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Author Topic: Fuel dilution in oil  (Read 397 times)

Offline 44 BU

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Fuel dilution in oil
« on: December 07, 2021, 03:26:30 pm »
Hi guys, just recently done an oil change on my edition 30, noticed a significant smell of fuel from oil, got an oil sample sent to Millers oils, the report came back with 3% fuel dilution. The car is a revo stage one, anybody on here had any oil tests done with fuel dilution figures? I'm aware the car will be running richer than normal because of the tune. The car is used for short journeys mainly but oil sample was taken after a good drive.

Thanks in advance   :happy2:

Offline Pudding

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Re: Fuel dilution in oil
« Reply #1 on: December 07, 2021, 05:10:51 pm »
3% isn’t a lot but worth checking the hpfp seal hasn’t gone and leaking fuel into the sump. The oil does stink though with aftermarket tunes! And no doubt you will have noticed how sooty the tailpipes get also!


2007 ED30 | 2009 TDI 140

Offline 44 BU

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Re: Fuel dilution in oil
« Reply #2 on: December 07, 2021, 05:14:35 pm »
Is there any way to check if the seal has gone on the pump, I have had it out but don't know what to look for. Would have taken it to r tech or aks but they're booked out for the next few months..
Thanks

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Offline 44 BU

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Re: Fuel dilution in oil
« Reply #3 on: December 07, 2021, 06:01:02 pm »
I've attached some pics of hpfp, maybe there are some tell tale signs you can see..






Offline Pudding

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Re: Fuel dilution in oil
« Reply #4 on: December 10, 2021, 12:19:30 pm »
There is no way of telling physically without stripping it down, but the obvious clues are:

Oil level rises over time
Oil stinks of fuel, and I mean literally reeks of petrol, not the usual rich mixture smell.
MPG absolutely sucks
Reduced performance
Possibly some fault codes about bank 1 mixture from all the petrol vapours getting through the PCV system.

I would say in your case, it's just lots of short journeys. Colder months = more fuel used to warm up the engine, and short journeys don't get the oil anywhere near hot enough to steam off the excess fuel.


2007 ED30 | 2009 TDI 140

Offline 44 BU

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Re: Fuel dilution in oil
« Reply #5 on: December 10, 2021, 01:12:57 pm »
Yeah I guess you're right, I have been doing constant short journeys and the car hasn't been warming up properly. Have got the same answer from a few specialists.
Thanks for your time, much appreciated.

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Re: Fuel dilution in oil
« Reply #6 on: December 31, 2021, 04:26:44 pm »
Interestingly enough, I checked my oil level today and it also stinks of rich running. Also Revo Stage 1  :grin:

Did your car exhibit any kind of part throttle weirdness?  A bit surgey, jolty and unresponsive?  But OK in boost?

I think my injectors are going bad (again!) as the above is a classic sign of one or more injectors on the way out.  Thought I'd drop that in here just in case you've got the same symptoms.

Basically, one or more injectors is dribbling causing a rich condition, which the lambda control fights, but also makes the working injectors run leaner as it only measures the sum of all 4 cylinders, not individually, hence the part throttle wobbles.

That would certainly make the engine oil stink of over fuelling.


2007 ED30 | 2009 TDI 140

Offline 44 BU

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Re: Fuel dilution in oil
« Reply #7 on: January 02, 2022, 12:03:42 am »
Ah, that makes sense. My car does feel jolty at times and tad bit irresponsive but I thought that's how they were. How would you describe the surge that it does?

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Re: Fuel dilution in oil
« Reply #8 on: January 04, 2022, 09:37:40 am »
Changed my oil over the weekend and it's fine again now.  I'd also over filled it at the last change (approx 7-8mm above the max mark) so it looks like the lambda control was indeed fighting excessive PCV gases.

Checked the spark plugs and they're all the same colour, so maybe the injectors aren't as bad as I suspected.

The surging is more noticeable when trying to hold a steady speed in 3rd or 4th.  It just feels a bit stumbly coming off/on the gas and also a wavy power delivery.  Not smooth and decisive as it should be.  Onset of boost is also bit unresponsive.  At higher speeds/gears, holding a steady speed needs constant throttle where normally it would just pull itself along, just by resting your foot on the pedal.

It's hard to explain really, but after driving a 'normal' car for a while and jumping back into the GTI again, you definitely notice it!


2007 ED30 | 2009 TDI 140