Valve Adjustment and Mileage

[Red Rocket]

About 3 weeks ago I decided to adjust my valves, as I had some idle clatter and shaking and such. I won't get into details about how it was done but the question is this:



Can the valves be far enough off to make a significant change in fuel economy? Having said that, I regret to inform that I hastily did this without measuring what they were. OOPS. I know some of them were way off.



I ask because I have never, and I mean never gotten anywhere near 20 mpg.

Not calculated, not on the readout, not in my dreams. I started to notice my first tank I got 450 miles out of, and I never got past 400, maybe 410, and this was almost all in town driving, averaging about 12-14. That 450 tank got me past the 15 mpg mark. Today, I went for a highway drive, 120 miles and by the time I got back my overhead was reading over 18, and I'm still over 3/4 tank on the guage.



All I did was adjust the valves, nothing else has changed. Is it possible this is some sort of emmissions change for the 06s that can easily be reversed, unlike EGR? Let's get some opinions on this, because my wife said she could definitely tell the truck runs different..... And she usually just rolls her eyes at me.



Can they be that far off, and could this be an ailment for all 06 owners?



Nick

 

[steved]

The 06s changed the exhaust valve lash didn't they? Something like 0. 026" from a previous 0. 020"??

If they were really bad, I could see how it could affect mileage... the engine is a big air pump; and the easier it pumps, the more efficient it will be...

 

[FJfonda]

At 40K miles I did a valve adjustment, fluid change (OEM fluids), serpentine belt, free flow exhaust, cool air hose and airbox mod. None of the valves were out of spec using the limits published in the manual, set them all to nominal anyway. The result was a reduction in valve train clatter at idle and 2 mpg gain. Anyones guess if it was all the mods or the valve adjustment... .

 

[steved]

At 40K miles I did a valve adjustment, fluid change (OEM fluids), serpentine belt, free flow exhaust, cool air hose and airbox mod. None of the valves were out of spec using the limits published in the manual, set them all to nominal anyway. The result was a reduction in valve train clatter at idle and 2 mpg gain. Anyones guess if it was all the mods or the valve adjustment... .

You changed a bunch of stuff that could affect mileage... the airbox and exhaust made a significant improvement in mine alone.



When I set mine, I found one intake was set as an exhaust...

 

[Bob4x4]

I adjusted the valves on a 24v Dually last wk-end for a cow girl(she really hauls cows)287k miles. She reported back she is up 1. 5mpg hauling her gooseneck.



Bob

 

[RankRam]

The 06s changed the exhaust valve lash didn't they? Something like 0. 026" from a previous 0. 020"??



If they were really bad, I could see how it could affect mileage... the engine is a big air pump; and the easier it pumps, the more efficient it will be...

SteveD,



Yes you are correct, the 06 and up 5. 9 Rams are set at 0. 026. for the exhaust valves.







Red Rocket,



Did you set your valves @ the 0. 010 intake and 0. 026 exhaust specification?





FWIW: I did the valve adjust on my new 06 @ 2,000 miles, the lash was "within tolerance" but they were all over the place. The truck did run smoother and quieter.

 

[betterthanstock]

A valve adjustment could affect mileage that much, is if at least one valve was at zero lash, with a warm engine, and leaking compression.



I personally adjusted a relative's Mercedes valves that was refusing to start. It sounded like it was starting on two cylinders. Turns out the lash was at or below 0 for most valves. Once adjusted, a little looser than recommended, so it won't need another job soon, it runs like brand new.



I'm surprised that the valves have not burned out.



But if they are too loose, you are effectively reducing the time they stay open. It will cause less air to go in, and less exhaust to flow out, sort of like an EGR.

I wonder how many degrees, with our cams, would a few thousandths of extra lash make.



I also wonder whether or not some valve seats were dropped due to tight leaky valves.



Red Rocket, did you find any tight valves (less than minimum), or were they all loose?