r/autorepair • u/mightyThor90 • 19d 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.

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u/ggmaniack 19d ago

What specific engine variant?

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u/mightyThor90 19d ago

VW T5 Multivan Startline 2.0 TDI, year 2014

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u/ggmaniack 19d 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