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Van has become gas guzzler after 180,000 miles. Why?

My 2000 Dodge Grand Caravan after many years of good gas mileage has become a guzzler. Has gone from 19 mpg to 10.2 mpg. Have had injectors cleaned, fuel system checked. What else can I have done? I really like this car.

When is the last time the spark plugs were replaced? While you are at it, you might consider also replacing the plug wires.

Check the oxygen sensors. They control the fuel mixture. A “Real Time” computer diagnostics scan will spot any sensor faults, fuel trim abnormalities, timing, all the operating parameters…A compression test may be in order. Brakes dragging (they would be getting hot)…There has to be a reason…

Check for a thermostat that’s stuck open. If the thermostat is stuck open the engine never reaches full operating temperature which will cause the engine to use more fuel. Also check for a faulty coolant temp sensor for the computer. If this sensor has failed where it’s telling the computer the coolant temp never reaches full operating temperature, the computer will think the engine is cold and this can cause the engine to use more fuel.


Thanks guys. I’ll take these suggestions to heart. If none of this works, I’ll be back.

Also look for a leaking fuel line or a leak in the fuel tank. These would not show up in diagnostics and can be very difficult to find when the leak is this slow.

I disagree with Caddyman’s advice to change the oxygen sensors. It might be the oxygen sensors, but oxygen sensors aren’t cheap, like spark plugs or a thermostat. If there is troubleshooting that indicates the oxygen senors are bad, change them, but when you throw parts at a problem, they should be inexpensive parts, at least to start with.

My advise to perform a real-time diagnostic test to monitor ALL the control inputs can spot bad sensors and thermostats very quickly with no parts purchased…Watching a good mechanic using a professional scan tool can be a revelation…I edited my poorly written post…

A clogged catalytic converter can also cause a big drop in gas mileage. You would also notice a lack of power on acceleration.

By removing the front oxygen sensor, exhaust system back-pressure can be measured. I think 6-8 psi is maximum when you rev the engine…Those numbers might be a little high…

Everything you guys are suggesting would cause a Check Engine light to come on. I don’t see the OP stating anything about the Check Engine light being on.


Everything except a leak.

A leak where?


Further up the thread.

#keith July 3 Report
Also look for a leaking fuel line or a leak in the fuel tank. These would not show up in diagnostics and can be very difficult to find when the leak is this slow.”

The OP reports about a 50% drop in fuel mileage. If half the fuel was leaking from the vehicle something like that would be very noticable.


Tester, I don’t agree completely with you on this. If the OP is filling the gas tank once a week, then a leak that drops the mileage from 19 to 10.2 would be a very slow leak. It would be leaking about a gallon a day at that rate, possibly from the rear of the vehicle.

The gas would evaporate too fast to leave a trail, but on a hot day, the OP might detect an odor if he/she circled the van while parked. If a fuel line was leaking, only under pressure, near the tank, they may not notice an odor unless they circled the vehicle right after parking it.

I only posted this as a possibility if none of the other suggestions did not uncover the cause.

I brought this up in another post as another possibility when someone notices a sudden drop in fuel economy. On occasion I notice a vehicle going down the road with something flapping under the vehicle, like a loose shroud (skid plate) under the vehicle. In this case, I don’t think it would cause an almost 50% drop in mileage, but it could be a cause in vehicles where someone notices a 20-25% drop.

Even if the vehicle were leaking a gallon of a gas a day you’ld be able to smell that. An injector can leak an ounce a day and you get the odor of gas.


I have to vote with Tester on this. Even the smallest of raw gas leaks can be noticeable and I would think that whoever did this (unneeded in my opinion) fuel system cleaning and fuel system check (?) would have noticed a raw gas leak.

At this point I don’t know what’s going on with the OP’s vehicle. How is the mileage being determined, any codes present, CEL on (assuming it even works), low tire or tires, any black smoke out the tailpipe, etc, etc, etc.

On second thought, I think it would be pretty obvious too, but I’m still saying that it is a possibility that the van could have a leak. Maybe the OP just forgot to mention the smell of gas.

Very true and especially considering just about no information at all was provided about the problem.