When you run your air conditioner, the compressor “pressurizes” your refrigerant. So, when you arrive home after a long drive, that refrigerant is under very high pressure.
Once the air conditioner is shut off, which happens when you shut off the engine, the refrigerant needs to return to normal pressure. And it does that by passing through something called an expansion valve. I think all you’re hearing is the pressure of the refrigerant equalizing by passing through that valve. It produces a soft whistling sound while it equalizes. Unless it’s really loud, or whistling a funeral dirge, I don’t think it’s anything worth worrying about, Jack.
If you were to shut off your air conditioner while you were driving, the same thing would happen. But that faint whistling noise would be drowned out by the road noise, the engine and the argument you were having with your wife about why you turned off the darned air conditioner.
Find a reason to do something else when you get home. Preferably something that doesn’t require you to be in the garage.
Chevy Bel Air has all original parts – even the smelly exhaust
Dear Car Talk:
I have a pristine 1960 Chevrolet Bel Air. I am the second owner. It has 95,000 miles on a 348 motor with a Powerglide transmission. It’s all original with no hot-rod modifications. The car runs smooth as silk. I drive it two or three times a month to keep it exercised. But my daughter complains that if she follows me in her car when we go to car shows, the exhaust really smells bad.
I have always used premium fuel in this car, and I drive it often enough that the gas is not particularly “old.” I know this car was built well before pollution controls were introduced, but I never remember car exhaust smelling remarkably bad as a kid. I have also noticed some of my vintage car show buddies have this issue with their 1950s-1960s cars.
Why do the vintage cars have "pungent" exhausts? – Joe
RAY: I didn't remember old car exhaust smelling bad when I was a kid, either, Joe. But a few years ago, we were lucky enough to take a trip to Cuba to check out the old, American cars there.
And guess what? Most of them stunk! I think, as the air has slowly gotten cleaner and cleaner over the course of our lives, we’ve all forgotten how bad it used to be.
Nowadays, if a car drives by that’s got visible or malodorous exhaust, it stands out like a sore Edsel. Back then, most cars did that.
Between 1960 and today, we’ve added fuel injection, computerized engine controls, oxygen sensors, catalytic converters and more, to the point where you could put your nose next to the tailpipe of a new car and not smell anything – but please don’t, unless you want to end up as dumb as me.
The carburetor on your car, in contrast, is the technological equivalent of pouring gasoline into the cylinders from a paint can. It’s sloppy, imprecise and dirty.
Now, it’s possible that there’s also something wrong with your Bel Air. And the problem most likely to make your exhaust even stinkier than usual is a fuel mixture that’s too rich.
So, if your carburetor jets, for instance, are all worn out after only 60 years, they could be pouring way too much gasoline into the cylinders. The engine wouldn’t be able to burn that extra fuel, and – without any emissions equipment – it would all come right out the tailpipe. And it would stink.
There are other things that can cause incomplete combustion and a rich mixture: low compression, incorrect timing, low engine operating temperature or a weak spark. It’s probably worth checking all of them.
But my first guess would be the carburetor. And it’s probably not too early in this car’s life to replace the carburetor, Joe. That may very well improve the odor to some degree.
If that still doesn’t improve the smell to your daughter’s satisfaction, you start following her to the car shows.