I was wondering if I get an oil change prior to getting a smog check - will it give better results for the smog check- please advise - thanks.
(btw - i have a 94 mercury van villager with 150,000 miles on it.)
If a car barely misses its smog test, the list of possible remedies includes an oil change. It may not help very much bit it certainly can’t hurt.
Actually, new oil will smoke less that older oil, so it might help in a marginal engine.
thanks for your opinions…
no
No. Smog Test measures fuel/air mixture, NOX, CO2, engine performance/timing, etc…
It most certainly can give you better results… Have you ever heard of blow-by??? Open up your oil filler cap when the engine is running. Feel the air coming from the crank case??? That is exhaust, or blow-by. If your exhaust can enter the crank case with the engine oil, then the engine oil can be contaminated with unburned fuel. This blow by gets sucked right back into the engine by way of PCV valve. Have you ever changed your oil and felt like the engine is running 100% better??? Think about it.
transman
Yes!
I once failed a smog check with a perfectly good car, by not warming it up sufficientlty. Make sure you have a new or very clean air filter, all plugs are firing properly and your crankcase ventilation sytem is working properly. These items are far more important than changing the oil. If the engine is old and tired, and has some blowby, you could put in a heavier grade oil to improve your odds. Make sure the engine is well warmed up; take it out on the interstate for a quick spin.
A smog test also checks for hydrocarbons.
If the oil in the crankcase has a lot of miles on it, it becomes more volotile. These oil vapors are then introduced into the combustion process via the PCV system. If there’s a lot of oil vapors in the crankcase gasses, this will effect the HC count.
Tester
Yes, changing your oil will lower the readings for the reasons already posted.
In most states, less than 3% of the cars tested “fail” the test. It’s just another revenue source, like a toll booth. With that low a failure rate, smog testing makes no difference in overall air quality. If the 3% that fail are ignored, it just makes no difference in air quality.
When 30% of the Diesel powered trucks start failing emissions tests, THEN you will know they are getting serious about air quality.
In most states, less than 3% of the cars tested “fail” the test. It’s just another revenue source, like a toll booth. With that low a failure rate, smog testing makes no difference in overall air quality. If the 3% that fail are ignored, it just makes no difference in air quality.
I wonder how many would fail the test if they did not know they were going to be tested. How many people would let more things go un-corrected or intentionally disconnect pollution control equipment if they knew they would not be tested?
It sould also be noted that most of the pollution is caused by a small percnetage of the cars. It has been suggested that we use available technology (simular to traffic light cameras) to identify that small percentage and eliminate regular testing, but the legal issues have kept it from being used.
Diesel trucks have been pretty much expempt from regulations, but that is (slowly IMO) comming to an end. The ULSD fuel now available is part of that change.
An oil change is always a good idea to help an engine operate at it’s optimum. The fewer volatile components you have in your crankcase is the fewer that can get drawn into the combustion process via the positive crankcase ventilation system.
However, a good tuneup with new plugs, wires, and filters is an even better idea. If you haven’t had one for awhile, do that. Optimum combustion gives fewer emissions.