Time to change oil?

How do you know when it is time to change your engine oil? Maybe there is a sticker on your door that is visible when you open the door and crane your neck down to waist level. But, you still need to subtract the mileage figure on the sticker from the reading on your odometer. It can work, but it is not a great system.

Step 1: Use the Change Oil light?

Modern automobiles have a Change Oil light on the instrument display. See the green box. It lights when it is allegedly time to change your oil. But, it is only a computer's guess that it is time to change your oil. Your engine's computer notices the amount of city driving you do in comparison to highway driving and guesses that your oil has reached a certain level of contamination from engine wear, water vapor in the crankcase, acids, and engine blow-by gasses. A truly accurate assessment of your oil's condition would require testing in a laboratory.

The Low Tire Pressure light next to the Change Oil light also does not really know if one tire is low. It makes a secondary measurement that is usually explained by low tire pressure. It compares the number of revolutions each tire makes. If a tire is low, it has a smaller effective diameter and must turn more times per minute to keep up with the fully inflated tire on the opposite side of the car. My Low Tire Pressure light has remained "on" since a mechanic worked on the braking system a couple of years ago.

Comments

[thorning]

I have a year 2006 Toyota truck with a V 6 engine and the manual recommends a service interval of approx 6000 miles before service is necessary. If you read the manual fine print it states that this is under ideal driving conditions- little or no stop and go driving or short trips. Many vehicles do not lead this kind of life. I try to use a rule that the oil and filter should be changed at 5000 miles or 5 months in my driving cycles . The Toyota scheme uses a simple reset arrangement using the trip odometer button to turn off the warning light that can be done by the owner. The service interval light appears to be triggered by a combination of time and mileage and it has nothing to do with the oil level as far as I can tell. A low oil level or low oil pressure is a different circuit as I understand the circuit. Having never had a low oil pressure or low oil level I cannot attest to this but believe I am correct.

[Yerboogieman]

I usually change mine every 3000 miles. and add oil after about 1000 or so miles of driving.

[Kiteman]

The oil light is a level indicator - it means there is too little oil to protect the engine properly.

_{^{And if you drive around without topping up the oil, there is a loud bang and a piece of your engine the size of your fist goes through the radiator, punches off the front grill and renders you subject to sarcasm from roadside assistance personnel...}}

[Phil B]

There is a check oil light. It runs off of pressure, or the lack of it. There is also a change oil light. It lights when the computer guesses that your combination of city and highway driving has contaminated the oil sufficiently that a change of oil and filter is required.

[jtobako]

Depends on age and make of vehicle. I've never had one, but heard of a change oil light and the difficulty in a home mechanic resetting it without going to the dealer and paying to have it turned off : P

[klee27x]

Mine has one of those. It's actually a service "light" that automatically changes from green to yellow to red, every 3000 miles. And it's not really a light, but a little plastic colored spot at the bottom of the speedometer. I forever thought that a mechanic had to do some wizardry in order to reset it. Then one of them showed me how it's done. There's a slot next to it. You stick your key in it, and it resets. Lol.

[Phil B]

My car is a 1999 Oldsmobile Alero. It has a change oil light. Resetting it can be done by the owner/operator. It involves pressing a red button in the midst of a bunch of fuses until a sequence of flashes is seen at the change oil light, then pressing it again. I always forget the exact sequence and have to use the description in the owner's manual.

[jtobako]

And?

[Phil B]

I was simply saying my ten year old car has a change oil light, so if it depends on the age of the vehicle, such lights were in use ten years ago on some models. The Check Engine lights usually must be reset by a dealer's shop, but the Check Oil light on my car has a procedure the owner can use to reset it. I do not know what point you were trying to make with your "And?" comment.

[jtobako]

I was wondering why you had to clarify something that I agreed with.

[NachoMahma]

. All the oil lights I've seen work off of pressure. It will still light up if the sump is full and the pump fails.

[Kiteman]

Ah, things must have changed since last I read the manual for a car (a period measured in decades).

[NachoMahma]

. BTW, I was talking about the "Oil" (or "Check Oil") light. I wasn't at all clear, was I? :(

[lemonie]

There was a time when cars would have an oil pressure gauge I believe. And you checked the level with the dipstick. _{and changed the oil to suit the seasons}

L

[NachoMahma]

. Those were the days, my friend ... heehee

[lemonie]

Thanks! But I was thinking of something more like this

L

[NachoMahma]

. ROFLMAO

[rimar2000]

A few months ago I read on the web that car manufacturers don't put in books the real time that lasts the oil in the engine, simply for the prospective buyer believes that the maintenance will be cheaper for what it actually is. Example: when they say that one must change the oil every 10,000 km, it is better to do it every 6 or 7 thousand. That is if you want that the engine lasts a long time. Please tell me if something is not understood, my English is argentinian.

[Phil B]

Rimar, Your points are well made and easy to understand. The metals used in engines are better now than several decades ago. Still, frequent oil changes will make an engine last much longer. It hurts to see an automobile only a couple of years old go down the street and gray/blue smoke comes out of the exhaust pipe when the driver takes his foot off of the accelerator pedal.

[lemonie]

I bet you work out mpg from paper records too? (sensible stuff, I like it) L

[Phil B]

Thanks, Lemonie. Forty years ago when I got my first automobile I kept track of mileage figures. Since that time I have been more likely to use my watch and mile markers at the roadside to check the accuracy of my speedometer. Most of the autos I have owned were made by General Motors. It seems their speedometers have often been inaccurate by about six percent. 3600 divided by the number of seconds required to cover one mile equals actual speed in miles per hour. The object has been to go as fast as is legal in order to complete a long trip without delay, but still avoid the long arm of the law.

[lemonie]

Yeah, I think everyone makes overstated speedos, erring on the side of caution? My dad tends to trust the GPS more (and he's always fiddling with the trip buttons on his Toyota...) L

[NachoMahma]

. I think it has more to do with erring on the side of making the warranty run out ASAP (speedo usually drives the odo, so the odo will read higher, too). I don't know if that's true or not, but is sounds good when wearing a foil hat. heehee

[Kiteman]

The law is that speed gauges must read within 10% of the actual speed, without going under. This is why the Association of Chief Police Officers have an official policy that triggers prosecution for speeding at 10% over the local limit, plus 2mph (so, in a 30mph zone, you are prosecuted at 35mph).

[lemonie]

That fits with what I thought, thanks for the official line on this. Although you can still be prosecuted at less than 10% +2 over if they feel like it? L

[Kiteman]

I would guess it depends on how they measure your speed - I got that information from a speed-camera website - but I would assume that they would have to give you the benefit of the doubt, unless they could show that your speedo was reading more accurately and you knew you were speeding. That would need them to get your car onto a rolling road, which could work out as more expensive than the income of the fine.

[lemonie]

I have a feeling that if they can provide reasonable evidence that you were speeding it matters not whether you knew it or not (hence the cautious speedos) My dad (I-was-looking-at Honest-John's-page...) would surely know.

L

[jtobako]

In Minnesota, they recently threw out all the camera based tickets because they couldn't prove that the owner of the car was the one driving and the law specified that the driver, not the owner, receives the ticket.