Dear Car Talk:
When the oil light is on, is the oil pressure low or is the oil level low? — Bob
Yes.
Unless otherwise noted, a red light that says “OIL” on the dashboard means your oil pressure is dangerously low. Of course, the pressure could be low because you don’t have enough oil in there.
But oil pressure can also be low because your oil pump is failing, because your engine bearings are all worn out and they’re too loose to maintain pressure or for a number of other reasons — none of which are good news.
So when you see a red light that just says “OIL,” that means your pressure is low, and you’ll want to pull over and shut off the engine as quickly as it’s safe to do so.
Sometimes you’ll see the oil light flicker, especially when you’re at idle — like at a traffic light. That’s when oil pressure is at its lowest anyway. It’s a sign that you’re on the verge of having a serious problem.
At that point, we usually recommend a mixture of 90 weight gear oil, sawdust and bananas in the crank case. Or whatever tropical fruits happen to be in season.
There are a few cases where the oil light comes on simply because the oil pressure sensor is bad. That’s a lucky break. But, generally speaking, seeing the oil light come on while you’re driving is bad news. And it’s a light you never want to ignore.
On the other hand, lots of newer cars also come with an oil level light, which is different. That’s not an emergency warning light. It’s more of a maintenance reminder light. The oil level light is designed to eliminate your need to check your oil with a dipstick.
Checking the oil used to be a regular chore for car owners. But most people don’t want to do anything other than start the car and drive these days. And based on the rush to self-driving cars, it’s clear we don’t even want to do that much anymore.
Over the years, we’ve made clear to car makers that rolling down our own windows or taking the key out of our pockets is way too much trouble, so many of them have eliminated the dipstick and replaced it with a sensor.
If your car has an oil level light, and it comes on, that’s just a sign that you need more oil. It’s usually not an emergency. That light will normally come on when you’re down a quart.
While it’s not ideal to drive around down a quart of oil, you can certainly drive until you can get to a gas station or a Cheapo-mart where
you can buy a quart. You shouldn’t do any lasting damage if you take care of it in a timely manner.
If the light doesn’t turn off after you add a quart, then drive it to your repair shop, because you may have a leak or some other problem.
Resist the urge to add a second, third or fourth quart, so you don’t overfill the crankcase and do more damage.
To sum up, as much as we hate to do this to you, Bob, we’re going to send you to your owner’s manual. Look up “oil light” in the index at the back of the book.
If you have two different oil lights, you’ll need to know that. And you’ll need to know how to distinguish between them so when one of them comes on, you’ll know if it’s time to mosey on over to your gas station or to your new car dealer’s showroom.
Dear Car Talk:
Why aren’t the fog lights on newer cars yellow in color? They are often plain glass, with white lights. They don’t even use yellow bulbs. Why is that? — Ross
Because yellow lights don’t help with fog.
I guess someone once thought that yellow light somehow cut through fog better. He probably mansplained about the Rayleigh law and wavelengths of various colored light. And he was completely wrong.
But he was apparently very convincing. And hugely influential in the fog light industry. Because back in the 1960s and ‘70s pretty much all fog lights had yellow lenses.
They certainly looked cool. I’ll give them that. But they did nothing to help you see in fog.
As you probably know, fog — which is droplets of water — reflects the light produced by your headlights, making it hard to see.
You probably also know that turning on your bright lights in fog only makes visibility worse because more light gets scattered and reflected back to you.
The only thing that helps at all in fog are lights that are positioned and aimed very low, toward the street. And that’s what proper fog lights try to do: light up the actual road right in front of you, shining as little light as possible directly into the fog at eye level.
Under certain conditions, that can help. But honestly, fog is tough. Sometimes, you just have to slow way down or pull over and wait it out.
The good news is that while yellow light doesn’t do any better in fog than white light, it doesn’t do any worse, either.
I mean, a yellow lens (or anything other than a clear lens) will reduce the sheer amount of light that gets through. But the color itself won’t aggravate the situation. So if you like yellow, Ross, go get a highlighter and have at it.