I recently took my 2011 Fit Sport (135k miles) for a basic oil change at a local oil changer. I've been running full synthetic oil since I bought it new and it's always gotten 30-32 MPG and it's been well maintained. Since the oil change mileage has plummeted to 22 MPG. It's not throwing codes and it seems to be driving fine. Maybe a tad sluggish. The only thing I can think of is someone there mistakenly added very high viscosity oil by mistake. Otherwise I can't think of anything they could have done that would have caused the mileage to drop like this.

Curious if anyone had a similar experience and/or thoughts.

 

If nothing else changed since then, and the mileage drop started right after that, I’d say you’re probably right. Unfortunately, you’ll probably have trouble convincing them that they might have done this, so I don’t know how easy it would be to get them to swap it out. If that’s what it is, you really want to get it out of there ASAP. If it were me, I’d just do it myself right away.

 

I contacted the shop. Turns out they used 5W30. This would cause a slight drop in mileage, but I doubt a 30% drop. Shop manager was pretty responsive and said they will flush it out and put in the proper oil and take a closer look at things to make sure everything is correct.

 

If nothing else, it sounds like a good shop. Agreed that the 5w-30 wouldn’t be enough to see that much drop; I was expecting that maybe they had used 50w or so.

 

How long/how many tanks of gas since the oil change? Are you calculating fuel efficiency at the pump or relying on the reading from the car? Nothing else has changed since the oil change: same commute at same speed, same tire pressure, same cargo/weight in the car, same weather? Do they switch to winter fuel in CA?

While I don't doubt that 5w-30 oil will reduce mileage in comparison to 5w-20/0w-20, I think the change would be small (e.g., 30-32 mpg might become 28-30 mpg).

In addition to getting your oil changed, I would check the usual suspects: alignment and tire pressure, brakes, engine air filter, unnecessary weight in the car, excessive speed, etc.

 

Two tanks. There was a noticeable drop after the first and I thought maybe I got a bad batch of gas. The second tank was worse. I calculate at the pump. The computer said I got 24.5 MPG. When I calculate at the pump is 22. Nothing has changed. Not towing anything, tire pressure is consistent. No huge change in weather, I don't speed or accelerate hard, new pads and rotors 20k miles ago, etc. Nothing changed since before the oil change. The only change was the oil viscosity.

I always get 270-280 out of a tank. I got less than 200 in the last two tank fulls. Plus, I had a mechanic friend hook up his computer and it didn't throw any codes. The only change has been oil, air filter, oil filter and cabin filter. I'm gonna change the oil back to factory specs and see if there's a change.

 

I took it to the shop and they took care of it. Changed the oil back to 0W20 along with a new filter and tossed in a set of wipers for my trouble, I took the scenic way home to feel things out. It's noticeably more responsive, and the computer is now reading 32 MPG, which while likely not accurate is still much higher than before. But I'll know in half a tank if I get better mileage, which is pretty clear I will.

The second gen Fit, or at least my second gen Fit, does not like even moderately thicker oil.

 

Thanks for the info, that's good to know. Though I suppose one could still suspect the shop used even higher viscosity then the 5W20 they claimed. Guess we'll never know and at least they made good on their mistake.

 

They used 5W30 actually. Or at least that's what the invoice stated. The manager acknowledged they shouldn't have used it and did right by me.

 

Sorry for the misread, that makes even more sense now.

 

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