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I drive an opel/vauxhall insignia. Often when i come to check the oil i find the oil level is above the max rating, I believe the oil level is also somehow raising (possible diesel slipping past the rings?) between oil changes, as I doubt the three garages it has been to have all been as incompetent as to not put the correct amount of oil in. Should i be concerned?

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    When are you checking it? The level will be higher when the oil is warm as it expands, so it's best to check it when it's cold, before you start the engine. – Nick C Jun 16 '16 at 12:02
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    How are you checking it? Oil splashes around when the engine is running, and that can get oil way up the dipstick. The recommended method to check is to pull the stick, wipe it, put it all the way back in and then take it out again to check the level. That will give you an accurate reading. – GdD Jun 16 '16 at 13:32
  • @NickC If i take an oil reading i try and park my car on flat ground the night before and check it in the morning, so definitely not when hot or running. I also do as you suggest GdD. – Trotski94 Jun 16 '16 at 22:36
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It depends on how much above max. You can read what happens when the oil level is excessive here.

Make sure the oil level is actually increasing. Hot oil expands and will show you a higher reading, which is why usually oil level is checked when the engine is cold.

If it really is increasing, on diesels this is usually caused by fuel getting into the oil, as you suspected. A common culprit is unsuccessful active DPF regeneration - if you fail to complete the cycle the extra fuel injected to increase exhaust temperature will not burn and drain to the sump. Doing this constantly by driving only short distances will accumulate diesel in your oil. A slight increase might be more or less normal, but if it is increasing so much that the level goes above max - you might have more serious issues going on, like a leaking injector. Either way, you probably have diesel getting in your oil somehow and you don't want that.

Diesel is a poor lubricant compared to motor oil and diluting the oil too much might kill your engine due to poor lubrication or even an engine runaway in the long term. Get this fixed as soon as possible.

It might also be coolant, however this is usually obvious and less likely. Coolant in your oil will cause it to develop brownish milky sludge when checked on the dipstick or under the oil cap. In this case you would have even more serious problems, such as a blown head gasket or a cracked/warped head.

An oil analysis will tell you what's in your oil if you're not sure.

  • The DPF had cost me close to £1000 due to inability to regen and was removed and the engine remapped, do you think it could still be attempting to regen even without one? – Trotski94 Jun 16 '16 at 22:37
  • Usually when the DPF is removed, the ECU is reprogrammed to cut any regeneration functions. So if you had it removed profesionally the DPF is probably not it. The next step would be checking the injectors. A bad injector might constantly leak diesel into the cylinders and if unburned it will make it's way to the crankcase. – I have no idea what I'm doing Jun 17 '16 at 7:23
  • That's what i assumed, ill try the injectors next. – Trotski94 Jun 17 '16 at 7:57
  • We went to all this trouble to have diesel cars to save a few cents on fuel, and they turn out to be balky, expensive, poor performing, complex, and to make more pollution. The only consolation is they last longer. – user29824 Sep 28 '17 at 12:33

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