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Airbox thermostat failure...

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.
1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70
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Volvo Repair Database Airbox thermostat failure...

Post by kelvin6 » Wed Nov 08, 2006 10:36 pm

If you own a N/A 850 or S70 (and maybe others), you may wish to check your airbox thermostat. What I discovered three weeks ago shocked me about my own 850.

For the 1.5 years i've owned my 850, i've been trying to figure out why i've been getting only 15-16mpg city and highway combined (mostly city stop and go). After a while i've gave up and just thought thought this is just normal. I've done all the stage 0 maintanance items over at volvospeed and somehow i can't even drag another 1MPG out of the car. Auto-Rx and everything, just can't get more for some reason.

So about three weeks ago i've opened up my airbox to check the filter. Now something was bothering me here, after 12000 miles, the air filter is still surprising clean. It was unusal, because in the environment that I live in, the filter would've been naturally much dirtier by now and i know the filter isn't the dust and crap get through. So after reading some TSBs on airbox thermostat replacement on AllDataDIY.com, I thought:

"If the car's thermostat failed, that would mean that the airbox has been sucking in hot air from above the exhaust manifold all this time and maybe thats why the filter is not dirty :P "

So I proceeded to take out the airbox thermostat. It was pretty easy, just open it up and at the bottom at where the air enters the box, there is a flat black plastic tab... pull it up and pull out the thermostat. Now you can't just leave it like that, because when the thermostat is cold it sucks in hot air... so I took a small fuel clamp and shoved it between the spring (that the thermostat would push against) and the where the plastic tab was, acting as a spacer, so that it would push the valve open to the cold air side. I did this so that I can run the car with cold air while I figure out this thermostat.

Well the first thing I did was take the thermostat home and inspect it. I cleaned off the dirt and crap on it and pulled out the center pin. I instantly saw why it failed. All the dirt and dust from the outside air accumulated on this thermostat, got past that seal where the pin goes in and contaminated the wax inside. I also noted that the pin was stuck when I applied hot water to the thermostat to try to simulated it.

Well three weeks later (and 300 miles later)... (today) OMG!! This car in the past three weeks have just amazed me in performance and fuel economy. The car really pulls now on the freeway and just so much more peppy. Today I filled up my tank and calculated everything, my combined MPG climbed 3MPG! I swear it could be more MPG if I didn't keep having my foot on the pedal (having too much fun with the newfound power).

I opened up the airbox today and the first things i've noticed is the airbox itself isn't as hot as it 'normally' was after driving it for a while and the air filter itself was suddenly DIRTY! For some crazy reason, in only 300 miles, my air filter literally doubled it's dirtiness!

I can't believe that i'm happy that my air filter is finally dirty! I highly recommend that every N/A 850/S70 check their airbox thermostat, because for me it really made a difference, a very noticable one!


1998 Volvo S70 T5 Auto

1995 Volvo 850 GLT <- RIP

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Post by luketrash » Sat Nov 11, 2006 9:45 am

Is there any harm in running my car in the winter in Iowa without the hot air circulation to the airbox???


It looks like I have the same thing going on. Admittedly, it's only 30 degrees outside, but after a long drive, I pulled the hot air hose to the exhaust off of my airbox and gave it some throttle.. All of the suction to the intake was coming from the exhaust side and 0% from the cold air inlet.

Not only does this feed hot air into your intake, but the size of the hole is physically smaller.

I have everything apart in my house now and I've got the thermostat piece in the fridge. How in the world do you test it? I ran it under hot water (110 degrees F) and the center pin pushed out only about 1mm

judging by the way this valve works, it'd have to be pushing a lot further than that to flip the valve over to 'the cold side'

My thermostat isn't filthy dirty or anything.. It just seems like it's not working (but I don't know how to test it..)


'94 Gunmetal Gray 855 2.4L 100% stock. This is Volvo #7.

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Post by luketrash » Sat Nov 11, 2006 11:10 am

Well, I have to thank you for the tip. I ended up using two pieces of wooden dowel to hold the flapper over to the cold side.

I'm not going to dragrace anyone, but it noticibly affects driveability! The car went from being the second slowest in my fleet to being the second fastest.

And since people put cold air intake systems on cars all the time, I guess I'll just not worry about the hot air.

The car also seems to idle a bit smoother better now as well. Hopefully I'll experience the increased fuel economy too.

Thanks!

Image

yes, that's snow on the ground :(


'94 Gunmetal Gray 855 2.4L 100% stock. This is Volvo #7.

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Post by MadeInJapan » Sat Nov 11, 2006 11:33 am

Where exactly is that piece you're holding in your hand? I've looked at my S70 and don't seem to find it. Maybe mine doesn't have it? However, if it does, I'd like to check mine to and make that modification. It doesn't get that cold here in E. Tenn and I'm sure that if I can keep hot air out of my intake it would do my gas mileage and umph a world of good.


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Post by billofdurham » Sat Nov 11, 2006 11:41 am

Remove the air cleaner assembly.

Remove the air intake body from the air cleaner housing by depressing the two tabs. That bit is inside.

Or check out
http://www.matthewsvolvosite.com/chat/p ... ght=airbox

Bill.


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Post by MadeInJapan » Sat Nov 11, 2006 2:15 pm

Okay, gotcha...thanks. I'll take a look in the next day or two...raining here and dark. Hopefully tomorrow will be sunny out and I can get a good look.


'98 S70 T5 Emrld Grn Met/Beige Tons of Upgrades Mobil-1
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'07 S40 T5 AWD 6 speed manual! Silver/Black Stage1 Heico & Elevate
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Post by luketrash » Sat Nov 11, 2006 2:29 pm

just take the top of the airbox off and reach into the place where the air comes in. The piece I'm holding is the fitting that both the cold air and hot air hook up to. It removes from the airbox in my case.

To remove the airbox, I just unhooked any plumbing to it, and undid two vacuum lines on some sort of valve that's screwed to it. I also undid the wiring connector that plugs into the valve. Then I was careful, but just pulled up and popped out two lower plastic connection points.. then the airbox slid in, toward the engine to release another plastic-in-rubber mount on the fender side.

It was pretty straightforward. Once I got the piece I'm holding off of the airbox, I was able to take it apart and see how everything worked.

If you're wanting the quick fix, just work the flap internally with your hand and hold it so that the cold air side is open. Then wedge the dowels or whatever you want into the spring assembly to keep it set at cold air only.


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Post by MadeInJapan » Sat Nov 11, 2006 3:49 pm

Strange I've never really noticed this...I've had the airbox out of the car a number of times.


'98 S70 T5 Emrld Grn Met/Beige Tons of Upgrades Mobil-1
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'07 S40 T5 AWD 6 speed manual! Silver/Black Stage1 Heico & Elevate
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Post by luketrash » Sat Nov 11, 2006 5:16 pm

These might only reside in NA cars.. I'm not sure.. My Volvo 240, 960, and 850 all have them. The silver colored ductwork from the exhaust manifold to the airbox is the giveaway I guess.

On several of my 240s, the metal tubing was gone, so I was just sucking in air from the engine bay, rather than off of the exhaust.


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Post by MadeInJapan » Sat Nov 11, 2006 6:11 pm

I don't have that silver pipe...and do have turbo on both cars...will take a look anyway. Thanks!


'98 S70 T5 Emrld Grn Met/Beige Tons of Upgrades Mobil-1
'04 V70 2.5T Red/Taupe Some Upgrades Mobil-1
'07 S40 T5 AWD 6 speed manual! Silver/Black Stage1 Heico & Elevate
'07 S60 2.5T Blue/Taupe- my kid's Volvo

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