Accurate Gas Gauge
Of all the vehicles I've owned, my Explorer has one of the most accurate gas guages I've seen. There is one exception however. When the guage gets down to approximately 1/8 of a tank it becomes very unpredictable. On average I get about 380 miles to a tank full, which is an average of about 19 miles to the gallon. That means with an 1/8 of a tank left I should get about 60+/- more miles (when you consider the reserve after the warning light comes on). However, when the guage hits 1/8 it will often drop rapidly to empty giving me maybe 25 more miles of gas. In fact twice I've run out of gas about 10 miles after the guage hit 1/8. Word of caution - It has also been observed that once the guage drops below 1/4 tank, hills affect the reading dramatically.
For what it's worth, do as my wife always says and fill up when the tank reaches half empty. But don't you get better gas mileage with an emptier tank and less weight? :-) I suppose less mileage is better than pushing.
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Check Engine Light codes and how to extract the codes ysuloerf: As for the low oil pressure, most likely the oil pressure sending unit needs to be replaced as it is a common failure part. An Engine Requires 10 psi of oil pressure for every 1,000 rpm. so at idle, it does not require much,,, at 3,000 rpm, the engine requires 30 psi. You can install an actual pressure tester at the sending unit port if you would like to see actual numbers for diagnosing. Replacing the sending unit will most likely take care of the oil pressure issue. I some cases the check engine light can be set with a check Gauges . But it is a good idea to check the codes and proceed once you have the actual codes.