I opened up my airbox the other day to check the thermostat - I want to reconnect my hot air hose for faster heat up during the winter. It's a good thing I checked because the flapper was frozen at full-hot. I used a hair drier to heat up the thermostat and it didn't move at all.

Well, not having a spare thermostat handy, I gutted the works and put my air box back in, after sealing up the hot air hole. I decided to cover the hot side because I also found water and filth in my air box that is likely from running with no belly pan and an uncovered hot air hole.

I do NOT want to reinstall the flawed thermostat system just to check it every few years to make sure it is still working, so here's my idea:

Instead of putting a thermostatically controlled flapper back in the air box, I could use a small electric motor (and a couple gears perhaps) to move the flapper from hot to cold. Forward moves it to hot, reverse moves it to cold. Inside the car (maybe installed on one of the empty accessory gauge squares) I could have something like this:



A return-to-center toggle swtich that when moved to either side would energize the motor in one direction. When the flapper reached full-hot or full-cold, it would make contact with another circuit that lights up one of the two LEDs in the car. That way you know where the flapper is, and you can adjust anywhere between the two extremes.

Granted, this method would mean more work, but all summer long the flapper is left to full-cold. Then, in the winter, you can put it on full-hot until the car warms up, then move it back to cold. The best of both worlds, no more thermostat failure.

Thoughts?
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'93 244: 'A' cam 4 deg. advanced, 25/22 sways, custom heim endlinks, poly bushings, and a lot more styling customization than I care to recount.

Sean, that's a clever idea, but... as others here have mentioned, that heated air setup does zilch for engine warmup. I found this out close to 20 years ago with my '88, and even in sub-zero New England temps with the car parked outside, the presence or absence of the heated air coming from the exhaust manifold "stove" made no difference in engine warmup or gas mileage. Subsequent experience with 2 other 240s confirmed my original observation.

The idea behind warming the intake air was simply to regulate the incoming charge air to within a fairly constant range. The engine controls (injection, ignition, throttle position, lambda system) were primarily driven by exhaust emission regulations, and all represent compromises of sorts which are optimized at a relatively narrow band of conditions. Regulating inlet air temperature helps by reducing one variable from a huge swing (say, -20F to 180F, typical underhood temps) to maybe a quarter of that.

One of the other posters indicated that he liked the idea of a warmer inlet charge because the air was less dense than colder air, so less fuel would be required. Absolutely true. But that also means lower performance... and with 113 hp schlepping around a 3300 pound vehicle, I'd rather opt in favor of performance!

I don't mean to rain on your parade... and again, you have a clever idea. It just is an answer to a "problem" that doesn't exist.
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No one ever went broke underestimating the taste of the American public - H.L. Mencken

Sean,

Not a bad idea, but I also see Ryan_R's side of the fence. If you want to move forward with this, for an actuator, consider a trunk or door lock linear motor from a 240. They have much more torque than you need so they might even be able to move a flap that is frozen in ice. I have a few spares if you are interested... let me know off-line. Beyond that, how about thinking a little further outside the box. Install a thermometer in the air box and wire it to a temperature display in the dash? Another option would be to make your own temperature display using a microcontroller that could also control the actuator position based on external air temperature. This one actually sounds like fun to me! Let me know if you are interested.

On a related note, I have the hot air intake blocked on our 245, now that it has gotten cold, mostly freeway MPG has dropped from 30MPG to 27.5MPG, so I am seriously thinking about getting that flap working again to see if it helps!

jorrell
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92 245 250K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently taking names and kicking reputations!

Thanks for seeing things my way! :)

Obviously, I do like the theory of a functioning airbox system, but I agree with you and others that a working T-stat flapper may not be significant for upping mileage in the winter.

I wonder if your decrease has more to do with "winter" gas formulations than intake air temp? It'd be a fun experiment for sure.

One happy medium that I'm sort of exploring involuntarily (because of broken bracket screws stuck in the exhaust manifold on one 240, and the next-to-impossible to replace T-stat on the 740) is to have the flex hose just loose in the engine compartment. That way it can suck in warmer engine compartment air when cold out vs. "burn the &%#@%!& out of your arm when changing the oil filter" hot air direct from the exhaust manifold. :-) This way a failed T-stat is far less likely to toast your AMM...

-Ryan
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Athens, Ohio
1987 245 DL 314k, Dog-mobile
1990 245 DL 134k M47, E-codes, GT Sway Bars, GT Braces
1991 745 GL 300k, Regina, 23/21mm Turbo Sway Bars

Thanks John, I actually already have a spare door lock motor; it was the first thing to pop into my head when I came up with the whole scheme.

Some good ideas there, but sounds pricey. I would love to do it whole-hog, and especially put a thermometer in the air box, but am too poor right now to get that fancy.

The mileage thing is definitely one of my chief concerns also, and I would love to get some data on incoming air temps vs. mileage. Mine always drops significantly in the winter, and I think most of us are in agreement that a properly functioning airbox flapper improves cold-weather mileage.

I will probably live with the airbox as-is for some time, but sooner or later I would like to solve the airbox flappper "problem" to my satisfaction.

P.S. I just realized that the rocker switch from a door is the perfect switch for my circuit too. I love recycling Volvo parts back into the car.
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'93 244: 'A' cam 4 deg. advanced, 25/22 sways, custom heim endlinks, poly bushings, and a lot more styling customization than I care to recount.

I just replaced my airbox stat and installed a new hot air intake hose but I didn't know where on the exhaust manifold to mount the hose's other end. I think my manifold's heat shield was removed some time ago, so I just placed the hose's open end right next to the manifold pipes so it can suck in any ambient warm air. I'm not sure how effective this will be.

I'm more interested in reducing emissions. I don't expect a dramatic increase in mileage, just enough to compensate for the lower MPG I get with winter fuel formulations.
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Mike F - 1984 244 DL - 265,000 miles
Original engine, transmission, drive train, alternator, starter
Undergoing reconstructive surgery with POR-15

sounds a bit like a "choke" wouldn't a cable setup be a lot simpler?

Really unnecessary. The hot air directed to the air box will not help warm up your engine any faster -- there's not nearly enough BTUs in such a low mass substance as air to make the least bit impact on engine temperature.
I've permanently blocked off my hot air opening and gutted the flapper -- only cold air (from in front of the radiator) enters my air box, all the time, and I have never had any problem with that, even in New England winters on a skiing vacation, even starting in a blizzard.
That whole air box contraption was just to satisfy some vague EPA requirement.

Ditto the flapper and haven't had any issues here in the snowbelt whatsoever. I didn't close off the preheat hole. Instead I zip wrapped a fine mesh stainless screen over the opening to allow additional air. No problem with emissions either. Better numbers then when stock.

It's not about engine warmup - it's about warmer air combusting better.
Well at least that's my belief. I do suspect that Ken C is correct in that the amount of heat via the duct doesn't help much in warming the engine. However, restoring the system has worked out well for me.

I do believe that with some good sensors and servomotors etc. you could build something better than stock. But the stock system is more advanced than what I've seen described so far in this thread. I got my info from Bentley, read below and learn what the Swedish + German engineers designed.

In case anyone here isn't already aware, the airbox flapper responds PRIMARILY to the temp of outside air, blowing directly on the t'stat sensor via a horizontal funnel-shaped duct that picks up air from in front of the airbox. And, it works the same regardless of whether the engine is stone cold or fully warmed up. That said, it does a decent job of keeping the intake air around 55 deg. F, +/- 3 deg.

I restored the preheat flapper t'stat last fall and had the best winter mpg ever. I have to admit that I also ran with only rear snows, instead of four snows, for the first time in quite a few years. Oh - I insulated the hot air duct with pipe insulation wrapped in duct tape, to provide max heat to the system.

Scorron, if you are interested in the airbox read up on it in Bentley. At two extreme temp points it blocks off either the hot or cold intake opening, as appropriate. Bentley states those blockoff temperatures. At temps in between those extremes the flapper is part way in between the two openings.

I bought a $10 interior/exterior thermometer at a big box parts store. Exterior sensor is inside the airbox, so I can see the intake air temp while driving. (If you cut the sensor lead for installation purposes you HAVE to solder it due to the high resistance value of the sensor. A crimp connector will work for a while and then build resistance; you'll think it's pulling way overheated air! BTDT.)

My own findings are that, in moderate temps, say between about 30 and 50 degrees, it provides about 52-58 deg. F air to the system. About 25 degrees or so and colder, the flapper blocks off all cold air and you get only preheated air, which in my case turns out to be about 80-85 deg. F. So in the coldest winter it's like summer air coming in. Above 60 degrees or so, the preheat flapper is fully blocked and you get straight outside air.

I wouldn't recommend doing it without a thermometer to read the intake temp. But that's really pretty simple to do. I got mine at Autozone.

--
Sven: '89 245 NA, 951 ECU, expanded air dam, forward belly pan reaches oem belly pan, airbox heater upgraded, E-fan, 205/65-15 at 50 psi, IPD sways, no a/c-p/s belt, E-Codes, amber front corner reflectors, aero front face, quad horns, tach, small clock.

That's a great idea. I think I'll try that with my car since I reinstalled my airbox stat. The thermometer would be a way to tell if the stat is stuck and is feeding too much hot air to the AMM and engine.
--
Mike F - 1984 244 DL - 265,000 miles
Original engine, transmission, drive train, alternator, starter
Undergoing reconstructive surgery with POR-15

You could easily accomplish this by using a RC Airplane Servo. They are available in excess of 100 inch/ounce power that will operate on 6.0 VDC You would have to pick up a step down unit from radio shack, but I think you could be operational for less than 50 bucks.

That's a good idea. I also disabled my hot air intake and looking for a better solution.

The Onan 4kw generator in my motorhome has a flapper valve for the air intake. It's a manual system. Flip it this way in the winter and flip it that way in the summer.

I was thinking maybe I could rig up a manual flapper control arm to the outside of the box. Lemme think about it some more.
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1986 Volvo 245

I thought of that already, and it would be pretty easy to do, but even in the winter I don't believe you'd want full-hot all the time. I also thought of a hood-cable like mechanism to actuate it from inside the car, but that sounds way too messy to me.

Perhaps I'm going about this the wrong way. Maybe I don't need the ability to control the flapper movement as much as I need something to warn me if the thermostat has failed. I could just repair the stock mechanism, then use the two LEDs to indicate full-hot/full-cold. I would know then if it had failed and needed replacement.
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'93 244: 'A' cam 4 deg. advanced, 25/22 sways, custom heim endlinks, poly bushings, and a lot more styling customization than I care to recount.

Dude!

My hat is off to you for thinking outside the box!

...but what says your system is going to be more reliable than the Ovlov system, which is elegant and simple?.... the original system simply needs a cleaning and a new T-stat once a decade. :-)

This system is universally hated on the BrickBoard because we always find the T-stat stuck in the hot position on a new-to-us 240. Why do we expect these to last 20 years?

Also, remember: the hot air induction system is not only a warm up device. It doesn't know that the engine is warm. In the dead of winter, it stays open part way bringing warmer (less dense) air into the engine. Less dense air needs less fuel.

I think I'm just jealous that you're thinking about Volvo's. It's too cold in Ohio to think of Volvo stuff. Though this morning I got to do some mild drifts in the empty, but frozen, work parking lot. :-)

-Ryan
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Athens, Ohio
1987 245 DL 314k, Dog-mobile
1990 245 DL 134k M47, E-codes, GT Sway Bars
1991 745 GL 300k, Regina, 23/21mm Turbo Sway Bars

Thanks Ryan. Actually, that's why I wanted the LEDs - if I know how long the flapper takes to get from full-hot to full-cold, I can adjust to positions halfway in the winter to see what effect it has on mileage/power. A lot of people wouldn't care to clog their mind with such data but...we're not "a lot of people," are we?

I'm still thinking/developing. And no, I really don't plan to work on the car much anytime soon - we've had high temps of 40 deg. and less here lately. Which is, however, the reason I've been thinking of faster warm-up times for the brick. :)
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'93 244: 'A' cam 4 deg. advanced, 25/22 sways, custom heim endlinks, poly bushings, and a lot more styling customization than I care to recount.

I'd be thrilled if my thermostat lasted a decade. Hell, I'd be happy if it lasted two years...

HI Laine! Yeah, I've seen them fail after a couple years too. It's too much of a chance to take with AMMs, there has to be a better solution. And anything that puts more mysterious switches on my dash is good.
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'93 244: 'A' cam 4 deg. advanced, 25/22 sways, custom heim endlinks, poly bushings, and a lot more styling customization than I care to recount.

Yep! If it gets you another switch in the dash, it's *always* a good idea. :-)

-Ryan
--

Athens, Ohio
1987 245 DL 314k, Dog-mobile
1990 245 DL 134k M47, E-codes, GT Sway Bars, GT Braces
1991 745 GL 300k, Regina, 23/21mm Turbo Sway Bars

Yeah, I figured this was just a ploy to get more switches on your dash.

That's at least as good as more switches!
About $10 at AutoZone for an interior-exterior thermometer. Install the sensor inside the airbox. Solder the wire lead if you have to cut it.

--
Sven: '89 245 NA, 951 ECU, expanded air dam, forward belly pan reaches oem belly pan, airbox heater upgraded, E-fan, 205/65-15 at 50 psi, IPD sways, no a/c-p/s belt, E-Codes, amber front corner reflectors, aero front face, quad horns, tach, small clock.

Eccentric, but it could work. Not sure if it would lend itself to reliability, and it would be pretty intensive to design. You might do better just installing a valve inline with the hot air hose at the air box and mating the motor to that, losing the flapper all together and you wouldn't have to worry about gears. Might be tough finding a small motor strong enough to move the valve for cheap.

Good luck!

Justin

Actually, I thought about that (the in-line butterfly valve to open/close the hot air inlet) and I realized that it would not perform the same function as the flapper, which not only opens the hot air, but also closes the cold air.

As for the motor, I believe the 240's window lock motor is both small enough, and strong enough for my purposes - and free, since I have several.

It will take some thought.
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'93 244: 'A' cam 4 deg. advanced, 25/22 sways, custom heim endlinks, poly bushings, and a lot more styling customization than I care to recount.