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Have we been doing it wrong?


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Not completely bike related, having a few glitches with car oil pressure so been checking what oils I can use etc... and stepping it up a grade.


But got me thinking about oil weights, as everyone knows modern oils have a cold/hot rating e.g. 10w40 is SAE10 equivelent when cold and SAE40 when hot. So when it is cold it acts like a thinner oil yet whenever we do an oil change first thing we do is 'warm it up so it comes out easier'.


Surely the oil is designed to be thinner when cold so would come out easier when cold?


I'm guessing with engines there is obviously a big lump of metal acting as a heat sink so when engine is totally cold (and days like this) oil temp is well below normal temp so would be a benefit to getting it slightly warmer but otherwise heating oil up we are just making it thicker and taking longer to come out?


Anyway no real point to this thread just thinking out loud, personally I like the dance with death where you remove a sump bolt from a warm engine and have to get your hand out the way of the hot oil stream before it disolves so will keep warming it up ;)

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I don't think the two numbers are comparable. I believe that they either use different units or a different scale or something like that.


Multigrade oil is definitely thinner when hot in my experience. You can tell that by the way it pisses off my hand and all over the floor missing the oil catch container.

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I always used to warm up the engine before dropping the oil, but then I thought why? When the engine is cold, all the oil is sat neatly in the sump ready to exit, what's the point of flinging it all back round the engine again for 5 minutes?

Unless you're leaving it to drain over night or using engine flush I can't see the point.

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I don't think the two numbers are comparable. I believe that they either use different units or a different scale or something like that.


Multigrade oil is definitely thinner when hot in my experience. You can tell that by the way it pisses off my hand and all over the floor missing the oil catch container.

 

Same scale...

 

The Society of Automotive Engineers (SAE) has established a numerical code system for grading motor oils according to their viscosity characteristics. The original viscosity grades were all mono-grades, e.g. a typical engine oil was a SAE 30. This is because as all oils thin when heated, so to get the right film thickness at operating temperatures oil manufacturers needed to start with a thick oil. This meant that in cold weather it would be difficult to start the engine as the oil was too thick to crank. However, oil additive technology was introduced that allowed oils to thin more slowly (i.e. to retain a higher viscosity index); this allowed selection of a thinner oil to start with, e.g. "SAE 15W-30", a product that acts like an SAE 15 at cold temperatures (15W for winter) and like an SAE 30 at 100°C.


Therefore, there is one set which measures cold temperature performance (0W, 5W, 10W, 15W and 20W). The second set of measurements is for high temperature performance (8, 12, 16, 20, 30, 40, 50). The document SAE J300 defines the viscometrics related to these grades.


Kinematic viscosity is graded by measuring the time it takes for a standard amount of oil to flow through a standard orifice at standard temperatures. The longer it takes, the higher the viscosity and thus the higher the SAE code. Larger numbers are thicker.

 

I am guessing it really boils down to the difference between the 2, do the manufacturers choose an oil that moves as easily when cold as it does when hot or one that is "ok" when cold.


So for 10w40 does does a cold SAE10 flow better than a hot SAE40 ... tried googling to find data and ended up realising I don't care that much :lol:


Now back to actually ordering some oil for my car...

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you will never get all the oil out.. whether you warm the engine or not. this is why in most manuals it gives various volumes depending on what exactly you are doing.


for my A.T. these are:


4.0 litres for an oil change

4.2 litres oil and filters

5.2 litres disassembly


so.. an ordinary oil change there will be around 1.2 litres remaining in the bike.


warming the engine is all about doing the job quickly. its not brought up to full temperature or it would be dangerous. its warmed up to reach that happy medium where it will flow a little quicker than when cold. likewise.. if you do it after a ride, its best practice.. and this is what most mechanics do, to let it stand for 30 minutes or so.

Edited by Gerontious
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Same scale, different functions.


Oils these days are multi-grade, which is how most earn their ratings.


When the engine is cold, you want good flow to avoid oil starvation during start up / warm up.

However when the engine is hot, you need the oil to be thicker so that the friction in bearings/piston rings/gears/clutch doesn't allow components to get too hot. By this point the engine will have also attained a healthy oil pressure anyway.


So you're right, it won't flow more easily, but that's not why you run the engine briefly before an oil change.


You run it before an oil change with or without a flushing agent as the heat helps to shift deposits. Think of it like swilling your mouth with mouthwash. There is no direct need to do it and I've frequently done it without firing the bike up at all, as the new oil/filter will sweep any lingering deposits away and be well within spec (especially as I change the oil more than the manual suggests).

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The numbers relate to molecule chain length - 10W40 will flow better in a cold engine than say 15W30. The larger number isn't how thick the oil is in terms of viscosity, it's the length of the chains which mean that some engines that use very narrow oil passages need a SAE30 rather than 40.


Hot oil is always 'thinner' in terms of viscosity than cold oil. So for an oil change warm the engine up, leave it a few minutes for most of it to drain into the sump, then drain. You won't get 100% of it out but you'll get more than draining a cold engine.

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When I bought my replacement engine as a non runner it still had the oil in it so I had to drain it cold . Despite leaving it to drain for a day , when I came to strip it there was seemingly oil lurking everywhere. Which got me thinking. Have a look at this chart of oil capacities for the ER5. In theory there is still 0.6 of a litre of old oil still in the engine when you do a routine oil change without changing the filter and 0.4 of a litre when the filter is changed .

131834575_wp_ss_20181203_0001(2).png.40e1fc358e7d33318041a5cffc2d2ed1.png

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Oil is thinner when hot than cold fact!

The oil grade is measured in two different ways, the first part for example 10w refers to the time a given amount of oil takes to drain through a given size hole, put simply a funnel.

The second part, for example ‘40’ is measure using what can be described as a plastic pan with a bit of metal in the bottom, and an electro magnet on the underside of the pan, the current in the magnet is increased until it moves the metal fragment through the oil.


The whole warm up thing is partly mechanical sympathy from old like a lot of things, the manufacturer says to use a 10w oil because at the given temp range that grade of oil will flow though all oil galleries at the correct oil pressure to avoid mechanical failure or premature wear, but when hot will not drop oil pressure to unsafe levels. And at the top of the scale the oil will remain the correct viscosity to lubricate and protect also


That aside the minefield isn’t what grade of oil you use as such because you will see that grade changes with temp range of climate but more the devil is in the api ratings, additives, friction enhancers and such like and that’s where your manufacturer recommendations really count

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I can't post them from work but watch Engineering explained. He did a series on oil types/flow rates etc.

He even did a comparison test of different oils, new and used, where he cooled them down to below freezing temperatures so that they would flow slowly enough we could see the differences (which is one of the industry standard tests). And the difference in some oils with the same rating was astounding.


But for changing oil, I think a point to take away is it's not damaging to do it cold. The oil will flow well enough, especially if it's a 0-10W oil, and even better if it's a synthetic.


Warming the oil is really only crucial when the oil is very old or well past the change schedule. As in the videos I mentioned above, their flow rate greatly degrades. How much and how fast it degrades depends on the quality of the oil.

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Oil is thinner when hot than cold fact!

 

 

I don't dispute that. but it depends doesn't it on what you mean by "hot". for an oil change we are not talking normal operating temperature. (which would pose a big scald risk) The oil (and engine/gear box) is just warm. you either have the engine running for a few minutes.. or wait half an hour after a ride out. And under those circumstances the oil does flow much better. if left alone it will drip for longer towards the end than if it was at ambient temperature. which is only useful if you want to get as much of the old oil out and get the job over quickly. But this isn't crucial for most people (including me) as no matter how you do the job there will always be a significant amount remaining.


I reckon this is why most mechanics warm the engine up before doing the job. It just means the change can be done a little quicker. Important when time = money.


But.. if you are doing this yourself.. then it hardly matters. especially if you are lazy (as I am) and often leave it to drip overnight.


warm or cold? unimportant... there is no harm done doing it either way. its mainly (for me) just habit. There will always be a significant amount of old oil left behind unless you are fully disassembling the engine. In the case of my bike thats >20% of the total volume. So for my bike a full oil change is a bit misleading. its an 80% change.

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Surely the oil is designed to be thinner when cold so would come out easier when cold?

 

Oil is more viscous when cold, and less viscous when hot. That's less to do with design and just physics/fluid mechanics.


 

Oil is thinner when hot than cold fact!

 

 

I don't dispute that. but it depends doesn't it on what you mean by "hot". for an oil change we are not talking normal operating temperature. (which would pose a big scald risk) The oil (and engine/gear box) is just warm. you either have the engine running for a few minutes.. or wait half an hour after a ride out. And under those circumstances the oil does flow much better. if left alone it will drip for longer towards the end than if it was at ambient temperature. which is only useful if you want to get as much of the old oil out and get the job over quickly. But this isn't crucial for most people (including me) as no matter how you do the job there will always be a significant amount remaining.


I reckon this is why most mechanics warm the engine up before doing the job. It just means the change can be done a little quicker. Important when time = money.


But.. if you are doing this yourself.. then it hardly matters. especially if you are lazy (as I am) and often leave it to drip overnight.


warm or cold? unimportant... there is no harm done doing it either way. its mainly (for me) just habit. There will always be a significant amount of old oil left behind unless you are fully disassembling the engine. In the case of my bike thats >20% of the total volume. So for my bike a full oil change is a bit misleading. its an 80% change.

 


Even at 10 DegC 10W40 is 4 times thicker than it is at 40C, from there on the viscosity doesn't change drastically. So there's no point really doing it above that anyway :D


Graph_Oil_MobilS_10W40_1024.png

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When the engine is cold, you want good flow to avoid oil starvation during start up / warm up.

However when the engine is hot, you need the oil to be thicker so that the friction in bearings/piston rings/gears/clutch doesn't allow components to get too hot. By this point the engine will have also attained a healthy oil pressure anyway.

 

Maybe I'm misunderstanding, are you saying the oil is thicker when hot & at operating temp?

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I thought he was a chemical engineer :shock:

Pretty sure he said he was sparks the other week...


I'll see if I can find the thing.

 

Sorry you're right, it's down as his occupation. It must have been for an oil company or something, I'm sure the fozster will let me know when he's back :)

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When the engine is cold, you want good flow to avoid oil starvation during start up / warm up.

However when the engine is hot, you need the oil to be thicker so that the friction in bearings/piston rings/gears/clutch doesn't allow components to get too hot. By this point the engine will have also attained a healthy oil pressure anyway.

 

Maybe I'm misunderstanding, are you saying the oil is thicker when hot & at operating temp?

 

I think I made edits mid post but left the word "thicker" in. It should read "you need the oil to be thick enough".

So that it reads that when cold the oil flows well enough it doesn't starve, but is thick enough when hot to protect.


I'm an electrical engineer in power generation currently, which I'm in due to the big dip in oil prices a few years back. I was an instrument design engineer previously for a company that built on/off shore rigs/refineries. The reason I have chemical knowledge is I would work with chemical engineers to specify control valves, sensors, etc that pumped various oils/chemicals to transport them, but also control the production process of various oil grades/types. So I'm not a specialist, but what I do know was largely gleaned from asking them.


The companies were quite tight lipped about which brand oil was what, but you could tell which was the higher quality stuff just looking at the production train. Higher quality oils would have twice the control systems and monitoring the lower quality ones would have. You could also pick up what various additives did etc but I'd bore you to tears :lol:

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..... but you could tell which was the higher quality stuff just looking at the production train. Higher quality oils would have twice the control systems and monitoring the lower quality ones would have. You could also pick up what various additives did etc .....

 

OK, so come on - what's the BEST oil for my bike ? :D

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..... but you could tell which was the higher quality stuff just looking at the production train. Higher quality oils would have twice the control systems and monitoring the lower quality ones would have. You could also pick up what various additives did etc .....

 

OK, so come on - what's the BEST oil for my bike ? :D

 

I use left over chili oil from pizzas, don't do engine any good but smells nice :thumb:

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..... but you could tell which was the higher quality stuff just looking at the production train. Higher quality oils would have twice the control systems and monitoring the lower quality ones would have. You could also pick up what various additives did etc .....

 

OK, so come on - what's the BEST oil for my bike ? :D

 

The safe answer is the one stated in your owners manual :thumb:

It will give a grade/standards that need to be conformed to.


This topic causes big kick offs on facebook so I won't delve into it. Just read any counter arguments with the pinch of salt that identical grade/standard oils can differ wildly. As some do the minimum to meet those requirements (in an effort to reduce production cost), and some go further. Those videos I mentioned by engineering explained test them I believe, so worth a watch :)

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Personally.. I would just go for one of the major brands. Shell, Mobil etc.


I'll be having my bike dealer serviced.. at least during the warranty period. and apparently they will be using Honda oil.. which is just relabelled Mobil.


I could never understand why some people get so overexcited about engine oil.. and go to 'virtual' war over the subject.. with a former Nazi leader usually mentioned within 3 pages - a perfect indicator of the quality of the arguments.

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