Full Engine Pulley Replacement == Massive MPG Increase

So an idler pulley started squeaking really bad on my 2005 4.0L and I replaced it. Within 2k miles another pulley completely seized up on me, snapping the serpentine belt. There was melted belt stuck to most of the idlers, and at 205XXX miles, I just decided to order a pulley/belt kit and replaced all the pulleys including the tensioner. The remaining pulleys I swapped out were not squealing, but they were definitely not spinning smoothly when I inspected them outside of the vehicle.

The first thing I noticed was that my engine was quieter. I then noticed slightly more power…I wasn’t sure if it was all in my head, so I just laughed it off. Old pulley bearings won’t rob THAT much power, right? WRONG.

When it came time to fill up, I saw I had gone over 270 miles on 3/4 of a tank. My truck is on 285/75r16’s with 4.10’s, a shell, heavy steel bumpers, and a winch. Driving a mix of city/highway in the mountains with lots of steep grades and the A/C on I got 17-18mpg. Previously, I was getting ~15.

Lessons to be learned here:
1) All the pulleys seemed to have a very similar lifespan, so if you replace one you might as well get a kit and replace them all
2) Bad pulley bearings add a LOT of drag. If your truck is high mileage, you might see a big mpg increase with new ones. I saw a 2-3mpg increase in hard-use type driving. I’m excited to see what I get on my next road trip.

TLDR: Don’t ignore your idler pulleys! Replace them if your mileage is getting high. In retrospect I should have done this as preventative maintenance around 160-180k.

 

I'll keep that in mind. My 07 is at 218,000 miles and my fuel mileage and performance is the same as new. For normal every day driving I'm at 16-17 mpg. On road trips 18-19. Same as 14 years ago. But if I do ever note a drop that is something I'll look at.

 

Good advice! I wonder what a reputable shop would charge for this?

 

The local Toyota dealer quoted $1200 to replace all the idlers and tensioner with a new belt on my '06.

I did the work myself. The only thing I couldn't remove was the tensioner. The bolts mounting the AC compressor were not accessible with the tools I have on hand. So, I replaced all the idlers and the belt. I suspect the tensioner will fail at a very awkward time.

 

What kit did you go with?

I’m at 212,277 miles with no service history from the previous owner so I imagine I should be looking into this soon.

 

I got the Continental kit on Rock Auto. All the bearings are Koyo.

 

I thought I had an issue with pulleys. I was getting morning squeaking. I got the replacement belt, checked all pulleys, all seemed fine except the tensioner was slightly wobbly, all spun freely including the tensioner. I stuck the new belt on, the noise is gone but mileage is still horrific.

I average around 11.5 mpg. If I baby it 12.5 to maybe 13 if I’m lucky. If I drive like what I would call normal, it’s 10.5 to 10.7. Yes normal is lead foot.

I was really hoping it was a pulley dragging badly. I stay on top of maintenance. Oil changes, plugs, gear oil, clean maf & throttle body, air pressure, etc. I really don’t drive it much so bad mileage doesn’t bother all that much. It’s a 4.0 manual.

 

Wow, that’s quite low. I’ve only got a few tanks’ worth of miles put on my Taco so far, but the worst mileage I’ve calculated is 17.2. That was with a lot of around town driving; over 19 on a mostly freeway drive. V6 w/auto, no cargo to speak of, few hills.

 

The tensioner pulley bearing is super easy to replace without having to deal with the whole tensioner assembly. Remove the pulley just like the others except be aware the bolt is left-hand thread so remove it by turning clockwise. Pound or press out the bearing, install the new one (about $39 on

$40 5203-2NSL Nachi Double Row Angular Contact Bearing 17x40x17.5 Sealed

Amazon) using the old bearing and reinstall. When I did it, cleaning up the pulley took me far longer than the rest of the work.

Refer to this thread that walks you through it.

 

probably at least 4 hours of labor of at least $100 per hour to do the whole front system not including the price of parts

guess how much you'd charge yourself if you picked up a cheap ratchet and did it at home
Zero

 

Thank you. Yes, I'm aware of that solution. Although, my '06 truck has 115,xxx miles, I know springs lose strength over time. My intention was to replace the entire tensioner assembly. Unfortunately, getting tool access to the AC bolts is outside of my equipment, so I'll have Toyota do the replacement sometime this winter.

 

My Taco has 111K on it but yours is older and that spring has been under load for 50% longer (if original). I was concerned that the tensioner spring in mine might be toast and I was resigned to replacing the assembly, but when I removed the belt for the pulley bearing inspection, it felt like it had plenty of life in it. Yeah, I know, a subjective, non-scientific test, but I was definitely comfortable at that point with just doing the bearing. I have read at least one post indicating that someone did the full replacement because the tensioner spring was clearly weak, but haven't seen any so far that indicated the bearing-only job was insufficient (although that of course must have been the case for a few). Worst case, you have a spare tensioner pulley to swap in next time around.

As far as I could tell before the inspection, the bearings weren't making any noise. But one of the idlers was clearly shot (spun like an old skateboard wheel) and another idler and the tensioner weren't smooth like they should be. Anyone doing their own basic maintenance should be loosening the tensioner and checking the pulleys every couple of oil changes. I didn't even need to remove the belt to do it. Since mine weren't going the opposite direction like the OP's (hard to turn), I'm sure I didn't experience any mileage improvement.

 

I can't imagine 1 or more belt pulleys could add so much drag to affect MPGs like that, and yet the friction does not melt them out of the engine bay. About once a month when I pull into the home garage, I sit there with the engine idling for maybe 15-20 seconds and listen for unusual sounds. The 2.7 engine is whisper quiet. I assume a bad pulley/bearing would be audible... maybe it will show up as excessive belt wear, which is also inspected regularly. Noisy or not, I plan to replace all the pulleys and tensioner (and belt) at 200k, currently have 171k. Thanks for the good post OP.

 

You’re gonna make me drop money just because, aren’t you

168k but has given me a lid of grief, bout to do it as preventative next time I’m under the hood

 

Well, that is why we bought our trucks in the first place, right? To have someplace to dispose of our disposable income?

 

I was gonna ask if you have huge tires or something but it appears you have an xrunner so I'd assume it wouldn't be the case... are you FI? I can't imagine getting that poor of mileage even driving around like a psycho lol. Even if I'm driving around in city, the worst I get is around 15-16mpg with 285/75/16 tires... if I'm towing my loaded trailer it drops to around 10-11mpg... I also have the 4.0 with 6 speed btw.

It sounds like something might be wrong for it to be sucking so much gas.

 

Ha! I thought so too. The engine had likely become louder so slowly that I didn’t notice it…I honestly didn’t notice the extra noise before changing the pulleys. Some of the pulleys had noticeable drag when holding them in my hands and spinning them, but I could still spin them on the engine.

When you think about it though, the AC causes a drop in mpg and I can easily turn the compressor clutch by hand…the pulleys all spin MUCH faster than the AC, and when 4 of them are going bad that adds up. The belt looked fine before the one seized pulley melted it fwiw. I was honestly really surprised by the change in mpg. I figured the extra power was all in my head until I filled the tank. My mind is still a little blown tbh.

 

change the fuel pump or pcv valve?

 

20% increase mpg

 

Eh, let’s say 10-15% to be conservative. I’ve been googling it though, and replacing worn idler pulleys seems to improve mileage for a lot of people. These engines have 4 idlers, one of which has two bearings, and they spin a lot faster than the engine. I didn’t measure the diameters, but I’d guess ~3x as fast.

I’m seeing posts of people with sedans getting a 20%/5mpg increase. It’s honestly not something I would have expected, but apparently it can happen.