Thinner oil = better start up protection?

[GoodCar]

I think for layman, just choose that thinnest oil possible as per the owner manual base on our local weather condition.

but Synthetic oil is always better.

[Dwoon]

I belive that each car would have their own characteristics. Clearances internally would be different as well as engine desgin iteslf. (I'm on boxer H4)

 

I wouldn't be surprised that some might not notice any difference in startup engine running sound, between thin & thick oils.

 

 

[Trex101]

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.

 

It's because thinner oil travel faster then thicker oil due to lower drag. That's why oil pressure is inversely proportionate to flowrate, the higher the pressure, the lower is the flowrate.

 

For example, you use a positive pump to pump water = given flowrate

but if you pump honey, there is no way honey flowrate = water flowrate

[Trex101]

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........

 

That's a misconception, thicker oil doesn't protects better than thin oil. If that's the case, we would all be using grease for our engine liao. Oil pressure(high viscosity) and oil flowrate(low viscosity) has to be balance for optimized engine protection.

 

Why your ride need thicker oil is due to your higher engine oil temp from forced induction and i suspect fuel dilution. Your thicker oil has a higher safety margin to withstand fuel thinning, so even with excessive fuel dilution, your viscosity might drop from w50 to w30 range. still within safety limits.

Edited February 5, 2010 by Trex101

[Zyrofillica]

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.

 

oil is more fluid at higher temperatures. The thicker the oil the less fluid it will be given same oil temperature. i would reckon that at 20 deg c, thicker oil would be less fluid than a thin oil. thicker oil will more surface tension and hence be able to cling onto the engine components better than a thin oil that would flow back to the pan due to gravity.

 

given our lowest climatic ambient temperatures is around 20 deg c, i would think that 20w-- oil would be the best oil in terms of startup protection. since MOST engine oils sold now are multiweight oils, at engine operation temperatures, 20w40 oil would follow characteristics of the upper weight figure. (40)

 

of course if u use 20w40 oil, fc will decrease compared to using 0w40 oil. This is because between the starting of the engine to the optimal operating temperature, the engine will be working harder with a thicker 20 point grade oil till it eventually behaves like a 40 point grade oil when your engine has entered the optimal temperature range

[Zyrofillica]

That's a misconception, thicker oil doesn't protects better than thin oil. If that's the case, we would all be using grease for our engine liao. Oil pressure(high viscosity) and oil flowrate(low viscosity) has to be balance for optimized engine protection.

 

Why your ride need thicker oil is due to your higher engine oil temp from forced induction and i suspect fuel dilution. Your thicker oil has a higher safety margin to withstand fuel thinning, so even with excessive fuel dilution, your viscosity might drop from w50 to w30 range. still within safety limits.

 

true if we could dump grease into our engines and still get good fc i would do it maybe my engine will last forever. But i bet grease in my engine will destroy the pump and give me 1km/litre. i think even cranking the car to start would be impossible with COLD solidified grease inside. not to mention even hot grease has lousy flowrates

 

engine oil is a balance between superior lubrication and superior fuel consumption/efficiency. Grease on one end and air lubrication on the other

Edited February 5, 2010 by Zyrofillica

[Zyrofillica]

come to think about it, those pple buying 0-30 oil and 10-30 oil, might as well use single weight oils like SAE 30? because since our temperatures dun go below 20 deg c, 30 weight oil is sufficient protection at startup. but im not sure if 10-30 oil is more expensive than SAE 30 oil in the first place or if SAE 30 oils has less protective additives added.

[Zyrofillica]

"oil is more fluid at higher temperatures. The thicker the oil the less fluid it will be given same oil temperature. i would reckon that at 20 deg c, thicker oil would be less fluid than a thin oil. thicker oil will more surface tension and hence be able to cling onto the engine components better than a thin oil that would flow back to the pan due to gravity."

 

ok i think i got it wrong. lower rating means oil is less viscous, so it is better to have a less viscous, more fluid oil at startup for good protection.

[Nmnhnlm]

That's a misconception, thicker oil doesn't protects better than thin oil. If that's the case, we would all be using grease for our engine liao. Oil pressure(high viscosity) and oil flowrate(low viscosity) has to be balance for optimized engine protection.

 

Why your ride need thicker oil is due to your higher engine oil temp from forced induction and i suspect fuel dilution. Your thicker oil has a higher safety margin to withstand fuel thinning, so even with excessive fuel dilution, your viscosity might drop from w50 to w30 range. still within safety limits.

 

Nope. Thicker oil does protect better than thinner oil. Thicker oil has higher shear resistance compared to thinner oils. It has thicker oil film and this helps to reduce oil consumption as well. Turbo engines run a greater cylinder wall clearance and hence thinner oil will result in increased blow-bys as well.

 

OIl film and shear reistance is very important for turbos as well. We are talking about over 100K RPM for Turbos and you need the oil film to protect the bearings. Else, your Turbo will go bye bye very fast.

 

 

[Octopus]

It's because thinner oil travel faster then thicker oil due to lower drag. That's why oil pressure is inversely proportionate to flowrate, the higher the pressure, the lower is the flowrate.

 

For example, you use a positive pump to pump water = given flowrate

but if you pump honey, there is no way honey flowrate = water flowrate

 

I disagree, the theory you've mentioned is more applicable to centrifugal pumps than positive displacement pumps.

 

A centrifugal pump then the discharge are shut, its still quite safe as the fluid inside the impeller will heat up, basically no need safety device such as relief valve for single stage centrifugal pumps.

Positive displacement pump on the other hand, something will give way if the discharge are shut and a safety devise must be provided. The volumetric discharge from a positive displacement pumps are constant, hence not affected by viscosity, unlike a centrifugal pump.

Edited February 5, 2010 by Octopus

[Octopus]

come to think about it, those pple buying 0-30 oil and 10-30 oil, might as well use single weight oils like SAE 30? because since our temperatures dun go below 20 deg c, 30 weight oil is sufficient protection at startup. but im not sure if 10-30 oil is more expensive than SAE 30 oil in the first place or if SAE 30 oils has less protective additives added.

 

I read that single 30 weight oil are extremely shear stable, and given our climate condition I would not hesitate to use it (provided that other specification meets my requirement). But so far I have not seen single 30 weight oil available locally. A 10W30 is the next best thing.

[Octopus]

Please see some write up on different pumps on below link.

http://www.pumpbiz.com/faq.asp#q198

 

9. What is different about centrifugal pump vs. gear pump?

A centrifugal pump is of kinetic energy type - it imparts energy to a liquid by means of centrifugal force produced by a rotating impeller, disk or other blade form. A positive displacement pump imparts energy by mechanical displacement. Piston, diaphragm, plunger, screw, vane, and gear pumps are some examples.

Centrifugal pumps are essentially high liquid volume-low pressure. A large amount of liquid can be carried between the blades of the impeller, but as this is not a positive displacement pump, the volume of liquid drops off in proportion to the back pressure (head in feet) applied. A PD pump large enough to match the volume of delivery of a centrifugal pump would have enormous gears or diaphragms, and be impractical. On the other hand, to obtain the pressures of a PD pump, the impeller diameter of a centrifugal pump would have to be increased to an enormous size, and this would also be impractical. However, multistage centrifugal pumps can be used in place of PD pumps in many applications. A multistage pump passes the liquid from one impeller to the next, at each stage it imparts more head (pressure) to the liquid. Therefore creating higher pressures.

Due to the centrifugal pumps design simplicity, high efficiency, wide range of flow and head, smooth flow rate, and ease of operation and maintenance. Positive displacement pumps are of lower flow range, have pulsating flow rate and are usually self-priming

 

 

 

12. How does viscosity affect a pump?

 

Viscosity affects centrifugal pumps to a different extent than it does PD pumps. First, viscosity is a value relating the physical property of a fluid resistance to flow. Water having a very low viscosity and molasses has an extremely high value. The some liquids change the viscosity the more they are made to flow and under temperature changes. For the most part a centrifugal pump has a very low limit of how thick or viscid the liquid is it is pumping. On the other hand a PD pump by its naturally low volume operation, slow speed and fixed volume operation, tend to handle high viscosity fluids with ease. PD pumps are the preferred choice. In either case consideration needs to be made for the high power (BPH) required or reduced flow rates.

[Octopus]

"oil is more fluid at higher temperatures. The thicker the oil the less fluid it will be given same oil temperature. i would reckon that at 20 deg c, thicker oil would be less fluid than a thin oil. thicker oil will more surface tension and hence be able to cling onto the engine components better than a thin oil that would flow back to the pan due to gravity."

 

ok i think i got it wrong. lower rating means oil is less viscous, so it is better to have a less viscous, more fluid oil at startup for good protection.

 

That is what I'm trying to say, but you not get my point.... the viscosity, whether thinner or thicker, do not make any difference at start up.

[Ithunk]

thanks for the info...great read

[Zyrofillica]

That is what I'm trying to say, but you not get my point.... the viscosity, whether thinner or thicker, do not make any difference at start up.

 

but thinner viscosity oil is better at start up. of course, if you talking about difference between 0w40 and 20w40 oils in singapore context, then both will be around the same viscosity at startup. But i think what has been established already is that lower viscosity oils provide superior lubrication due to increased flow rates through the pump at any given temperature.

[Octopus]

but thinner viscosity oil is better at start up. of course, if you talking about difference between 0w40 and 20w40 oils in singapore context, then both will be around the same viscosity at startup. But i think what has been established already is that lower viscosity oils provide superior lubrication due to increased flow rates through the pump at any given temperature.

 

That is the myth I'm trying to inform here. The person making that statement probably have limited knowledge on the principle of how pumps works, not likely mechanical trained. Could be a chemist specialising in blending lube oil or markting people. I had given the fact that different pumps the working principle are different, and that so called "established statement" only applicable to centrifugal pumps. And lube oil circulation pumps inside an engine are NOT centrifugal pumps, hence not applicable.

 

Have you ever wondered how come turbo-charged engine where thicker lube oil are specified do not have problem with ability of oil to flow to various parts at starting time? Lubrication for turbo-charged engine is more sever than NA engine, especially the lube oil need to get to the turbocharger fast during start-up. Its because gear pumps allow either thicker or thinner oil to be pumped to where it is needed at same time/speed.

 

Nowadays the trend is towards thinner oil, a major reason is CAFE. Whether the thinner oil route had compromised on protection, I think that is another debateable topic. Thinner oil only gives better fuel consumption because less resistance inside the engine, but time for it to circulate are no difference when compared to the thicker ones.

[Ithunk]

wat u guys think of Ravenol engine oil?

[Zyrofillica]

errr, but turbo oil uses only a higher weight oil at operating temp. at startup temperatures, the oil is the same viscosity as a any N.A car. eg 0w30 for NA vs 0w50 for turbo in a winter climate.

 

i understand centrifugal pumps and i take your word that the pumps in an engine are built to circulate oil at the same rate at any viscosity. i understand where you are coming from by looking at the mechanics of the pump.

 

however consider the effect of viscosity on film protection, this may be the reason why thinner oils protect parts better even though both thick and thin oils are being circulated at the same rate in the engine.

 

"2. What is viscosity ?

 

Viscosity is a measure of a fluid's resistance to flow. For lubricating oil in general, viscosity is the most important physical property. It is viscosity, as well as the pressure and speed of movement, which determines the thickness of an oil film between two moving surfaces. This in turn determines the ability of the oil film to keep the two surfaces apart, the rate heat is generated by friction and the rate the oil flows between the surfaces and thus conveys the heat away.

The oil should have a viscosity at the operating temperature that is correct for maintaining a fluid film between the bearing surfaces, despite the pressure tending to squeeze it out. While a reasonable factor of safety is usually desirable, excessive viscosity should be avoided because this can create more drag and therefore unnecessary heat generation. "

Edited February 6, 2010 by Zyrofillica