Poor gas milage in a rebuilt engine

Recently after an oil change, the oil filter fell off, the oil ran out and the enginge siezed. The auto shop rebuilt the engine for me. I get 30 mpg on the highway but only about 20 mpg in town. Can you think of any reason why the car should have such a huge difference in mpg? Is there some adjustment they can make for this?

Can you think of any reason why the car should have such a huge difference in mpg?

Huge difference between city and highway? (Not “huge difference from before the rebuild,” as we don’t have those numbers.)

The EPA’s fuel economy data shows a spread of 8 MPG city/hwy for a 1.8L, 2003 Sentra (guess?) and a 5 MPG spread for the 2.5L. So, allowing for variances in driving styles and congestion, etc, it’s not really out-of-line.

The bigger problem is that (it sounds like) you had the same shop that was responsible for the engine seizing rebuild the engine. This means that a) they have a huge conflict of interest, and b) you know that, so now every idiosyncrasy for here on will have you questioning.

I’d get a second opinion to allay my fears somewhat, but there’s only so much about the quality of the rebuild that can be told this way.

The fuel mileage discrepancy doesn’t concern me too much; the fact that the shop that made the mistake is also the one rebuilding the engine does.
The word “rebuilt” is also one of those well used and abused words in the automotive field that can mean a number of things.

My suggestion is to have someone else run a compression test and then post the figures back here for discussion. If this engine has been rebuilt properly, if at all, you should have readings of about 180-190 PSI on each cylinder; at a minimum.

Just being curious, what year Sentra, how many miles on it, and what kind of shop made this mistake? (reg. auto garage, fast lube facility, chain operation, etc.)

I should have added that the PSI figures do not reflect the main cause of damage due to lack of oil but if the figures are low, even on one cylinder, this means the engine was not rebuilt or not rebuilt properly.

Drive it for 3,000 miles and check again. It needs a break-in period before the gas mileage will be at its best.

What was the mileage beforehand? Obviously we need to know that.

A few clarifications. The engine wasn’t rebuilt, it was a drop in from another used car. The milage from the engine before the oil filter fell off was 211,000 and it got 38 on the highway and about 28 in town dirving.

So they replace the engine with one that 110,000 miles. Using another engine but using parts off of my car to put it back together. That is why I say it was a rebuild, but in car terms maybe it’s not because they had to drop in a who different engine.

I was very proud of my engine. It ran like a top. I am the original owner and kept the oil changed and kept it in perfect contition. So I think I could have gotten antoher 50,000 miles or so out of it. People don’t believe me but it’s true!

How do things look under the hood? what I mean is are all retainers present and used? does the routing of wires and hoses have that “factory” look to it? If the answers are yes then this nightmare (for both you and the shop has ended)My advice is move on, you have suffered extreme inconvience but you got a engine with much fewer miles and in my book you are doing just fine.

BUT keep an eye on things for a while, I would hate for this “lost” fuel to be diluting the engine oil and causing harm.

Yes, things seem to be in order. I appreciate your advice.

What year Sentra is this? A few possibilities I have can vary based on year.

1997 Nissan Sentra GXE

What year was the donor car?
Did they also use the donor’s ECU?
What parts did they take from your engine and put on the donor engine?