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Only getting 5.5 mpg

I have a 99 Durango. thermostat is stuck, so it is tapdancing that jazz. On top of that, it is only getting 5.5 mpg in the city. On the highway it is getting 14.9. I don’t have the money to replace the thermostat right now. What can I do about the mileage problems?

Fix the thermostat it is 99% the reason for the fuel MPG issue.

Thermostat is stuck? How do you know? Stuck open or stuck closed? Stuck open is my guess, that’s why the mileage is so bad.

Thermostats cost about $15. Buy one and install it. Problem solved. Both problems, actually.

If you can afford 5.5 mpg you can afford a thermostat. How are you measuring the mileage?

Please post video of your Durango tap dancing.

“If you can afford 5.5 mpg you can afford a thermostat”

mcparadise makes a very valid point. The replacement of the thermostat will pay for itself with lower fuel costs within a couple of weeks.

I think that you can’t afford to NOT replace the thermostat.

There’s nothing you can do but replace the thermostat. If it’s stuck open, the engine never reaches the operating temperature. So the computer thinks the engine is still cold so it’s going to enrichen the fuel mixture. But not only is this causing lousy fuel mileage, it’s loading up the catalytic converter with raw fuel resulting in overheating when it does light off. Also, you might be loading up the crankcase oil with raw fuel from unburned gas.

Replacing the thermostat will seem like a bargin compared to replacing a cat and/or replacing an engine.


I use simple math to measure the mileage. I pay 20 bucks for gas when the tank is on empty, and I am out of gas by the time the odometer has registered 110 miles driven. The DTE estimate is always higher than what the odometer reveals. Thanks for connecting the dots for me. I am currently homeless with my child, and I donate blood plasma for gas money. I am not sure how many quarts of blood my stuck thermostat has cost me, but I have to pay for everything else too. I quite buying cigarettes May 15. Then my mom died from lung cancer on May 19. So I have saved some money!

I am curious as to what temp the gague says the engine is running at,perhaps half of normal? I do know the theory of the cold engine staying in open loop but I could not have predicted that much of a penalty.

Can you do the job yourself? Do you have a friend with tools that could help? If no to both, maybe you could work out a payment plan with a mechanic. With better gas mileage, you might pay it off quickly.

P.S. If you go to church, ask folks there for help. Not money, but help replacing the thermostat.

Also what about basic maintenance, air filter and spark plugs, in the last ? miles?

I am not sure a stuck thermostat would cause your mpg to be that bad. Is your speedometer working properly? A lot of these trucks have bad speed sensors in the rear differential that cause the speedometer not to work until you hit about 45mph. The check engine, ABS and brake light are usually also on when this happens.

Looks like you are getting 13.48 MPG overall. $20 buys 8.16 gallons of gasoline. 110 miles divided by 8.16 equals 13.48 MPG. I always think that somebody’s uncle has money and might help out when needed. Someone will help you soon. The Durango is supposed to get 13 MPG overall. Do check the oil.