Changed my oil today but like a fool overfilled when topping up, I did not notice this at first as I have a strange dipstick and fresh oil is pretty difficult to spot however I overfilled by around 5cm over the max point. Without noticing I drove the vehicle to work (30 mile drive).

I plan to drain the oil to the appropriate level however I am a little worried about oil foaming. My heart says that it's fine but my brain wants to ask you good people for advice.

Is there any way I can determine if oil foaming happened or is happening e.g. bubbles on dipstick?

I also have some other questions post to the previous question, does oil foaming damage the properties of the oil if it were to foam.

Should I drain my oil and start again?

I am probably being a bit of a hypochondriac but never hurts to get advice rather than remaining ignorant.

The car is a 2007 ford fiesta style with a duratec 1.25cc engine.

  • Possible duplicate of How far can I drive with 1 gallon too much oil? Dec 21, 2015 at 21:54
  • I hope the engine is a little bigger than 1.25cc's ... I think I had toy air planes with bigger engines than that :D I'm sure it feels about that size when driving it, though. Dec 21, 2015 at 21:55
  • @Paulster2 I"m thinking the foaming component of the question would make it a bit different from the indicated duplicate?? Dec 21, 2015 at 22:27

2 Answers 2


Is there any way I can determine if oil foaming happened or is happening e.g. bubbles on dipstick? Yes, small bubbles on the dipstick is a good indication of foaming, there should not be any in normal operation. They will not stay long after engine shut down. Quality oil will have an anti-foaming additive that will cause them to dissipate. In extreme cases oil can leak from the PCV breather system. Look inside the air intake tube.

The foaming is caused by the crankshaft dipping into the oil pool. The dipstick max oil level is well below the crankshaft. Think eggbeater. A couple of centimeters overfill is OK, but the safe overfill amount varies with engine design.

Does oil foaming damage the properties of the oil if it were to foam. No, that by itself will not change the oil chemistry.

Should I drain my oil and start again? To be safe and alleviate worry, given the relatively low expense, I would. Do not drive it with the oil level too high. The bigger concern is possible engine damage. But since there is no quick way to determine if damage happened I would drain and fill, run it at idle for a few minutes and then do a gentle test drive. Time will tell after that. Damage would, most likely, be first seen at the crankshaft rod bearings. These bearings can fail due to air in the oil allowing metal to metal contact on the bearing to crank journal surface. We hope that has not happened.

  • I once had a helpful compatriot at a shop I was working at fill a bike that I was working on with oil and then not tell me. Problem was, I had already done that and started the engine. It blew out the main seal from the pressure. Would this be a concern for automobile engines as well? Are you referring to that with "...be seen at the crankshaft rod bearings."? Or are saying the rod bearings themselves would have an issue? If so, what's that concern? What could potentially happen? Dec 21, 2015 at 21:37
  • That's a great answer thank you, I am afraid I messed the question up a bit :( I was supposed to write 5mm, maybe 1cm at the most not 5cm sorry =/, hence why I mentioned I may be being a hypochondriac, I won't change the question as you gave a great answer and it fits perfectly but do you think the 5mm will make a difference? I shouldn’t write questions when in a rush =/ won’t happen again sorry.
    – ceefax12
    Dec 21, 2015 at 23:19
  • @ceefax12 A 1cm (~1/2") over fill is very unlikely to cause foaming and therefore no damage. Dec 21, 2015 at 23:30
  • @DucatiKiller Auto engines do not often blow the crank seals on an overfill. Probably due to the larger crankcase volume and vent system. Dec 21, 2015 at 23:33

I know that it's a year old post, but my problem is with the gasket being worn out and allowing the coolant to leak into the oil contaminating it. I'm replacing the gasket and doing an oil flush before moving the car.

The symptoms were constant light metallic rubbing noise(lack of lubrication), higher oil pressure on the gauge (my guess is lots of foaming), foam on the dip stick, and ~1/4 lower reading of oil on the dip stick when stopped after a drive.

From what I've picked up from other discussions that people suggest to replace all the oil if there is a little of contamination, and it's reasonable to believe as well, as I know the importance of not contaminating the breaking fluid with a single grain of sand due to really drastic consequences which I'm not even exadurating.

All the oil in the engine is about 4-5 liters (1.3 US gallons) that needs to be flushed, with using oil flushing liquid and replacing the oil filter that is likely to hold the contaminant as well.

In my case it will cost around $200.

Your owners manual must have the specifications for the type of oil to use. Unless you have the extra buck, it's best for dealers to sort it out.

In the end its: 5l oil, gasket, oil filter and oil flusher in my case.

Not every case is the same, but hope it will benefit here to others to find their issue.

  • 1
    How does this answer the question of the OP? They are asking about oil foaming. You are talking about something else entirely. Nov 12, 2016 at 20:57
  • @Pᴀᴜʟsᴛᴇʀ2 I said "gasket is worn out and allowing the coolant to leak into the oil contaminating it.", Which causes the oil to foam. When I was looking for an explanation, I came across this question and found an answer to my problem, which I decided to share. The "correct" answer above is just a bunch of questions and answers to common facts without actual troubleshooting. Does my answer seem irrelevant? I don't mind removing the answer. Nov 12, 2016 at 21:13
  • The other answer copies (in bold) the questions specifically asked by the OP and directly answers them. Please don't delete your answer. Nov 12, 2016 at 21:34

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