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Thread: Engine oil

  1. #51
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    Quote Originally Posted by Jim_S-V6_2004 View Post
    .
    Does engine oil circulate through the turbos Vic?

    Better remove them along with the DPF and EGR!

    .

    It does on BMW from my experience Jim so I would assume it does on the Jaguar. It's the supercharger that you have to change the oil on I think but I am not sure as they are out of my price range.
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  2. #52
    Senior Member payno's Avatar
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    Quote Originally Posted by ducmon View Post
    It does on BMW from my experience Jim so I would assume it does on the Jaguar. It's the supercharger that you have to change the oil on I think but I am not sure as they are out of my price range.
    Correct the turbo has a direct oil feed from the engine and the SC has its own oil as a self contained unit
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  4. #53
    Senior Member Jim_S-V6_2004's Avatar
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    Thanks Vic, ducmon, payno.

    I knew the STR has its own oil supply, but hadn't thought about the diesel turbos.

    Some more questions on this then...

    So this means that the diesel S must burn engine oil, albeit slowly when everything is normal, right?

    It also partly explains why fresh oil in diesels with turbos turns black very quickly even though it's still in good condition?

    So it's even more important to dip the oil level regularly, not only to check for diesel dilution?

    .

  5. #54
    Senior Member Neilr's Avatar
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    Quote Originally Posted by Jim_S-V6_2004 View Post
    So this means that the diesel S must burn engine oil, albeit slowly when everything is normal, right?

    It also partly explains why fresh oil in diesels with turbos turns black very quickly even though it's still in good condition?
    Burn oil because it has a turbo or two? Not if everything is in good shape and you don't thrash it and then turn it off immediately. The heat from the uncooled turbo can apparently coke some oils. Most turbos lubricate the shaft with the engine oil flow, so just like at the pistons, some oil could be lost at the seals.

    Why a Diesel engine turns its oil black quickly: Diesel is a more traditionally "dirty" fuel and the new oil has fresh detergents and it is dissolving and keeping soot, dirt and other combustion contaminants in suspension to be ditched at the next oil change. Best to change the oil before the oil is no longer able to cope with the contaminants in the system (engine or in the oil already).
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  6. #55
    Senior Member paulkebab's Avatar
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    Jim, AFAIK all turbo's have their own oil supply as they can run above 100,000 rpm (yes that fast) and the heat generated is immense, they would probably self-destruct in seconds without oil. Also when a turbo 'blows' it's usually one of the oil seals that fails, so the oil supply starts leaking directly into the exhaust with obvious tell-tale results.
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  7. #56
    Senior Member martin.rowe's Avatar
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    Modern oils can be too good, and can lead to polished bores, particularly on short journeys. How many drive their car hard enough to need better lubrication ?. many engines that we strip in the w/shop have lost compression / burning oil, not due to wear, but down to polished bores which stops the rings sealing correctly.
    Fully synth oils were introduced to cope with extended service intervals. We were told that these new oils would last 50k miles, but who leaves it in that long, only the HGV guys I think.
    Its food for thought.

    Quote Originally Posted by Jim_S-V6_2004 View Post
    .
    Hi Martin.

    How do you mean, because it cleans crud and might expose old leaks?

    Or just the cost?

    And do you know why Jaguar advise against synthetic oil for the AJ6 engine?

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  8. #57
    Senior Member Jim_S-V6_2004's Avatar
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    Quote Originally Posted by Neilr View Post
    Burn oil because it has a turbo or two? Not if everything is in good shape and you don't thrash it and then turn it off immediately. The heat from the uncooled turbo can apparently coke some oils. Most turbos lubricate the shaft with the engine oil flow, so just like at the pistons, some oil could be lost at the seals.

    Why a Diesel engine turns its oil black quickly: Diesel is a more traditionally "dirty" fuel and the new oil has fresh detergents and it is dissolving and keeping soot, dirt and other combustion contaminants in suspension to be ditched at the next oil change. Best to change the oil before the oil is no longer able to cope with the contaminants in the system (engine or in the oil already).
    .
    Ok.

    I was thinking of the temperature of the turbo shaft Neil, that at those temperatures it must boil some of the oil as it passes over the shaft and its bearings?

    Are the diesel S Type turbos dual shaft, to provide some heat protection, or single?
    .
    Quote Originally Posted by paulkebab View Post
    Jim, AFAIK all turbo's have their own oil supply as they can run above 100,000 rpm (yes that fast) and the heat generated is immense, they would probably self-destruct in seconds without oil.
    ...
    .
    Right. I just hadn't spent any time wondering where they got oil from.
    .
    Quote Originally Posted by paulkebab View Post
    ...
    Also when a turbo 'blows' it's usually one of the oil seals that fails, so the oil supply starts leaking directly into the exhaust with obvious tell-tale results.
    .
    Yes that's pretty much what I imagined Paul. I thought in the back of my mind that some burnt oil from the turbo shaft(s) must find its way back into the sump, blackening the sump oil.

    Thinking more deeply, the oil in my turbo diesels, the Merc and 2 Peugeot 306's, got very black almost immediately after their oil changes.

    Whereas I didn't notice that in the couple of older non-turbo diesels that I worked on, their oil was certainly much darker brown but not black.

    Good info, thanks everyone.

    In passing, the turbo on my infamous Merc whined like a New York 1950s Police car undulating siren. It had always done that and I quite liked it.

    Am I right in thinking that that is due to carbon building up on the vanes?

    .

  9. #58
    Senior Member Neilr's Avatar
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    Quote Originally Posted by Jim_S-V6_2004 View Post
    I was thinking of the temperature of the turbo shaft Neil, that at those temperatures it must boil oil?
    Well it depends on the inlet temp and the flow rate. When the flow stops but the turbo is too hot, that's when the problems start. The shaft gets hot from rotating yes, but the main source of heat is from the exhaust gases used to turn the drive side of the turbocharger.

    Quote Originally Posted by Jim_S-V6_2004 View Post
    Right. I just hadn't spent any time wondering where they got oil from.
    If it is not the engine sump then where? Most turbo cars don't have a separate oil system do they? Many turbos are also water cooled, I expect also from the engine cooling system.

    Quote Originally Posted by Jim_S-V6_2004 View Post
    In passing, the turbo on my infamous Merc whined like a New York 1950s Police car siren.

    Am I right in thinking that that is due to carbon building up on the vanes?
    I would guess that the highest likelihood is worn bearings unless that application has a known weakness that leads to whinning.
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  10. #59
    Senior Member Jim_S-V6_2004's Avatar
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    Quote Originally Posted by martin.rowe View Post
    Modern oils can be too good, and can lead to polished bores, particularly on short journeys. How many drive their car hard enough to need better lubrication ?. many engines that we strip in the w/shop have lost compression / burning oil, not due to wear, but down to polished bores which stops the rings sealing correctly.

    Fully synth oils were introduced to cope with extended service intervals. We were told that these new oils would last 50k miles, but who leaves it in that long, only the HGV guys I think.
    Its food for thought.
    .
    Oh, that's unexpected Martin.

    What's a typical mileage of those cars?

    And can we leave synthetic oils (that's mostly what we think we're buying as you can see above in this thread) in for say 10k miles without worrying, since many people just forget or are too busy driving long distances for work or let the miles slip by between changes?

    I change mine every year or 5k miles, it's just to know from your experience.

    .

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