Ok keep in mind I probably put less than 7,500 miles a year total on my 2001 Supercrew. It only has 32,000 right now...

Last June 2005, I decided to go with synthetic oil. I put in 6 quarts of Castrol 5w20 Synthetic and put in a new Motorcraft 820S filter. I drove it about 4,300 miles (6 months) before I figured I'd better do another oil change. In looking over my service chart this morning, I realized that I FORGOT entirely about my new setup and put in regular Castrol GTX 5w20 last December! Now three months later my fuel economy has taken a dive... down from about 16 city to 10mpg!!! I could shoot myself! I know this is somehow related.

My tires are new stocks, the air filter is fine and I'm easier than ever on the gas pedal. Any suggestions? Did I damage my engine?

Thanks...
Jon

 

It is highly improbable that the mileage problem has anything to do with switching back to dino oil.

 

agreed...and using any oil that meets the required specification is not worth worrying about.

 

contrary to previous posts, i would say that the dino oil is the primary reason for a drop in mileage. however, i do agree that no damage has been done due to switching between dino & synth. just don't mix the 2. personally, i would run your current setup for a couple of months & switch back to synth

 

How would changing from synthetic to dino oil cause such drop in mileage? Also, don't many companies already sell blends of synthetic and dino oil? How would combining them be harmful?

 

Dino oil is not going to cause 40% drop in mileage. Get real. Search around these boards for the whole synth vs dino debate and you will find that there is no measureable difference in mileage (except for the Amsoil salespeople, who somehow get these wild increases in mileage and HP that no one else seems to get when they run Amsoil). There is something else going on with his truck.

 

I observe that for the same continious overall driving, the outside temp and the gas qualty count for 98% of all the changes in fuel milage as long as the truck has no known engine operating faults.
Gas qualty is a bigger issue than most think.
Iam finding that GULF in my area is one of the better fuel to use.
Go accros the state line and the fuels are really bad with there different formulations as mandated by their state laws and whatever the vedor does to keep the price lower.
You get what you pay for very often.
Low price causes you to burn as much gas as using a better fuel at a higher price so there is no real gain in the lower price..

 

Check your EGR valve. That thing killed the mileage in my Ranger until I replaced it.

 

The change in oil didn't cause the huge drop in fuel mileage. No way.

Outside temp. plays a big part in mileage. When it gets colder the truck runs richer longer.

When you're ready to change oil again, just change back to synthetic. No harm done to engine from oil change.

 

Well I'm glad the consenus is that the engine isn't damaged. Shows how little I know about these things. I will have the EGR valve checked. Also, I don't believe the fuel filter has been replaced since day one.. maybe time? I guess those 30,000 mile maintenance packages are there for a reason huh?

Thanks,
Jon

 

Using Dino oil won't hurt a thing. Going 4300 miles on Dino oil won't hurt anything. I change my Dino oil every 5K miles regardless of how long it has sat in the pan. No one has yet convinced me oil goes bad sitting in the pan for more than 3 months.

Usually, weather has the greatest effect on fuel economy. I usually lose 3-4MPG in the winter. Also, new tires can have a 1-2 MPG effect. From tire pressure to rubber composition to tread style... all have an impact on fuel economy.

 

FYI... I am real & I am speaking from personal experience. Which is part of the reason for forums such as this one. Someone asks for someone elses opinion & my opinion is given. That said, I have personally seen differences (1-2 mpg) between the use of synthetic vs. dino. I'm sorry you haven't benefitted the same.

Crewd... I would have to say that the colder weather may have something to do with your results as well. (this my opinion ONLY!!)

 

Wild4kst8,

I'm assuming you've seen an increase in mileage using synthetic correct?

In regard to the tires. They're new Michelin LTX/MS's ... same size as the original. The maximum tire pressure (on the sidewall) is 35psi. Would bumping them up a bit help or is that a dangerous option?

 

Just because they are the same size does not mean they will not affect mileage. Tread pattern will affect mileage, as will several other aspects of design of the tire (load range, side wall flex, etc...).

As for expecting to increase your mileage by changing to synthetic oil, don't get your hopes up on getting anything measurable. Real world results are something like .5mpg from changing engine, trans, transfer case and rear diff to synthetic. I have yet to see anyone able to prove (from actual detailed mileage records) that changing just the engine oil to synthetic gains anything.

 

Yes, I've seen an increase in MPG with using synthetics. And yes, I've gone fully sythetic from front to rear.

In my opinion, you've probably got the best tires for MPG. I have the original Goodcraps AT/S & run 38 psi front & 35 psi rear. You'll probably want to experiment to find the best for you as far as ride & MPG. However, given you only drive 7.5k a year, it may be difficult to determine what psi to run at. Good luck.