2002 Saturn SL dropped 10mpg after oil change

Jalen · #1 10-05-2008, 08:35 PM

Well, I thought I'd front the question here. All through March, April, and into July, I was getting between 42-45mpg, driving in city, average trip about 10 miles (each way to and from work). So about 25 miles a day, 4 days a week.

Now, at the end of July, I took a small road trip from Denver to St Louis Missouri. Roughly 850 miles each way. I got back from that trip, having just pushed over my 3000 miles since my last oil change.

Now, a little back story, since I bought the saturn last november, I've had all of the oil changes done at the dealership. I was getting a discount, so I figured I might as well. I have no idea what the Saturn dealership was putting in other than that it was the 5w20 that was reccomended by the manual. I've since been told that the normal oil is akin to Valvoline durablend synth blends.

I took the Saturn to a Valvoline Instant Oil change and had them just do a basic filter swap and oil change with natural oil.

Since then, I can barely get 38mpg, no matter what I do. I have been averaging 35mpg or so since, but I have to drive it very gingerly, and all the tricks that got me 45 before aren't working to the effect they were before.

Tire pressure is good (max sidewall), fuel's stayed the same (from the same station every time), and this was a very sudden drop.

Would the oil be a likely cause of the FE drop? Would going to a durablend or adding a synthetic stabilizer like Lucas help increase my FE?

Thanks for any advice you all can give.

xcel · #2 10-05-2008, 08:56 PM

Hi Jalen:

___10 mpg from an oil change is not it. Even the switchover to Winter RFG will not cause that either. One item that could however is colder temps.

___Good Luck

___Wayne

Jalen · #3 10-05-2008, 11:38 PM

That's what I thought at first, but there's only two big events that coinside with the drop in milage. One is the 1700 mile trip. The other is the oil change. But what about either of those would cause the huge change?

Unless of course they didn't put 5w20 in at the oil change...

Elixer · #4 10-06-2008, 01:17 AM

How many tanks are you basing your info off of? Hang on at least another tank and see if your results stay the same. However it's worth checking a few things like:

air filter
battery
spark plugs

After a long trip it's possible that your car needs a bit of maintenance to get things tip-top again. Or just that the fuel happened to switch off later than normal, so your FE on this tank will be really high. Or your SG is miscalibrated or got reset for some reason.

Jalen · #5 10-06-2008, 02:12 AM

I know my fuel log here does not go back very far, however I have been tracking the fuel on my own since I bought the car. My average was 42mpg over april, may, june, and most of july. My average for August (post trip and change) was 35-36, then September average is 33-35. If you look my Saturn up in the Mileage Log, you can see how it seems to go up and down a lot, but sticks at an average of about 35. (http://www.cleanmpg.com/index.php?pa...)&viewcar=2491) I'll give it another tank and see where it lies, but... I'm just not getting what I used to.

My air filter is clean, and I just replaced the plugs 2 tanks ago... They did need it bad. The battery seems to be ok too.

I do not yet have a Scangauge yet, I'm basing my numbers off of miles traveled/gallons to fill tank.

diamondlarry · #6 10-06-2008, 04:30 AM

On a Saturn, one of the things that are important to keep an eye on is the coolant temp sensor. Another thing, if you have a fair amount of miles on the odometer would be to see if the O2 sensor might need changing. The one right there on the engine under the hood is usually good for 80-100K or so, I hope that helps.

2TonJellyBean · #7 10-06-2008, 06:18 AM

Big change...

Cooler weather?

Is there too much oil in the crankcase?

Do all of the wheels rotate easily?

Maxx · #8 10-06-2008, 07:44 AM

I'll take the easy answer. I'll bet the Saturn dealer was pumping up your tire pressure, and the Valvoline guys pumped it down. I'd check that first. Then check to see if they overfilled your oil. Also - you could bring it back to Saturn for your next oil change and see if it gets better. The Valvoline oil or filter may be of lesser quality.

99LeCouch · #9 10-06-2008, 09:04 AM

Do your own if you can.

Also Valvoline oils and filters (IIRC a Champion Labs product) should be just fine. Well, maybe not the bulk stuff.

Pretty much any SM rated oil will do the job.

Check all that stuff listed above and see what shakes out.

ALS · #10 10-06-2008, 12:50 PM

Why are you doing 3K oil changes? Today's conventional oils can easily go 5K miles. I'm betting your owners manual states 5K mile OCI's. If your worried about going that far between oil changes then go to a synthetic oil such as Mobil 1. There is no need to be doing 3K mile oil changes with the quality of today's oils. Wally World sells gallon jugs of Mobil one for around $23. 15K miles a year 3 oil changes vs 5 with 3K mile OCI.