Gas milage shrank from 15 mpg to 13.5 mpg

[gringostar]

Hi

 

For the past five years I've gotten a solid 15 mpg and now I'm getting a solid 13.5 mpg. That's a 10% reduction. My rig is a 1986 4 cylinder automatic transmission with 89k miles. I'm using southern California gas and I keep it between 55-60 mph. Any ideas why? 

Edited August 18, 2020 by gringostar

[WME]

Calif Gas!! 😡

Actually a full tune up- check timing, spark plugs, vacuum hoses, check the valve adjustment, air cleaner, PCV valve and egr valve.

[Scott iv]

If someone finds the answer let me know. I get a solid 13-14mpg on my 1987 19' escaper 22re automatic and only do better down hills and with strong wind at my tail end. I do worse against wind and with speeds in excess of 60 mph. I would love to get the solid 15 you were getting. 

[linda s]

When my gas mileage goes down I always adjust the valves. Not hard to do on a 4 cylinder. My valves always get looser not tighter. 

Linda S

[Maineah]

I have never done much better that 13-14 with my Nova Star and I made my living for 38 years a a mechanic working on foreign vehicles. Linda you are right loose valves retades valve timing huge difference doubtful but you need every ounce you can get from a tiny engine with a house on it's back.

[jjrbus]

No nothing about a 4 cyl.   The service manual for my 93 says to replace the 02 sensor at 80k and the dealer will do it for free!  When my mpg dropped noticeably I could find nothing wrong!   When I tested the 02 sensor it passed but I noticed it was very slow to react compared to the videos I was watching, referred to lazy 02 sensor.  I detest throwing parts at a problem but had  nothing to loose I threw some parts at it,  02 sensor, fan clutch and thermostat.  Should have done 1 at a time and tested, but mpg is back up now.