Exhaust Mainfold and Fuel Mileage

[Whiteramsport]

So I own a 21 Ram 1500 Sport with the 5.7. Mileage in this truck has sucked from the day I got it when compared to my 2016. Started it recently with the passenger side next to the garage and heard a pretty serious exhaust leak. Took it to the dealer and sure enough the exhaust manifold was cracked. Replaced both and had the trans and transfer case flushed and filled right away. Got it back and there is a noticeable difference in fuel mileage, like 3ish MPG so far on the highway. Is it possible the manifolds had that much of an effect on performance? Could the trans fluid change and filter have made a difference? Has 64,000 miles.

 

[seems fishy]

Are you saying 3 more or 3 less mpg? I am guessing 3 more?That is a big improvement.I'd assume clean fluids would help with mileage.The engine is performing as it should obviously.A cracked manifold may have had the PCM alter the normal settings to compensate changing your mpg.What is your mileage now(mpg)?My 2023Ram
5.7 does 23mpg usually, hiway,and being Canadian,mine is in litres per 100kms,working out to 11.2,on my best day of cruising this year.As it gets a bit cooler recently ,that mileage is not quite as good but still only by a litre here or there more for 100kms.Are you changing your driving style recently?

 

[Whiteramsport]

Sorry 3 more miles per gallon. averaged about 14 before and got 17.6 coming back from the northwoods today!

 

[Wild one]

Sorry 3 more miles per gallon. averaged about 14 before and got 17.6 coming back from the northwoods today!

A cracked manifold will let air into the exhaust and really mess up your 02's,which can cause them to dump more fuel into the engine