This will likely be my most controversial article to date.. In this article I want to talk about oil temperature. This is my opinion and I know a lot of people will want to debate me on this, it has happened a lot over the years. Just hear me out, and then form your own opinions. This is what I have found works for me and why.
The big question is, what is too hot for oil temp? I have found that reaching anything over 200 degrees should concern you. In Redding, CA, we experience extremely hot temps. It is not uncommon to see 110+ in the summer with no humidity. What’s humidity got to do with it? Well, put water through a fan what have you got? A swamp cooler. So high temps with water is better than high temps with no water. Let’s start with the obvious, all oils have a thickness. As the oil heats up that thickness goes away. At 212 that oil is at its minimum thickness for proper lubrication and any thing over 212 the thickness goes away fast. That is when I see premature wear on engine bearings etc.
Can oil be too cold? Yes. If it is too thick (too cold) then it has a hard time getting into tight clearances in a motor. That’s why when we start a motor we will have a higher oil pressure than after the motor is warmed up. That is also why there are pressure relief springs in a motor. These blow off the excess pressure.
I have people tell me all the time that they run and will continue to run temps higher than that. Ok, that’s your deal. Go for it. Here’s my reasoning for keeping your oil temp lower. Let’s look at water-cooled cars. How hot do they run? Most new cars stay at 190. When a water-cooled car gets to 210, their needles on the gauge are getting into the red. “Yeah, but that’s water temp not oil temp.” Guess what? If the water temp is that high, so is the oil. An oil cooler on a water cooled car IS the water.
I often hear the people say that an air-cooled motor can handle hotter oil. Really? Why’s that? An air-cooled VW motor has way tighter clearances than most other vehicles, wouldn’t it make sense to not only keep it topped off, but also to not get it so hot that you burn off the viscosity and are left with no lubrication in the tight clearances? Doesn’t sound like a very good idea if you ask me.
So what causes high oil temps? This magazine isn’t big enough to list all of the causes, because just about anything can cause it. When building a daily driver motor, you should have oil temp in mind first, then build a motor that does its best to keep this temperature in check for the climate you’re going to be driving in.
What’s the best oil to run? Let’s go over what’s going on, then you can be the judge. On start up, you have the normal weight of the oil. Let’s say 30w for example. When it’s cold, it will be really thick and again have a hard time getting into tight places. Once it reaches temperature then no problem. As it gets hotter, it thins out. If you start reaching temps over 200 then the rate it thins out is rapid. Now lets take a multigrade like 20/50. That is 20w oil with the viscosity of 50. So on start up it’s thinner than the 30 weight and can make it into the tight areas of the engine. So it’s starting off thinner. Now, when you heat it up over 200 then the viscosity (thickness) starts to diminish much more rapidly than the straight 30w would. At 215 you now only have hot 20weight oil. In my opinion, that is not ok. So like many things it’s a trade off. Muiltigrades are better for start up, but not so good after the motor has gotten hot. What about synthetic oil? That is great stuff because it is thin at start up and it doesn’t break down at temp like regular oil. The problem I have with it is that it’s so thin that it seems to find its way out of every seam, seal, crack, etc. I found that it’s better to just pour it on the ground first, because that’s where it’s going to end up anyway. It just doesn’t want to stay in a VW motor.
Here is what I use. If you live in a really cold climate, use a multigrade like 10/40 or 20/50 because the motor will never see operating temp. The oil won’t have a chance to break down. In Redding, I use straight 30 in the winter, and straight 40 in the summer (above 90 degrees outside regularly). I also wouldn’t recommend just hoping in your car and taking off. I’d let the motor idle for a bit before stepping on the pedal. This ensures that the oil has a chance to thin out to its best thickness to get where its supposed to go before putting a load on it. That has worked out well for me over the years and I am sticking to it.
In my opinion, if your oil temp gets to 200, you might want to change your driving habits. At 210, you should pull over for a bit to cool off. And anything over 215 you need to turn the car off immediately and figure out how you’re going to pay for that new engine you’ll need soon.