Thinner oil = better start up protection?

[Octopus]

Hi all,

 

I believe we have all heard that the thinner the engine oil, the easier it is to flow to various parts of the engine thereby giving better protection during start up?

 

But, I realised that lube oil pumps are basically gear pump, they are positive displacement pumps, where capacity is directly proportional to the rotation speed. The capacity of gear pumps should not be affected by the viscosity of engine oil under our local climate, whether 0w20 or 20w50 the flow rate from a positive displacement pump should be almost the same, right?

 

Maybe cold countries where temperature are freezing and the pour point of oil are affected, then perhaps the engine oil viscosity would affect the capacity of gear pumps. The oil if get too thick due to cold weather then the relieve valve of the pump will blow (by-pass back to suction?) due to higher pumping pressure, so discharge volume will reduce.

 

If that is the case, then for our local environment whether using thinner or thicker oil the protection should be same at start-up? Perhaps the advantage of thinner oil is only for better fuel efficiency only? What do you think?

[Darkblue]

Perhaps the advantage of thinner oil is only for better fuel efficiency only?

 

With the rising fuel prices, this reason is enough to sway alot of users into using thinner oil

[Octopus]

So you also believe that thinner viscosity offer better start-up protection is over-hype? Its more of a marketing statement rather than truth?

[Trex101]

Hi all,

 

I believe we have all heard that the thinner the engine oil, the easier it is to flow to various parts of the engine thereby giving better protection during start up?

 

But, I realised that lube oil pumps are basically gear pump, they are positive displacement pumps, where capacity is directly proportional to the rotation speed. The capacity of gear pumps should not be affected by the viscosity of engine oil under our local climate, whether 0w20 or 20w50 the flow rate from a positive displacement pump should be almost the same, right?

 

Maybe cold countries where temperature are freezing and the pour point of oil are affected, then perhaps the engine oil viscosity would affect the capacity of gear pumps. The oil if get too thick due to cold weather then the relieve valve of the pump will blow (by-pass back to suction?) due to higher pumping pressure, so discharge volume will reduce.

 

If that is the case, then for our local environment whether using thinner or thicker oil the protection should be same at start-up? Perhaps the advantage of thinner oil is only for better fuel efficiency only? What do you think?

 

It's true that engine oil pump are positive gear pump but viscosity is a measurement of drag. That is why even here in our tropical weather, thin oil like 0w20 or 5w20 will still give some measurable % FC gain compare to thick 20w50 oil.

 

Example:

- thicker oil = higher startup viscosity = higher pressure = higher drag = more engine loading = less fuel efficiency

 

[Octopus]

It's true that engine oil pump are positive gear pump but viscosity is a measurement of drag. That is why even here in our tropical weather, thin oil like 0w20 or 5w20 will still give some measurable % FC gain compare to thick 20w50 oil.

 

So basically you're saying that thinner oil only offer better fuel efficiency. But not so affecting better start-up protection?

 

The following I extracted from internet:

 

Gear pump is a rotary positive displacement pump with positive pressure characteristic. The capacity of the pump varies directly with speed but remain constant against pressure, however due to running clearance between the casing & impeller some liquid always by-passes to suction causing sleep, which depends upon the differential pressure, viscosity of the liquid & ofcourse the workman-ship. The pump do not develop pressure on it's own but has capacity to over come the back pressure on it way with out substantial drop in capacity. The pump s are capable of handling any viscosity the sleep reduces with viscosity but the viscous power increases. The pump has a self-priming capability but some net positive suction head (NPSH) is always required depending upon the viscosity & pump speed to avoid caviation.

 

The bold sentence I interpret as gear pumps can overcome viscosity drag (at discharge piping) without much loss in discharge flowrate? Hence, viscosity of oil will not affect the flowrate much, so start-up protection should be same?

[Dwoon]

I should think the thicker oil will provide better protection. (ignoring whatever losses in FC, efficiency, etc)

 

Have you also noticed that the ECU will run the engine at higher rpm during cold starts (i.e. if you never depress the accelerator, else it'll drop abit).... the rpm drops gradually as the engine temp warms up.

 

Engine temp characteristics between thin or thick oil is another thing. I noticed that thinner oils warms up much faster (cools down faster as well). Thicker oils take longer to warm up, but also longer to cool down. The thinner oil max temp on cruise is usually ~2 degrees cooler compared to thicker oils (for my car)

 

 

My 2 cents........

Edited February 5, 2010 by Dwoon

[Octopus]

I should think the thicker oil will provide better protection. (ignoring whatever losses in FC, efficiency, etc)

 

Are you refering to during normal operation, or during start-up? Or maybe both cases?

 

 

Have you also noticed that the ECU will run the engine at higher rpm during cold starts (i.e. if you never depress the accelerator, else it'll drop abit).... the rpm drops gradually as the engine temp warms up.

 

I believe the higher rpm when first started is 1) to warm up the catalytic converter and O2 sensor faster. 2) allow the oil to circulate faster thru out the engine for better lubrication/protection.

 

 

Engine temp characteristics between thin or thick oil is another thing. I noticed that thinner oils warms up much faster (cools down faster as well). Thicker oils take longer to warm up, but also longer to cool down. The thinner oil max temp on cruise is usually ~2 degrees cooler compared to thicker oils (for my car)

 

That's interesting.

[Dwoon]

Sorry for not clarifying the very 1st line..... what I'm saying is for cold startup.

 

My comparison is between 0W-40 vs 5W-50 vs 15W-50. (All Mobil 1)

 

Even between the 50 weighted oils. there is a noticeable difference in startup engine sound (15W-50 sound much quieter.... tappet sound is softer) But not much diff when engine is fully warmed up.

Edited February 5, 2010 by Dwoon

[Darkblue]

Protection wise hard to say.......

 

Castrol, Mobil, Amsoil, C-Lube, Ultraman, 5W40 all offer different protection....

 

 

 

Amsoil 0W-30 = Superior protection over C-Lube 5W-40. Some may argue thicker = more protection, IMO, not true.

[Priest7]

what will the impact to our engine if we use too thin oil? Engine wear and tear faster?

like assuming for a new <40km car, using 5w20 all the way.

 

Will it have less protection and impact compare to of those 5w40?

[Zyrofillica]

Most modern motor oils are formulated from various grades of oil so the oil will have the best characteristics of both thick and thin viscosity oils. Multi-viscosity oils flow well at low temperature for easier starting yet retain enough thickness and film strength at high temperature to provide adequate film strength and lubrication.

 

A thin oil such as a straight SAE 10W oil designed for cold weather use would probably not provide adequate lubrication for hot weather, high speed driving. Likewise, a thicker high temperature oil such as SAE 30 or 40 would probably become so stiff at sub-zero temperatures the engine might not crank fast enough to start.

 

Multi-viscosity grade oils have a wide viscosity range which is indicated by a two-number rating. Popular multi-viscosity grades today include 0W-20, 5W-20, 5W-30, 10W-30, 10W-40 and 20W-50. The first number with the "W" refers to the oil's cold temperature viscosity rating, while the second number refers to the oil's high temperature viscosity rating.

 

Note: Motor oils that have a wider range viscosity rating such a 5W-30, 5W-40 and 0W-40 are blended with more base stocks and additives. Because of this, it may be harder for a wider range oil to remain in grade as the miles accumulate (which is why GM does NOT recommend using 10W-40 motor oil. They say it breaks down too quickly and does not say in grade as long as 10W-30 or 5W-30. Also, an oil with a lower winter rating like 0W-20 or 5W-20 will contain a higher percentage of thinner base stock oil (which is typically a synthetic oil). This requires more viscosity improver additive to achieve a the same high temperature rating as a 10W-30, 10W-40 or straight 30 or 40 weight oil.

[Zyrofillica]

 

 

[Zyrofillica]

Most vehicle manufacturers today specify 5W-20 or 5W-30 for newer vehicles for year-round driving. Some European car makes also specify 0W-20, 0W-30, 0W-40 or 5W-40 for their vehicles. Always refer to the vehicle owners manual for specific oil viscosity recommendations, or markings on the oil filler cap or dipstick.

 

As a rule, overhead cam (OHC) engines typically require thinner oils such as 5W-30 or 5W-20 to speed lubrication of the overhead cam(s) and valve-train when the engine is first started. Pushrod engines, by comparison, typically specify 5W-30, 10W-30 or 10W-40.

 

As mileage adds up and internal engine wear increases bearing clearances, it may be wise to switch to a slightly higher viscosity rating to prolong engine life, reduce noise and oil consumption. For example, if an engine originally factory-filled with 5W-30 now has 90,000 miles on it, switching to a 10W-30 oil may provide better lubrication and protection. The thicker oil will maintain the strength of the oil film in the bearings better so the engine will have more oil pressure. This will also reduce engine noise and reduced bearing fatigue (which can lead to bearing failure in high mileage engines).

 

For sustained high temperature, high load operation, an even heavier oil may be used in some situations. Some racing engines use 20W-50, but this would only be recommended for an engine with increased bearing clearances. Increasing the viscosity of the oil also increases drag and friction, which can sap horsepower from the crankshaft. That's why 20W-50 racing oil would not be the best choice for everyday driving or cold weather operation for most vehicles. The latest trend in racing is to run tighter bearing clearances and use thinner oils such as 0W-20, 0W-30, 5W-20 or 5W-30 to reduce friction and drag.

 

ALL TAKEN FROM THE WEB.

[Octopus]

As a rule, overhead cam (OHC) engines typically require thinner oils such as 5W-30 or 5W-20 to speed lubrication of the overhead cam(s) and valve-train when the engine is first started. Pushrod engines, by comparison, typically specify 5W-30, 10W-30 or 10W-40.

 

How come thinner oil will reach the OHC faster then thicker oil, given that the oil pumps are positive displacement type? I'm refering to our local climate, not other country where they have winter.

[Octopus]

Protection wise hard to say.......

 

Castrol, Mobil, Amsoil, C-Lube, Ultraman, 5W40 all offer different protection....

 

 

 

Amsoil 0W-30 = Superior protection over C-Lube 5W-40. Some may argue thicker = more protection, IMO, not true.

 

Not discussing about different type of oil and their additive here, I just want to clarify that oil viscosity does not have much impact on starting time for it to circulate to various part of the engine.

[Octopus]

Sorry for not clarifying the very 1st line..... what I'm saying is for cold startup.

 

My comparison is between 0W-40 vs 5W-50 vs 15W-50. (All Mobil 1)

 

Even between the 50 weighted oils. there is a noticeable difference in startup engine sound (15W-50 sound much quieter.... tappet sound is softer) But not much diff when engine is fully warmed up.

 

I feel its difficult to confirm that thicker oil offer better protection at starting time base on sound alone. It might be just only thicker oil absorb the sound wave traveling to outside to be heard.

[Dwoon]

Yes, its difficult to confirm that thicker oil = better protection at startup.

 

As wear is directly related to mechanical interactions. (therefore sound or noise)

 

I equate that to the level of protection.

 

Just my views.

 

I feel its difficult to confirm that thicker oil offer better protection at starting time base on sound alone. It might be just only thicker oil absorb the sound wave traveling to outside to be heard.

 

[Octopus]

That's a reasonable assumption.