2000 Caravan with Poor Gas Mileage

[bardiferous]

Hi, Got a 2000 Dodge Caravan 3.0L with just over 100,000 miles. Just got it in mid-June and all I know is that it was faithfully garaged kept and truly driven by a nice older lady whom doesn’t drive anymore (one owner - I know the owner).

The EPA mileage rating is 16 city 23 highway and 19 overall.

Regarding my gas mileage, my first full tank yielded about 19.5 MPG, the 2nd about 22.5 (boosted by 16 oz SeaFoam), then 21.2, 20.3, 19.6, 17.9, then 17.5. Most of my mileage is highway.

Unfortunately, there were no service records maintained other than the 3K mile oil change sticker.

My Maintenance to date (about 3K miles since mid-June) I replaced the air filter within the first 100 miles. I’ve been on the fence about the plugs, wires, rotor & distributor cap since the back plugs are a major PITA to access. But that’s where I think the issue resides.

Transmission fluid was very low
Cold starts are usually easy, I turn over the key and hold for 1/2 second and release, no gas pumping. It usually starts between the 1st and 4th attempt. If I’m in a rush, I’ll just crank it til it starts, maybe 4-6 seconds.

Warm starts are easy, almost always on the 1st attempt.

While running, the smell of fuel is fairly strong in the exhaust. I haven’t driven any other similar Caravans, so I have no idea what kind of performance it should have. It is OK but I would expect a bit more power from a 3.0 L V6.

Help!

[COROLLAGUY1]

Check the fuel pressure while running & make sure it holds psi when engine is off, You might have leaky injectors or a leaky fuel pressure regulator. A bad O2 sensor can cause similar symptoms.

[circuitsmith]

I suggest replacing the thermostat, based on age.
Might as well replace coolant and radiator cap too.

[Whitey]

Anything above 16 MPG is within the normal range, and could be an effect of using different fuel pumps, some in need of calibration, temperature differences throughout the day, different routes taken, different drivers with different driving habits, a lead foot at highway speeds, etc. If your fuel economy drops below 16 MPG, that would be an indication you might have a mechanical problem.

Also, I’m pretty sure you didn’t run the gas tank dry after you put in that can of Sea Foam, so the declining numbers could be a mathematical function of the remnants of the extra volume left behind. If you didn’t add the volume of that can of Sea Foam to your initial calculation, you made a mathematical error.

[insightful]

@bardiferous

While running, the smell of fuel is fairly strong in the exhaust.

Pull one of the front spark plugs to see if it’s black (running rich).

[the_same_mountainbike]

@bardiferous

I’ve been on the fence about the plugs, wires, rotor & distributor cap since the back plugs are a major PITA to access. But that’s where I think the issue resides.

Do you plan to change them? If they’re due, that could easily cause low mileage. Although to me that mileage doesn’t look outside the norm.

@bardiferous

While running, the smell of fuel is fairly strong in the exhaust.

This could be caused by a leaky injector. When you change the sparkplugs, “read” the business ends. If you have a wet plug, you probably have a leaky injector.
Although, if you did I’d expect even worse mileage than you’re getting. So I’m thinking that your gasoline smell is probably caused by a plug misfiring.

I’ve attached a spark plug reading chart for your convenience. Okay, so I did it because it was from “Gasoline Girls”… but you can use it anyway.

[oldtimer-11]

You are right to suspect the spark plugs and wires. The 3.3 and 3.8 engines need spark plugs replaced every 100,000 miles with iridium plugs.

The 2.4 and 3.0 engines came with copper plugs and need replacement every 30,000 miles and the wires every 60,000.

This is one instance I might recommend something other than the factory plugs. If it was my van I would try iridium plugs, just because of the difficulty of changing them.

The above info came from Chilton Library because I could not find a maintenance schedule anywhere else.

I do know that my 1994 Plymouth Voyager 3.0 came from the factory with platinum plugs that were supposed to be changed at 50,000 miles and I mistakenly believed at the time they were 100,000 mile plugs so I didn’t change them at 50,000. The van started misfiring going up steep hills at less than 53,000 miles.

If you can download an owners manual it will absolutely have the right maintenance specs.

[Waterbuff]

@oldtimer-11

The 3.3 and 3.8 engines need spark plugs replaced every 100,000 miles with iridium plugs.

IIRC, these engines (at least 3.3 and 3.8) take Champion double platinum plugs and can be finicky if others are used. The key is to match what Dodge used originally.

[Nevada_545]

The Mitsubishi 3.0 liter engines came with steel tip spark plugs to be changed every 30,000 miles. The 3.3 and 3.8 L engines began using platinum spark plugs in 1996 with a replacement schedule of 75,000 miles and higher in later years.

Misfires are rather disturbing so if you haven’t noticed a problem replacing the spark plugs and wires won’t make a difference in fuel economy but may prevent future problems.

Check the engines operating temperature. The Mitsubishi thermostats often break during the first ten years of service allowing coolant to flow when the engine is below operating temperature.

[Whitey]

Is there any chance that the smell of fuel from the exhaust at cold startup could be normal? Doesn’t the computer intentionally make the fuel air mixture rich when you start a cold engine?

[the_same_mountainbike]

@Whitey

Is there any chance that the smell of fuel from the exhaust at cold startup could be normal? Doesn’t the computer intentionally make the fuel air mixture rich when you start a cold engine?

Nope, there isn’t.
It doesn’t make it that rich. The bypass mode only bypasses the oxygen sensors. The MAF, the crank speed, the throttle position, and the other “engine demand” signals are still part of the algorithm.

[Nevada_545]

@Whitey

Is there any chance that the smell of fuel from the exhaust at cold startup could be normal?

Yes, customers often misidentify vehicle odors. The smell is likely normal cold start exhaust odor and not “fuel”.

[circuitsmith]

The cold startup smell is how all cars smelled before there were catalytic converters.

[the_same_mountainbike]

@circuitsmith

The cold startup smell is how all cars smelled before there were catalytic converters.

Only because we pumped raw fuel into the venturi with the accelerator pump in the carburetor before starting, the engines ran rich and didn’t burn all the fuel anyway, and there were no cat converters… hence, no “secondary burn”. Modern cars should not smell gas upon cold start up.

[Whitey]

@the_same_mountainbik

The bypass mode only bypasses…

If the vehicle in question were in bypass mode, wouldn’t there be a “check engine” warning light on? I didn’t think bypass mode was for startup. I thought the engine’s computer used the oxygen sensors to control the air-fuel mixture during cold startup, just like it does the rest of the time.

[Whitey]

@Whitey

Is there any chance that the smell of fuel from the exhaust at cold startup could be normal? Doesn’t the computer intentionally make the fuel air mixture rich when you start a cold engine?

@the_same_mountainbik

Nope, there isn’t.

@Nevada_545

Yes, customers often misidentify vehicle odors. The smell is likely normal cold start exhaust odor and not “fuel”.

Well, that makes things as clear as mud.

[circuitsmith]

@the_same_mountainbik

Modern cars should not smell gas upon cold start up.

Non-gearheads often mistake exhaust fumes (with partly burned hydrocarbons) for raw gasoline.
On a cold start the converter is too cold to work for at least 30 seconds or so.
Even without enrichment untreated gas engine exhaust is not odorless.

[the_same_mountainbike]

@Whitey

If the vehicle in question were in bypass mode, wouldn’t there be a “check engine” warning light on?

No, the ECU simply ignores the upstream O2 sensor and meters the fuel a preset amount. Once the engine reaches operating temperature the ECU begins to monitor the upstream sensor again. It’s all taken care of in the program.

I stand by my statement. If your (modern) car’s exhaust smells of gasoline on startup, you have a problem, likely either a leaky injector or a misfiring cylinder. You’re blowing unburned hydrocarbons into the air, and that ain’t good.

I find the contention that a motorist who has been filling his/her tank at filling stations for years cannot recognize the smell of gas to be inconceivable. Saying that it’s probably the driver mistaking his/her exhaust smell for a gas smell is IMHO ridiculous. That’s something a shop tells a motorist to get rid of them.

[Whitey]

@the_same_mountainbik

I find the contention that a motorist who has been filling his/her tank at filling stations for years cannot recognize the smell of gas to be inconceivable. Saying that it’s probably the driver mistaking his/her exhaust smell for a gas smell is IMHO ridiculous. That’s something a shop tells a motorist to get rid of them.

Why would a shop say that to a motorist rather than sticking a sensor in the tailpipe to confirm it?

[Nevada_545]

@the_same_mountainbik

If your (modern) car’s exhaust smells of gasoline on startup, you have a problem, likely either a leaky injector or a misfiring cylinder. You’re blowing unburned hydrocarbons into the air, and that ain’t good.

Do you think the OP is ignoring the check engine light?

@the_same_mountainbik

I find the contention that a motorist who has been filling his/her tank at filling stations for years cannot recognize the smell of gas to be inconceivable. Saying that it’s probably the driver mistaking his/her exhaust smell for a gas smell is IMHO ridiculous. That’s something a shop tells a motorist to get rid of them.

How many days do you keep a customers car in an attempt to confirm the reported fuel odor before concluding it is the normal exhaust odor?