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Thread: 4 sec knocking after oil change

  1. #11
    Still Plays With Cars Loren's Avatar
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    A little "rattling" or "tapping" on a cold start after an oil change is totally normal. How your ear perceives that is highly variable, I'm sure. And there are lots of things that can be making noise due to lack of oil pressure on a modern engine. There are the traditional noises like bearings on the crankshaft (not likely, as there's still plenty of oil there), and "piston slap" from the not-warmed up piston scraping against the not-quite-lubricated cylinder wall. And we have a timing chain, so there's potential for noise there with no oil pressure. And we have an oil-operated variable valve timing control system that could potentially make some noise while oil pressure comes up. It takes oil pressure 3-5 seconds to build up.

    Protection from this kind of thing is what synthetic oil is good for. You have a good film of synthetic oil on all of the moving parts even after draining the oil. Something might have enough clearance to rattle a little bit, but it's not going to hurt anything. A 900 rpm idle speed is 15 revolutions per second. Your four seconds adds up to 60 revolutions of your engine, probably less.

    There are also other things that make noises under the hood that you might not notice if you're not thinking about them. The ABS pump does a self-test/purge cycle at some point after startup. Fuel system purge control solenoid. It's hard to say for sure what you're hearing. But if it's only happening for 4 seconds at startup, and only immediately after an oil change... it's not a problem.


    Last edited by Loren; 06-18-2018 at 10:16 PM.
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    Fummins (06-18-2018)

  3. #12
    Quote Originally Posted by hflaisher View Post
    I dont think it is normal. No car should make any grinding/knocking sound on startup for any amount of time. Perhaps its acceptable for under a second after a change, but under normal conditions, it should not happen. I will update when I next change, and it will be mobil 1 from now on if it solves this problem. Thank you for your opinions.
    It's possible you're hearing something different than I have been hearing over the last 4 years? But I doubt it. There isn't much insulation under the hood and no huge piece of plastic and Styrofoam engine cover on these cars to help muffle noise. As mentioned, it's likely the cam timing adjuster thing.
    This kinda reminds me of a video I saw on youtube where people were staring at their 3cylinder Mirage engine shaking(like normal) at idle saying it's not supposed to do that and there's a problem with the car. I'm not sure if it was joke or not?

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        click to view fuel log View my fuel log 2014 Mirage SE wussie cvt edition. 1.2 automatic: 37.7 mpg (US) ... 16.0 km/L ... 6.2 L/100 km ... 45.3 mpg (Imp)


  4. #13
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    No, the engine is smooth and quiet. Just after this oil change and sometimes right at start. I will report back after next oil change w/Mobil 1. I doubt it's the oil though, probably just needed time to get the oil circulated. maybe it would be wise next time to start seconds after putting the oil in the valve cover, before it has drained down to the pan, I think I will do that next time.

  5. #14
    Still Plays With Cars Loren's Avatar
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    Here's something you can do that will help.

    Some cars are good for this. If you have the push-button start, probably not. But, after your oil change, on that first start, just bump the starter. Enough to turn it a little bit, but not enough for it to actually start. Do that a few times. It gets the oil pump turning, and moves some oil around. You're still getting those "dry" engine revolutions, but they're happening at starter speed (300 rpm) rather than idle speed (900 rpm).

    If you're REALLY anal about it, do whatever you need to do to disable the ignition or fuel system so the engine CAN'T start. Then you can crank it for a few seconds before starting. On an old car, that was easy, just disconnect the coil wire. The Mirage is surely coil-on-plug, so you'd have to disconnect three coils.

    It's all overkill, though. Every engine since the dawn of internal combustion has been doing cold starts, and doing a "dry" start after each oil change. Synthetic oil eliminates almost all of the wear associated with that. It's really, really not something that you need to worry about. Really.
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    thanks, on my Geo Metro, I always used to disconnect the coil wire and ground it after an oil change, then cranked until the oil pressure light went out.

    Unfortunately with coil on plug, I wasnt sure how to safely do that. If someone knows for sure, plmk. Just ground each plug wire? If I knew it was safe and the proper way to do it, I would.

  8. #16
    I'd say start pulling fuses til it doesn't start but probably not a great idea. If you kill spark and not fuel you'll probably end up back on here saying your car won't start and it smells like fuel. You could just jump your starter solenoid, or find your starter relay(if it has one) and jump it at the fuse box? There's more than one way to do it.

    Personally I still think you're worrying way too much about this unless you just really like changing your oil every week or something?

    Starting the engine after an oil change before the oil reaches the bottom of the pan might be doing more harm than good. Might be kinda hard on bearings and whatnot. I'd prefer to let it sit for a few minutes before starting it. The oil pump picks up oil from the oil pan not the top of the engine. The noise you're hearing is caused by oil starvation. Oil gets picked up from the pan by the oil pump, and pumped and spat all over the places it needs to go.

    Seems like most (if not all) engine failures that I've heard of on this forum were from 2014's that didn't get the recall to prevent overfueling on startups.

        __________________________________________

        click to view fuel log View my fuel log 2014 Mirage SE wussie cvt edition. 1.2 automatic: 37.7 mpg (US) ... 16.0 km/L ... 6.2 L/100 km ... 45.3 mpg (Imp)


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  10. #17
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    thanks, I like the idea of fuses, just need to check that I wont get some voltage buildup somewhere and fry the ign system.

  11. #18
    Moderator Eggman's Avatar
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    I'd advise against altering your ignition. I would expect the safer route would be to disable fuel delivery, not spark. Could this be achieved by simply unplugging the wiring to injectors?

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 49.6 mpg (US) ... 21.1 km/L ... 4.7 L/100 km ... 59.5 mpg (Imp)


  12. #19
    Senior Member Top_Fuel's Avatar
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    You're probably worrying too much. I change my oil and just fire it up. It rattles for a few seconds and it's fine. I have the most tested engine oil of probably any Mirage on the planet...and my oil is fine. And on top of that...I even use 5W30.

    Now...if you want to crank the engine without starting it, the easiest way to do this is to floor the accelerator and then crank it. This is called Clear Flood Mode. Here's a demo...



    Just be ready to take your foot off the accelerator quickly because sometimes a car may still fire and start under these conditions. But I've never had it happen in all the times I've used this trick.

        __________________________________________

        click to view fuel log View my fuel log 2015 Mirage ES 1.2 manual: 52.2 mpg (US) ... 22.2 km/L ... 4.5 L/100 km ... 62.6 mpg (Imp)


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  14. #20
    Still Plays With Cars Loren's Avatar
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    I didn't expect this notion to take off. (as several of us have said, it's not something you really need to worry about)

    Okay, safest way to get a no-start after an oil change.

    Find the fuel pump fuse.

    Before you turn the car off the last time before changing the oil, PULL the fuel pump fuse. Give the engine a last rev, and let it stall from lack of fuel.

    Now you have no fuel pressure and no power to the fuel pump. You can crank all you want, the engine's not going to start. And no fuel pressure means no fuel is going into the engine to wash out the oil on your rings or cylinder walls.

    When you're happy, put the fuel pump fuse back in.

    You could possibly set some kind of CEL doing this. Have a means to reset that handy, just in case.


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