Better MPG and power - Volvo timing belt?

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howie2092

howie2092

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2007 Volvo XC70 - 2.5L turbo: Replaced the timing belt, water pump, tensioner idler pulley, and coolant at 124,000 miles (late I know). No other changes. Very careful to maintain timing from old belt to new. Did not reset the computer.

Surprisingly, the MPG went from 19.5 to 22.5. The car accelerates more smoothly and has a bit more power. Wife commented the same. Not what I expected, but I'm not complaining.

Doesn't make sense to my engineer mind. Any ideas why?

Maybe my gas station just switched to summer gas the same weekend I did the TB?
 
If the timing belt had started to stretch , or the old tensioner was worn to the point that the timing started to get off - I could see that causing some mileage and power drops.
 
You bumped the timing when you did the work. It was/is common to get better performance from actually getting all the timing optimized. Somewhere you moved it one tooth
laugh.gif
 
Maybe the old idler and tensioner pulleys were dragging, or the WP impeller is a different, lower friction, design. Valve timing isn't ignition timing so you didn't change that.
 
Agree with lower friction on new components, but the big player is that ignition timing is now in spec...


Folks in my family owned several older Chryslers with the 318. The 70s versions' timing chain would stretch over 60-70k miles and when replaced we noticed the same benefits you have.
 
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It's possible the timing has changed detonation during a piston stroke. It's also possible the coolant is dissipating heat better, so the coolant temperature sensor is sending a signal to lean out the fuel air mix better/sooner
 
a worn timing belt is thinner, this changes the valve timing (but not the ignition timing which uses a crank signal).

valve timing is back to spec now.
 
Originally Posted By: Kuato
Agree with lower friction on new components, but the big player is that ignition timing is now in spec...


Folks in my family owned several older Chryslers with the 318. The 70s versions' timing chain would stretch over 60-70k miles and when replaced we noticed the same benefits you have.


A friend's Jeep 4.0 picked up some power with a new timing chain. It was pretty stretched.
 
Originally Posted By: Miller88
Originally Posted By: Kuato
Agree with lower friction on new components, but the big player is that ignition timing is now in spec...


Folks in my family owned several older Chryslers with the 318. The 70s versions' timing chain would stretch over 60-70k miles and when replaced we noticed the same benefits you have.


A friend's Jeep 4.0 picked up some power with a new timing chain. It was pretty stretched.
My grandfather's 96 Cherokee 4.0L 4x4 picked up some mpg with a new timing chain, it too was stretched. 5 people, trunk full and loaded down, BFG All Terrains, A/C on on freeway 65 mph we got 21.8 mpg.
 
That's a VVT design (mine's not). Possible you changed it (just a bit) and the results were in your favor.

I paid an indy shop years ago to do all the TB components + crank/cam seals & water pump. They got the exhaust cam off by one tooth. Result? Poorer MPG, it was a dog going up hills, all the fun was gone. Took me years to figure it out......

Guess who did the next one?
 
About a year ago, I had the belt/tensioner/idler/WP changed when I owned my S60 2.5T. Most obvious effect of the change was the engine being much more quick to rev.

Just recently did the same timing service on my '05 XC90 with the 2.5T, as well. Noted the same improvements as OP - I'm fairly certain that the new belt/tensioner allow the VVT to function properly.
 
So I'm not losing my mind. Other BITOG's have noticed an improvement on Volvo motors with new TBelts. Good to know! I'm loving the +15% MPG plus better throttle response. Feels like a new car.

Upon further inspection of the old parts: The old belt is stiff, non-supple, and the smooth side is worn to the fibers. The old tensioner is difficult to turn but is smooth/quiet. Idler bearing is about the same as the new one - smooth but does not spin freely. Old water pump was wobbly on it's shaft, but not leaking (yet). Old WP does not spin freely on its' shaft. New WP is wobble-free. Plus the old coolant was maple-syrup-like.
 
Seriously, 22.5mpg vs 19.5mpg is an amazing change. Volvo owners - change your TBelt long before 125k miles. I waited too long.

Volvo book recommends 105k. Indy mechanic recommends 120k. Just do it at 100k!

I did a full coolant flush, and switched to Supertech All-Makes/All-Models, to be consistent with my other vehicles. Hope I don't regret that. Temp gauge has been rock-steady and the heater works perfectly.
 
Originally Posted By: Nick1994
Originally Posted By: Miller88
Originally Posted By: Kuato
Agree with lower friction on new components, but the big player is that ignition timing is now in spec...


Folks in my family owned several older Chryslers with the 318. The 70s versions' timing chain would stretch over 60-70k miles and when replaced we noticed the same benefits you have.


A friend's Jeep 4.0 picked up some power with a new timing chain. It was pretty stretched.
My grandfather's 96 Cherokee 4.0L 4x4 picked up some mpg with a new timing chain, it too was stretched. 5 people, trunk full and loaded down, BFG All Terrains, A/C on on freeway 65 mph we got 21.8 mpg.


It was around 18 degrees off for timing. So the spark timing was way off ... as was the cam timing (obviously). It's a 1990 so it has the Renix system. It actually felt like it could rev above 2500RPM afterwards.

I was looking at the chain on my 2000 when I took off the oil pan. It is definitely in need of a new one as well.
 
Originally Posted By: howie2092
old belt.... smooth side is worn to the fibers. The old tensioner is difficult to turn but is smooth/quiet. Idler bearing is about the same as the new one - smooth but does not spin freely. Old water pump was wobbly on it's shaft......Old WP does not spin freely on its' shaft. New WP is wobble-free. Plus the old coolant was maple-syrup-like.
shocked2.gif


Small wonder your MPG improved: wobbly WP spinning "maple-syrup" like old coolant. Your belt doesn't have to break to ruin the engine: It just has to slide off. A wobbly WP is all it needs.

You were incredibly lucky...........
 
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