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DIY: Externally adustable airbox flap for P80 NA w/pics

Longtime MVS Contributor Dosbricks developed a neat trick to permanently fix stuck airbox flap on non-turbo P80 Volvos like 850, S70 and V70. These airbox flaps fail, and the air mix becomes hot all year round, causing a drop in MPG and power. Here’s a DIY to fix that.


Many folks have discovered that almost all the thermostats on an NA airbox intake eventually fail in the heated air position choking off the the larger fresh air port. Last fall I decided to make a way to adjust the flap from summer to winter mode incrementally as the season changed–and with an external adjuster. I just did the same for the S70. This is a quick and easy DIY.

Photo #1 shows the end result of this airbox flap DIY fix.

Photo #2 shows the dowels I previously used to switch the flap from winter to summer (or vise versa), alongside the device required to make the new adjuster.

Photo #3 shows the parts:
3/16″x 2″ screw (brass plated is better), stamped-steel 3/16″ wing nut, 3/16″ self locking nut, and lastly, the type anchor used to screw into wood to hold a regular threaded screw.

Tighten and epoxy the head of the screw into the wing nut. Drill a 21/32″ hole for the furniture anchor and epoxy it into the airbox securely. Insert the screw and add the self locking nut for more bearing surface on the flap and to prevent the adjustment screw from accidentally being backed all the way out.

Photo #4 shows the airbox flap set for summer operation with full open fresh air and the heated air nearly closed off.
Photo#5 is the flap adjusted for winter operation with hot air open plus enough cold air to allow the engine to fully breath.
Photo #6 is looking down from above the air box. It’s tight but there is just enough room to get my hand down there to turn the screw.

Externally adustable airbox flap for P-80 NA w/pics

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