Thought: Heavy oil better at cold starts?

[LucasDK]

Hi,

I was just wondering: It is common knowledge that everybody recommends a light oil such as 0W-XX or 5W-XX in winter conditions. It is easier to crank the engine because the oil flows easier compared to a heavy oil like 15W-XX.

But then again. If you stop your engine and let it rest during a cold night, how will a 0W-XX act against a 15W-XX in the oil gallery and all the parts (bearins, valve train etc) that need oil during start up? I'm just thinking that the 0W-XX would disappear much faster from the vital parts due to gravity and the low viscosity. And the 15W-XX would have an increased tendency to stay in the upper parts (higher viscosity during cool down of the engine, sticking effect??) of the engine and thus more close to the parts needing lubrication in the morning. Of course the 15W-XX will be thicker in the morning, but it will be physically closer to the parts needing lubrication.

What are your comments to that thought?

Lucas

 

[addyguy]

Still not a good idea.

When you stop and engine after driving, the oil is very hot (usually). The 'difference' in viscosity between a hot 15w40 and a hot 0W-40 oil will be negligible, b/c they are both a 40-weight hot.

Hot oil is very, very thin, so I'd say there is very little difference in how fast a hot 0W drains off parts, and a hot 15W does. Both, I'd guess, will leave about the same amount of oil on the parts.

This little bit of oil that is on the parts is just enough to get the engine through a few revolutions until the bulk of the oil comes 'to it's aid', so you want that oil there fast, and a 5W or 0W oil will get there a lot faster in extreme cold than a 15W oil.

 

[MonumentOiler]

Since it's at operating temp at shut down when it drains away from the lube surfaces both will have the same "sticking effect". Higher operating temp viscosity might have some effect like you describe.

Low cold viscosity = right for cold start up. This is solidly established as fact and every engine manual and oil manufacturer recommends it. Not much room to challenge it.

 

[PontiacFan]

Originally Posted By: LucasDK
Hi,

I was just wondering: It is common knowledge that everybody recommends a light oil such as 0W-XX or 5W-XX in winter conditions. It is easier to crank the engine because the oil flows easier compared to a heavy oil like 15W-XX.

But then again. If you stop your engine and let it rest during a cold night, how will a 0W-XX act against a 15W-XX in the oil gallery and all the parts (bearins, valve train etc) that need oil during start up? I'm just thinking that the 0W-XX would disappear much faster from the vital parts due to gravity and the low viscosity. And the 15W-XX would have an increased tendency to stay in the upper parts (higher viscosity during cool down of the engine, sticking effect??) of the engine and thus more close to the parts needing lubrication in the morning. Of course the 15W-XX will be thicker in the morning, but it will be physically closer to the parts needing lubrication.

What are your comments to that thought?

Lucas


You might want to get a Pre-Luber if you are concerned about startup wear.

 

[Quest]

unless you are waayy overboard on the high viscosity part, otherwise: startup wear on your engine is overrated, IMHO.

(*chances are, your engine may fall apart on other things (body rust, etc.) sooner than your engine's lubrication-related parts.)

Q.

 

[cmf]

The ability for the oil to maintain a layer on the engine while not running is much more dependent on chemistry than viscosity.

 

[dparm]

Correct, that's why we use esters -- they have a polar attraction to metal surfaces and do not "run off" as fast.

 

[TomYoung]

Originally Posted By: cmf
The ability for the oil to maintain a layer on the engine while not running is much more dependent on chemistry than viscosity.


Really? Isn't that the definition of viscosity? Isn't viscosity a chemical property?

 

[cmf]

Originally Posted By: TomYoung
Originally Posted By: cmf
The ability for the oil to maintain a layer on the engine while not running is much more dependent on chemistry than viscosity.


Really? Isn't that the definition of viscosity? Isn't viscosity a chemical property?


Viscosity is a physical property. It is studied by rheologists. Rheology is a division of physics.

 

[dparm]

Heavy is not always better. You want as light as possible to maintain the proper oil pressure. Too heavy and you introduce extra heat and drag on the oil pump.

 

[UNC017]

Originally Posted By: TomYoung
Originally Posted By: cmf
The ability for the oil to maintain a layer on the engine while not running is much more dependent on chemistry than viscosity.


Really? Isn't that the definition of viscosity? Isn't viscosity a chemical property?


No, viscosity is another word for "thickness." A milkshake is more viscous than milk. Syrup is more viscous than water. Its a physical property, although its determined by things like the length of polymer molecules and their attractiveness toward each other- you can't REALLY escape chemistry altogether. Surface adhesion, on the other hand, is much more chemical in nature because its determined by how much the oil molecules are attracted to OTHER materials.

 

[A_Harman]

I switched my Cummins turbodiesel from 15w40 to 5w40 last fall. During cold starts in the winter I noticed that engine knock before the oil pressure increased immediately after startup was louder with the 5w40. However, the length of time that startup knock occurred was less.

At cold start temperatures, the viscosity of 15w40 will be much higher than 5w40, so it will form a thicker film between moving surfaces. This would mean a few extra seconds of protection before oil pressure builds up and provides fresh oil to replenish the hydrodynamic wedge. If the oil pump is unable to pump the oil from the pan in these few extra seconds, the bearings could be damaged, and you'd be better off using oil with the lower W-rating.

There are two low-temperature performance parameters that qualify an oil for a given W-rating: Cold Cranking Simulator, and Cold Temperature Pumpability (aka MRV, which stands for Miniature Rotary Viscometer.) CCS gives an indication of how hard the cranking system has to work when you turn the key. Think of how much torque would be required to pump a fluid with the viscosity of sour cream, and you'll get the idea.

MRV gives an indication of how well the pump can pick the oil up from the pan and its ability to continuously supply the engine after initial startup. The MRV test was developed when it was discovered that under certain ambient conditions, the oil would turn to gel, and the pump would suck a hole in the oil, then would start sucking air, effectively starving the engine for oil.

So during an extreme cold start event, there are two stages of success:
1. Can the engine be cranked over?
2. Can the oil be pumped continuously after startup?
In some cases, it would be a blessing is disguise to not be able to crank the engine if the oil cannot be pumped afterward.

 

[tig1]

Your theory is wrong. I use Mobil 1 0w20 and even after days without starting there is an oil film on the cam lobe which I can see and feel. 0 wt. oils will lube better and faster than the 15 whatever you speak of on starts.

 

[chubbs1]

I see your point, but the flow of a 0w or 5w oil overrides any benefits left by residual lubrication from the 15w. They will all drain down while the engine is cooling.

 

[Ken2]

Keep in mind that part of the lubrication system is a pressure control valve. The oil pump turns, but if the pressure it puts out exceeds the setting of the pressure control valve, some of that oil is dumped back into the sump. When the oil is as thick as caramel ice cream syrup, not much gets pumped into the engine...and maybe not much even flows to the oil pump suction. Put a quart of 15w40 into your zero degree freezer at home (or even better, turn down to -10°F), then see if it'll even pour from the bottle. You're now getting an idea of how it'll flow to the oil pickup before even trying to get through the screen on the oil pump inlet.

 

[Jim Allen]

Lubrizol has a great video on the gear oil site that shows what happens to high viscosity gear oil in a diff. A 75 W gear oil has roughly a 15W motor viscosity and it was amazing how long it tool to change from "play-dough".

I vote for more copious amounts of a lighter oil faster as opposed to a little residual thick oil and a longer wait for more flow.

 

[Skid]

There's almost no load at startup on bearings and so forth, so the tiny film from the residual oil should be enough. I agree with Quest. Startup wear is very overrated.

Here is a link to an old case regarding false advertising in connection with motor oil.

http://law.justia.com/cases/federal/appellate-courts/F2/977/57/305505/

"Castrol's three experts focused on the role of residual oil. They testified that the small amount of residual oil left from a prior running of an engine provides more than adequate lubrication at the next start-up. Moreover, they asserted that this residual oil remains functional for a significant period of time so that both PMA-based and OCP-based 10w30 motor oils reach the engine parts before this residual oil burns off. Thus, they maintained, there is no second boundary lubrication period and Quaker State's faster oiling time is irrelevant to engine wear."

 

[The_Jeff]

Get your hands on some 30 weight bar and chain oil and some 30 weight regular motor oil.

Both will dribble through a cup with the same size orifice on the bottom at the same speed.

The bar and chain will stick to, well, everything, because it has tackifiers... it's what it does. An extreme example of what esters and what not do anyway.

Here's my challenge, get a wrench oily with 0w20 (or any oil you choose) and put it away. Find it months later, it will still be oily.

Even if the oil went away from moving parts momentarily, the anti wear additives will stick around and protect them.

 

[zyxelenator]

your theory might be right, is you compare 10w30 oil and 10w-60 oil...

 

[LucasDK]

Originally Posted By: PontiacFan


You might want to get a Pre-Luber if you are concerned about startup wear.


Yes, it sounds like a tempting solution, however the reviews of these systems are extremely limited. I really have no idea if they can do the job - I mean, how can this small pump force the thick oil through the small hoses at 0 degrees?

Lucas