I've noticed this a few times, the last time today:


It's a big cylinder-shaped "tank" (for water?) outside of the front part of the truck. What's the purpose of this thing?


They are external air filters for the engine.


Donaldson type air filters.air intakes through those filters directly through the turbo charger,which is spun up via the exhaust side of the engine through a separate intake port and turbine vanes. The cold air is compressed as it Is passed into a charge air cooler,radiator like in its construction,and condensed,so more oxygen is available to the engine...in simple terms.without the air filters the engine would be ground to dust by dust and fine particles.

  • $\begingroup$ "separate intake port"? a turbo has two turbines one driven by exhaust gas and the other acting as the compressor... $\endgroup$
    – Solar Mike
    Mar 16 '20 at 15:24
  • $\begingroup$ Donaldson is the mfg, the type is known as "cowl mounted". Donaldson makes all manner of intake air filtration housings and media. $\endgroup$
    – Phil Sweet
    Mar 16 '20 at 16:26

Definitely air filter housings. Contrary to popular belief they are not chrome. They are stainless steel. There is very little if any chrome on nicer big trucks anymore. Chrome will crack due to rock chips an water, road grime and road salt will eventually cause the chrome plating to peel off the steel. Stainless bumpers are double the price but unless you are a jacked driver and mess it up it will last forever and stay shiney.

In the days of 55 stay alive most trucks had the air filter housing on the passenger side and either one or two fuel filter housings on the drivers side.


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