From 18mpg to 16mpg after Seafoam, Undercover, and New Tires?

I have a 2004 Double Cab Prerunner 3.4L auto with 84k. It has had all factory recommended service at the local Toyota Dealer since I bought it used in 2007.

I was running 265/70/17 Firestone Destination A/T tires until about 3 weeks ago. I switched to 265/70/17 Bridgestone Dueler Alenza's. I am running 34psi in the tire, Max is 44psi. As expected, the ride has improved quite a bit going away from an A/T tire.

I put an Undercover Tonneau on about 2 weeks ago and a ran the seafoam treatment through the engine about a month ago.

I also started using Chevron 87 octane gas exclusively. In the past, I would just get gas at the nearest station

I did not expect the tonneau cover or any of this to improve the mileage, well maybe a little? I did not expect it to get worse.

Am I running the tire pressure to low?
Are these tires known to get worse mileage?
(I am still in the 30 day exchange period on the tires at Firestone if I choose.)

Did seafoam cause fuel filter issues? Any issues?

I am open to any ideas or suggestions to improve mileage. I did search Gas Mileage threads, but I thought I would put my specific information hoping that would help?

 

I don't think Seafoam would cause FF issues. It is just solvents. Pull your spark plugs (or a plug, to start) and check the burn. Make sure they did not get fouled during the Seafoam. Also, did you change your oil right after seafoam? Not that that alone would cause a mileage drop, but it should be done after all the carbon is knocked loose, and to get the solvent out of the oil system.

BTW, I have only ever done seafaom in the gas tank and some in the oil right before an oil change. I have never done the vaccuum smokestorm seafoam method.

Also, when was he last time your throttle body was cleaned?

 

myth busters did a think on toneau covers. the best gas mileage was open bed with the tail gate up

 

I did not check the spark plugs. Check the Burn? What exactly do I look for on the plugs and how do I tell if they are bad? (I am not much of a mechanic.)

I did not have the oil changed. It has only been about 2000 miles since last one. (I guess I should have waited on seafoam.) I did seafoam smokestorm method and rest in gas tank. Not as much smoke came out as expected, but I guess that is a good thing.

I have no idea about the throttle body cleaning? If it was part of the attached maintenance schedule below 84k, I have done it. If not, is that something I can do or about how much does it cost to get done?

 

I think the tonneau cover is part of the problem as it add's weight to the truck and effect the arrow dynamics ( air flow ). Big ties don't help either.

If you are concerned about carbon build up I run a bottle of Techron through mine once a year and with quality gasoline there should be no carbon build up, the reason I ran it was I bought the truck used and was not sure about previous owners maintance.

I would never run any additive into the intake some guys swear its the thing to do.

If your thermostat is out of wack and not heating up to normal that could tell the computer to run the engine a little richer.

 

Behold the goldmine of information we have assembled for you here:

http://www.tacomaworld.com/forum/1s...y-how-thread-compiled-list-helpful-links.html

Specifically:

SparK Plug Replacement:
http://www.4runners.org/writeups/sparkplugs/
-Spark plug read-up. How to diagnose spark plug for engine troubleshooting:
http://www.aa1car.com/library/cm1196.htm

There is no 1st-gen-specific write-up here for the TB cleaning, but there is a 2nd gen writeup. It is recommended maint. as needed. Procedure and parts are the same, but it just looks a little different. Note that this includes cleaning the MAF sensor (mass airflow sensor), which you should also do while you have it apart.
http://www.tacomaworld.com/forum/technical-chat/94203-how-throttle-body-cleaning-2005-v6.html

These are both great DIY projects for you if you are comfortable with them. Cost is virtually nothing...just your time and patience.

 

False. It was open bed with net tailgate

 

Well i have an A.R.E. cover for my truck and i did so much mpg caculating before and after and from what i can tell the tonneau cover increased my gas mileage by 1 to 2mpgs and i did the average both times on three fill ups. i do mostly all highway driving also but i feel that it is more airo dinamick****(f' ed that word up) i get almost 19.5 from my 18 previous

 

Even if the tire size remains the same there could be a weight difference in them.

Look up the specs on tire rack or some place like that to see if they are heavier.

 

On my last truck 05 Dodge Ram quad cab Hemi with the 20' wheels, I averaged 15 mpg for about 2 years. Then I added an Undercover toneau and my milage dropped to 14.5. I am convinced the aerodynamics were the cause. The weight of the Undercover was 55 lbs. I cant see the weight making that big of a difference on a truck with 345 hp. Some people think I'm crazy, but I checked my milage regularly even though the truck had the cpu that calculated it. I even came to the conclusion that the cpu gave me an extra 1/2 mpg than what I figured, It consistantly gave me the extra .5 mpg over my figures. Anyway, weather it was the weight difference or the change in the aerodynamics, I saw my milage drop by a 1/2 mpg.

 

Seafoam could have fouled your plugs, change em out.

 

34 is kinda low psi for street use, pump it up to 40 and see what happens.. dont worry, obama said 40 is ok

 

It could honestly be any number of things. The added weight of the toneau, most likely not. 34 is a little low for street use, and yes the messiah did say 40 was an ok PSI to use, so go for it, cause he's never wrong (ok I'll leave the politics out from here on out). Could be the weight in tires, could be the seafoam. Could be the winter weight packed on over the last couple months. Could be your plugs. Could be you got a crap batch of gas the last time you filled up. Could be you got some crappy oil for your last oil change, or your oil filter is clogged, or your fuel filter is clogged. Or it could be you just put your foot in it a little more with the new tires and Undercover.

There are so many variables when it comes to fuel mileage that you really have to take an average account over a long period of time. One calculation does not a diagnosis make. Go to WalMart or your local parts place and get some Chevron Fuel System cleaner. Go to Chevron, put the cleaner in your tank, fill up the tank with the good stuff. Drive it through and then on your next tank do a calculation, and see what you come up with.

Oh btw. Mythbusters is awesome. I would love to have that job, you get to blow stuff up and shoot stuff, and get paid for it. That's one heck of a job. They did a really elaborate test. Open bed with a net gets the best gas mileage. Then the toneau closed bed. Then the open bed closed gate, and the worst was the open bed open gate.

 

Aero Dynamic

 

According to Tire Rack, the Alenzas actually weigh a pound less each than my old Firestone destinations. The Tonneau only weighs 55 lbs that shouldn't cause a loss right?

Since I didn't change the oil right after seafoam last time, should I seafoam again a few days before oil change?

I am going to pump up the psi to 38-40 and run some chevron cleaner through my next tank and check it out. My next oil change, I will have Toyota check throttle body, fuel filter, and plugs. I will report back my findings.

Thanks for all of the advice!

 

i dont know about everyone else but
I saw my 2002 do better with shell than cheveron I used up more gas when I use cheveron although it ran a little smoother

 

Toyota will clean and replace whatever you want but your fuel filter isn't bad, they're lifetime filters and your not even at 100k. I bet it's winter gas

 

stock size for the first gen TRD is 265-70-16, but you are running a 17" wheel...

radius and circumference of the 16 is 388.62mm and 2441.7mm

on the 17 its 401.32mm and 2521.4mm which is pretty close to a 265-75-16 in which case, i could see where the MPG would start to decline...

 

I understand, but I was running 265/70/17's Firestone destinations for 45k miles and was getting 18mpg. The Alenzas are the same size.

 

I had a drop in mpg by 2 miles after I switched tires simply because my new tires are heavier. you could be having the same issue.

However, this past weekend I seafoamed engine, replaced plugs, and cleaned throttle body. Its still early but it seems I like I might have gotten those 2mpgs back.