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Semi synth to Fully synth?

Discussion in 'A4/S4 forum(B5 Chassis)' started by NineNails, Jul 30, 2010.

  1. NineNails
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    NineNails Proud sponsor of the snack food industry

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    I'm pretty sure now that previously my 1.8t (AJL) has had semi synth oil in it. Is it ok to swap to the correct fully synth or will it cause problems?
    Thanks
    Si.
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  2. Matt82
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    Matt82 Active Member

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    no reason for that to cause issues
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  3. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    Although you might want to give it a good flush, as if its run semi-synth oil on longlife servicing its going to be particularly manky inside.
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  4. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    Semi synth is supposedly better for older angines, and cheaper, just change it more regularly
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  5. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    i've heard people say that, but imo semi-synth oil has no place in a turbocharged engine, and theres no real reason why semi would be better anyway.
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  6. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    Likewise longlife oil but that doesn't stop Audi recommending it. Personally I'd rather use semi synth and change it every 6k
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  7. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    "long life" oil is just normal synthetic oil...

    I use synthetic and change it every 5k
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  8. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    Sorry meant longlife oil/longlife servicing. Seems pretty OTT to use this oil and then change it every 5k especially when our engines were designed this oil didn't even exist, but each to their own.
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  9. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    Its only a few quid more than semi-synth oil, and given its importance in the engine, plus the problems these engines have with their oil, i'd rather spend the small amount every 5k to change the oil, than risk the engine dying due to sludge or whatever.
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  10. Jp-tqs
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    Jp-tqs Member

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    For me, semi-synth cheapo oil = new oil pump at great expense and inconvenience! The 1.8t isnt a bullet proof engine in my experience, oil seems to be its major weak spot. Fully synth and regular changes from what i can work out is the best way to prevent problems. Big diference in noise of my engine since i changed too.
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  11. mwarrey
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    mwarrey Member

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    My 1.8t had synta semi-synthetic all its life and got to 170k with no issues at all, my previous golf over 200k on synta. so can't be too bad. Long life servicing rather than the oil itself seems to be bad news for sludge issues as well as low mileage, short journeys and prolonged lack of use.
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  12. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    The S4 also specified 10w40 semi-synth before long-life servicing came in... Would you run your S4 on it?
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  13. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    Yes, as long as it was changed every 6k or so. People only get into difficulties when they chip the **** out of their turbo's then wonder why reliability goes down the pan. If your car is standard and you change the oil every 5-6k then there is no reason to go fully synth, but obviously it can't hurt. As said AVS servicing is the reason turbo's die early. Apparently the sludge issue can be worsened by mixing semi synth with fully synth i.e. when topping up between changes with a different type of oil.
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  14. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    Well each to their own i guess.

    A gallon of synthetic oil is only a few quid more than a gallon of semi, and regardless of whether you think the engine needs it, it IS better oil, so i'll be sticking with the synthetic stuff. If you want to save yourself 3 quid every 6 months then thats your call.
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  15. Oranoco
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    Oranoco Well-Known Member

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    Don't forget to factor in the fact that a very large proportion of "Fully Synthetic" oils are actually not what they say on the packet and are a hydracracked mineral oil, for an engine oil to be genuinely "Fully Synthetic" it must be a PAO (Poly Alpha Olfin) or ESTER based oil.

    For me it's fully synthetic and changed with filter every 5k miles
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  16. Matt82
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    Matt82 Active Member

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    i dont think ive ever (knowingly) bought 100% man made synthetic oil, but with my vag turbo cars (now on a golf 1.8t) ive used VW's quantum platinum. in my 2.0 16v golf it dropped the oil temp more than any other "synthetic oil" ive use. in the turbo ones (S4 and 1.8t, both known for running extremely hot and being hard on the oil) it hasnt burnt any oil at all so im sticking with that and its bargain cheap too
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  17. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    hydrocracked mineral synthetic is still an improvement over the lesser grades, its just not as good as group 4 and 5 oils.

    Some of the PAO and Ester based oils are blended with group 3 (hydrocracked) oil anyway, so even though it says PAO on the bottle its still not pure.

    A lot of the rumors floating around about synthetic oils making old engines leak is down to early synthetic oils (like the original Mobil1 forumula) being pure PAO, as PAO has a tendancy to shrink rubber seals.

    Most modern "proper" synthetic oils tend to be a blend of PAO and Esters, because esters tend to swell seals, and a balance between the two gives you no change. The lesser synthetics can be either a blend of hydrocracked oil and PAO/Ester types, or streight up hydrocracked oil for the cheapest stuff.

    Pure PAO/Ester oil is likely to be 50quid or so a gallon, blended stuff somewhere in between and the hydrocracked stuff is what you get from halfords or your local motorfactors budget brand for 20quid.
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  18. Jonion
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    Jonion Member

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    over the years it's apparent that most oil leaks caused by synths in older/higher mileage engines is mostly simply due to the better cleaning abilities of the synth, it simply cleans away a lot of the old sludge and goo that mineral and pseudo-synth oils leave and use to actually keep bad seals sealing.
    Wash this **** away and the bad seal is exposed to slippier oil (not different viscosity) which then leaks, causing people to think the synth oil is no good as the engine they thought was still good now leaks.

    Triple ester synth is what I use in my hard worked 175k m car.
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  19. THE MONSTER
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    THE MONSTER Member

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    I have said many times on here I use Mobil 1 0-40w and use it mainly for the Turbo as already stated about the need to use these Oils for that reason alone..

    I think that by just putting in a type of Oil that makes your car leak you have issues anyway...again just my opinion..
    Last edited: Aug 3, 2010
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