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Sudden mileage drop in '13 Buick Enclave

Computer has always shown 21-23.5 mpg but suddenly it has dropped to 13-15mpg. What would cause this

Some drop is expected w/colder ambient temperatures. If it drops more than expected even so, and everything else is the same as before, then next up would be that the coolant isn’t reaching normal operating temperature, for example due to a faulty thermostat.

Temp is normal, we are snowbirds so outside air is always between 50&85 degrees. Mileage 70000. Would like ideas before taking it to dealer and having them tell me I need a new car or at least tranny, engine and

The only accurate way to measure mileage is to keep track of how many miles you go between fillups, and then calculate it based on how many gallons you put in.

Vehicle mileage computers are sometimes accurate, and sometimes wildly off.

Compute your mpg manually for the next few fillups and see if your figures agree with the computer.

Assuming you really are getting 13-15mpg, that’s low for that car even around town. The first thing I’d check would be to see if a brake caliper is stuck. Easy test. Drive on the highway for 10 miles, then stop and feel each wheel. Is one really hot? That’s the one with the stuck caliper.

You are right but all this technology is making us lazy. We would rather stare at a screen than think a little.

Has it switched from an MPG readout to a litres per 100 km readout? The owners manual will show how to switch back and forth. It can be done without intending to.

The fuel economy change may be due to shorter trips in your new winter location. The Enclave is rated at 16 MPG city, 22 highway, unless trips to the grocery store are 100 miles you aren’t likely to see 22 MPG during daily use.

5yr old, 70k miles? i bet the dealer would love to get that on a trade?

If there’s an actual decreased mpg problem that’s not the thermostat, and the check engine light isn’t on, and there’s no diagnostic error codes in computer memory, these are other possibilities

  • coolant temp sensor
  • injector(s)
  • fuel pressure regulator
  • brakes or e-brake locked partially on
  • routine maintenance needed, such as spark plugs, engine air filter, idle rpm, ignition advance, valve clearance

Ask your shop if a “fuel trim” measurement would be diagnostic.

Thanks, good tips

First data I like to see when economy is in question are fuel trims. Do they look normal?

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