Airbox thermostat failure...

Post by **polskamafia mjl** » 21 May 2009, 12:30

Hey guys, I just did this mod about half an hour ago. I have a GLT and the airbox is just a tiny bit different than that on what stone36 was working on. I did a quick write up for the GLT with pictures. =]

Post by **tjts1** » 21 May 2009, 14:16

It looks exactly the same as my base 96. How is the airbox different?

Post by **polskamafia mjl** » 21 May 2009, 20:56

I don't know what stone36 has but if you look at his pictures, his airbox is different than the GLT. Aside from the MAf, I have some other hose coming off the airbox, I don't have any Torx screws like he does, and I didn't see any wires poking out of his airbox. I've only ever seen my airbox and pictures of his so I have no idea what the other ones look like.

eyeballumbrella · Post by **eyeballumbrella** » 31 May 2009, 12:02

What I did was I just took out the thermostat completely and replaced it with a flexible rubber hose. Anybody see any foreseeable problems that I dont? thanks

Post by **stone36** » 07 Jun 2009, 21:28

To add some results. I am on my second tank of gas since doing this mod. The first ended with me averaging 30.1 which was about 2/3 highway and 1/3 city, not too bad since usually I get 30-31 if I just do highway. I was also about 1/4 into the tank before I did it.

What I did notice that is dramatically different is when I go to the airport (100 miles each way once a week) I have to go through a canyon that gains and loses about 1500 feet in elevation. On the way up the hill doing 60 the car would down shift 10 or more times, now it only does it once or twice. Also when going down hill with cruise set at 62 (anal cops) it will run about 2500 RPM when using power and I can actually feel the engine "disengage" when the downhill is sharp enough and the RPM's drop to 2100. That has never happened before and would definitely mean my MPG's are on the way up...

Post by **erikv11** » 25 Jul 2009, 14:43

Hey I just thought I would read through this, I finally propped open the airbox t-stat on my 855 last summer. But not without issue - I am really surprised that no where in this long thread has anyone mentioned the known drawback to this mod.

In very cold weather you may need to have a working airbox thermostat. Not for cold starts, but for keeping the throttle plate from icing up.

Here's the deal: If there is only cold air coming in, and it is bitter cold outside like in the teens, and there is any moisture in the intake (which is very likely in the winter), then the throttle plate gets so cold that moisture can freeze on it, and from the ice the throttle can get stuck. Usually stuck open which can be dangerous.

It happened a few times to my car this winter, always on the freeway where the heat of the engine does not have a chance to warm the throttle body. And probably the throttle was hardly moving, gave the ice some time to build. Freaked my wife out because she was driving to work and when the throttle gets stuck open the car just revs no matter what you do. I told her to just pull over shut the car down and let the throttle warm up (thaw). That takes like 5 minutes and always worked but she had to do it 3 times over a couple cold weeks (temps in the teens I think, even after I cleaned the throttle body to be sure) until I just unstuck the t-stat to let it do its job. No problems after that. Come April I just propped it back open.

So for west coast cars no worries, but you might not want to rip everything out as there is no real advantage over just propping it open. Then the car still has options, you never know when you may suddenly move from the bay area to Iowa

.

Post by **stone36** » 26 Jul 2009, 10:30

erikv11 wrote: In very cold weather you may need to have a working airbox thermostat. Not for cold starts, but for keeping the throttle plate from icing up.

Here's the deal: If there is only cold air coming in, and it is bitter cold outside like in the teens, and there is any moisture in the intake (which is very likely in the winter), then the throttle plate gets so cold that moisture can freeze on it, and from the ice the throttle can get stuck. Usually stuck open which can be dangerous.

Good point but from what I understand, the t-stat only pumps watm air in until the car reaches a normal warm operating temp anyway and then opens up for cold air intake. For me in northern Utah on a 10 degree day that still only takes about a mile... So highway driving would be the same, as the working t-stat would be set to how I glued it anyway.

Am I wrong on the operation? Either way I am happy with it an appreciate the improved performance.

Post by **erikv11** » 26 Jul 2009, 13:17

I'd say not quite right on the operation. Note they put a thermostat in there not just a switch controlled by the ECU.

The airbox thermostat doesn't respond (open or close) according to engine temperature which I think is what you mean by "normal operating temperature" (the temp gauge on the dash measures the temp of the coolant leaving the engine block, near the coolant thermostat), it responds to the temperature of the airbox t-stat itself. Because of where the airbox t-stat is located, it responds to the temp right there in that intake channel, giving nearly direct control of the air temp at the throttle body.

So when you start the car on a cold day, the airbox thermostat is closed and at first only hot air comes in. That hot air gradually warms up the airbox t-stat and the t-start starts moving, to begin letting in cold air. Driving around town the whole engine compartment gets warm enough that even with cold air intake, the airbox stays warm and likely keeps the t-stat fully "open" (in the cold air position). If you get on the highway and start sucking in enough cold air and pulling enough heat away from the engine compartment, the airbox t-stat itself will cool off which causes it to switch back to letting in warmed air. For example, even though your car stays at "normal operating temp" on the highway, in order to do that it must shut down the coolant pathway thermostat a little bit. If you've ever run a car with a stuck open coolant thermostat, or without one, you know eactly what I mean. It is a lot cooler in the engine bay when you are going 70 mph.

I don't think this is a huge problem, just a potential drawback to the mod that is important to be mentioned here. So people can decide what they want to do depending on their maintenance preferences, driving habits, location etc. And if they do the mod, and the throttle sticks open on some winter day then they'll know a possible reason why.

Probably it is rare to have enough moisture in the air to ice up the throttle plate. My car takes a lot of short trips in the winter so we get moisture in the oil due to condensation, this is very common. I think that is why we had throttle freezes on this car, due to moisture delivered to the throttle plate by the PCV. At least I know the PCV is working OK.

Post by **jmyers** » 22 Aug 2009, 22:11

I just ran across this thread and checked the airbox t-stat on our '95 850. T-stat was stuck on the hot side as so many others are. Since we live in Texas and have mild winters I just removed the stat, ground down the housing and set the diaphram with a screw.
Thanks for the tip!