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Fuel Economy Taking A Huge Nose Dive

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3.3K views 19 replies 13 participants last post by  dixiedawg  
#1 ·
Hi everyone,

In the past three weeks, my pat has taken a huge nose dive when it comes to fuel economy.

I have been driving my pat for 15 months now and I get 450km per tank.
In the past 3 weeks, I get about 350km per tank.
Its a huge loss.

My driving habits haven't changed one bit.
I know fuel economy goes down a little during the winter months, but I did get a consistent 450km per tank throughout last winter and summer. And this winter has been warmer than the last. So I can take that out of the equation as well.

The decrease seems to coincide with a recent oil change I had made about three weeks ago. I drove my Pat into the local Canadian Tire shop to have the oil changed since they had a deal for mobil1 synthetic for $32.99

I had them change the oil, rotate the tires, adjust air pressure in the tires, and check/blow out the air filter. They confirmed the air filter was fine.

I have been driving my Pat since sept. 2009 and just hit the 20k mark on the odometer last week. It a north edition, fd1, cvt, 4x4.

Any ideas on what could have happened? I'm thinking they may have knocked off a switch or sensor while working on the truck???
I did a quit visual check for this, but couldn't find anything wrong.
 
#2 ·
wow, that's a drop from ~23 mpg down to ~18 mpg, about a 5 mpg drop all together. There's not much under the hood hose wise that I think could do that. There's only one vacuum hose, and the air intake pipes. And if they knocked off a sensor wire, a check engine light would certainly pop up. That much loss would point to more then one thing I would think. I'd double check the tire pressures, perhaps they only put like 30psi in when it needs 35psi, and you may have had them higher then that.

Have you changed where you're getting fuel? If not, maybe the station got a load or two of bad gas, or recently changed suppliers? Only other thing I can think is perhaps the thermostat stuck open and the engine is running too cold. How's the heat working and/or does the temp gauge read in a normal position? I had a 93 Saturn that had this happen to it and I went from 31-32mpg to 27-28 mpg.
 
#3 ·
That thermostat seems a possible candidate, doesn't it? The performance drop would be far more noticeable too, if your mileage was made up mostly by short journeys. This would mean that the engine never really got up to a decent working temperature from one fill-up to the next. The only really effective way to check up on a defective thermostat is to take the thing out and see if it's open or shut at outside temperature. One jammed at open is easy to spot, because it's, well, open! One jammed shut has to be checked by sticking it in the cooker and watching through the glass to see when it starts to open up. The books all say you can do this by plunging it into boiling water, but this often doesn't work because you can't re-create the coolant conditions inside an operating engine. For instance, some thermostats are designed to open at about 220-plus Fahrenheit; you can't get water to boil up to that without a pressure cooker_and then you can't see the thermostat!
If it's suspect, don't worry; they're as cheap as chips to buy from Halfords (UK) or O'Reilly's (US). I'm sure the same will be true in Canada.

Rocal
 
#4 ·
Well, our little Patriots actually have two thermostats. The primary stat opens at 180 deg. F, and the secondary one opens at 203 deg. F. It would be the primary stat stuck open that could cause the engine to run cold, but you would see that the temp gauge on the dash would probably have the needle pointing in the bottom 1/4 range. When fully hot in winter, mine is usually between 1/4 and 1/2 range and in the summer, very close to the 1/2 range reading. My Scangauge II usually shows about 172-177 deg. F in the winter, and 198-202 Deg. F in the summer.
 
#6 · (Edited)
todde702 said:
When fully hot in winter, mine is usually between 1/4 and 1/2 range and in the summer, very close to the 1/2 range reading. QUOTE]

same here
I would check air filter and suprisingly the PCV valve.SLowly my jeep kept getting worse mileage and I couldn't understand why and I read somewhere that stuck PCV valve could lower gas mileage.I changed my PCV and now I am back to 22mpg around town like when I first bought my patriot also ran fuel injector cleaner 2 weeks before that
Click to expand...
 
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#9 ·
I'm thinking that your oil change guys did a number on you. 10w40 would do that to you. Tire pressures can make a HUGE difference, too. $32 is CHEAP! I dont think I can buy the oil and filter at Autozone for that.
 
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#10 ·
I'm going in for the third oil change on my Chrysler service plan today. Back in the fall they advertised this plan, 4 oil changes for $39.99, so of course I bought it. There is no way I can buy the oil and filter for $10, and this time of year is tough for me to do my own anyway. I did post here when they were running that special, I'm surprised that everyone did not run out and buy that.
 
#11 ·
Thanks for your input everyone.

Well...I think I can eliminate the t-stat. I get the same nice toasty air coming into the vehicle. The temp gauge is showing normal operation, which is/has always sat around the half-way mark...as Dixiedawg mentioned.

Todde702 : I do +- 70%highway driving. And I make a point of *almost* always fuel at the same gas station (shell). I think shell makes/distributes their own gas but i am not 100% sure. Anyhow, I did fuel-up again last night at this shell station. So I will see if bad gas is a possibility. I like your thinking!

rskitall : I will check the PVC valve this weekend. The cost of replacing it is very cheap. Just one question though : Where is it????

afmcronnie : How would the wrong grade decrease fuel economy? Unfortunately, there is no way for me to check that. The $32.99 is a 5 litres jug of Mobil1 synthetic. This does not include the price of the filter and labour.

As far as outside temp is concerned...we have been averaging -10C....and in the last week or so, we had a few days of -25C...not enough to warrant such a drop. As I said before, we had a colder winter last year and my pat was running +-22mpg consistently.
 
#12 ·
I also use Gumout fuel injector cleaner, add one each time I change the oil. I've had them clog before, no fun. That will drop your MPG too.

You just hit your 20K mileage mark? gee, I've had mine since Aug 08, and recently hit 60K miles.

You could change the plugs too, what the heck, should be less than $20 if you do it yourself.

Let us know what you figure out on this.
 
O
#14 ·
I also have seen a 4 mpg drop this winter from my summer mileage, I am in a Cold area of Michigan with a winter fuel mix containing ethanol and whatever else they put in it. I maintain my tire pressure at 35 psi with a tire gauge, the vehicle readout does not read as accurate as a gauge does, and alot of my trips are a short distance year round and city driving, so in the winter i waste fuel during the short warmup period of driving that I do. At least I get to park in the garage or I might lose 5 mpg also. My wifes 2008 Liberty also loses 2 to 3 mpg in the winter but she drives further then me and has more time on the highway so it does not suffer as bad as my mileage does.
Last year the Government started allowing up to 15% ethanol to be put into gasoline instead of 10% maximum, Maybe the Shell station you go to is using the higher ethanol amount in the fuel that you buy, check with them, this could be a reason you have seen a change from last year. Good Luck Jeff.
 
#15 ·
if you take off the engine cover you will see it on your left (facing vehicle).There is a black hose that connects to it
 
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S
#16 ·
I joined this forum today to ask this exact question.
My wife owns a 2008 4x4 Patriot with the CVT, 2.4l. Bought it new and it now has around 45,000 kms on it. Up until several months ago she would average around 450km per tank. One day she mentioned it seemed her mileage had really dropped. This was still in the summer/fall so I don't think temp has anything to do with it. Seems to only squeeze out barely 325kms or less these days. I actually was starting to think someone was siphoning gas from the tank at night so we started to park it in the garage. That didn't help. I am going to replace the air filter today and perhaps the pcv valve if I can find one today. I am hesitant to bring it to the dealer as I don't have huge confidence that they will find anything, but be happy to present us with a huge bill for doing nothing.
Her driving habits have not changed, have given it regular oil changes, etc. Seems to run fine. I am wondering if the CVT has anything to do with it, or if perhaps the brakes are partially sticking.
 
#18 ·
welcome to the forum.

I keep track of my fuel mileage and use it to indicate somethings need looking into.

You said your replacing the air filter and pcv valve that's good.
You may also want to replace the spark plugs as they are almost due.
You may want to have your brakes checked, when checking get them cleaned (just blown with air) and have the sliders on the calipers removed and greased with a synthetic grease. If any or all this solves it great, otherwise keep checking.
 
#19 ·
Well hopefully this thread won't go to waist with all the good info posted by everyone.. Because I feel kinda stooopid this morning. :(

So in the past recent weeks, my fuel gauge has been going doing as fast as my temp gauge is going up. This is, until I checked and re-adjusted the tire pressure. Now all is back to normal.

It's soooooo nice to know that I can rely on such great and competent service from the kids at Canadian Tire. I had asked the service desk to adjust the tire pressure specifically to 35psi and had him write this on the work order. It so happens the they adjusted the air pressure evenly across all 4 tires...but to 32psi.

Makes me wonder what else they can *&?%-up when they cant even do a simple task right.

Doesnt matter know. I'm done with that shop now matter how low a price for the oil jug! I already paid the price difference in gas $$$ :mad:

Oh and....thanks for the PCV valve info rskitall...found it, checked it, all is fine!
 
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