pressure and fixed pressure/variable volume pumps. However the most enthusiastic thin oils fans flatly ignore all these inconvenient facts and keep on harping flow=lubricating arguments.

Last edited by KrisZ; 02/13/18 02:36 PM.

2015 Dodge Grand Caravan-27k miles.
2006 Mazda 3-163k miles
Re: Thicker oil better for engine start up? [Re: DriveHard] #4664814
02/13/18 02:37 PM
02/13/18 02:37 PM
Joined: Jul 2008
Posts: 826
Iowa
fsskier Offline
fsskier  Offline
Joined: Jul 2008
Posts: 826
Iowa
Just a few quick thoughts: The oil pump is a positive flow pump...but the oil pressure relief valve dumps it all back into the crankcase. The multifaceted report....funded by GM and several major oil companies and published years ago in the SAE journal (sadly, you need to be a member to read) noted that:

The pistons/cylinders are only lubricated by oil that flys offs the rod bearings and the tiny squirter hole on the rods. The crankshaft oil is fed from the mains, though the crank, then into the rod bearings....by then under almost no pressure and no flow when thick and cold....the end result is only one drop every few seconds flying up to the cylinder/piston interface. Later, when the oil is hot and thin this is a continuous shower of oil. The conclusion of this study was related to the switch from 10W30 to 5W30.....and that many typical driving profiles that this alone would increase engine life by 30 percent. Data was reinforced by multiple testing procedures, including pistons, rings and sleeves using various radioactive isotopes and running instant real time wear measurements. The first few minutes of operation cause more wear then the next hour!

Wish I could provide a link to this published study (likely 30 years ago) but years ago while using 10W40 and 20W50 I often rebuilt engines after 100K miles. Now using 0W20 in sometimes identical engines and with no substantial design changes for 300K miles and seeming no wear from a users viewpoint.

Yeah, no reason to doubt that thinner oil at startup is important for those of us in the north.

fsskier

Last edited by fsskier; 02/13/18 02:38 PM.
Re: Thicker oil better for engine start up? [Re: DriveHard] #4664820
02/13/18 02:49 PM
02/13/18 02:49 PM
Joined: Dec 2017
Posts: 2,315
SE British Columbia, Canada
Snagglefoot Offline
Snagglefoot  Offline
Joined: Dec 2017
Posts: 2,315
SE British Columbia, Canada
Originally Posted By: DriveHard
I see and read lots of people talk about how thinner oil is better for engine start up because it "gets to the bearings faster". I have not really put any thought effort into it, and generally considered it an acceptable argument. After some thought, I am not so certain this is a valid argument.

Assumptions:
the viscosity of the oil is not so high that it would cause oil pump cavitation
oil follows the same path for

Some quick points:
in general, Volumetric efficiency of a fixed displacement pump INCREASES as fluid viscosity increases

so, when an engine is first started, the pump starts pumping the exact same theoretical volume of oil (displacement * speed), but the volume of oil being pumped is actually a function of its volumetric efficiency (displacement * speed * Ve), where the efficiency decreases the volume of oil being pumped. If the volumetric efficiency for two identical pumps is the same, and the only difference is the viscosity of the fluid, then the pump pumping the fluid with the higher viscosity will be pumping more volume.

If the pump pumping MORE fluid due to the higher viscosity has the same oil passages to fill to get to all the parts of the engine, then how does it take longer for the oil to get to all the components when the oil has a higher viscosity? Not to mention that the volumetric losses through bearings/etc. are lower due to the higher viscosity, further increasing the volume of oil available to fill the oil passages, and get to the extents of the oil system even more quickly.

Another question...does bulk modulus also increase with increased viscosity? If so, that would also help this argument.

Looking forward to the discussion.


Good discussion. I suspect if the oil was very cold and thick the pump might cavitate because it is simply atmospheric pressure (approx. 14.7 psi) that feeds the inlet to the pump. The pump is bolted to the block but there is a pickup tube extending down into the sump. That would be one issue.

Sf


If you want the job done right......do it yourself.
Re: Thicker oil better for engine start up? [Re: DriveHard] #4664824
02/13/18 02:52 PM
02/13/18 02:52 PM
Joined: Oct 2014
Posts: 11,836
Idaho
CT8 Online content
CT8  Online Content
Joined: Oct 2014
Posts: 11,836
Idaho
What most miss is depending on the temps at start up is how long the oil takes to go from the oil pan to the oil pump. At room temps a straight 30 or 40 will get to the pump plenty fast. At -5*f it may never reach the pump


"Don't let your preconceived notions get in the way of facts."
Geoff Metcalf
Re: Thicker oil better for engine start up? [Re: fsskier] #4664832
02/13/18 02:59 PM
02/13/18 02:59 PM
Joined: Apr 2008
Posts: 37,110
Ontario, Canada
OVERKILL Offline
OVERKILL  Offline
Joined: Apr 2008
Posts: 37,110
Ontario, Canada
Originally Posted By: fsskier
Just a few quick thoughts: The oil pump is a positive flow pump...but the oil pressure relief valve dumps it all back into the crankcase.


It definitely does not dump it all back into the crankcase. This is easily demonstrated with a valve cover off and watching the oil come out the pushrods. One can also overwhelm the bypass, which is observed by indicated oil pressure exceeding the relief pressure. I've seen both on a cold start with heavy oil in an SBC.


2018 RAM 1500 Big Horn EcoDiesel
2016 Grand Cherokee SRT
Re: Thicker oil better for engine start up? [Re: Snagglefoot] #4664833
02/13/18 03:00 PM
02/13/18 03:00 PM
Joined: Apr 2008
Posts: 37,110
Ontario, Canada
OVERKILL Offline
OVERKILL  Offline
Joined: Apr 2008
Posts: 37,110
Ontario, Canada
Originally Posted By: Snagglefoot
Originally Posted By: DriveHard
I see and read lots of people talk about how thinner oil is better for engine start up because it "gets to the bearings faster". I have not really put any thought effort into it, and generally considered it an acceptable argument. After some thought, I am not so certain this is a valid argument.

Assumptions:
the viscosity of the oil is not so high that it would cause oil pump cavitation
oil follows the same path for

Some quick points:
in general, Volumetric efficiency of a fixed displacement pump INCREASES as fluid viscosity increases

so, when an engine is first started, the pump starts pumping the exact same theoretical volume of oil (displacement * speed), but the volume of oil being pumped is actually a function of its volumetric efficiency (displacement * speed * Ve), where the efficiency decreases the volume of oil being pumped. If the volumetric efficiency for two identical pumps is the same, and the only difference is the viscosity of the fluid, then the pump pumping the fluid with the higher viscosity will be pumping more volume.

If the pump pumping MORE fluid due to the higher viscosity has the same oil passages to fill to get to all the parts of the engine, then how does it take longer for the oil to get to all the components when the oil has a higher viscosity? Not to mention that the volumetric losses through bearings/etc. are lower due to the higher viscosity, further increasing the volume of oil available to fill the oil passages, and get to the extents of the oil system even more quickly.

Another question...does bulk modulus also increase with increased viscosity? If so, that would also help this argument.

Looking forward to the discussion.


Good discussion. I suspect if the oil was very cold and thick the pump might cavitate because it is simply atmospheric pressure (approx. 14.7 psi) that feeds the inlet to the pump. The pump is bolted to the block but there is a pickup tube extending down into the sump. That would be one issue.

Sf


That's what the MRV test is designed to replicate, the ability for the oil to be drawn into the pump.


2018 RAM 1500 Big Horn EcoDiesel
2016 Grand Cherokee SRT
Re: Thicker oil better for engine start up? [Re: DriveHard] #4664835
02/13/18 03:01 PM
02/13/18 03:01 PM
Joined: Dec 2006
Posts: 7,641
Toronto, Canada
KrisZ Offline
KrisZ  Offline
Joined: Dec 2006
Posts: 7,641
Toronto, Canada
That is why winter rating was developed. The MRV test ensures no cavitation will happen as long as the W rating temperaturę is not exceeded. Why is all of this news to people? I thought this was an oil forum.


2015 Dodge Grand Caravan-27k miles.
2006 Mazda 3-163k miles
Re: Thicker oil better for engine start up? [Re: DriveHard] #4664861
02/13/18 03:32 PM
02/13/18 03:32 PM
Joined: Jan 2013
Posts: 354
West Yorkshire, UK
NGRhodes Offline
NGRhodes  Offline
Joined: Jan 2013
Posts: 354
West Yorkshire, UK
http://www.emeraldinsight.com/doi/pdfplus/10.1108/00368790010352691

"This study has demonstrated a correlation between relative average cylinder liner wear rates at low engine start-up temperatures, base oil composition and oil viscosity"

Emphasis mine.

Re: Thicker oil better for engine start up? [Re: DriveHard] #4665130
02/13/18 08:17 PM
02/13/18 08:17 PM
Joined: Dec 2009
Posts: 25,355
Regina, Saskatchewan, Canada
Garak Offline
Garak  Offline
Joined: Dec 2009
Posts: 25,355
Regina, Saskatchewan, Canada
Shannow has posted extensively about timed oil flow. If he stumbles across the thread, he might be able to post his charts again.


Plain, simple Garak.

2008 Infiniti G37 - Shell ROTELLA T6 Multi-Vehicle 5w-30, NAPA Gold 7356
1984 F-150 4.9L - Quaker State GB 10w-30, Wix 51515
Re: Thicker oil better for engine start up? [Re: Garak] #4665136
02/13/18 08:26 PM
02/13/18 08:26 PM
Joined: Sep 2010
Posts: 6,988
Texas
4WD Online confused
4WD  Online Confused
Joined: Sep 2010
Posts: 6,988
Texas
Originally Posted By: Garak
Shannow has posted extensively about timed oil flow. If he stumbles across the thread, he might be able to post his charts again.


This chart would be interesting with very cold oil:


Re: Thicker oil better for engine start up? [Re: Garak] #4665198
02/13/18 09:18 PM
02/13/18 09:18 PM
Joined: Oct 2012
Posts: 4,602
Taiwan
Ducked Offline
Ducked  Offline
Joined: Oct 2012
Posts: 4,602
Taiwan
Originally Posted By: Garak
Shannow has posted extensively about timed oil flow. If he stumbles across the thread, he might be able to post his charts again.


This is the usual counter-post, though its from a rather old study and you'd think there'd be a bit more data on this rather basic question. IIRC rocker oiling time was judged on the basis of sound.


Re: Thicker oil better for engine start up? [Re: NGRhodes] #4665208
02/13/18 09:26 PM
02/13/18 09:26 PM
Joined: Oct 2012
Posts: 4,602
Taiwan
Ducked Offline
Ducked  Offline
Joined: Oct 2012
Posts: 4,602
Taiwan
Originally Posted By: NGRhodes
http://www.emeraldinsight.com/doi/pdfplus/10.1108/00368790010352691

"This study has demonstrated a correlation between relative average cylinder liner wear rates at low engine start-up temperatures, base oil composition and oil viscosity"

Emphasis mine.


So I have to pay 32 USD to read that and then if I'm convinced I have to buy "full synthetic SAE 5W40 grade oils based on Polyalphaolefin"", and a diesel truck.

Ooer! Just as well cold starts mean 10C here.

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