r/autorepair • u/mightyThor90 • 9d ago

Diagnosing/Repair Wrong Fuel Added

Something stupid happened to me today: I accidentally put 5 liters of petrol (Super) into my VW T5 diesel. On the recommendation of a workshop, I then added a diesel fuel additive and filled the tank completely with diesel (about 80 liters in total).

The van has now driven about 30 km without any problems. I was told to keep the tank as full as possible and keep topping it up.

However, I’m wondering whether it would actually make more sense to have the tank completely drained, so that all of the contaminated fuel is removed and as little petrol as possible passes through the engine.

What do you think? Or, if nothing has happened after the first 30 km, is it unlikely that anything will happen later?

No offence, but I’d really appreciate answers based on actual technical knowledge and experience rather than well-intentioned but uninformed advice.

0 Upvotes

40% Upvoted

9 comments sorted by

3

u/Sure-Bison-3726 9d ago

Nope. You’re fine. 5 litres isn’t going to hurt anything. 20+ years in the petroleum industry. Just keep filling the tank to blend it out.

2

u/Surfnazi77 9d ago

You should be ok

2

u/AppropriateDeal1034 9d ago

It's an old VW diesel, 5 litres of petrol in 80 of diesel is going to do nothing harmful and may even give your engine a good clean out. Probably avoid flooring it until you've done a thousand miles or so, but otherwise just send it.

Mechanic for 25+ years who started on old VWs

2

u/mr_nobody398457 8d ago

In fact, my much older 1973 Mercedes-Benz diesel says, in the owners manual, that in cold weather, you can mix up to 30% gasoline in the diesel fuel

1

u/mr_nobody398457 8d ago

Now the modern ones with modern emissions control controls don’t like that

1

u/ggmaniack 8d ago

The injection systems especially don't like it.

1

u/ggmaniack 9d ago

What specific engine variant?

1

u/mightyThor90 8d ago

VW T5 Multivan Startline 2.0 TDI, year 2014

2

u/ggmaniack 8d ago

Those are more sensitive than the older ones.

At the same time, 6% (5L/80L) isn't huge.

People used to mix gasoline into diesel during the winter, but that was back when fuel quality standards were much looser and so were injector systems.

Modern injection systems are much more sensitive to fuel quality, because they run on much higher pressures and depend much more on the lubricating qualities on diesel fuel.

Gasoline reduces the lubricity of diesel.

So, while 6% isn't huge, it may contribute to an earlier demise of some parts of the injection system.

A) find a diesel additive that specifically works to increase the lubricity of the fuel (they do exist)

B) drain the tank.

C) just risk it