Airbox thermostat failure...

dasapir · Post by **dasapir** » 11 Nov 2006, 20:17

MIJ, I just had the air intake box and the air intake tube (no body) out this past week when doing the PCV system and replacing the vacuum lines. I have absolutely now recall of an air intake body or valves. I did depress the 2 tabes and pulled the airintake tube out of the air intake box. It is a staight shot. If there is an air intake valve I "shur as heck did miss it.
so now got me curiosity roused. will look too.
Must say though with the K&N air filter I need to keep braking to keep the car going slowly. So air the car is getting there.

Post by **MadeInJapan** » 11 Nov 2006, 20:22

Thanks, dasapir. I'm thinking that our Turbo'ed cars don't have the warm air switch with a thermostat in the bottom of our air boxes.

dasapir · Post by **dasapir** » 11 Nov 2006, 20:27

Well, I just went out to my car and nope, there is no warm air valve switch. Wheter this is just on turbos or on non-turbo S70 I cannot say. What I can say is that the switch is not there on my 98 S70 turbo. And thank you.

Post by **luketrash** » 11 Nov 2006, 21:07

I notice they don't say "just run the car without the thermostat"

However, they also say that 100% hot air all the time kills MAF sensors... I'll let you know if I have trouble with 'cold starts' It was 29F tonight and my car was at operating temperature within 2 miles of my house.

I've survived one winter with a non-working glowplug in my TDI bug haha!

From: http://www.volvoclub.org.uk/faq/EngineF ... ction.html

Air Box Thermostat Change. Note: Non-turbo cars have a thermostat inside the air box that shifts air intake from heated air to cold air when the engine is warm. This is done to improve combustion at cold starts. Early turbos also had this thermostat, ending around 1988; later turbos do not. [Query:] Can I change the air box thermostat in 7xx/9xx cars with an integral lower air box/thermostat combination? [Response: Steve Seekins] You can change just the thermostat element on any of the cars that are equipped with it. You only need to change the flapper if the hinges are worn or broken, or if the gaskets are destroyed. See below for instructions on thermostat removal on 90+ cars with integral air boxes. [Editor] You can buy a replacement thermostat from an aftermarket supplier for about $10.
[Editor] Spring is an appropriate time to test the function of your airbox thermostat and change it if needed. The thermostat can seize, allowing hot air to enter the air mass meter and dramatically reducing its lifetime. Note that many turbos do not have these thermostats since the turbo itself adds heat to the intake air. [Tech Tip from Walt Posluszny] 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 up a fairly constant 4 percent grade for 4.5 miles. Halfway up the road the thermometer registered 160F before it literally melted down. I pulled the air mixing box, and jammed the air door to open/cool air, replaced the still-operable remote thermometer, and took it up the same grade. The temperature declined to 73.5F in the airbox even though I was climbing the same 4% grade. Lesson: check your airbox thermostat and replace it if needed.

To test the thermostat:

Remove the air intake pipe from the grill hole to the air box extension.
Start your engine. As the engine warms up, the flapper inside the hole should move to the fully closed position in moderate to warm weather. If it does not, then you need to change the thermostat. See the FAQ section for test temperatures and flapper positions.
To change the thermostat in a 90+ car with the assembly inside the airbox :

Remove the air box from the car.
Spray PBlaster around the air pipe joint where the extension tube enters the airbox. This joint will be very tight.
Gently depress the tabs and twist to loosen and remove the extension tube assembly holding the thermostat mechanism. Be careful that you don't crack the tube or the box while working on it.
Once this is free, you will be able to see and access the brass thermostat.
Depress the spring using either plier jaws or a two-pringed body clip remover tool. Push this down sufficiently to expose the thermostat piston rod.
Pop the thermostat out and insert the new one in its place. Make sure the rod goes in the hole at the top of the spring.
Make sure the flapper assembly operates correctly.
Clean everything up, lube the assembly with non-silicone lube, and re-assemble.
The only risks are being a little too brutal and cracking the plastic, or breaking an air box clip on removal. Be careful.

I remember buying metal blanking plates for small block chevy intake manifolds from Summit racing. It blocks off the EGR function from the car.. I guess I never heard of any issues when using those. We don't have emissions testing in Iowa. Plus, I imagine the EGR valve is already letting in some heated air on my car. The turbos apparently make enough hot air to not need either device! Lucky you

Post by **kelvin6** » 11 Nov 2006, 23:42

Currently I have no plans to replace the thermostat...

The car just benefits so much without it...

I live in San Francisco, California and it never snows here and its a pretty stable temperature environment all season long, around 60-70F. So having the colder air come in to the airbox is no problem at all for me. Today I got my new Mann filter in the mail, so i can soon replace the finally dirty air filter.

Post by **luketrash** » 12 Nov 2006, 00:14

I see the thermostats are $28.00 on www.fcpgroton.com

I might buy one if I notice problems with the car running rough in cold weather. Honestly, I think with this many miles, running rough when cold isn't going to be that noticible compared to 'running as good as it's gonna'

Post by **Ozark Lee** » 20 Nov 2006, 19:12

This has been a very useful thread. I have been grousing about the fall off in mileage since my ignition tuneup and thought the Bosch platinum plugs were the root of the problem. After changing to the FR7DC's I noticed an improvement in power and a smoother idle but, after going to the cabin this weekend, my mileage is still in the low 20s. I popped the air filter while the car was warm and found that the air box thermostat is indeed toast.

Funny thing, after I got the car home from Indianapolis and started on the ignition work I noticed that the heated air hose was disconnected from the air box and, of course, hooked it back up. I think my mileage drop off is more related to that "repair" than the plugs.

I didn't have any dowels laying around like Luke but I did have some yellow Scothlock electrical wirenuts that are about the same diameter. They indeed closed the damper door.

The Jury is still out on mileage but I think it will improve. Once again, thanks to all who contribute.

...Lee

Post by **luketrash** » 20 Nov 2006, 20:10

The funny thing is that all of these threads are recurring on a cycle

I vaguely remember the same threads now about Volvo 240s. I found that info on a UK Volvo board, and I'm sure BrickBoard has had 1000 posts about this, but their site is impossible to search the archives very effectively.

So, I hope the thread here has caught up a few more people and spread the knowledge of the problem. Then when one of us sees it pop up again, we'll be able to answer everyone else that's having the problem two years from now, haha.

Post by **kelvin6** » 20 Nov 2006, 21:25

There are so many N/As out there that probably have this problem, and I tell you if every N/A checked their thermostat and did something about it, there would be less complaints of low MPG and less people saying that thier 850 N/A is slow. Seriously, I gained some power from this mod, and the car can really pull on the freeway. MPG has gone up for sure. It varies for me, depending on mood and agression level while driving

.

My latest mod is changing the PS fluid to Mobil 1 ATF and it really loosened up the steering, as in lot less force required to turn the wheel, heck I can even jiggle the wheel with a finger while sitting at a light... feels nice, but thats for another thread.

Can a mod please please pin this topic, i'm sure it will come in handy for years to come.

Post by **MadeInJapan** » 20 Nov 2006, 21:42

Done! Put it in the helpful post section (for both 850's and 70's)...Repair Database. Go check it out if you want.