Emissions problem and low oil

October 2, 2012 4:50 PM

My car, for the first time in 12 years, did not pass an emissions inspection in California. Right before this, my oil light had started to periodically blink. On inspection, my oil was very (very) low. I filled it back up after the test. What are the chances that this caused the high emissions levels?

I have a free retest coming up, and I'm trying to figure out if I should pay for a mechanic to investigate and potentially fix a different problem. Or, is it likely that low oil would have led to testing problems. In this case, I would retest right away.

posted by SpacemanStix to travel & transportation (16 answers total)

Low oil will not effect your emissions.
posted by tylerkaraszewski at 4:58 PM on October 2, 2012

Low oil may, however, be a symptom of what caused you to fail your emissions test. If your oil is low, it's going somewhere. Usually that means it's being burned because it's making its way inside your cylinders. You should get a mechanic to look at it before you try a re-test.
posted by straw at 5:18 PM on October 2, 2012 [2 favorites]

Yeah, what straw said.

One thing to look for... when you first start up your engine in the morning after sitting overnight, do you get smoke out of your exhaust? If so, what color is it? If it's blue smoke, then you're burning oil.
posted by hippybear at 6:03 PM on October 2, 2012

My recent forays into finding a cheaper smog test place led me to believe that having lighted engine alerts on your dashboard = automatic failure of the smog test in California. If the low oil light lit up during the test, this may be the problem. (i have never failed a smog test, but don't they tell you why it failed on the certificate/report?)
posted by holyrood at 6:16 PM on October 2, 2012

Give Marvel Mystery Oil a try. Thick like molasses, add to oil not gas. Ran this in my old Fiat Spyder. Not necessarily the best for your engine long term though so act accordingly...
posted by cosmac at 6:19 PM on October 2, 2012

Right before this, my oil light had started to periodically blink.

Your oil pressure light? Normally, that's kind of a big deal when it comes on, but once cars get old the light will flash at some points when there's really nothing to worry about. I had a truck with close to 200K miles on it where the oil light would come on when I made a quick stop, but it wasn't actually a problem, and the manual for the car mentions that this happens at higher mileages. So, if that's the case, the oil light and the smog failure could be related, but only in they're both symptoms of an older car, not one causing the other.
posted by LionIndex at 7:24 PM on October 2, 2012

Thanks everyone. Yes, I suspect that there's an oil leak problem somewhere, as this is the second time in a year or so that I've had to put oil in there. But it's not leaking on the ground that I can see. Would this potentially be a symptom of something costly to repair?

Your oil pressure light?

I think so? It's the only oil light on the dash. It stops blinking when I put oil in the engine.

The car has a lot of miles on it, and we've determined to just run this one until it can't go anymore without breaking the bank. I wonder if it's getting time to retire it.
posted by SpacemanStix at 7:28 PM on October 2, 2012

Also, no smoke coming out the back that looks odd. But I'll double-check in the morning.
posted by SpacemanStix at 7:55 PM on October 2, 2012

Would this potentially be a symptom of something costly to repair?

If you're burning oil, it means there's something going on inside the engine itself, like in the cylinders or whatnot, and yes, this is costly to repair. At the very least, if you have to get your rings replaced, you're still looking at someone tearing apart your entire engine, which will involve a lot of labor costs. If it's something that involves having your engine rebored, the costs go up even higher.

Seriously, look for blue smoke when you start the car up after having set for a while. You might try some of the smoke treatment stuff, which can help if things are very very minor as far as a leak goes. Also, high-milage oil with lots of PTFE can help. It sounds like if you do have a leak, it's pretty minor all around.
posted by hippybear at 7:55 PM on October 2, 2012

How old is the car - is it twelve years old or have you just owned it for 12 years? How many miles? Have you been getting a check engine light? Also, what reason did they give you for failure?
posted by azpenguin at 8:28 PM on October 2, 2012

My car uses oil like crazy, and has for the past 10K miles. There are no visible oil leaks and as far as I know, no funky smoke. I'm told that fixing it would cost more than the car (2000 Corolla) is worth.

Surprisingly, however, it has passed CA emissions tests twice since it started burning (or otherwise losing) oil. I can't know for sure if these things helped it pass, but what I've done is:
a) changed the oil immediately before taking it to be tested
b) changed the air filter (not sure how much that helps, but it's easy)
c) driven the car around on the highway for 15-20 minutes before taking it to be tested

I also noticed that most emissions levels were lower this time around, after I had my spark plugs changed.

How far above the allowed emission levels was your car?
posted by needs more cowbell at 8:36 PM on October 2, 2012

The car is 12 years old and has almost 160K miles. No check engine light.

The reason for the failure is that the HC (PMM) numbers were high. At 15 mph the max number is supposed to be 61 , and the it registered at 61. At 25 mph the max is supposed to be 45, and it came in at 90. This is where the test failed.

I have no idea what those numbers mean.
posted by SpacemanStix at 8:49 PM on October 2, 2012

In my unprofessional experience, high hydrocarbon at low rpms is almost always because of the effectiveness of the catalytic converter. And low oil could absolutely lead to the failure of the cat.
Low oil leads to a higher engine temperature, leads to higher exhaust temperature, leads to higher cat temperature, leads to cat failure. The higher rpms runs the fan faster, cooling everything down.
That's just one possibility.
In the future, especially with a car that has that many miles on it, check your oil between changes, and always change the oil, check tire pressure, etc before getting smother.
posted by gally99 at 10:44 PM on October 2, 2012 [1 favorite]

HC (PPM) is unburned Hydrocarbons, measured in parts-per-million at the tailpipe. It shows that your engine is not burning all of the fuel/air mixture in the cylinder or your catalytic converter is not working as well as it should. This is (often) an indication of:

- A failing O2 or mass airflow sensor, which would cause the car to run rich.
- Low compression, which can be caused by worn rings (which also would explain the oil burning)
- a cold catalytic converter. Did you drive the car 30-60 minutes before taking the test?
- Old spark plugs that aren't igniting the fuel as well as they should.

A fresh oil change, new plugs, and a good drive before the test might get you through -- the key word is "might". If your rings are shot or you need a new catalytic converter, that's going to be expensive.
posted by toxic at 12:03 AM on October 3, 2012

That's a great help. Thanks everyone.
posted by SpacemanStix at 8:27 AM on October 3, 2012

If it's useful at all, as a datapoint:

With original spark plugs, at around 90K miles, my oil-guzzling car had HC emissions of 53 ppm at 15 mph and 10 at 25mph.

5K miles later, after I changed the spark plugs, it had 44 ppm at 15mph and 11 at 25mph.
posted by needs more cowbell at 12:12 PM on October 3, 2012