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1997 T/tb
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Discussion Starter #1
I like to change my oil at least every 6,000 miles.

so this weekend i put in some Mobil-1 (15w/50) for high performance turbocharged engines.

its not reccomended by subaru, for some reason they only reccomend 10w/40semi synthetic, i have no idea why, personally i would never use semi synth on a FI engine!

however, the knockin on cold start up in the morning has become considerably quieter, and the engine is running sweeter than ever! and so much smoother through the rev range!

im hoping it wont cause any problems using a thicker oil (i cant see why it should)

what does everybody else use?

Frazer
 

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1997 T/tb
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Discussion Starter #4 (Edited)
15W-50 is too thick IMHO
for what reason?.... "its too thick" doesnt help much.....

it is recomended for turbocharged high performance engines.
my car is a 2.0l turbo. (Japanese import) with around 260bhp (i think) which kinda puts it into that bracket.

the last oil i put in was mobil-1 10w/40 (high milage) the stuff you guys get in wallmart.... its not available over here!
it ran well but seemed to be very tappety, and knocked loud in the mornings.

with this oil it runs much better....... can anyone explain?
 

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1997 T/tb
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Discussion Starter #5
this is on the data sheet from Opie oils...

Mobil 1 15W-50 is recommended for all types of vehicles, suitable for use in high-performance turbo-charged, supercharged gasoline
and diesel multi-valve fuel injected engines found in passenger cars, light vans and trucks.

· Mobil 1 15W-50 is suitable extreme engine stress conditions, where conventional oil often can’t perform.
 

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2008 2008 2.5i-2018 XT
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for what reason?.... "its too thick" doesnt help much.....

with this oil it runs much better....... can anyone explain?
What oil again does Subaru recommend? There is simply no advantage going to a thicker oil and the disadvantages are higher fluid friction and less power.
 

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2000 S-Turbo Manual
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118 Posts
I'd personally go with the 5W-30 Edge, or Mobil-1 0W-40.

The former is recommended by Subaru, largely because it helps (a leeeeeetle!) with fuel consumption.

I'd be tempted to use 0W-40 for a highly tuned (>100bhp/litre) engine - round the bearings/turbo slightly quicker on start-up, and less likely to degrade after 'fast-road' action.

And would reserve 15w-50/10w-60 and the like for track thrashing (which I don't do anyway).

In reality you can probably safely use 0W-20 fully synth in any road-going car and not risk premature wear but it is such a hard area to actually get useful evidence (even used engine oil assays have significant confounding factors) that recommendations are largely "IMHO" rather than backed up with evidence....

A quiet engine doesn't necessarily mean one that is likely to last longer - I'm sure if you put toffee sauce in the sump it would be nice and quiet (and smell good too!) but might struggle to reach the end of the road.
 

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2000 Forester
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Technically, as far as I have been informed, the thicker the oil, the more heat, stress and abuse the oil can with stand. ie. semi trucks and race engines use fairly thick oil compared to the conventional commuter car. Though, I guess I can't say why it would run smoother.
 

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1997 T/tb
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Discussion Starter #9
What oil again does Subaru recommend? There is simply no advantage going to a thicker oil and the disadvantages are higher fluid friction and less power.
other than smoother and less noisy???

id say that was an advantage.... getting the same fuel consumption too

Subaru recommend 10w/40 semi synthetic. I have no idea why..... when an oil says semi synthetic, what it actually means is there is a small amount of synthetic addative added to a mineral oil.....

with a turbocharged engine, the addatives are broken down very quickly. it will cook a mineral oil. as the mineral oil is comprised of lots of different oils, the heat of the turbo will burn off all of the light boiling parts which firstly leaves you with a heavier oil, and also the burnt oil forms contamination. in the remaining oil the detergent then gets used up instead of cleaning the engine of normal contaminants.

synthetic oil, as it's all the same molecule in the base fluid doesn't suffer in the same way, and has other advantages in that it holds its viscosity better at high temps naturally.

so why do Subaru recommend a semi -synth in our cars?

today it has been 8 dergrees outside (46 fahrenheit if my maths is correct) so its getting pretty cold, and it seems my car has never run better. i cant explain why thicker oil has made a significant differance,.... It just has!
 

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99 UK S-turbo
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Bearing clearences and running surfaces are designed to go hand in hand with oil spec, as are oil gallery diameters, pump dimensions (including the pressure relief valve) etc

Thicker oil will reduce fuel economy, I would guess you'll see about 6-7% worse - maybe more if the PRV can't cope so you end up increasing oil pressure as well, also it will take longer from cold start to get the more viscous oil into the bearings/cam followers etc.

You may also end up running LOWER oil pressure at your bearings (if the PRV can maintain designed oil pressure at pump outlet) due to the loss in pressure through the oil galleries.

Personally I wouldn't have done it!

Of course I'm sure you're few hundred mile test so far is more meaningful than all Subaru's engineers could achieve through 100,000's of miles of test and dev't, and that they penny pinched to semi-syth with no testing at all and are just hoping that no problems occur, subaru's legendary reliability is purely an accident of circumstances and not a result of 100's of hours of intelligent dedicated engineers work!

You've also read too much marketing bull on the benfits of spending more money on synthetic oil's I'm afraid, the life benefit means you can use it longer, the semi would be fine to Subaru's service interval, so running synth means you can now circa double that, if you don't its a waste of money!

Simon
 

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1997 T/tb
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Discussion Starter #11 (Edited)
Bearing clearences and running surfaces are designed to go hand in hand with oil spec, as are oil gallery diameters, pump dimensions (including the pressure relief valve) etc

Thicker oil will reduce fuel economy, I would guess you'll see about 6-7% worse - maybe more if the PRV can't cope so you end up increasing oil pressure as well, also it will take longer from cold start to get the more viscous oil into the bearings/cam followers etc.

You may also end up running LOWER oil pressure at your bearings (if the PRV can maintain designed oil pressure at pump outlet) due to the loss in pressure through the oil galleries.

Personally I wouldn't have done it!

Simon

Simon

What do you run in yours?

i assume its a real thin synthetic considering the mods you have...

I have loads of different types of mobil 1 in my shed, (it comes free free from america) im just going through them all to see which one works the best. my reason for trying out this thick oil was to reduce the knocking on cold start up, and the tappet noise.

not entirely true on all the "marketing bull"... i was part of the "Oil Health Monitoring Program" out in Iraq.

all the military vehicles at the time ran on whats called OMD90 (oil mineral detergant) which is a semi synth manufactured by FUCHS. we tested loads of different oils and from our research heres what i leant,.... any synthitic oil (even the cheapest!) is better than any part / semi synthetic oil. Changing to fully synthetic has made a considerable impact to the cost (tax payers money!) and time wasted on over serviceing.

semi synth breaks down far too quickly in turbocharged engine... it lasts almost 3 times as long in N/A engines. I know this because i tested it, however i just dont know that much about the Subaru engines yet.


Frazer
 

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I run the oil specced for the 01 onwards cars, its the same engine, just Subaru shifted all their cars at 01 to 30weight, so using that, I do 7.5K miles a year, so do an annual service, don't bother with the 6 months now as yes its on the full synth as specced for 01on cars.

I agree full synth will save money IF you use the extended service interval it can manage, if you don't there is no point unless you've changed other aspects outside of Subaru's design parameters.

There is no evidence that semi-synth causes a problems in cars with water cooled turbos' as ours are, non water cooled (most if not all Diesels as per most your engines in Iraq at a guess) are more critical, and they also have 'soot' problems which further exacerbate the hot oil breakdown that we don't get in our non DI petrol engines. Diesels operating at high loads at low road speed (so tending to run higher coolant and oil temps) have always been the worst case scenario for oil (well ever since we got semi-synth and water cooled turbo's in gasoline engines in the early '80s anyway)

Simon
 

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2007 Forester
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I have a Forester 2007 model 159hp so what oil is the best for our car, i live in Greece and most of the time the temperature is hot and rarely in winter some times below zero for 2 or 3 days.
I started with liqui-moly 10-60 and now i use ENEOS 10-40 from Nippon Oil
 

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I suspect that car manufacturers don't radically change their recommendations for oil all that regularly - if only because if they say for 4 years that semi-synthetic is best then change their mind and say fully syn is better then all the high mileage people will say well you told me semi was adequate now you say it isn't. Now my engine is lunched and it's your fault.

Not long ago fully syn was the very latest thing now it's common. Having said that semi is probably way way better than mineral - esp on cold starts and fully is even better. I think the old argument you used to see on car and bike forums (fora?) about 'is synthetic better than mineral' (these things used to run into hundreds of pages) is now dead and everyone knows that syn rules.

Fully synthetic is best. Whether you stress your car enough to warrant the extra cost is arguable but very likely not provable. Personally I always use syn and now have it in the tranny as well because it's cheap insurance. It's my money to waste but Simon is quite right when he says it might well be marketing BS.

I always think my engine runs a little sweeter right after an oil change.
 

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1997 T/tb
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Discussion Starter #15
There is no evidence that semi-synth causes a problems in cars with water cooled turbos' as ours are, non water cooled (most if not all Diesels as per most your engines in Iraq at a guess) are more critical, and they also have 'soot' problems which further exacerbate the hot oil breakdown that we don't get in our non DI petrol engines. Diesels operating at high loads at low road speed (so tending to run higher coolant and oil temps) have always been the worst case scenario for oil (well ever since we got semi-synth and water cooled turbo's in gasoline engines in the early '80s anyway)

Simon
I totally agree, most of the engines were diesel a hand full of petrol engines. the heat and the sandy conditions were a contributing factor, so it really was "worst case Scenario" - funily enough the E-type jag engines did pretty well out there.

all oils were affected out there, braking systems, hydraulic systems etc.

the heat got so bad that it made landrover brake lines soft, so when you put your foot on the brakes the flexi hoses just balooned = No Brakes!!:rock:

My concern is the knocking in the mornings when its cold. although everyone says its normal, it certainly doesnt sound normal! - the thicker oil is an experiment (that seems to have worked). when the engine is hot it runs superb and real quiet. but it sounds like a 30 year old john deere first thing in the morning - i supose the only way to monitor is to fit an oil pressure gauge. - anybody know where the best place to tap in to monitor oil? it looks a tight fit to fit a sandwich plate between the filter

it seems from what has been said that semi synth oil was the recommendation at the time of manufacture, but now even though our cars have the same engine, the recommendation is fully synth, and maybe a liability issue will arise if they change their oil specs, even now synthetic oils are being improved, to this extended service / long life oil. - i certainly dont know what to make of that stuff!
 

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2008 2008 2.5i-2018 XT
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I suspect that car manufacturers don't radically change their recommendations for oil all that regularly - if only because if they say for 4 years that semi-synthetic is best then change their mind and say fully syn is better then all the high mileage people will say well you told me semi was adequate now you say it isn't. Now my engine is lunched and it's your fault.
Car oil specs are based on API (American Petroleum Institute) and ILSAC (International Lubricant Standardization and Approval Committee ). Doesn't matter if the oil is Group II, II+, III,IV, or V. That's the bottom line.
 

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1997 T/tb
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Discussion Starter #17
Car oil specs are based on API (American Petroleum Institute) and ILSAC (International Lubricant Standardization and Approval Committee ). Doesn't matter if the oil is Group II, II+, III,IV, or V. That's the bottom line.
I dont understand what you are saying. what is the bottom line?

the same engine went into a newer model forester, however the oil specification changed from semi synth to fully synth.

the statement that was made is that subaru cant go back and say "we now dont recommend semi synth in the older foresters".

the recommendations remained the same
 

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Discussion Starter #19
Car has been left all day....

just started it up to go to the shop, and its just as noisy as it was previously!

Bang goes that theory!

SO...... if its normal... what causes the dreadfull knocking noise! and can it actually be rectified?

i have been a mechanic for 15 years and hardly ever touched Subarus (theres probably a damn good reason for that!) but im still not convinced this noise is a normal characteristic for this engine.
 
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