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Cadillac ATS Technical Discussion Forum Discussion, turbo timers ? in Cadillac ATS Discussion Forums; How much is it a concern to turn off the car with a hot turbo ? I try to let ...
  1. #1
    transam00 is offline Cadillac Owners Fanatic
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    turbo timers ?

    How much is it a concern to turn off the car with a hot turbo ? I try to let it cool down for 30 sec to a min. , I'm to lazy to sit in the car any longer . Any thoughts on this .

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    Bertha D Blues is offline Cadillac Owners Fanatic
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    Re: turbo timers ?

    One day I had a lapse in judgment and decided to see how fast I could go in my driveway, from a standing start up the hill to my garage. I shut down at 50 mph (it’s a long driveway) and parked the car in the garage. About fifteen minutes later I went into the garage and could smell the hot turbo or hot whatever was close to it. I didn’t find any damage but I always allow cool-down time now. Fortunately, the last half mile of my daily commute accommodates a cool down, shenanigans aside. Bert

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    rsingl is online now Cadillac Owners Fanatic
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    Re: turbo timers ?

    I have never owned a turbo car but I am on my third turbo-diesel pickup. When running hard (sustained interstate run, steep mountain grades) I always let it idle for a couple of minutes before shutdown but diesels tend to cool quickly at idle. Any time you have the turbo very hot a minute or two of cool down is a good idea to prevent "coking" of the oil in the bearing area. This is probably more important with DEXOS spec oil as opposed to something closer to full synthetic.

    Damage to the turborcharger from hot shutdown is generally not instantaneous but results in a slow death from deposits building up in the oil feed/drain line which over time will restrict oil flow to the bearing. It is not unlike cholesterol/plaque buildup in arteries and neither is healthy. If running around at 30 MPH you can safely shut off without concern but if you have been running the engine hard a couple of minutes at idle would be a good idea.

    Final word is it will make it through the warranty period OK even if you ignore proper shutdown as long as you don't constantly run it hard and then shut down instantly, if normal operation without cool down resulted in rapid failure then it would have a turbo timer from the factory. But if you plan to keep it for awhile (or do a favor for the next owner) treat it properly.

  5. #4
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    Johnm05 is offline Cadillac Owners Fanatic
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    Re: turbo timers ?

    Doesn't our car circulate coolant even after the shut down? I can hear it and feel it in the coolant line. On mine it usually does it every 30 sec at first and then longer intervals after.
    SLA likes this.

  6. #5
    ontogenesis is offline Cadillac Owners Fanatic
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    Quote Originally Posted by Johnm05
    Doesn't our car circulate coolant even after the shut down? I can hear it and feel it in the coolant line. On mine it usually does it every 30 sec at first and then longer intervals after.
    I want to say all cars do that as a result of the thermostat being operated by a bimetallic spring. As it heats up the spring shrinks and allows coolant to move from the top of the engine into the radiator and once cooler fluid begins to flow over the spring, it's cooled down and closes. At least that's what I'm familiar with in sbc's... I'm pretty sure that the oil doesn't do anything like that and the turbo is cooled by engine oil, so when the car shuts off, the oil pump stops pumping and the oil that doesn't drain out of the turbo sits there and cooks or cokes up (think of coking as taking a can of coca cola and heating it up until the water begins to evaporate and the coke becomes syrup....that's what oil coking is)

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    SLA
    SLA is offline Cadillac Owners Fanatic
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    Re: turbo timers ?

    Most modern turbos are water cooled. Like john said, the water still circulates after the engine is shutoff. You don't have to let the engine cool down before shutting it off to let the turbo cool, but I would also not immediately shut the engine off after running it hard or revving the engine. Imagine what would happen if you had your turbo spinning at 100k plus rpms and then cut off its oil supply. Just make sure you drive normally for 10 seconds or so after running it hard before shutting the engine off.

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    ontogenesis is offline Cadillac Owners Fanatic
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    [QUOTE="SLA"]Most modern turbos are water cooled. /QUOTE]

    I stand corrected...guess I still have a ton to learn about turbos....the coking part is still accurate tho...

  9. #8
    rsingl is online now Cadillac Owners Fanatic
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    Re: turbo timers ?

    [QUOTE=ontogenesis;12702193]
    Quote Originally Posted by SLA
    Most modern turbos are water cooled. /QUOTE]

    I stand corrected...guess I still have a ton to learn about turbos....the coking part is still accurate tho...
    Exactly. Coking can still be an issue even with turbos that have a water jacket around the bearing assembly. The cooling helps control heat but shutting off the engine with a very hot turbo is going to cook (and thus "coke") the oil in the bearing area. My last two pickups have water cooling of the variable vane turbo bearing assembly but the engine must still operate at idle for a couple of minutes after working hard to avoid coking.

    It takes awhile for this buildup to occur so you won't notice the problem until the oil supply to the bearing is reduced enough to starve the bearing. Water cooling helps to manage the problem so that no problems will occur with immediate shutdown in "normal" operation but shut down heat is still excessive if the engine has been under high load.

  10. #9
    SLA
    SLA is offline Cadillac Owners Fanatic
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    Re: turbo timers ?

    Drivers of cars really don't have to worry about oil coking. Advances in oil technology have pretty much eliminated any worries about that.

    It can be an issue in diesels still because of the the sustained high EGTs seen during towing.

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