What's wrong with my car? (Special Audio Edition!)

[Koyaanisqatsi]

My car has been making odd noises on startup after it sits overnight and the exhaust fades from medium-gray to clear over about 45 seconds. There's also been a ~2MPG drop in fuel economy over the last several months, but that could easily be a change in driving patterns (went from long highway commutes to short in-town driving.) I don't know anything about cars and trust the mechanics around here about as far as they could throw me, so...any guesses? It's about 7.5 years old, 75k miles.

(Yes I realize the futility of asking this over the Internet, but...oh well.)

Thanks...

[BlackCat]

In "old" days (70'es and older) short trips could clog up the engine - not sure that problem is solved in modern, so your change in driving pattern could be the reason.

[rah]

From a web site


Media Credit: Tony Blazejack * Ka Leo O Hawai'i
Exhaust pipe smoke can indicate problems in an engine's fuel, cooling and lubrication systems.
Tony Blazejack * Ka Leo O Hawai'i



Smoke coming from your tailpipe can either be a sign of normal engine operation or a sign of major engine troubles. Tailpipe smoke comes in three colors: white, black and blue. Each color is an indication of a separate symptom, which range from normal to troublesome. The following is a short guide to the three smoke colors and what they indicate, along with a few remedies and tips.
White Smoke

In cold climates, a small amount of white tailpipe smoke indicates condensation caused by hot exhaust gases mixing with the cold exhaust pipes and atmospheric conditions. You may even see a few drops of water, which is perfectly normal since water is a by-product of combustion.

However, white, billowing smoke indicates that coolant is getting into the cylinders and is being burned with gasoline inside the combustion chamber. Occasionally, a milky residue will form in the tailpipe, also indicating that coolant is getting into the cylinders. This is usually caused by a blown head gasket, cracked cylinder head, or, in extreme cases, a cracked engine block.

The head gasket seals the surfaces between the cylinder head and engine block and has passages that allow engine coolant to flow freely between the cylinder head and the block. If the head gasket goes bad due to overheating or other less-than-optimal engine conditions, coolant will leak from one of these passages, pass the gasket, and end up in the cylinders. A head gasket can cost over $500 to repair, depending on your engine type. To prevent this, always ensure that your car is at operating temperature and not overheating, as indicated by the dashboard lights and gauges.

Black Smoke

Black smoke indicates fuel system problems and a fuel-to-air ratio with too much gas and not enough air. Older cars equipped with carburetors may require adjustments or a replacement. Newer fuel-injected cars require a mechanic's diagnosis, as the electronic control module controls things like fuel delivery and fuel injector pulse time. A thick, sooty residue, accompanied by a rich exhaust smell from the tailpipe also indicates fuel system problems.

A common problem that causes black smoke is a dirty or clogged air filter. This restricts air flow into the engine, creating a lack of air reaching the combustion chambers. Air filters can be easily checked, and if held up to the sunlight, light should be seen. If you see no light, the air filter is dirty. An air filter can easily be cleaned out with compressed air, but because a replacement air filter is cheap, it would make more sense to purchase a new air filter instead.

Blue Smoke

Blue smoke indicates that an engine is burning oil. Blue smoke is often accompanied by an oily residue on the tailpipe and an acrid smell. When an engine burns oil, it indicates that the engine is internally worn out, and oil is getting into the cylinders. Common components that wear out include valve seals, seats and piston rings.

Unfortunately, there is no easy fix for oil problems. If an engine is worn, the only cure is an engine replacement, which can cost thousands of dollars. If a repair is necessary, the cause of the burning oil should be properly diagnosed with a dry and wet compression test to save as much money as possible. With these compression tests, problems regarding the valve seats, seals or piston rings can be properly identified. Although all engines will eventually start to wear internally, it can be avoided by performing regular oil changes and by not severely abusing the engine during normal driving.

[Koyaanisqatsi]

Yeah, I can find stuff on my own for that (not that I don't appreciate you looking it up, Rah, thanks!) I was mostly hoping that somebody with more knowledge than me would be able to tell something from the noise. It's hard to Google for "it sounds like VRROO-pft-OOO-pft-pft-OO-pft-OOM"...

[Spec]

Originally posted by BlackCat
In "old" days (70'es and older) short trips could clog up the engine - not sure that problem is solved in modern, so your change in driving pattern could be the reason.

Not really. Driving at low RPMs ALL the time does that to an engine, even today. Carbon build-up is what its called. Its always good to open up a car once a month.

Spec.

[Spec]

Originally posted by Koyaanisqatsi
Yeah, I can find stuff on my own for that (not that I don't appreciate you looking it up, Rah, thanks!) I was mostly hoping that somebody with more knowledge than me would be able to tell something from the noise. It's hard to Google for "it sounds like VRROO-pft-OOO-pft-pft-OO-pft-OOM"...

Can you make a quick vid? If so, I could probably tell you.

If not, let me ask you a couple of questions. Does it stop spurting after it gets hot? Does the chock come on when you start it up or it idles at 800rpm? Year, make and model? If you floor it in neutral when you just started the car, does it easily go up to the redline or does it sputter? When did you do your last tune up? You say the smoke is gray, what outside temperature is it when you start the car? Does it seem more like white or blue smoke? If you floor it in neutral at start up, does it smoke more or does it stop suddenly?

I know, this is a lot of questions but I just might be able to tell you what is wrong.

Spec.

[Koyaanisqatsi]

Originally posted by Spec
Can you make a quick vid? If so, I could probably tell you.

Possibly...let me do some checking. If so I wouldn't be able to until tomorrow.

If not, let me ask you a couple of questions. Does it stop spurting after it gets hot? Does the chock come on when you start it up or it idles at 800rpm? Year, make and model? If you floor it in neutral when you just started the car, does it easily go up to the redline or does it sputter? When did you do your last tune up? You say the smoke is gray, what outside temperature is it when you start the car? Does seem more like white or blue smoke? If you floor it in neutral at start up, does it smoke more or does it stop suddenly?

I know, this is a lot of questions but I just might be able to tell you what is wrong.

Spec.

Answers, in order: Yes, it stops after about 45 seconds. Chock = choke? If so, I was under the impression fuel injected systems didn't have them, if not, don't know what you're talking about. 2001 Pontiac Aztek (stop laughing). Dunno, haven't tried. It's been a while. Low 50's lately. Doesn't seem to have a color to it, so I'd say white. Dunno, haven't tried (hard to do with only one person).

[Spec]

Originally posted by Koyaanisqatsi

2001 Pontiac Aztek

Theres your problem.


No, seriously, try to make a vid if you can.

And yes, cars have a choke, even today, thats what makes the car run at 2000rpm when cold.

And please try to floor it in neutral at start up to see if it easily goes to the redline or it sputters.

Spec.

[Koyaanisqatsi]

Originally posted by Spec
And please try to floor it in neutral at start up to see if it easily goes to the redline or it sputters.

Tried this today, it gets to about 3500RPM then drops to 2500 and goes back and forth several times. When I let off the gas and tried a second time it was fine.

[Wezil]

I'm guessing head gasket.

[Spec]

Originally posted by Koyaanisqatsi


Tried this today, it gets to about 3500RPM then drops to 2500 and goes back and forth several times. When I let off the gas and tried a second time it was fine.

@Wezil: Its not the head gasket.

Sounds like a sensor in the Air flow meter (Or master air flow) might be fubar because of condensation (which goes away when air dries it out). Could also be time to change your wires and spark plugs. The latter seems more probable though.

A regular tune up would most likely fix the problem.

Is your check engine light on? If not, i'm 90% sure your spark plugs are going slowly.

Why I am suggesting the spark plugs is because wen the car is cold and the plugs are cold too, they might not ignite the mixture as they are supposed to, but when the chamber heats up, the high tempertures help for combustion. If it was 100F outside, I bet you wouldn't have that problem. And thats probably why you have smoke coming out of your exhaust the first 45 seconds or so, poor combustion until the cylinder heats up.

Spec.

[Wezil]

Originally posted by Spec


@Wezil: Its not the head gasket.

Alright. It's usually a good guess.

[Koyaanisqatsi]

Originally posted by Spec
@Wezil: Its not the head gasket.

Sounds like a sensor in the Air flow meter (Or master air flow) might be fubar because of condensation (which goes away when air dries it out). Could also be time to change your wires and spark plugs. The latter seems more probable though.

A regular tune up would most likely fix the problem.

Is your check engine light on? If not, i'm 90% sure your spark plugs are going slowly.

Why I am suggesting the spark plugs is because wen the car is cold and the plugs are cold too, they might not ignite the mixture as they are supposed to, but when the chamber heats up, the high tempertures help for combustion. If it was 100F outside, I bet you wouldn't have that problem. And thats probably why you have smoke coming out of your exhaust the first 45 seconds or so, poor combustion until the cylinder heats up.

Spec.

No, no engine light. I wouldn't be surprised if it was something like that, it hasn't had anything done to it beyond oil and filters since the warranty (and service package that goes with it) ran out. Thanks!

[Wezil]

The suspense is killing me....

[Koyaanisqatsi]

No confirmation, but when it sat in the sun all day so the thermometer in the car read 95 when I started it it was fine, so...

(Trying to decide if I did a good deed by replying or missed an opportunity...)