10

Title pretty much explains,

I change my oil every 4-6k miles depending on how generous I’m feeling, however will the oil dirty oil that’s already in the sump mix with the clean oil when topping up?

Normally I just top up but in this case I have had to drain about half a litre out on two occasions

First when I changed the oil as I overfilled

Second when topping up (overfilled again after 3k miles)

so it's had quite a bit of new oil mixed with the original stuff, just wondering will the new stuff mix fine with the old, if not I’m going do an early change and try not to be such a dope when topping up.

  • Just to be clear, when you change the oil, do you remove the sump plug and let as much drain out as possible, before you put the new in? – HandyHowie Feb 11 '16 at 8:45
  • yeah, every 4-6k miles it's a complete drain and new filter. – ceefax12 Feb 11 '16 at 17:20
10

Mixing new with the old will cause you absolutely no issues. As long as you are using the same weight oil, it will mix up and you'd never know it. Continue to change your oil at the specified interval and you should be golden.

  • 1
    The manufacturers interval states every 12k miles =/ that seams way too long to me so I went with a compromise on every 6k. – ceefax12 Feb 14 '16 at 16:07
  • @ceefax12 - The 12k miles is their recommendation ... there is nothing saying you cannot do it sooner than that. This action does not void the warranty or anything, so good on yah. – Pᴀᴜʟsᴛᴇʀ2 Feb 14 '16 at 17:44
  • I was too worried about this But, the maintenance light/engine oil is still showing. What to do? – Masud Rahman Nov 14 '16 at 17:21
  • @MasudRahman - It seems you have a separate issue. Please feel free to ask this as a question so it will get some deserved attention! Click here to start a new question. – Pᴀᴜʟsᴛᴇʀ2 Nov 14 '16 at 17:39
  • @ceefax12 What YMM? I would be very surprised to learn of a 12k Mile Severe-duty Interval. Is it a Diesel? – NitrusInc Apr 9 '18 at 12:06
3

Usually when changing the oil you won't be able to fully drain the old oil anyways and the old and new oils will mix, like it or not. Usually this is not a problem even if the weights are different, though it's safer to stick with the same brand, as some argue the components in the oil being incompatible may cause issues.

What you should be wary of is mixing synthetic oil with mineral oil, it i said that this causes problems more often.

  • I have heard it said about not mixing synthetic and mineral oil and never looked into whether it is true. Isn't that what semi-synthetic oil is? Do you know what the difference is? – HandyHowie Feb 11 '16 at 8:33
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    @HandyHowie As far as I know it's exactly that - mineral oil with some part synthetic oil. Might be an urban legend, but compatibility issues between natural and synthetic oils are said to be more pronounced. When semi-synthetic blends are made the manufacturer probably knows what to mix and what not to mix. Probably won't kill the engine and it's better to add some mineral oil than to drive low on synthetic, but this could reduce destabilize the oil and reduce it's performance. – I have no idea what I'm doing Feb 11 '16 at 8:42
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    I personally think it's not that much of a big deal, mixing brands is alright and mixing synthetic with mineral is alright only if there is no other option. – I have no idea what I'm doing Feb 11 '16 at 8:43
  • @HandyHowie is spot on. There is no issue with mixing Dino oil and synthetic, as that's what the "blend" oils are all about. There are no compatibility issues with doing so. This will not cause more sludge or have a chemical reaction of some sort. – Pᴀᴜʟsᴛᴇʀ2 Feb 12 '16 at 3:35
  • @ᴘᴀᴜʟsᴛᴇʀ2 any references? It's a very controversial subject, so I would rather err on the safe side. – I have no idea what I'm doing Feb 12 '16 at 8:38
1

Mixing old with new won't hurt anything. If your engine is consuming too much oil, for instance, you would need to add new oil more frequently because you need the right oil level all the time. I have got cars that needed as much as 1L of new oil every 1 or 2 weeks because the oil piston rings where kaput. Nothing happened except $ going down there as frequently as not eager to :)

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