What could cause MPG to drop from 25-26 to around 17 in a 98 Honda CRV?

IN the last 2 months I’ve seen the MPG in our 98 Honda CRV drop by 35%. Any idea why?

I had the tires rotated and balanced as I thought it might be something like that.

Then there is the AC, but I tested without AC also.

First off; does the vehicle appear to run fine? Any Check Engine Light on, etc.?
How is the mileage being determined; dashboard gauge or the fill, refill, and use the tripmeter method?

How long have you owned the vehicle…long enough to develop a history?
When was the last good, thorough tuneup?
Have you checked anything at all yet?
Any changes to your driving habits?? Like driving with the windows down now that the nice weather is here…and getting caught up in tourist traffic?

Two conditions that would cause lower gas mileage without setting the Check Engine Light (CEL) are a bad thermostat and a bad Engine Temperature Sensor. If the first item is faulty and stuck open the engine may not reach full operating temperature where the computer goes into closed loop giving optimal fuel efficiency. If the second item is faulty, the engine may be warming up to full operating temperature but the computer gets the wrong message from the ECT that the engine temperature is too low and doesn’t switch to closed loop operation.

Hope that helps
Let us know what you find

A failing oxygen sensor can cause that too or anything that will tend to richen the fuel mixture. Its probably time to get a general computer diagnosis to see what the block learn memory says for fuel ratio and what the other sensors are doing.

Worn out fuel injector(s). Not really likely but possible. Worn out tie rod end(s). Odometer so far off that the mileage is impossible to figure accurately. Anything wrong with transmissions, differentials or CV joints. The things mentioned by the other posters are less wild than the ones I listed here. Parking brake stuck partially engaged.