I had a car problem Friday - oil leak in my driveway, engine knocking. I walked to the nearest filling station, bought two litres of oil, topped up the car, drive it six blocks to a Midas and got it fixed.
Apparently there was a double problem: there was a leak in the oil system, plus the sender to turn on the “low oil” alert wasn’t working. (Where’s our old friend Smacky emoticon when you need him??)
However, got it fixed and the knocking is gone.
But: when I went to get the two litres of oil, they only had 0W30. The car takes 0W20. So it’s now got a mix of oils: two litres of 0w30, the one litre of 0W20 that Midas topped it up with, and whatever was left of the 0W20 from pre-leak.
Is this a problem? Should I go to one of those quick oil change places to get it all replaced with 0W20?
What kind of car? Regardless, it’s probably not an issue. Plus it’s summer where you are. I would have the oil changed before winter, though, using 0W-20.
A bigger issue is that the engine was apparently running with poor oil pressure. I would have someone do a compression test on each cylinder.
It’s probably not as big of an issue as a leak that is causing you to add two liters of oil between changes which shouldn’t be the case in any car build in the last quarter of a century. I’d get the car serviced (not at a quickie old change place, an actual mechanic) and make sure you don’t have a bigger problem with the leak and engine ‘knocking’.
In general it’s okay to mix different kinds of oil. Some luxury cars are finicky about the oil they need. You might hear some odd clickings if it’s not the right kind. But it would be a good idea to do a full oil change since you were driving with the oil 2 quarts down. The remaining oil in engine would have had more heat and stress and may be more worn out than it normally would be.
Using a 30-grade oil in a car that requires 20-grade is a problem.
Mixing it with 20-grade gives you something like 25 grade. It’s not the mixing that is the problem.
Using a heavier grade oil will give you: Better piston sealing. Better wear protection. Slight power loss due to pumping losses. Possible oil damage due to shear. Possible catastrophic engine failure due to not being able to pump the thick oil around to where it is needed.
It’s the last one you should worry about. Keep the RPM low until you replace the oil.
On the other hand, if you are losing oil, then maybe your rings and cylinders are shot anyway, the radiator is glugged so cooling is poor, oil circulation is not something to worry about because the engine is already worn in and worn out, and you need a thicker oil just to stop it pouring out when the engine is at operating temperature: oil loss is more likely to cause catastrophic failure than oil thickness.
Not in the real world.
First of all, both oils were 0 weight. The oil the OP added is thicker in the winter, so as long as he changes the oil in the next few months there will be no significant difference.
But, even running a thicker oil is not generally a problem.
e.g. -
As I understand it, 0W is the starting/cold thickness. 20 is the thickness at operating temperature. One oil is 20 at operating temperature, the other oil is 30 at operating temperature.
I agree with GM: thicker oils give better engine protection.
Thinner oils are used by race cars because they take less power, and because the race engines operate at higher RPM.
I have destroyed a motor-cycle engine by using an oil that was too thick. The engine seized up.
Engines are designed with a certain viscosity in mind. The less you stray from the specs, the better. As you stray farther and farther away from the specs, the greater the likelihood there will be engine damage.
Straying a “little bit” is O.K., for a short duration (less than six months). The OP’s car is in this category.
Race car engines also typically get torn down and rebuilt every few races, or in some cases, like F1, they just replace the whole thing. Maintenance and wear on race engines is very different from the world of passenger cars.
As others have said, running 2 quarts low on oil probably did no/very little damage to your engine over a short span, but the remaining oil had to perform under harsher circumstances and may be carrying a higher load of contaminants, plus the fact that you heard knocking probably indicates excessive heat, so change it soon. It’s not “get this done tomorrow” critical (unless it’s a race car) but I’d try to get it in the next couple weeks at a good mechanic, and ask them to check for metal in the oil.
I’d worry most about the knocking but if the leak was repaired, the knocking stopped, and the mechanic who fixed the leak wasn’t worried about additional engine damage, perhaps the car will be fine.
The oil he used is 0W-30. The “W” stands for winter, which means the oil he used nominally has the same viscosity in winter as the recommended oil. There is no particular reason to change it because of looming winter (if winter were looming).
The problem is that at operating temperature, the oil is thicker (30 weight) than recommended the recommended 20 weight. In most cars, the heavier weight means the engine has slightly more protection against wear in summer heat at the expense of slightly higher pumping losses and imperceptibly worse fuel economy that might be measurable under lab conditions. In a small subset of cars, perhaps the higher viscosity oil would circulate poorly enough at operating temperatures to cause lubrication problems but in most cars, I doubt there would be any problem.
I fully agree.
Not just in Canada. Three of my four cars in the US, including one that is 19 years old, call for 0W-20.
I race what are basically junk cars in endurance racing. There are a mix of theories among other racers but most racers tend to use heavier oils than called for. Stuff like 20W-40 instead of 5W-30. Engine durability is more important than squeezing an extra tenth of a horsepower out of a car. Some drivers even mix in some incredibly thick gear oil to toughen their motor oil up even more. Cold weather performance is basically irrelevant because the car will start once, be warmed gently in the pits, and then run for 400 miles at high temperature without stopping. Better protection at high temps is worth more than thinner oil for faster protection at cold startups. Some minority do use thin oils thinking it means that the oil flows through the engine better. My team uses thin, low-viscosity oil mainly because one of the team members got a shit-ton of it for free and we go through 1.5 gallons every day of racing. Since making this pragmatic engine viscosity choice, we have noticed no particular adverse lubrication or engine wear problems, so we’ll stick with it until the oil runs out.
I think the problem with those engines is/was the variable flow oil pumps that don’t always seem to pump enough oil. The thicker oil is at best a band-aid to hopefully protect the engines by just enough extra to nurse a few additional engine blocks past the warranty period.
Ask two gearheads about oil and you’ll get at least three opinions.
