I am new to these cars so forgive my ignorance. I would have searched for this, but I wouldn't even know what to call this. Clearly this has been made inoperable by the screw. What is this and what is its function? Any harm in leaving it inoperable or are there benefits to making it work again?

Car is a 1991 245 with a gas engine and automatic transmission if this matters.

 

i believe that is the flapper for the preheat hose. probably the hose is missing for many years. i had a mouse that got stuck in there for who knows how long and well it wasn't pretty ! since we don't have emissions tests here in Mass for cars this old you can leave as is.

 

use a bit of bailing wire to secure the flap in the bottom of the airbox closed.

 

The flapper device is intended to allow warm air drawn across the exhaust manifold in cold conditions. There is a thermostat on it that it closes the flapper so it doesn't draw hot air when it is warm out. Usually that thermostat fails and leaves the flapper open drawing hot exhaust air into the airbox which ends up frying the air mass meter. For this reason many people disable the mechanism just like Pierce described.

I have mine disabled as well and I live in the Chicago area. This really kills my gas mileage in cold weather but it runs ok.

 

I was wondering what effect it would have on the car's gas mileage. Why do people not replace the thermostat if that is the failure point? Are the NLA?

 

my flapper was jammed open by a mouse trying to break and enter the airbox. the mouse got trapped and its skeleton kept the door open. i don't care if i get one mpg better or worse. the mouse is buried, RIP....
i think a new/clean air filter is more important !

course it's now way cleaner than a copper clapper!

 

Our 89 740 with 360K miles on it still has a working unit. I replace the hose every year.

 

You should still be able to get replacement thermostats for the air box. A couple of years back I so them on fcpeuro's site. I didn't replace mine since the heat shield on the exhaust manifold rusted out so I had nowhere to connect the hose.

 

there is the issue of the AMM getting over heated and failing from a faulty thermostat that is in the airbox. i would rather not replace the very expensive AMM, thanks. Since we have no California type 'smog' checks here in Mass. they don't check this system at inspection time!

 

even in California, they only check for the presence and condition of the heat riser hose, they do NOT check the air flapper.

 

ahh so they expect it to work so to speak but if that hose isn't there then they fail you?
over here i have never seen a 240 with that hose still attached! here in Mass any gas engine car older than 15 years is exempt from emissions testing.. (the reason we harp on about inspection stickers here is that it means 2 points on your license automatically, big increase $$ on insurance, plus a fine if you don't have a current one...)

 

in california, originally any car 1968 and newer needed smogging. awhile back, they started to raise it each year but when it hit 1975, they changed their minds and froze it there. so now, any car 1975+ needs smog check every two years.

 

I guess I will just leave it as it is. The corrugated tube on my car was still there and in good shape.

 

if you live where it gets very cold in the winter, a functioning flap does help it run better at extreme low temps, it will warm up faster, etc. us coastanoans out here on the left edge think a 48 deg morning is chilly.

 

I live in New England, so it does tend to get a bit colder here than on the left coast. For on $10.00 I will see if I can get this back functioning again. The foam seal crumbles to dust at the slightest touch, so that will have to be addressed as well.

https://www.fcpeuro.com/products/vol...mostat-1266826

 

I replaced mine - and my car warms up much more rapidly now - and seems more "perky" at low temperatures (Well, as perky as a stock 1988 240 can be)
Additionally, I tested it on a 23°F day - with a wireless BBQ Thermometer - poked into the duct after the air filter, before the Air Mass Sensor.
(Let me know if you think this was not an ideal location)
Freeway speed - engine fully warmed up - the little thermostat kept intake air 62° - 69° F
Took off the Pre-heat hose and the incoming air was 36° - it was pulling air from around the engine.
Pre-heat hose off and the connection blocked - so all the air was from the front and the thermometer measured 33°
Of course I'm terrified this little wax think will malfunction - and feed the air mass sensor and engine super heated air in the summer so I check it often in warm weather - 2 - 3 times a year Summer. I wish this thing failed in the closed position - less harm.