Question away mate, I'm just another guy trying to figure it out !!

We don't see too many 2001 onwards cars yet for rebuilds as they have been under warranty until quite recently. So that rush is yet to come.

I think I understand the concept of the 0W and 5W thing well enough now, and my only comment is that;

Whilst that oil can almost certainly be used in an Impreza, a selection of other 'faults' combines to overcome the protection of the oil and 0W and 5W seem less able to cope with those factors.

My over-riding opinion/ impression of the crank bearing failures is that it's primary cause is Det. The shock wave transmitted down the con rod overloads the oil film and the shock is passed into the bearing shells which due to their small dimensions are already working hard.

The Det is caused by a, UK fuel of a lower Ron than the car is mapped for. [ we're talking imports here don't forget] b, low fuel in the tank causing aeriation?, aereation?, airriation?, OK, bubbles, bubbles = weak mixture, hence det again! c, Then lastly, high road speed changing the laminar airflow over the I/C scoop and the I/c temp rises and here comes Mr Det.

So to sum up, 0w & 5w are probably OK, if everything else is OK. That's in the lap of the user.

David APi Engines / APi Impreza
www.apiengines.com

 

Old I may be, but at least I'm not ugly !!

David APi Engines / APi Impreza
www.apiengines.com

 

So many opinions about oil........................ it don't matter what oil i put in now i'm going to be worried that i've put the wrong one in, this subject needs a conclusion lol

 

David,

Thanks for the reply and it sounds credible although you know more about these engines than I do.

I'm strongly of the opinion that the oil is not to blame, an sae 40 is an sae 40 afterall and provides the same level of protection at 100degC whatever the "w" number is.

The only factor to take into account is the different qualities (basestocks and addative packages used) of different brands.

I've always advocated the use of certain "race spec" sae 40's rather than the run of the mill ones which are less thermally stable and therefore more prone to shearing with use. Quality is a factor that should not be ignored with tuned/high performance engines!

At the end of the day although the viscosity of 14cst at 100degC is a common level of protection for an sae 40, the question that is key is for how long? A semi-synthetic or hydrocracked sae 40 will not remain at that viscosity for many miles, a true synthetic one will and that's the difference.

Cheers
Simon

 

Listen to Oilman, he knows his stuff. Pick an oil from his list up the top of the thread. Sounds to me like any of them will do.

David APi Engines / APi Impreza
www.apiengines.com

 

No please don't, some of them won't do as they're not fully synthetics.

I was illustrating that a 40 was a 40, not how long they would stay as a 40.

Always ask what's best, don't assume that the oil is good because the word synthetic is mentioned in the name or on the can.

Cheers
Simon

 

Probably a silly question - what is cst? I missed that bit somehow.

David APi Engines / APi impreza
www.apiengines.com

 

It's a measure of viscosity known as "centistokes".

Cheers
Simon

 

Well, definatly wont be using 05-30 as it specifys that in the hand book , however oilman recommends it?............ There must be a reason why subaru don't recommend using it. I just want the best quality oil for normal driving and the odd redline. I think the main reason for engine faliures is probaly abuse(constant redline, not heating the car up , not cooling it properly), abuse combined with the wrong oil , bad servicing techniques is just the recipe for engine faliure. i aint an expert but i've read a lot off these forums and Api David see's the end results (blown engines) and therefore most likely finds out what oil was in the car and other details which over time i guess you begin to notice certain patterns, I think after all the reading i've been doing on the issue i'm going to use a fully synthetic 10w-40 and do a oil change as normal but make sure the engine is slightly warmed , i have oil in the oil filter. Thats the conclusion ive came to after reading a lot on the subject

 

You missed the point, I'm not recommending 5w-30 or 0w-30. I'm recommending 5w-40 on later models above 10w-40 as they give the same protection at 100degC!

Cheers
Simon

 

That's what I thought !! So the bigger the number at 100c the better? or is it not that simple?

Thanks Simon

David APi Engines / APi impreza
www.apiengines.com

 

David,

I wish it was, It would make my job easier and I may have fingers left!

As I posted before, an sae 40 is around 14cst regardless of the "w" number.

The bigger the number at 100degC depends on whether it's an sae 30, 40, 50 or 60. SAE 60 is obviously the biggest but as I've said on many occassions not necessarily the best for your cars.

You always need to use the lowest viscosity oil that will cope with the tolerances of the car concerned as it has more benefits than downsides as mentioned in this thread already.

If you don't need to drag an SAE 60 (24cst) around the engine and an sae 40 (14cst) can cope then why do it. You are merely asking for trouble long term with higher engine wear.

If you want to discuss anything here, please feel free to call me 01209 215164, I'd be happy to chat, it's quicker and less time consuming than by two (worn down) finger typing!

Cheers
Simon

 

hi david, do you see a lot of your re-builds because of oil flushing?
would seem to make sence to 'flush' prior to oil change , rather than contaminating the new oil ,no?

 

I ain't no expert , but i agree with david about not using engine flush, i used it on my old rover 220 tomcat turbo , low and behold the engines blows up 10 mins after , im just guessing that the flush will remove all the protective lining therefore leaving the engine unprotected , id say if you have changed you oil regually then why risk it?

 

Simon,

Thanks for clearing this up (again..!).

So from this, would it be safe to say, given the chioce, you'd always use a 5w 40 over a 10w 40..?

Jason

 

If appropriate yes.

Apart from Motul 300V Chrono, most 10w-40's are semi-synthetic which I wouldn't recommend whereas most (but not all) 5w-40's are true synthetics

A 5w-40 can just about be blended by using an element of true synthetic (pao or ester) and hydrocracked (mineral oil) which would make this inferior performance wise to a true full synthetic (pao/ester only) and no mineral oil content.

Cheers
Simon

PS. Sorry it's complicated - Oil is not a simple topic although most people don't see it as so.

 

I did some project work when I was in Uni that investigated the breakdown of the lubricating oil film under various load/bearing surface combinations and I believe that it sheds a bit of light on the Scooby what oil saga...it basically supports bits of what API David and Bob etc have seen through experience and what Oilman shows via techs on oils...and at the end of the day I think the Scooby issue is all down to the clearances that the engines run,the loads on the bearings/crank, and temps...Nothing new really but a standard engine has more latitude in terms of what it may be able to get away with...ie some run on 5w30 succesfully...in a tuned Scooby IMHO that's more than tempting fate a little...If the film breaks down under load...which is more likely the more heavily tuned the motor is, then it's goodnight...but the thing is that because theres variation in the tolrances between motors and the spec of the motors and the way they are driven the patterns are a bit confused...but what seems to be the case here is that the 10w upwards winter rated oils are better at preventing the film layer breakdown...whatever the claims are that 5w should be safe or that I've used 0w and got away with it...and the fact that it's the high temp 40/50/60 rating that you'd expect to have the greatest influence when the engines under load..being ragged this isn't the complete picture which is why there appear to be contradictory experiences..Oilman and API David both mention the interaction of clearances and viscosities...that's the crux here...but the oils hydrolastic behavior under load is affected by it's overall chemistry not just the high/low rating if you see what I mean...That's what I found anyway...that the 10w 40 upwards rating oils gave best protection against shock loads..and temp induced stress..which would seem to be the achiles heel of the Scooby motor...

 

Crusher,

Very interesting post and much of it I am in agreement with.

There is however one point that I should make which would influence this type of research - Oil Quality.

If you take the rate at which an oil shears (loses viscosity with use), you see very different results with different oils.

For example you could compare the rate of shear on two oils of similar quality (basestock groups and percentages) and if they were both 100% poly alpha olefin synthetic basestocks (like Mobil1) but were a 5w-40 and a 10w-40 you would get very similar shear rates.

If you compare the rate of shear of a 10w-40 semi-synthetic 100% petroleum basestocks (like many off the shelf oils) and a 5w-40 which was 100% pao or ester/pao synthetic you will get very different results.

The 10w-40 in this case would start to lose viscosity within 1000 miles and after 3000 miles it would have sheared to 10w-30 or 10w-20 in a high performance engine.

The 5w-40 (pao or pao/ester) oil would still remain in grade for 6-9000 miles with very low shear losses.

The reason for this is that synthetics (group IV or group V) are far more thermally stable than mineral oils (group I, II & III) which means that they require little or none of the very addative that shears - Viscosity Improvers.

These long chain molecules remain coiled at low temps and uncoil as temps rise helping the oil to "fight back" against viscosity loss. Remember, look at any oil data sheet and you'll find that all oils are thicker at 40degC than at 100degC!

The less of these added to an oil the lower the shear rate as the oil has nowhere to shear back to. As most of the top quality oils are made of synthetics and not petroleum basestocks, they are by their very nature more shear stable in use, protecting the engine at higher viscosities for longer.

To summerise what I've said, quality is important and should not be overlooked.

API and ACEA have a test called HTHS (high temperature high shear) where oils are tested at 150degC and then scored.

You can often find that for example that a synthetic 5w-40 has a better score than a non-synthetic 10w-60 and this is totally down to the quality of the oils basestocks!

I have some interesting comparisons but maybe for another day.

Cheers
Simon

 

Just realised that I probably did not explain this as well as I could have so, here's a further explanation of shearing (loss of viscosity) and why it occurs.

Viscosity Index Improvers.

An oils viscosity will decrease as the engine temperature rises. Viscosity Index Improvers are added to reduce this thinning. They are a key addative in the production of multigrade oils.

VI Improvers are heat sensitive long chain, high molecular weight polymers that increase the relative viscosity of the oil at high temperatures. They work like springs, coiled at low temperatures and uncoiling at high temperatures. This makes the molecules larger (at high temps) which increases internal resistance within the thinning oil. They in effect "fight back" against the viscosity loss in the oil.

"Shearing"

The long chain molecules in VI Improvers are prone to "shearing" with use which reduces their ability to prevent the oil from losing viscosity. This "shearing" occurs when shear stress ruptures the long chain molecules and converts them to shorter, lower weight molecules. The shorter, lower weight molecules offer less resistance to flow and their ability to maintain viscosity is reduced.

This shearing not only reduces the viscosity of the oil but can cause piston ring sticking (due to deposits), increased oil consumption and increased engine wear.

Like basestock quality, VI Improvers also vary in quality. The best quality ones are normally found in synthetic oils (Group IV - PAO / Group V - Esters) and it is important to understand that the less of these in the oil the better the oil will stay in grade.

Which oils require more VI Improvers?

There are two scenarios where large amounts of these polymers are required as a rule.

Firstly in "wide viscosity" multigrades. By this I mean that the difference between the lower "W" number and the higher number is large for example 5w-50 (diff 45) and 10w-60 (diff 50) are what is termed as "wide viscosity" oils.

Narrow viscosity oils like 0w-30 (diff 30) or 5w-40 (diff 35) require far less VI Improvers and therefore are less prone to "shearing".

Secondly, mineral and hydrocracked (petroleum synthetic oils) require more VI Improvers than proper PAO/Ester (Group IV or V) synthetic oils as they are less thermally stable to begin with and this is due to the non-uniform molecules in petroleum oils as opposed to the uniformity of synthetics built in laboratories by chemists.

It is a fact that some synthetics require little or no VI Improvers to work as a multigrade due to their superior thermal stability.

How to identify a good "shear stable" oil.

API and ACEA both conduct tests called HTHS (High Temperature/ High Shear) and all oils carrying these specifications are tested and scored.

For all oils, these test results are available however, they are often ommitted from the oils technical data sheet! Oil Companies have a tendency to publish the figures that they want you to see and therefore you often need to dig further or ask for certain information when comparing the performance of various oils.

High-Temperature/High-Shear

This test is a simulation of the shearing effects that would occur within an engine. In fact, it's actually designed to simulate motor oil viscosity in operating crankshaft bearings.

Under high stress conditions where shearing can occur, the VI Improvers (polymers) break down. As they do, the viscosity of the oil decreases. This is what the High Temperature/High Shear test checks for.

The HT/HS test is measured in Centipoise (cP) as the Cold Crank Simulator test is. However, in this case, because you're hoping for the least loss of viscosity with an increase in heat and stress, you want the cP value to remain high.

Each SAE multi-viscosity grade has a specific lower limit for the HT/HS cP value. If a multi-viscosity oil cannot achieve a cP value above that limit, it cannot be classified under that viscosity grade. For instance, according to the SAE specifications, an oil must achieve an HT/HS cP value of 3.7 or higher in order to be classified at the 15w40 viscosity grade.

The thinner the oil the lower the number.

That's better.

Cheers
Simon

 

Simon,

I recall you posting a list of HTHS numbers on a previous thread. Castrol RS 10W-60 came out looking very poor indeed. If you look at the same oil on the Castrol Australia site however the HTHS number is much higher.

http://www.castrol.com/liveassets/bp...tic_10W_60.pdf

Is it the same oil sold in the UK and Australia or is there a misprint on one of the datasheets?

Andrew

 

Hi Simon,
I don't disagree with anything you say,what I was trying to do was simplify things a little by keeping oil types out of it...by as you say you can't really because the fully synthetics behaviour is different. Its this falling out of grade issue that is a player as well IMHO...Some get lucky using inferior oils BECAUSE they don't drive hard enough to cause a big fall out of grade..or they change oil very frequently so that they get away with it...My dark side tells me to use a 10w base just in case it shears towards a 5w before I change oil...even when using the synths!...Paranoia!...The best synthetics are the best option IMHO as they provide the most stable viscosity under use...and are able to operate in grade at the higher temps/loads than semis are...
As to Bob's question, hi Bob,it's interesting that you find the castrol to give good results during it's time in the car...it must have a very good additive package ...and a very good ultra cracked base...but I would still err on the side of safety and go for a fully synth...Have you ever thought of using Millers 10/60 back to back as a comparison with the castrol?....Imho the 10/60 is a good grade to use if your getting into high temps...but as Oilman says, why use the "thicker" grade if your temps are resonable as the heat disipation/cirulation should be good enough using a 50 rated oil....Personnaly I've also never liked using oils with such a wide range of grade as it must be quite a feat to engineer the oil that way...so stability has to be an issue...the narrower grades being more likely to stay in grade IMHO...but then if they fall back to a 50 say with hard use then thats not so bad!....
Certainly with your engine spec I'd advocate 10/15lower to upper 50-60...the 40 would be too marginal IMHO in the Scooby ...imagine it falling to a 30 or 20 with high loads/ temps....No thanks!

 

Hi Oilman,
What are the effects on the engine if for some reasons different oil viscosity/brand/type is poured into the engine to top up oil level?

Chan

 

I buy and sell the stuff and the UK data sheets show 3.7 as the HTHS.

here's the link to the sheet on the Castrol Uk website.

http://129.35.64.91/bpglis/lubtds.ns...B?OpenDocument

I can only assume that the Australian one is closer to the TWS spec which seems to be a better oil.

Cheers
Simon

 

Oila can be mixed but they will create an "odd" viscosity if different. Addative packs vary and so does quality.

The main point is mixing a fully with a semi will lessen the benefits of the fully.

Cheers
Simon

 

And from the Italian site
http://www.castrol.com/liveassets/bp...la_RS10W60.pdf

Also take a look at this over at bobistheoilguy
http://theoildrop.server101.com/cgi/...c;f=1;t=010100

Just wondered if you had any contacts at Castrol who could shed any light on the differences between UK Castrol RS and those from other countries.

Thank you.

Andrew

 

...just to speculate, comparing a V300 5W/40 with same series 10W/40 means the first includes more viscosity improvers to achieve the wider viscosity, VI are less stable in HTHS conditions, so the conclusion is the 5W/40 can't protect in the end your engine the same with the 10W/40, however they both have 40 as high viscosity index!
Which leads me to the conclusion some of the assumptions of the profs regarding 0 or 5W in Subaru engines are based in the above theory!
Or am I wrong?
And if yes why Motul doesn't suggest mixing 5W/40 with every other V300 series oil when the others are mixeable? (Actually isn't reccomended from chemists to mix oils with different viscosities even if they are same brands/series but this is a different story).
JIM

 

with the NEW range of 300V (which has a slightly differing formula from last years...........) - MOTUL now do not recomend any cross mixing of differing viscosity

hope this helps, alyn

 

delayed replies to the questions coming up.

Yes NF is octane booster

Normal driving oil temps are between 90 and 95 degrees, during heavy use they drift up to just under 110 degrees, if they get any where near 115 I cool it. measured in the oil gallery just above no 3 cylinder wich is the main oil feed to the drivers side bank.

session timing limited by oil temperature rise, typically 20-30 mins although temps are normally still ok at that.

BHP above stock, well its not stock, do you mean a eurospec car or a JDM, its circa 250 bhp above euro spec and 200 bhp above JDM Sti.

Engine is custom, semi closed deck block based (MY2001 onwards), rest of the spec is posted above.

bob

 

Andrew,


Castrol UK have confirmed HTHS, although I still not believe it is correct, and they had no knowledge of the Australian version.

Per Simon the WRC team use 5W40 rather than say a 15W40, which for Redlines racing ester based synthetic could be termed a 40wt. However the Motul 5W40 uses a high polymer ester and claims 0% shear loss. A mineral would have to start with say a 15WT base and add vis improvers to blend a 15W40, although the oil after thinning will then start to thicken which is more of a problem.

The 0W 5W oils do give increased flow for cold starts not only getting oil around engine but also the aw additives. As thin oils cool better due to flow then they will not thin as much as a thick oil. HTHS is at a fixed temp.

The Castrol 10W60 makes no sense whatsoever based on Castrol UK published HTHS.

 

Some cutting and recycling of info there Simon, but some good info

Would you say in Bob's instance a thinner oil would be better, to ensure a more fluid / quicker heat transfer past the rotating / frictional parts would be the aim, or a slightly thicker one (at operating temp) to cope with the much higher shear forces placed on the oil? Genuine question. I know Bob and others with big BHP have been using Motul long term with no issue. Although its 15w it looks like water a room temp?!

MB