fuel milage has dropped with new tyres and oilchange

[duffbeer911]

hey everyone,
I have a 98 V6 sr5 over here in Sierra Leone and have been tracking the fuel consumption. When I first got it I was getting 12 or 13mpg with bad tyres and no idea when it was last serviced. I put some new tyres on, did an oil change (well, some bloke down the road did an oil change) and now it seems I have lost a couple mpg. My last 3 tanks have been either 9 or 10mpg.

The driving here is almost all steep, dirt tracks, often very rough and crawling, no highway. I can usually get around in 2wd, but some of the worse roads I need to engage 4x4 for a mile or two. I rarely get above 40mph.

I have been using the AC a bit more recently, would that make such a big difference? I also haven't yet got the wheels aligned, will that make a big difference considering most of my driving is slow/off-road?

any other tips much appreciated!

thanks!

 

[wardriver]

With all those back roads how does that air filter look?

 

[IanB]

AC makes a big difference, it takes somewhere in the range of 10-15hp to operate, so that will make a big difference to your fuel economy, especially if you're doing mostly low rpm driving as described.

You also didn't mention, did you put the same size tires on as you took off the truck?

 

[duffbeer911]

ok, will check my air filter tonight ...

the tyres are a tiny bit bigger (as in, diameter) than the old ones. The new ones are 275/70R16.

also, not sure if it would effect fuel consumption .. but the guy put in castrol SAE40 engine oil, and then today another guy said that is the worst stuff you can get and suggested a 20w50.

thanks for the info about the AC ... have been trying not to use it for a full tank to see the difference.

thanks agian for the help

 

[duffbeer911]

air filter doesn't seem too dirty (does it?) ... a lot of red dust came out when I shake it out ... see attached.. you think i need a new one??

 

[IanB]

It's supposed to be white, change that thing.

 

[GladeRunner]

Yes the filter is bad, change it.

 

[Whitson Metalworks]

SAE40 and 20W-50 might as well be molasses, toyota calls for 5W30 if im not mistaken (i use 10W30 full syn). i agree, replace the air filter and take a look at the maf and see if its dirty too.

 

[wardriver]

Yea, change it. You should also check to see how your spark plugs look. Both are an inexpensive fix.

I would consider running for a can of Seafoam or some Marvel Mystery Oil through the fuel. (And the Seafoam through the intake) You probably have some carbon build up in there that is hindering your MPG.

We had to change the air filter on our farm vehicles very often. If you are in a remote location you might consider buying a K&N or a Fram Air Hog filter. They can be field serviced with a recharge kit and a few hours to dry.

 

[duffbeer911]

ok, first stop tomorrow is a new air filter! and oil ... is there any reason the guy would recommend 20w50? Climate? it gets very hot out here in dry season ... dust? very dusty in dry season too ...

 

[Kurtis]

How hot are we talking? The numbers are the viscosity of the oil. I run 5W30 in all my vehicles. I can't think as so why someone would run 20W50.

 

[Whitson Metalworks]

20w50 is for harleys and other briggs and stratton type motors :boxer:

 

[duffbeer911]

not crazy hot ... like 35 degrees C in dry season

 

[T4R2014]

The guy who changed your oil must have been a baboon. Dump out the SAE40 and put in 5W30 or 10W30 ASAP. Get a new air filter and clean your MAF as well. You can check the Tutorial and Documentation reference for any guides. Make sure you use at least 87 Octane fuel as well.

 

[duffbeer911]

argh, its really hard to find qualified people here who know what they are doing ...I'm a total beginner with mechanics but still find it is best to do things myself! Tomorrow I will drain the SAE40 and replace with 5W30 ... get a new air filter .. and find some MAF cleaner I hope...

Unfortunately I don't get any choice of fuel here ... its just either petrol or diesel ... I try to fill up at NP (Nigerian Petroleum) rather than the no-name stations as I hope they have better quality fuel...

 

[Whitson Metalworks]

If you suspect poor quality fuel you might want to read up on changing your inline fuel filter. Once replaced, crack the old one open and see what all you've run through it. Can you get the fuel additive Seafoam there? If you can, use it.

 

[duffbeer911]

well i put in a new air filter and replaced the oil with 5w30 ... and filled up the tank, so we'll see how it goes on milage this time around. I feel like it has a bit more power just from this ... would it be that noticeable???

i'm still planning on cleaning the MAF but not sure i'll be able to find the cleaning spray here.

thanks for the help, i'll keep you posted

 

[T4R2014]

Fuel filter wouldn't a bad idea to change either. Also check your plugs and wires.

 

[hrt4me]

how difficult/easy is it to change the fuel filter?

 

[duffbeer911]

thanks, i'll look into changing the fuel filter myself ... the same guy who put the SAE40 in said the fuel filter was fine, but he also must not have bothered looking at the air filter ... so I won't take his word on the fuel filter.


A side note to this story ... I just noticed a sticker under a whole lot of dirt on the engine that says the timing belt was changed at 137,000 miles ... BUT, the clock only shows 89,000 miles ... ?!?! would it be easy for someone to wind back the odometer? I've only got registration records back to when it was imported to Sierra Leone so it could have been done by the person who imported it ....