WRX-DAN

Sorry i know alot of you guys think threads about oil should be banned but i want to ask for some opinions....

My brother has a 2002 wrx that has done around 96K on the original engine, it isnt knocking and drives well but from reading a thread earlier i have gotten a bit paranoid for his car.

He changed the oil himself and used Mobil 1 0w-50 fully synthetic, he never disconnected the crank sensor just changed it the normal way. Is this oil no good? It seems to be the case that people change their oil to the type he has chosen and then within 2000 miles they have an expensive problem on their hands!

I have a 2001 wrx uk300 that was rebuilt by APi and the paperwork from them says they only recommend 10w-40 or 15w-40 OR 10w-50 or 15w-50

So has he turned his car into a ticking time bomb? Any opinions or past experiances please share and what would you recommend he should do?

Thanks

TonyBurns

iTrader: (3)

Basically a 0w oil is a as it doesnt provide enough protection on start up to the main bearings (this is where your main failures are) and that oil sucks tbh, you can run a 10w40 or a 10w50 or a 5w40 but no 0w unless you want a potential engine failure on your hands

Tony

bigbruiseral

iTrader: (1)

got me worried now, i only had mine a week and the garage changed the oil for me before i picked it up using 0w-30 will it be ok untill next oil change?

TonyBurns

iTrader: (3)

Put it this way, I wouldnt want it in there, if the car is also a classic then i would be seriously worried

Tony

bigbruiseral

iTrader: (1)

07 wrx if that makes a diff?

TonyBurns

iTrader: (3)

Not really subaru say you can use a 5w30 fully synthetic on your car, if you look at the manual you will note they dont recommend any 0w oils, if I were you I would choose another garage to go to!
I would run a 5w40 fully synth myself (and do on both my classic and new age STI )

Tony

ALi-B

iTrader: (1)

0w-50 is thicker than 10w-40. So it'll be fine.

People who scaremonger over 0w don't actually know how the viscosity system works.

kirstybumx3

iTrader: (22)

Mobil 1 15w-50 fully synthetic

is that any good for a classic?

ian7675

I was under the impression it was wise to avoid Mobil 1 for these cars.

TonyBurns

iTrader: (3)

The cold weight is thinner, ie 0, the hot weight is thicker, ie 50 over a 5w40 say, its that cold weight on start up that wont give your subaru its proper protection hence why even subaru dont recommend 0w oils for its turbocharged cars.

Tony

ALi-B

iTrader: (1)

Tony, you don't seem to recognise where that 0w measurement came from: Its only thinner at or below -30°C degrees! The thickness of oils between -10°C to +39°C degrees is not quantified.....

To recap:

Cold pumping ability(Cp = Centipoise) - the number before the W:

0W 6200Cp @ -35°C
5W 6600Cp @ -30°C
10W 7000Cp @ -25°C
15W 7000Cp @ -20°C
20W 9500Cp @ -15°C
25W 13000Cp @ -10°C

A stark contrast to the ambient temps experienced in the UK

Bearing in mind this is centipoise which is the oils dynamic viscosity which is a multiple of its specific gravity (density). The hot ratings are in centistokes which is kinematic viscosity, and are as follows (the number after the 'W' )

20 = 5.6 to 9.3 cSt @ 100°C
30 = 9.3 to 12.5 cSt @ 100°C
40 = 12.5 to 16.3 cSt @ 100°C
50 = 16.3 to 21.9 cSt @ 100°C
60 = 21.9 to 26.1 cSt @ 100°C

There is an inbetween stage between those two extremes, where we have ambient temperature (say -5°C to +15°C the average UK cold start depending on season), and its viscosity during the 'warm up' phase of a running engine. Where during that phase the polymer chains expand and the basestock thins out. At what temperature that occurs is down to the oil's individual composition.

As a result 0w-50 is no thinner at normal ambient temperatures to a 10w-40 AND thicker when hot. The 'W' rating comes from its pumping ability at -35°C degrees! The average worst case cold start temperature in the uk is -10°C degrees at the very coldest; Where any oil af any viscosity grade oil will be ALOT (by thousands of Cst) thicker than its viscosity at normal operating temps.


Because the rate at which the polymer chains expand differs between differing oils; The typical viscosity of a 0w-50 @ 40°C degrees (during warm up) is almost the same as a 10w40 oil......

Mobil1 racing 0w-50 Viscosity (full synth)@ 40°C degrees = 100cSt (centistokes)
Millers 10w-40 viscosity (full synth) @ 40°C degrees = 90cSt

Or in some cases thicker:
Castrol Magnatec Viscosity (semi synth) @ °C 40degrees = 106cSt

One consistency though will be at full operating temperature (100°C degrees), where the 0w-50 will always be thicker than a 5w-40, 10w-40 or 15w-40 oil (but a 0w-50 will be slightly thinner than a 15w-50 or 10w-50 @ 100°C degrees).


The 'big issue' with a 0w or 5w oil is its dependence on polymer chains to get its wide viscosity index. This in turn relates to its breakdown after prolonged use (i.e not changing it when its needed). A high quality 'racing' oil should resist shear forces (the oil pump tearing the polymer chains) and high temperature break down. But that is a unmeasurable quality which has little to do with the viscosity and more to do with the quality of the oil's ingredients and basestocks in combination with how the car is driven and what consideration is taken to its oil change regime.

In other words the problem arises from an oil that has degraded, be it from hard use and/or not changing it before it degrades or become contaminated (be it from short journeys or fast/race use or towing). This affects ANY oil, but obviously ones using thinner basestocks and more polymer chains will suffer more. So the real problem here is on the nut behind wheel not taking their driving habits into consideration when their engine's oil needs changing.

JohnD

iTrader: (5)

Scaremongering from a previous thread?
Surely a 0w or 5w will provide better cold start protection due to it's ability to flow faster at low temp. When hot however, the dreadfully narrow main and big end bearings in the flat four configuration benefit from a rather more full-bodied lubricant - min. 40, preferably 50. I've always thought a 5w/50 would be a good compromise (Millers do such an oil but not in their CFS range, as do Valvoline)
One point - There's reference to a 0/50 Mobil - never heard of that! should that have been 0/40?

JohnD

ian7675

The Bugeye manual says use 5w-30 so that's what I'm going to use. Reading these threads is a nightmare.

WRX-DAN

Thanks for all the input this is defiantly something that divides opinions!*

So to recap as long as he changes his oil before it degrades the 0w-50 should be ok?

How come APi only suggest 10w-40 or 15w-40 or 15w-50 or 10w-50?*

Tbh I have no idea which I will now select when I change my oil but I think I will be nervous about the first few miles due to the nightmare it is picking the right oil lol.

Cheers

Gear Head

iTrader: (2)

If Subaru themselves do not recommend a 0w oil in their own handbook, why would anyone use it?

bugeyejohn

iTrader: (11)

God knows,i would have thought 10w would be ok unless its really cold like minus 20 or something then maybe 5w. Logged in

Maz

iTrader: (34)

Very informative post. You do know you are adding to the confusion though.