I stuck a wireless household thermometer in the airbox of our 95 960 152,820 miles today. The outside temp was 70F and the temp in the airbox steadily rose while we were driving around. We live up a rural road that has a fairly constant 4 percent grade for 4.5 miles. Halfway up the road the thermometer registered 160F before it litterally melted down (you should see it) and stopped transmitting it's signal.

I pulled the air mixing box, and jammed the air door to open/cool air. I put the badly deformed (but still operable) remote thermometer back in the airbox and took it up the same grade. The temperature was going down (73.5F) in the airbox even though I was climbing a 4% grade for 4.5 miles. This makes sense since there is plenty of air coming into the airbox. Interestingly, going downhill, the airbox temp. gained a few degrees. This makes sense as well since there is little airflow coming thru the box with the throttle closed and the airbox was picking up engine compartment heat.

It's amazing the engine can even run at those intake temperatures. There was a noticeable incease in engine spunk after blocking the hot air intake. A difference of at least 80+ degrees of cooling. I realy don't know how hot it got in there due to the meltdown of the thermometer and it exceeding it's operating range of 160F.

This will be fine for the summer but what about winter when it's -15F outside and I'm driving down the freeway at 75 mph. Oh well, I guess I'll cross that bridge when I get to it.

CHECK YOU AIRBOX THERMOSTAT!!!

DEWFPO

--
1998 S90 068,300 and 1995 964 152,300

Thanks for great info. I have been a proponent of the airbox thermostat in the past, but am now looking at my third failed unit in two years. The risk of frying the AMM is just too great in warm months, so I now disconnect the heat tube. Even then, the air coming through its airbox port is downstream of the radiator, and is hotter than outside air. Fixing the flap in the cold position seems to be the answer.

I use one of those little indoor/outdoor digital thermometers with a 10-ft cord and the readout sitting on the dash, and check the cars regularly.
--
Bob (son's 81-244GL B21F, dtr's 83-244DL B23F, "my" 94-944 B230FD; plus wifemobile Dodge minivan, hobbycar MGB, and numerous old motorcycles)

Hi Volvodad,

The diameter of the hot air side of the box is noticeably smaller than the cold air side. Diconnecting the hot air tube is easy and a great step in the right direction, but it still creates a significant restriction in the airflow at higher RPM's.

Some folks have just drilled a hole through the plastic manifold just big enough for a small wooden dowel that can be inserted clear thru the manifild after pushing the flapper to the cold air position. It can then be removed whenever needed fairly easily.

Happy Father's Day VolvoDad!

DEWFPO
--
1998 S90 068,300 and 1995 964 152,300

thanks for the wishes! Both kids called from their summer job locations in SoCal with father's day greetings and to report that their Volvos are running fine, and they ARE checking the oil, coolant and tire pressures occasionally.
--
Bob (son's 81-244GL B21F, dtr's 83-244DL B23F, "my" 94-944 B230FD; plus wifemobile Dodge minivan, hobbycar MGB, and numerous old motorcycles)

One other thing I forgot to mention in my previous post.

The diameter of the hot air supply side is noticeably smaller than the cold air supply side. I would estimate that the area of the diameter is about 1/2 that of the cold air side.

It amazes me that these engines could even run at high rpm with that air flow restriction in place and the 160+F intake air temps going into the engine. Simply amazing.

We have to travel over two long (about 6 miles), and high (over 10,000 feet in elevation) mountain passes fairly often. That means high rpm & high load for several minutes at a time when the air is getting noticeably thinner the higher we go. I'm surprized we ever made it to the top.

DEWFPO
--
1998 S90 068,300 and 1995 964 152,300

Sometimes a heated air inlet to the air box does more than an emissions thing. My daughter's late, unlamented, Honda was carbureted. This car had a thermostatic valve which mixed air from the cold air intake with heated air off the exhaust manifold, much like the Volvo. When that thermostatic valve failed in the open position, only cold air got in. If you drove that car on a cold, foggy night, ice would form in the venturi of the carburetor stalling the car. She would leave the car by the side of the road and call me for a ride. Sure enough, when I arrived, the car would not start. The next morning, I'd go to get the car and it would start just fine, the ice had melted, you see.

I had the car towed to an older mechanic who said he thought he knew what the proble was. Sure enough, it was that thermostatic valve. He told me when he first ran into that problem, it took quite a bit of head scratching to figure out what was going on.

I haven't heard of Volvos icing up at the throttle body and, with fuel injection, it probably wouldn't stall the engine anyway even if there was ice. Just thought the forum might find this interesting.

You make a good point! While it is unlikely that icing will occur with the injectors right at the intake valve, the car will warm slowly on a cold winter day here in New England.

Now if someone would instrument one with a properly working thermostat.....

I now make it a habit to occasionally feel the air box after a trip home to make sure it isn't running hot with a failed airbox thermostat. Mine always feels like it is at ambient temperature so far. (My old diesel car did have a failed airbox thermostat once and the improvement in performance was noticable with a new one.)

I'm guessing there is little downside to keeping a properly working thermostat system in place and it will surely reduce emissions in the winter.
--
'96 965 with 16' wheels at 117K. Had '85 745 Turbo Diesel for 200K.

This will be fine for the summer but what about winter when it's -15F outside and I'm driving down the freeway at 75 mph. Oh well, I guess I'll cross that bridge when I get to it.

This is one of the most misunderstood parts in the Volvo world. It is an emissions-control device, nothing more nothing less. The faster you warm the motor up to operating temp, the quicker the emissions settle down to desired levels. Any benefit to the driver by getting the engine warmed up faster is purely coincidental. There is no need for the warm air once the engine is operating at temp, and the continued operation of the flapper at this point is actually undesireable (colder, denser intake charge = a bit more power.)

I epoxied the flap shut in my 240 over 6 years ago, and I've never looked back. I used a sheetmetal screw through the backside of the airbox on my 940 to hold the flapper shut. This one's been going for 4 years like this. Having seen negative teens temperatures, and 70+MPH speeds on the interstate, quite a bit the past two winters, there were no drawbacks to the hot air deletion.


--
Speed Racer, '83 240 R, '74 164 E, '93 940 OL1 (Manchester, CT)

Mr Speed Racer! How the hell are ya?

Remember me? I got your wind deflector awhile back. Still at Pratt? How are your many pets? All doing well I hope.

Anyway, I was wondering about that hat air flap on the airbox. I am now driving a '93 940t and one of the first things I went to do was to seal the hot air inlet. When I got everything out I was surprised to find that it was already sealed, AND it appeared that it came that way from the factory as there was a fitted plastic blocking the inlet instead of the flapper. I had forgotten about this until I saw that you also have a '93 but with the flapper.

Am I missing something, or where there two different configurations?

You might also be able to inform me as to whether or not all the foam in the air box does anything? I took it all out, but am wondering if that's a good thing.

Thanks!

We should get together again over some coffee.

Ian

Dude! I thought you disappeared?! I've been busy at Pratt, school, and with this crazy F+T project on my '83. Yeah, we should do coffee.

As you might have seen mentioned in one of the other posts, the Turbo models did not get the flapper - the thought being that the turbo's compression action would be heating the air more than enough.

That foam in the airbox was put there to quiet induction noise. It is common for it to start flaking off when it gets old, and that is bad news for the AMM downstream. Its best IMHO to remove it all before it causes trouble.
--
Speed Racer, '83 240 R, '74 164 E, '93 940 OL1 (Manchester, CT)

Ah yes, now that I have read all the messages I see the post regarding the turbos and the flapper. I was confused because both my '87 and '88 745 turbos HAD the flapper. Go figure...

Good to know about the foam, now I can throw it in the garbage.

Send me an email at ian forbes at snet dot net (removing all spaces and changing the at to @ and dot to .) and let me know a good time for a little get-together.

Ian

Dear gt6,

May this find you well. Could you describe in detail, where you put the screw into the 940 airbox, to hold the flapper in position?

That is, could you start with a common reference point, and provide measurements. Sometimes, being 1/4" out of position can damage something, that otherwise would be fine.

Thanks for your help.

Yours faithfully,

spook

Spook,

There is nothing so detailed that you need worry.

What I did was simply this - open the airbox lid and removed the filter - you are now looking at the bottom of the airbox, with the flapper valve in plain sight on the pass side of the airbox. I held the flapper shut, and came in from the back wall of the airbox with an average-sized sheet metal screw. The screw was placed so as to hold the flapper shut, like a little deadbolt, so to speak.

I did this with the thought that if I ever did discover that I needed this flapper mechanism, I could simply remove the screw and seal the hole.
--
Speed Racer, '83 240 R, '74 164 E, '93 940 OL1 (Manchester, CT)

Finally some hard numbers. Your post belongs in the FAQ.
Now it would be interesting to try using 87 octane if you have been using 91. Nobody seems to believe that this car runs fine on 87. Mine was stuck in the hot air position and so was my cousin's 92 740. I have removed the flapper mechanism all together. My cousin's only took one rivit to keep the flapper in the cold air position. Cold weather is not really an issue here in SoCal.
I bet the colder air intake will also help the engine live longer since there is less change for knock.
I always knew the intake air would get hot. But I had no idea it was that bad.
Thanks again dewfpo.

94 965 98k

The number one cause of faulty AMM's.
--
Warren Bain - '99 V70GLT G-Valve > 80K mi, 89 300SE, '96 965 >120Kmi, near Manassas Va.. Check the 700/900 FAQ via the 'features' pull down menu. This post written with 100% recycled electrons.

Wouldn't this show up by throwing a code?
--
John Shatzer, '97 V90 @ 105K

Our 95 960 had no MIL lit. It's not OBDII compliant so I couldn't hook up the scan tool and read the inlet air temp as I can on our 98 S90.

DEWFPO
--
1998 S90 068,300 and 1995 964 152,300

What are you refering, bad AMM or no hot air?

Mine has no code at all. I really need to PC program OBD-II.
--
Warren Bain - '99 V70GLT G-Valve > 80K mi, 89 300SE, '96 965 >120Kmi, near Manassas Va.. Check the 700/900 FAQ via the 'features' pull down menu. This post written with 100% recycled electrons.

Sorry, I was wondering whether the OBC would show a code for the airbox thermostat, but now that I think of it , it would more like show as a fault with the AMM. Just curious.
--
John Shatzer, '97 V90 @ 105K

Great information. True for 2s,7s, and 940s too. These are cheap to replace or can be defeated to stay in the open position. I had drilled a hole for a 1/4-20 bolt from the outside through the flapper. I just snugged the flapper closed to warm air and double nutted the bolt.

T owners, don’t bother looking for this thermostatically controlled bidirectional air flapper. All y' all ain’t got one.
--
Tom F. Three 940s. '93 T-Rex now running. Mods, RainX. Lien holder on two more (the kid's). Rust In Pieces, '78 245