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Hi, so I've noticed we're getting consistant poor mpg with our 2008, has new platinum spark plugs, no warning lights are on. We're getting about 14mpg in mostly city driving, I've even tried turning off traction control, still haven't seen a bump at all. Are there some other things I can try? The air filter is also ok. Thanks!
 

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Hi, so I've noticed we're getting consistant poor mpg with our 2008, has new platinum spark plugs, no warning lights are on. We're getting about 14mpg in mostly city driving, I've even tried turning off traction control, still haven't seen a bump at all. Are there some other things I can try? The air filter is also ok. Thanks!
What do you see on the highway for mileage?
 

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Haven't been able to track much highway mileage, it's the wife's kid shuttle to and from school, work. I did do a reset this morning and it looked like with about 60% of my drive being hwy (12 miles) it was averaging about 21. Not terribly scientific.
 

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Our 07 3.8L burned some oil and slowly plugged the catalytic converter. It caused progressively degrading power and MPG until it finally threw a code and clued me in. The engine's power would decrease as it got hotter and it wasn't till it almost had trouble maintaining highway speeds that the light finally came on.
 

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Mostly city driving is horrible for gas mileage. 14 sounds low but not by all that much. On the highway it should get low-mid 20s, which it sounds like it might be doing.
 

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In addition to clogged cat converter, I also got a noticeable gain in MPGs after replacing a bad EGR valve.

How is operating temperature? Does your gauge fairly quickly warm up to 205* and then holds at that temp, or does the temp bounce around lower? If the latter, a stuck open t-stat or bad coolant temp sensor can also cause bad mileage particularly for city MPGs.
 

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Haven't been able to track much highway mileage, it's the wife's kid shuttle to and from school, work. I did do a reset this morning and it looked like with about 60% of my drive being hwy (12 miles) it was averaging about 21. Not terribly scientific.
Kinda suggests to me that it is how your wife drives, not the car.

My wife still uses her left foot to brake (it's how she learned). I suspect a lot of people who do this sometimes get tired or something and slightly depress the brake. I've seen cars on the hwy whose brake lights come on and off, where I suspect that is what is happening.

She also stays on the gas until right before braking, whereas a normal driver may lift off the gas and coast down to a red light.

She has a lot of bad driving habits but I did get her to stop shifting out of R in to D while the car was still rolling backwards, so I have that going for me, which is nice.

I think my wife gets 15~16 mpg in city driving (2002 3.3 and 2009 4.0)
 

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A common issue with the 3.3L & 3.8L, clean or replace the PVC. Then take the TB off and clean that too. WATCH the YT vids on how to clean the TB. It has electronics behind the black plastic cover that should NOT get carb/TB spray in it.

Ideally, you would want to route that rear hose from the PVC forward to join the front hose. Add a Y-fitting to allow the mucky oil gasses to the air-intake oil chamber. This will help with MPG too. I hypermile with my GC 3.3L and achieve 29-ish MPG hwy. You should be able to get 27-ish MPG with the 3.8L. 21MPH hwy is actually low for the 3.8L.

As for plugs, the Autolite single platinum has provided good response and good MPG. Avoid plugs that have too many ground hooks as the gas vapors to ignite are slightly delayed with city driving.
 

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A common issue with the 3.3L & 3.8L, clean or replace the PVC. Then take the TB off and clean that too. WATCH the YT vids on how to clean the TB. It has electronics behind the black plastic cover that should NOT get carb/TB spray in it.

Ideally, you would want to route that rear hose from the PVC forward to join the front hose. Add a Y-fitting to allow the mucky oil gasses to the air-intake oil chamber. This will help with MPG too. I hypermile with my GC 3.3L and achieve 29-ish MPG hwy. You should be able to get 27-ish MPG with the 3.8L. 21MPH hwy is actually low for the 3.8L.

As for plugs, the Autolite single platinum has provided good response and good MPG. Avoid plugs that have too many ground hooks as the gas vapors to ignite are slightly delayed with city driving.
 

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Discussion Starter #10
I know that when my wife drives, off the line she'll routinely get it up to 4k between the first couple shifts. So I'm sure she's got something to do with it. I drive it way differently for sure. As far as the temp goes, it does warm up pretty quickly and then stay in the middle of the gauge. Is it a good idea to replace the EGR anyway? I'm not aware of any codes, I don't have a check engine light yet. I'll also look at a reroute of the PCV hose.
 

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I found a video for how to remove and clean the TB, very straightforward. Can't find much on the PCV location and then your rerouting. Any chance you could point me in the right direction?
 

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PCV valve location
https://forum.chryslerminivan.net/showthread.php/23672-2008-Town-and-Country-PCV-Valve-Replacement-3-8L

EGR can probably just be cleaned. Replacing seems like a lot of money for something that may not be an issue (that same money buys a lot of gas :)).

The only car I've had EGR issues with are my Saturns (not really issues, but I cleaned them as preventative maintenance). Then again, I have no experience with the 3.8 - two of my vans were 3.3L (very similar engine) and my current is 4.0L (completely different engine).

I'm not familiar with the re-routing business, but if you are concerned about the crank gasses and the oil mist that comes with it, you could look up "oil catch can" - it's a fairly cheap/easy DIY way to keep the throttle body clean from the PCV gasses.
 

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PCV valve is known issue and relatively inexpensive. But be sure to use OE Mopar for replacement part.

The EGR valve would likely have caused engine issues if it were going bad. Usually starts with rough running when cold and as that worsens it will lead to stalling when the motor is cold, and a bit worse when ambient temps are also cold. Stalling like within first 1/3 mile of house on your first run of the day. Once the motor warms up, the stalling goes away. The EGR valve will go bad when the coolant plastic Y-diverter cracks and leaks coolant onto the EGR valve while driving, if the coolant leak isn't caught soon. So if you haven't experienced any of these things, then I wouldn't throw money at parts with a new EGR valve.
 

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PCV valve is known issue and relatively inexpensive. But be sure to use OE Mopar for replacement part.

The EGR valve would likely have caused engine issues if it were going bad. Usually starts with rough running when cold and as that worsens it will lead to stalling when the motor is cold, and a bit worse when ambient temps are also cold. Stalling like within first 1/3 mile of house on your first run of the day. Once the motor warms up, the stalling goes away. The EGR valve will go bad when the coolant plastic Y-diverter cracks and leaks coolant onto the EGR valve while driving, if the coolant leak isn't caught soon. So if you haven't experienced any of these things, then I wouldn't throw money at parts with a new EGR valve.
 

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So a bad PCV valve wouldn't necessarily cause the check engine light to come on, right?
Almost nothing to throw codes.

I have to re-route my rear hose to join up with the front one and then into the air-intake side-chamber that acts sort of like a catch-can. At the present, both hoses just run into open-cell filter material on the ends of the hoses. When sitting at a traffic light or a long stop, the HVAC system will pull in the oily smells of those hoses. I had posted a few images in the 3.8L TB to the 3.3L engine thread here of the air-intake box mods.

As for the EGR, it's cheap to replace from ROCKAUTO.COM BUT, be sure to use a shop-vac and clean out the engine block ports! on my old 2005, it had a huge amount of carbon soot. Usually, the EGR problems will throw a code or two or even three! HINT. If you grind just a smidge off [3/64ths] of the top alternator casted mount, you will not need to remove the alternator nor pull the passenger wheel and inner plastic cover off! This way, you can just get a tool in there to remove the EGR bottom fastener.
 

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So a bad PCV valve wouldn't necessarily cause the check engine light to come on, right?
Almost nothing to throw codes.

I have to re-route my rear hose to join up with the front one and then into the air-intake side-chamber that acts sort of like a catch-can. At the present, both hoses just run into open-cell filter material on the ends of the hoses. When sitting at a traffic light or a long stop, the HVAC system will pull in the oily smells of those hoses. I had posted a few images in the 3.8L TB to the 3.3L engine thread here of the air-intake box mods.

As for the EGR, it's cheap to replace from ROCKAUTO.COM BUT, be sure to use a shop-vac and clean out the engine block ports! on my old 2005, it had a huge amount of carbon soot. Usually, the EGR problems will throw a code or two or even three! HINT. If you grind just a smidge off [3/64ths] of the top alternator casted mount, you will not need to remove the alternator nor pull the passenger wheel and inner plastic cover off! This way, you can just get a tool in there to remove the EGR bottom fastener.
 

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On my '08 it was the brakes that killed my mileage. They were dragging. The brake pads were too tight. I cleaned the brake pad channel, then used a bench grinder to grind the tabs down a little bit until the pads slid freely. Gas mileage returned and the brakes felt much better.
 

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My experience with my 2006 3.8 Touring, I had noticed the MPG progressively getting worse over the years with wife driving to and from school/work. It probably took it's toll on the rings. The code for the catalytic converter eventually tripped. Had that replaced, but I think a clogged CC probably contributed to the PCV going bad? A lot of oil inside the PCV hose. Seems that pressure was building because the rear valve cover began to seep oil as well. I wound up replacing the valve cover gasket also. It was much easier to replace the PCV with the cover off, and the rubber grommet was very brittle. Don't want those cracked pieces falling into the valves.

The MPG got as bad as 12 for city driving. I now drive it as my commute vehicle which is probably 40/60 highway to city driving, and I average around 20.

If you happen to have an OBDII scan tool, that can tell you if your CC is starting to go bad. The O2 sensor bank 2 voltages will be all over the place.
 

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My experience with my 2006 3.8 Touring, I had noticed the MPG progressively getting worse over the years with wife driving to and from school/work. It probably took it's toll on the rings. The code for the catalytic converter eventually tripped. Had that replaced, but I think a clogged CC probably contributed to the PCV going bad? A lot of oil inside the PCV hose. Seems that pressure was building because the rear valve cover began to seep oil as well. I wound up replacing the valve cover gasket also. It was much easier to replace the PCV with the cover off, and the rubber grommet was very brittle. Don't want those cracked pieces falling into the valves.

The MPG got as bad as 12 for city driving. I now drive it as my commute vehicle which is probably 40/60 highway to city driving, and I average around 20.

If you happen to have an OBDII scan tool, that can tell you if your CC is starting to go bad. The O2 sensor bank 2 voltages will be all over the place.
I think you meant Bank 1, Sensor 2.
 
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