2005 R52 Mini S
Contaminated Gas/Fuel Pump and Filter
This process applies to the following models:
MINI Cooper 2002-2006 (R50)
MINI Cooper S 2002-2006 (R53)
MINI Convertible and S 2004-2008 (R52 or R52-S)

The R52 and R52-S came along slightly later in the life cycle of the first generation MINI, but finally offered the drop-top convertible fun many enthusiasts had been clamoring for.

This particular R-52 is the S model, replete with a supercharger. It's a very nice example of the car. The vehicle arrived with complaints of turning over, but not being able to fire. Let's pick up in the middle of the diagnosis. We verified that spark signal is getting to the spark plugs, and inspected the spark plugs. They were original to the car, and therefore had some miles on them. While they aren't the problem, they were replaced for good measure. Now lets continue. Follow along with the pictures for more details.

So, it appears we have a fuel pump that locked up from sitting and/or age. It's also possible that it was a victim of these more modern ethanol blended fuels we're seeing nowadays. While not the most common failure, it's certainly isn't unheard of. While we're getting the pump replaced we'll go ahead and replace the fuel filter as well. Follow along for details.

So with the car running well, and seemingly repaired, we gave it back to the owner. Things were fine, for about a week or two.

That should have been the end of the story, but it wasn't....

Our original diagnosis for 14-15 year old car with less than 90k miles on it was that the fuel pump had simply locked down from sitting a long time. It's a pretty common way for fuel pumps to fail. However, about a week or two later the owner reported the car behaving the exact same way. So it was brought back in to check things out. First we verified that indeed the new fuel pump was dead. Since this was the same OEM brand as used by BMW when the car was new, it was safe to say it wasn't just from a cheap part. The old filter looked fairly clean, and the very new filter we'd just installed still looked basically brand new. If it wasn't dirt and trash, what was making the pumps fail?

We're fortunate that we know someone in the automotive fuel systems design and component construction industry, and he said he had a theory but would like to come investigate. Follow along with the pictures.

Our associate went on to explain that this brown substance is a polyacrylate chemical compound used in fuel filters to try and trap/remove the water inside fuel. The chemical is used in fuel filters found at gas stations where they are used to strain the gas of water and other contaminants before it's pumped into your vehicle. He went on to explain that water in high enough amounts actually pulls the chemical out of the filter in high concentrations. As it is pumped in, the chemical mixes well with the fuel and the fuel pump runs fine. However, once the fluids settle for a period of time, like overnight or while you're at work, the chemical separates out into concentrated clumps or beads. A fuel pump that ingests a concentrated slug of this chemical will often lock-down since it is not designed to pump this gel-like compound.

With this very interesting bit of information we gave the owner the bad news that they were looking at yet another fuel filter and pump, and that we would need to drop the fuel tank out to drain and clean it. Let's get to work.

We'd pumped out most of the fuel before lowering the tank, because fuel weighs about 8lbs a gallon, and 10 gallons of gas adds up fast when you're trying to hold a tank over your head. However, there was still a little fuel left in the tank, and after we little it settle for several hours we were pleased with what we found.

From here it was a matter of cleaning out the inside of the fuel tank and the filter housing as best as possible before installing the new components and reinstalling the tank. Just to be thorough, we put several gallons of non-ethanol 93 octane fuel in the car to get the owner on the road. While ethanol is not the exact reason this situation happened, ethanol mixes more readily with water and absorbs more water than regular gasoline. Since high water concentrations pull more of this chemical out of gas station filters, the likelihood of this situation happening is greater when dealing with fuels that contain ethanol. We'll let the owner decide where they buy gas from now on, but anyone should be aware of the benefits and risks associated with ethanol blended fuels.

That is all. This car is happy, running, and ready for weekend fun. The fuel filter is an important bit of MINI maintenance, regardless of whether or not you run into this situation. While MINI either doesn't have a maintenance schedule for the fuel filter or says it lasts the lifetime of the vehicle, that simply is not how filters work. Replace filters. HPMotors recommends replacement at least every 60k miles. Please call if you'd like this preventative bit of maintenance for your MINI.

This Mini is finally repaired and back on the road.