In this cold weather, it is beneficial to use an oil that has good cold start flow properties as it will get to the parts of the engine that need it far more quickly.
The "w" number which means winter is the key here and the lower the better.
It may seem odd but a 15w or 20w will struggle to get around the engine in very cold temps and I would strongly recommend a 10w or better still a 5w for better cold start performance.
90% of all engine wear occurs on cold start because the oil get thicker the colder it is which causes engine wear.
These numbers explain what I mean and bear in mind that the oil will be the following thickness at 100degC (sae 40 = 14cst, sae 50 = 18cst and sae 60 = 24cst)
At 0degC these are the numbers (thick!)
Grade.................At 0C.........At 10C...........At 100C
0W/20.............328.6cSt......180.8cSt..........9cSt
5W/40.............811.4cSt......421.4cSt..........14cSt
10W/50............1039cSt.......538.9cSt..........18cSt
15W/50.............1376cSt.......674.7cSt.........18cSt
20W/50.............2305cSt.......1015cSt..........18cSt
If you are using anything more than a 10w oil, always warm the car properly before driving it hard as the oil needs time to circulate.
Just a word of warning really.
Cheers
Simon
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Mr Oilman, would Mobil 1 0W-40 be OK in my Focus TDCI?
Or would I be better using 5W-30 that Ford recommend?
Looking forward for your answer.
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5w-30 is fine for the Zetec.
Cheers
Simon
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If 5W30 is fine for his Focus, then surely OW30 would be even better?
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"always warm the car properly before driving it hard"
This advice is well used, quoted in just about all the handbooks I've ever flicked through. This might be an appropriate time (and person) to ask, why?
For some reason, I was always thought it was because oil didn't lubricate as well when it was cold, basically, its lubricating properties weren't as effective when cold.
But, after reading what you say, is it partly due to there being less of the oil being pumped around the system? I always imagined that there was the same amount (by volume) being pumped around the system when cold, as there would be when its hot.
I've kind of come to my own conclusion that the lubricating quality is roughly the same, but it doesn't reach those areas with very tight clearances like valve seals and piston rings, as well as it would when hot. Is that right?
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The data shows the thinner oil is still much thicker when cold than even the thickest oil is when hot. So when cold it will not flow as well through restrictions such as the filter, and camshaft spray bar and piston cooling nozzles, these will be more of a lame water pistol type jet than a spray. Also, don't forget the gearbox and differential will be cold and the oil will have to be flicked around to coat everything.
maybe also there is thermal shock issues with making some parts of the engine very hot while most is ice cold..
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It is also to do with thermal expansion. Basically a lot of the parts are the 'wrong' shape when the engine is cold - i.e. clearances etc. You can also get big temp gradients if you drive the engine hard when cold.
Some cars (e.g. ALFA) have/had a warning light when the engine is cold - goes out once its warm enough to thrash!
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Yes you are quite correct, it's about flow/viscosity.
Cheers
Simon
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Bit confused by this - I owned an Impreza turbo (1998 year) for 3 years and a lot of the experts/racing companies insisted any 0W** or 5W** oil was too thin, and a minimum of 10W** or 15W** was recommended, so 5W40 was not recommended but 10W50 or 15W50 is fine.
Now I can understand why the hot oil rating on a Scooby needs to be 50+ to ensure there is a strong working film of oil at working temperature to protect the engine/turbo, but I never understood the bit about 5W (or 0W) oils not being recommended.... any ideas??
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Just in case the wrong end of the stick is grasped, I'd suggest that Simon the Oilman didn't intend "warm the car properly" to be interpreted as "leave it idling for a few minutes before you start moving". I recall again HJ's report of a Ford engineer describing cold idling as "incredibly damaging". It also guzzles fuel, maximizes pollution and annoys neighbours, especially in the early morning.
Start up and get moving gently as quickly as possible. Don't hammer it until you've done at least five miles. (Don't hammer it anyway . . .)
That's what I do; I do wish my neighbour would do it too.
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The start up period is the time when the engine experiences the most wear. By accelerating before the oil reaches the top of the engine, five or more seconds depending on the vehicle, you can do a considerable amount of damage and speed up engine wear. If you have an oil pressure gauge you can see when max pressure is reached and the pressure is the feedback from the oil reaching the bearings. With cold thick oil high pressure maens oil bypasses the engine via the pressure relief valve and also the oil filter, allowing unfiltered oil into the engine.
During very cold winter starts when an engine is cold and the oil is thick, the best compromise is to wait, then drive slowly for the next five to 10 minutes until the engine reaches the proper operating temperature.
Moving off as quickly as possible speeds up the warm up process therefore minimising the start up wear period.
Oil also contains anti wear additives which are temperature/pressure activated and an oil temperature of 70c is considered to be the temperature that these additives begin to be activated.
When an oil has a large spread 0W40, a compromise is made by using a thinner base oil and adding viscosity improvers. With a high performace track car a better option is to avoid viscosity improvers and use say a 15W40.
On the API chart there is a column for HTHS (far right) which is a measure of viscosity at 150c approx oil temp at bearing. The higher the number the better the protection the downside is a thicker oil generates more friction heat and wastes energy bhp. The way around this is to use a better quality synthetic base oil called esters which are found in race oils like Redline Motul 300V and Silkolene pro.
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Good point, I never thought of that - there is something called zinc dialkyldithiophospahte in the oils which is an anti-scuffing additive it only works above about 60deg.
So it is important not to apply extreme pressures to moving metal parts, including the transmission until it is this temp.
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Most of the oil advice given on Scoobies is myth.
A good 5w-40 or 10w-50 is all you need and in fact stock road cars benefit from a decent 5w-40 synthetic for all year round use but the key is to use a decent shear stable synthetic.
Cheers
Simon
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I put 10w30 in a Rover K-series Metro instead of 10w40.
I realized what I'd done about a month later, by then the head-gasket had gone.
Would the thinner oil have resulted in damage if this had happened?
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PS - Nissan recommend 15w40 for my current car, a Micra.
Would there be any cold-start protection advantage if I used 10w40 instead?
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Yes, 10w-40 will be fine.
Cheers
Simon
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myth.
some other myths busted here:
www.mobiloil.com/USA-English/MotorOil/Synthetics/M...x
Myths
People have a lot to say about synthetic oils. Unfortunately, it?s not always accurate. But ExxonMobil is here to clear things up. Read below to get the truth behind some of the most common misconceptions about synthetic oils and your vehicle.
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Simon
Is that stunning numerical statement -- "90% of all engine wear occurs on cold start" -- based on a notional estimate or on researched numbers? I don't disbelieve it, but am curious to know, as I'm often telling people that cold starting is damaging and that cold idling is an original sin.
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SAE paper a few years ago
Effect of Break-In and Operating Conditions on Piston Ring and Cylinder Bore Wear in SI (Spark-Ignition) Engines, Schneider et al:
The rate of wear is much higher within 15-20 minutes of start-up than after reaching normal operating temperature. The initial start-up time period (first 20 minutes) result is 100 nanometers of wear whereas the steady state wear rate was only 4 nanometers per hour thereafter. This justifies the statement that 95 percent of engine wear occurs just after start-up).
Stopping the engine for 10 minutes after reaching full operating temperature did not cause any start-up like wear. The wear rate picks up right where it left off before shutdown.
Since then additive technology has improved and there are at least two AW additives, a primary and a secondary, ZDDP being one of them, although this is being slowly replaced by other AW additives, some purely organic, such as specialized esters.
One of the AW additives is for cold temp operation and the other one or two are for high temperature operation. A primary ZDDP could be called a mid-range AW additive, a secondary ZDDP (or equivalent) could be called the high temp AW additive, while Boron, Calcium and others could be called the low temperature AW additives.
High contact pressures can lead to localized high temperatures such as found at the cam lobe/tappet interface. These high pressures would in turn cause high temperatures which would cause the ZDDP or equivalent AW add to activate or plasticise and reduce wear.
These additives are left deposited on metal surfaces after shutdown.
At cold temps, one wants to establish a hydrodynamic film as soon as possible. This is where the starting viscosity of the oil comes into play, but since it cannot do this instantaneously, the AW additives reduce wear until the hydrodynamic film is established.
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