I changed my air box thermostat last night.

The one I took out had a very small pin coming out of it, whereas the one I got from FCP Groton had a longer pin, at least twice as long.

I put in the new thermostat. Once installed the flap went over the cold air intake. Tight.

Questions :

1) The spring that is being pushed by the thermostat is very hard to push by hand. Is that OK? Should it be that hard?

2) I assume that the pin comes in or retract when the weather is warmer, and the spring can extend more. How can I test that the thermostat works well? I am want to make sure that I am not going to fry my AMM.

Thanks.
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'89 244DL M47 158K miles

You could have used a hair dryer while it was out of the car.

The old one had a pin that was smaller...it was probably binding in the open possition...not good for the AMM
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'75 Jeep CJ5 345Hp ChevyPwr and two motorcycles: it wasn't Volvos safety , it was Longevity that sold me

The new one you put in sounds like its ok.It is normal for the new thermostats to default to cold air intake.I guess because its so cold in Sweden,the t-stats were designed to default to hot air intake in case they failed.

Right now the flap is covering the cold air intake, that is hot air is what is coming in. Doesn't that mean that it is defaulting to hot air intake? Should I be worried about damaging the AMM ?
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'89 244DL M47 158K miles

The Bentley manual states that the air flap should be at full cold air input at temperatures above 59 degrees F (15C) and full hot air input below 41F (5C).
The manual suggests removing the air box to make these tests. What you might do is open the box and remove the air filter. If it is cold out, the flap should be in the position to let in all hot air. Then take a hair dryer and aim the hot air at the thermostat and see if it closes, It will be slow acting.

Another way to test is to see if the thermostat closes the hot air and lets in cold after the car is fully warmed up. The problem with this is the thermostat may have time to open the hot air while you are trying to open up the box.

Yes, that spring on the thermostat is very stiff.

Because it is not often below freezing here in western Oregon, I removed the thermostat and flap and blocked off the hot air inlet to my air box in my '88 240. It starts just fine even on cooler mornings. We had to replace the AMM in it and I didn't want to have it go out again from overheating. (I can't be sure what made the original AMM go out though.)

You question reminds me tha that I need to check the air box thermostat in my '93 940. This car has the Regina system so there is no AMM. However, if the thermostat is stuck on the hot air position, it will affect the gas mileage, I believe and maybe make it run poorly when very hot. I need to do some research on this. Thanks.

Jim - I have one of those cheap 'n nasty little indoor/outdoor LCD-display thermometers that you find hanging on a card in the Wal-Mart 'useless car trinkets' aisle. The wire is about ten ft long so I can hang the sensor in the airbox. On the 240's there is a rubber plug in the top which I remove, hang the sensor, then replace. Run the wires along the fender and up through the hood/fender crack and into the car. The door weatherstrip won't crush them.

The heat response after a cold start is pretty quick - comes from the exhaust manifold, after all. It overshoots to about 24C in a few minutes, and eventually settles to about 13C-17C in our 0C mornings. It depends on throttle opening - when you lean on it to climb a hill, the temp goes up about 5C. So it seems to work OK. This is ONE of the two I got from FCP 18 months ago. The one in the 81 has already failed - temp goes to 35C-40C (95-105F) and stays there. As the car is a K-jet and it's cold here (just S. of the Oregon border) right now, I don't think it will hurt, but I'll change it before Spring.

On our 940 I just put the sensor in the airbox, and closed it up. The lid pinches the wire, but no sign of problems. The 940's stat is probably OE and is (touch wood) still working OK.
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Bob (81-244GL B21F, 83-244DL B23F, 94-944 B230FD plus grocery-getter Dodge minivan, MGB, and numerous old motorcycles)

Great idea! I've been think9ing about getting one of those and mounting it on the dash to read outside temperature.

I've been running with one now for three-four weeks or so and the night before last I had the queen of ice commutes on the evening ride home. Spent so much time creeping at 1mph or controlling a skidding descent I was really surprised to arrive home without putting it into a ditch or bending the sheetmetal. The thermometer read anywhere from 34 to 37 degrees just below the air dam in front of the passenger side tire. But the ground has been frozen for a month. Maybe a better sensor would work like one of those IR guns, aimed at the pavement.
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Art Benstein near Baltimore

Art, in regard to the slip and slide trip home, I recall that ice will melt slightly under pressure. (If I recall my physics correctly) This means that it is possible to have a lubricating layer of water under the tires as they press on the ice. Of course this make ice driving even more hazardous.

You're right about the outside temp measurement not being a clear indication of the road surface condition. I wonder if anyone has tried the IR sensor idea. Sounds like you may have an invention idea.

When I lived in Iowa and Minnesota, I learned to look for likely areas where black ice would be found such as shelter belt tree shadows and road cuts.

Take care on the roas. We have had only about a week of bad roads here in Oregon and that's enough. We are unlikely to have more this winter.

Last weekend I opened the front door to what I figured to be some kids selling raffle tickets, but instead they pointed to their car which was well embedded in my wife's honeysuckle hedge. If my daughter had been home, her 244 would have damage. If those bushes weren't there and strong as wild ones are, those kids would have rolled that camry on the hill in our side yard. The street was a river of snowmelt the day before; no salt left behind when it froze.

when the road gets like that it's pretty hard to keep any control without chains or studded snows. Glad you didn't have any greater damage. Weather like that is fairly uncommon where I'm at and I don't miss it. Take heart, spring is coming.

Art - my el-cheapo also reads about 3-5 degrees high depending on the temperature it's seeing. I checked/calibrated it against a known good thermometer over a range of temps. When I quote numbers from it, I'm correcting to actual.
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Bob (81-244GL B21F, 83-244DL B23F, 94-944 B230FD plus grocery-getter Dodge minivan, MGB, and numerous old motorcycles)

Hi Jim,

I will do the test with a blow dryer.

In the Summer I think I'll just take out the flap and thermostat.
What do you use to block the hot air duct? What do you put in there?

Thanks for the tips.
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'89 244DL M47 159K miles

I used some aluminum tape and replaced the hose over the tape.

I live in New York. It's been a cold winter here. I took that T-stat out and pulled the Flex hose off the car all together. I end up with a car with two cold air inlets and no chance of the T-stat frying my AMM. The car takes about another mile to warm up to Temp. That doesn't bother me.
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'75 Jeep CJ5 345Hp ChevyPwr and two motorcycles: it wasn't Volvos safety , it was Longevity that sold me

"...pulled the Flex hose off the car all together..."

Is the Flex hose to which you refer the pre-heat hose (aluminum hose that runs from air box to engine block)?

Is that Ok for the engine not have the pre-heat hose there ? No risks of anything getting in there ?

Wouldn't it be better to 'plug' the end of the pre-heat hose where it connects to the air box?

Just wondering.

Thanks.
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'89 244DL M47 159K miles

The only problem is that you might not pass the visual part of a smog inspection. They might notice that it's gone and fail you.

Is the Flex hose to which you refer the pre-heat hose (aluminum hose that runs from air box to engine block)? YES

Is that Ok for the engine not have the pre-heat hose there ? No risks of anything getting in there ?

On the Manifold side,It just draws the hot air up, it goes nowhere. On the Air box side, All the air goes through the filter before continueing on. Maybe a mouse could cause problems, chewing up the filter.

Wouldn't it be better to 'plug' the end of the pre-heat hose where it connects to the air box?

You could. The dopey Preheater hose tend to break right where it connects to the Exhaust manifold So I thought it made for a cleaner look to just remove.

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'75 Jeep CJ5 345Hp ChevyPwr and two motorcycles: it wasn't Volvos safety , it was Longevity that sold me