CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Petrol in a diesel Jetta?

My '09 Jetta TDi is in the shop. The dealer told me the fuel pump came apart, and myriad parts are required in the fuel system. They stated that petrol was mixed in with the diesel and caused these problems, but they are fixing the car under warranty. I am not so sure about this accusation, as I would not put petrol in my diesel car. I even followed up with the gas station where I most recently fueled up to learn that they experienced no other problems. I suspect that the tech surmised from the damage that I used petrol, but never really tested the gas. Here are the symptoms: Full tank of gas. Drove the car 20 miles with no symptoms. Then saw warning messages and the car would not accelerate quickly or go more than 40 MPH. I could floor the pedal, and the car would slowly climb in speed taking probably 20 sec to reach 30 MPH. I drove the car to the dealer this way Christmas Eve, which was 5 miles away. If there really was petrol in the tank, would the car have made it this far? Wouldn’t I see black smoke billowing, hear strange sounds from the engine, or simply have the engine seize?

That could be gas, but it also could be other things. From here it is going to be difficult to say.

It would Have been interesting if you would have sniffed under the gas cap and gasoline has a unique smell. How you car may react depends on how much was mixed in and how long you drove it. Gas in not good in a diesel.

I find the part about them taking care if it under warranty interesting. If they do I believe you may be the first one on record to have a gas in tank issue fixed for free.

Just from my experience working with VW I can they are professional, thorough, and don’t take BS from dealers lightly.
If this pump failed due to what is claimed then VW would not pay for it.

Just to verify this, contact the VW regional office and without giving any details, inquire as to whether there are any warranty claims on file. If this repair was performed under warranty then it should, and better, be on record.

A small amount of gasoline in a diesel engine will not harm it. It will “rattle” a little more than normal, but that’s about it.

If you can get a sample of the fuel in your tank, put a small amount (one ounce or less) in a small container and try to light it with a match. Diesel fuel will not ignite in this manner. If there is any appreciable amount of gasoline in the fuel, it WILL ignite and maintain a flame on the surface of the liquid. Do this in an open, well ventilated area and limit the quantity of fuel to one ounce or less…

This is an easy accusation to use as an excuse try to weasel out of warranty costs but it appears that may not happen.

Older IDI VW diesels can tolerate up to 30% gasoline in diesel fuel for emergency anti-gelling in winter but injection pressure and therefore, I expect, mechanical pressures are greater and therefore the fuel lubricity requirement is more stringent in TDI diesels. Even so, a small amount of gasoline with inherently less lubricity should be tolerable but I can’t say how much. It would not be realistic to not expect a dollop or two of gasoline in diesel fuel now and then as diesel is sold alongside gasoline and people make mistakes; that is guaranteed. In addition, the present very low sulfur diesel fuel depends on people to make sure that the needed supplemental lubricant is added and mixed properly.

It would be advisable to begin documenting everything in case of a legal fight. Include names, dates, statements made by yourself and others, everything and a sample of the fuel!

You might want to post this on www.tdiclub.com for views from many TDI owners, some who are quite familiar with VW TDI diesels and dealers.