Timing belt and its effect on fuel economy
 

I have a 99 runner 3.4 and I was wondering what a worn timing belts effect may have on fuel economy. I bought the truck used and the dealer did not have any records of the prior owners service so I dont thing he has changed the timing belt in quite some time. The truck has 147k on it.

So the current situation is this, I know its winter and I know its a truck so I never have expected GREAT gas mileage, but the last several times I have filled up I have clocked about 11.2 mpg and that seems unacceptable to me.

I have already done a full tune up to no avail, the timing belt is the only thing I have left to do...could it have anything at all to do with that poor of fuel economy? I mean I think I should be getting atleast 13-14 mpg in town.

Thanks.

Shouldn't have any effect on fuel economy. Timing belts dont wear or stretch. The only way it could affect the engine is if it lost a tooth, in which case you would notice more than poor fuel economy.

At 174k if that's still the original belt it's definitely time for a replacement. The recommended interval for the 3.4 is 60k or 90k depending on the year. I can't remember which it is for a 99.

For the V6, it's 90k, for the 4 cylinder (if they had one in '99), it would be 60k.

Wowsa! gotta love toyota for the ability still have a timing belt at that point :)

Make sure you change the water pump too as its supposed to be changed every 2 times you change your Tbelt, but since your already almost double over might as well do it now :)

i have never seen a dealership or indept mechanic who didnt put a timing belt mileage sticker on the fan belt shroud/cover. did you see if there is one on there indicating when it was changed?

yes, 90k is the change interval. along w/ the water pump and thermostat while its all taken apart. at your mileage interval, id do all three including all of the drive belts

bob

i changed my water pump after 180k miles (second timing belt change) and it still wasnt leaking or making noise....but most of the time people do...some shops even change the idler pulleys and everything!

isnt this like if you wax it youll pick up like a good 2 tenths of a mpg?!?! :roll:

You can take that 2 ways.

1. Thats a quality belt.

2. My 04 is still using timing belts?! My 99 s-10 had a timing chain that didnt warrant replacement ever.

hehehe

Yeah! The next big thing...timing gears! Lego style baby! :laugh:

Or continously varible timing connection...VVT-i squared!

Timing chains have guides...those should be replaced around 140k miles too :) :cry:

the new honda crv's don't have belts or chains. ...they are gear driven. no maintenance at all.

now thers a thought!

T/belt change 90K for the 5VZ... the only 60K T/belt recently was the older body style 4 cyl Camry... everythings going to chain. No reason to replace your idler pulley unless its faulty, same with water pump. Although if your water pump has never been changed out do it for preventative maintance. They will leak if never replaced. The factory didn't apply enough FIPG to seal it long term. They just recently came out with a gasket, no more FIPG. After the first replacement there is no need to replace unless it does leak. But do your t/belt if its never been done. Your motor isn't interference, yet it will leave you stranded where ever it breaks.

As for bad gass mileage... that could be a huge number of things. Depending on where you live winter time gas can have an effect on mileage. Plus now that they've allowed dirty fuel in places, that could effect it... and the list goes on. We get a lot of complaints about poor gas mileage during the winter, and it all comes down to the fuel they change over to that prevents freezing...

I know i never change the idler pulleys and what not my taco is over 230k miles and still going strong...and that thing sees redline on a daily basis.

THe shop is a audi/vw shop so i dont blame them for wanting to change everything :spank:

Which idler pulley? If your talking about your idler bearing, I've seen them go bad, but its always associated with a broken timing belt, a confused customer and usually a seized water pump. But yeah, overall they don't go bad.

The early 5VZs had a recommendation of 60k on them for the timing belt (I think they changed in 1998).
That being said I never saw one that didn't make it over 90k so I use that interval to change mine.

All 5VZ t/belts are 90k... the only reason the old 4 cyl Camrys were 60K is they work off a non-hydrolic tensioner... I've probably done 30+ timing belts on 5VZ-FE motors alone not to mention the 40 or so t/belts I've done on the 5S-FE (ie: older 4 cyl Camrys and Rav4) and 3VZ-FE transaxle vehs (ie: older 6 cyl Camrys and Siennas)

https://www.yotatech.com/forums/f2/timing-belt-info-21821/

The belt technology has improved since so everyone (including most dealers) has switched to 90k for the timing belt maintenance interval

I am just giving advise per what our Toyota dealership and others follow for maintance rules. Since we are "governed" by Toyota itself our guildlines must meet a certain criteria...

That was Toyota's criteria initially (people on YT didn't make that up).....they later revised it to be 90k across the board.