High Fuel Dilution

[Spetz]

Hi everyone,

I have done a UOA on 2 of my cars which both use Shell Helix Ultra 5W40.

Both came with high fuel dilution (3% but the max reading for the test is 3%. So minimum of 3% and realistically no idea how much).

What could be causing this, and what would I be testing for?

Car 1:
Daily driver and tow car. 2003 Mitsubishi Diamante with a 6G74 3.5L at 155k miles.
6k miles on the oil.
Runs fine, fuel consumption seems reasonable.

Car 2:
Mitsubishi 6A12 MIVEC engine in a track car.
500 miles on the oil.

Any help would be greatly appreciated

 

[VeryNoisyPoet]

How long are the trips in the daily driver? Lots of short trips and idling can cause fuel in the oil. Towing usually raises oil temps and helps evaporate off fuel and water but can also contribute if the engine is running rich under heavy load. At that mileage and age, perhaps due for fuel injector cleaning and flow/spray pattern testing. You could have poor spray patterns and not know it.

What kind of racing does the track car see? Drag? Circuit? Autocross? Any modifications or aftermarket tuning? Like the tow vehicle, racing can cause high oil temp, but also lots of rich operation due to heavy load. A proper tune will often run richer than stock for power gain and cylinder cooling. A bad tune could be dumping in excesss fuel.

Was there any abnormally high wear patterns in the UOA? Or just fuel but no other problems?

 

[Popsy]

Can you post the UOA (or point to them if already posted) ?

I too had high fuel dilution in my turbo Mitsu (4G15T, a different animal).

 

[SteveSRT8]

While there is much discussion regarding fuel dilution there are extremely few cases of any real damage to an engine from it.

 

[BMWTurboDzl]

Car 1 : Leaking injector(s)?

 

[Spetz]

Car 1 (daily driver):
It is mostly driven in the city, but I take it on occasional long runs.
Spends a fair bit of time idling in traffic but trips generally are about 10 miles
Injectors had been ultrasonically cleaned about 30k miles ago.

Car 2 (track car):
This is used on a circuit.
Though it has a few (15-20) short starts as it is not street registered and I need to move it at times.

I have not yet received the UOA, just a phone call stating the fuel dilution is in excess of 3% and hence wear metals will be high as a result.

Once I receive the UOA (2 day turnaround) I will post and link them.

 

[stockrex]

just change often, most of my hondas had fuel dilution issues.

 

[andyd]

Can you smell gas on the dipstick? Go for thicker oil. and shorter OCIs

 

[Speak2Mountain]

Run a thicker oil.

 

[Spetz]

Is running thicker oil to prevent blow by?

 

[Popsy]

If it can reassure you, this was my UOA with "2,5% fuel" : https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/4214407/1

Did you sample cold, of after a short trip ? Do you have an OBD scanner ? They can show the sort term and long term fuel trims...if the ECU is compensating say an exhaust (or intake) leak and putting more fuel than necessary, it can show. Just a suggestion.

 

[Spetz]

For car 1 (daily) it was after a relatively short trip.

For car 2 I started it, warmed it up, then took the sample.

They are not OBDII unfortunately as both are old cars.
The track car used a stock ECU with a piggyback as the engine is mostly stock with bolt ons.

 

[Popsy]

2003 and not OBDII ?
If the sample was after a short trip, it can be a factor. I'd say wait for the UOA before thinking of taking action.

 

[Spetz]

2003 but the model came out in 1996 so fairly old technology.

Yes I am awaiting it before doing anything but I would need to find a cause for this.

Especially the track car as it has so few miles on the oil and yet fuel dilution is at the very least 3%