I just brimmed my 2003 Opel Agila to the tank (35 litres) with regular unleaded from Tesco (large supermarket).

On the way home, it just seemed to be completely gutless, and struggle a lot more when driving.

Is it likely that I have put bad fuel in my car? Is there a way for me to check?

  • 1
    That's a tough one. You can put some fuel treatment specific for water, because that is the usual cause of bad fuel. That may help, but beyond that, you'd need to extract a good quantity of fuel from the tank, put it in a clear bottle and see if the water/gas might separate. Maybe someone else has a better idea, but it's the only way I've ever figured it out. Nov 29, 2015 at 21:36

2 Answers 2


A fuel test procedure and kit (without sending out to a lab) involves 3 steps.

  1. The first involves lowering a probe to the bottom of the tank with a paste that changes color if it touches moisture. The probe almost resembles a bicycle cable in a clear sheathe. This requires the probe and the color changing paste.
  2. The second involves retrieving a sample of the gasoline. Place the gasoline in a graduated cylinder. Add some amount of windshield washer fluid. Cork the sample and shake the tube. Wait until it settles. Compare how much gasoline you put in to how much is left after everything settles. This shows how much alcohol is in the fuel. It should be no more than 10%. All this test needs is a graduated cylinder that can survive gasoline. This is the easiest thing to acquire.
  3. The third involves retrieving a sample of the gasoline. This tests the volatility of the gas known as Ried Vaper Pressure and requires another special testing tool. Chill the gasoline and tool on ice for 30 min. Pour the fuel into the tool and close it. Place the tool into hot water for 10 min and measure the water temperature. Read the pressure from the gauge on the tool. Compare the pressure and temperature to a table that comes with the tool.

Only #2 can be done without super special tools.


If it doesn't smell kosher, drain it out and fill up with a known good gas. Don't waste your time with testing. It'cheaper and easier in the long run to just bite the bullet and go for the cure!

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .