I searched on this topic two weeks ago without satifactory results. My mechanic showed me how to replace this small device. Take your time as you are dealing with plastic parts and you will need to remove the airbox first.

Air box thermostat replacement requires two people. Remove the thermostat and it's mount from the air box. One person with strong hands compresses the springs holding the thermostat in it's seat. These springs are very stiff! Compress by grasping the base of the mount and the seat of the thermostat. The second person slips the old thermostat out and slips the new one in. This is a 5-10 second maneuver. Compressing the stiff springs is the difficulty because the mount is plastic and the springs are stiff!

Since we have had a week of mornings with 14-20 degree Fahrenheit temps in Salt Lake, I'm glad I have a new thermostat in the air box. Cold starts are not a problem when this device is functioning properly. This is the first replacement in 209,000 miles and coincided with a first replacement of a new (remanufactured) air mass meter. My 240 was gasping for fuel on a local summit.

re: "...This is the first replacement in 209,000 miles and coincided with a first replacement of a new (remanufactured) air mass meter...."

Actually, it wasn't a coincidence. Your faulty air box thermostat caused the AMM to become cooked!

I would remove the whole mechanism (including the flapper), rip out the hose from the manifold, and put some plug in the opening in the airbox (to prevent drawing in air from behind the radiator) so that the only air coming in will be the cold air in front of the radiator. That's what I did with my '84, and my two '93's.
Not only will the engine run better (always getting cooler air), but my AMM will probably run forever.

Smitty is right, a cold engine is a cold engine. That door does absolutely nothing to help a cold start. Ask yourself where is the heat supposed to come from in the first couple of seconds you crank the engine over until it starts? You new AMM had more to do with your 'better starts', real or perceived.

What it does do is help the engine warm up a little quicker. Exactly how much quicker is a subject of debate.

unheated>...................................
heated>>>..................................

I know if no code readers that will reset the service light. You need a SLR tool to reset the light, and the least expensive if seen is the Draper OSR sold in the U.K. Problem is finding a UK company that will ship to the States. The Draper sells for approx 60 U.S. Dollars, but the carriage (freight to us) may be steep.

BB

This is the only code reader I know that will do it for under $3000

http://www.onboarddiagnostics.co.uk/volfcr/index.htm



It can be used with these interfaces:

http://www.planetfall.com/~jeff/obdii/

http://www.obdtool.com/

http://www.obd-2.com/ (iso direct only)

The air box t-stat has no effect on cold starts whatsoever, since with a cold engine there is no hot exhaust manifold to heat the air.

In practice, I never had any driveability problems after completely disconnecting the preheater hose from the manifold 'stove' to the air filter box. This includes 12+ New England winters with no garage, lots of sub-zero temps.

Good to hear your back in shape.
The easiest way to replace the air thermostat is to put the air box/damper assembly into a large vise, carefully compressing the spring and holding the damper, then extract the t-stat. No need to remove the t-stat mount from the front 1/2 of the airbox. Usually when you attempt to remove the damper mechanism from the airbox, you'll break one or more of the plastic snaps that hold the mechanism to the box becasue they get hard and brittle over the years(then you screwed!), so it's best to never remove the assembly unless it's broken.
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'89 245 Sportwagon, '04 V70 2.5T Sportwagon