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Old diesel fuel and emissions test

I got a 2003 Jetta TDI that’s been sitting parked for about 2 years. Before my wife parked it I asked if she ran it dry and the response was yes. We need it again so I got it running new oil, filter, fuel filter, air filter and a few other things. But it has about 3/4 tank of diesel that was left in it. I opened up the fuel tank and inspected the fuel and it looks fine with no water, rust or growth.

It needs an emission test so will this old fuel cause a fail? Is there something we can add to it? Or should I just drain it out? The issue with draining is 3/4 tank is about 10 gallons and I got nothing to store it in.

Diesel emissions testing measures for soot and NOx.

So if the diesel fuel isn’t funky, there’s no reason it shouldn’t pass.


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You might ask on the TDI section of and There might be an additive that could help a little, but I have no idea what it would be.

Diesel doesn’t go quite as “bad” as gasoline does. That’s why lots of large county owned backup generators are diesel - at least in my area, no natural gas lines!

Curious…if she “ran it dry” why is there fuel in the tank?


What could be the only reason?

I don’t think someone filled the tank after the vehicle was parked.

So, the only other explanation has to be, she didn’t tell the truth.


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Diesel is very stable and remains usable for years…Drive on…

Yep she lied or didn’t understand the question. Trust but verify comes to mind. I’d be very surprised though if there wasn’t stuff growing in the bottom of the tank ready to plug the filter up.

Maybe she meant the crankcase … :wink:

Thought it tended to support microbial growth if left alone, especially if any water gets in. I’ve heard horror stories about old Diesels with “slime” in the fuel tanks!

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I imagine a long-term diesel tank pulls fuel from above the bottom exit so goo can collect below it. When I decommissioned my home fuel oil tank, there was about one inch of goo on the bottom after 25 years of use (and many refills).