MPG not what it used to be, any ideas?

I have a 2003 Galant with the 4G64 4cyl. 186K miles. I know its probably getting tired with that mileage, but my fuel economy isn't what it used to be. I owned the car since 2005 when it had 37K miles on it, and up until about 150K I always got 390 to 400 miles on a tank (~29 mpg), for the last 30K miles, I've been averaging only about 300 to 330 miles per tank (21 mpg). Air filter is good, tranny was flushed at 150K, tires are good, timing belt and balance belt with all pulleys/bearings were changed at 160K. The only things I could think of are maybe plugs/wires, or maybe the timing isn't quite spot on. I don't have any error codes, but I might replace the 02 sensor just because its never been done. Any other ideas/suggestions?

change the plugs first since i change mine every year just for the reason that their dirt cheap and i run nkg iridium about 7 bucks a piece and then move on to more expensive things if that doesnt solve your gas milage problem

Tune up would really help.

Seafoam it and see where that gets you!

IRC im geting 250miles a tank :S im at 200 now and the needle is near the bottom
i do drive responsibly but i do push the paddle sometimes

Ok, I replaced the plugs, wires, and upstream 02 sensor. I haven't driven it enough to see if there is a difference, I'll post back after I've put a tank of fuel through it (with SeaFoam of course!). However, while changing the plugs I noticed there was a significant amount of oil pooled up around the spark plugs and plug wires (down in the spark plug holes in the head). I'm guessing this is due to some seals between the valve cover and head, at each cylinder? Is this an easy fix, or is there some other cause for this, maybe a common issue?

Thanks again.

dude i used get 250 a tank. and i just put in new sparks, wires and belts. i still get 250 lol. the old plugs were dry as desert sand.

ive got the 03 I4 and i get 350 a tank easely still

run a scan on your car and that might show you if anything is wrong with it like a bad sensor etc

a scan how?

Quote:

---

Originally Posted by specter6633

a scan how?

---

I thinks he means like getting the car checked at autozone where they plug into the obd2 port and check for codes.

ohh i did that and i have no codes. those 100 miles are drivin me insane bro, maybe its cuz im fat?

edit: im going to fill up till the pump clicks then im going to drive like an old lady and see how many miles i get. i do about 28 miles a day. ill report back..... should be saturday.

Has your route changed recently? When I was doing only city driving I was getting only about 240 ish. Now with mostly all highway driving out went up to 330 ish to a tank.

Quote:

---

Originally Posted by PlorkZ

Ok, I replaced the plugs, wires, and upstream 02 sensor. I haven't driven it enough to see if there is a difference, I'll post back after I've put a tank of fuel through it (with SeaFoam of course!). However, while changing the plugs I noticed there was a significant amount of oil pooled up around the spark plugs and plug wires (down in the spark plug holes in the head). I'm guessing this is due to some seals between the valve cover and head, at each cylinder? Is this an easy fix, or is there some other cause for this, maybe a common issue?

Thanks again.

---

Change the valve cover gasket and spark plug tube seals that should cure the oil on the spark plugs, use some grey RTV gasket maker on the gasket and on each tube seal.

The issue with the tube seals can cause bad mpgs. Replace them as mentioned above. Difficulty of task between 1-10 is like 2.5-3.

Quote:

---

Originally Posted by E_Emerson88

Has your route changed recently? When I was doing only city driving I was getting only about 240 ish. Now with mostly all highway driving out went up to 330 ish to a tank.

---

i drive 3 blocks to the sawmill parkway then exit at Yankee stadium. then its 5 blocks to the parking garage. in total 12.3 miles. and then after work same thing, 5 blocks city driving then highway to house. another 12.3 miles. i do occasionally beat it so i can hear the nice cold air intake sound. :) but i don't think its 100 gas miles worth lol

I get about 24mpg city and haven't tested highway. So about 350 a tank just doing city driving.

found this here : http://65.110.63.50/showthread.php?t=2536
going to switch to synthetic see next oil change.

My route hasn't changed, I do about 18 miles total, 13.5 or so at 60mph and the rest is in town.

Thanks for the tips on changing the valve cover seals, that sounds easy enough to fix, I'll make that my next project.

Also, I just changed the oil, I have always been using pennzoil conventional oil in the car, I've tried castrol synthetic in the past but I really noticed a difference in the engine with the synthetic, engine was noisier, etc. so I just stuck with pennzoil. Is there a synthetic anyone else recommends?

Thanks again for all the useful help!

ok so i did it for a 3 weeks. drive like an old lady and you will get almost 382 out of it till the light goes on. drive a little spirited and you get a little under 298. drive so u can hear your cia and make car alarms go off and 246 is what i get. problem solved. if you get 250 mpg, get new feet.

Replace pcv valve and run sea foam.

haha, good point, I'll agree that can make a big difference, although I don't drive it hard, at 187K miles I can't be too hard on it or something will break!
Since my last post I had a chance to put a few tanks of gas through the car (after replacing plugs, wires, and O2 sensor), and I have noticed a consistent increase in fuel economy, I'm not getting about 330 to 340 out of a tank before I fill up (12 gallons to fill up so I'm getting about 27 to 28 mpg now), the fuel light is not on at that point yet. So replacing those parts did help noticeably, but I will also need to replace the valve cover seals yet.

whats that? ohh 10 bucks on ebay not bad. i shall do it.
edit: which is the right one? angled or no angled?

Quote:

---

Originally Posted by PlorkZ

haha, good point, I'll agree that can make a big difference, although I don't drive it hard, at 187K miles I can't be too hard on it or something will break!
Since my last post I had a chance to put a few tanks of gas through the car (after replacing plugs, wires, and O2 sensor), and I have noticed a consistent increase in fuel economy, I'm not getting about 330 to 340 out of a tank before I fill up (12 gallons to fill up so I'm getting about 27 to 28 mpg now), the fuel light is not on at that point yet. So replacing those parts did help noticeably, but I will also need to replace the valve cover seals yet.

---

can you tell me what o2 sensor i should get. i checked ebay but they are so many different ones i cant figure out which is right.

Quote:

---

can you tell me what o2 sensor i should get. i checked ebay but they are so many different ones i cant figure out which is right.

---

I often use RockAuto.com for parts, I bought part # AP4127 (mfg by APWI) from rock auto. That is the upstream O2 sensor, but they have listings for downstream as well. If you go to www.rockauto.com you can select your make, model, and year of vehicle and pick through all the part categories and find what you want.

i get about 10mpg. lol very heavy foot, have to show stangs and camaro's whos the boss though. spring time comes i will try all of your guys input as well. along with the g75 mani too. :)