Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Changing oil hot vs cold

As things go, I’ve learned a lot from my father. One of those is changing oil. As I’ve gotten older, I feel like I’m beginning to debunk some of his logic. He had always told me to run the engine for a few minutes before I change my oil. This logic stems from the idea that hotter oil has a higher flow rate, thereby insuring you get all the oil out of the engine and oil pan. This has lead to many scars from burning myself on the engine, and the dumping of hot oil on my hands.

I on the other hand, think that after an engine has sat overnight, and all the oil has made it’s way down to the oil pan will make for a much easier oil change. Not to mention, a little less burning of the hands. Thoughts?

Cold is easier, but I think you’ll get a more complete drain hot. However, the difference is probably pretty small. A half-cup of ‘old’ oil isn’t going to hurt anything.

Good question, and it’s been discussed several times in this forum. You’ll find strong opinions in both camps on this.

I’ve never seen anyone able to find any evidence of shorter engine life for those who changed their oil when cold. If anyone knows of any evidence, please share it.

Cold is fine, it just takes a little longer for the oil to drain from the pan. With today’s filter location, I prefer doing it this way.

Based on what I have read, Tom and Ray (Click and Clack) seem to agree with your father. I also change my oil when it is hot. The idea that it is thinner when it is hot is actually not the reason.

The way multi-viscosity oils work, they are actually thicker when they are hot. A 10W-30 oil is 10 weight oil when it is cold, and 30 weight oil when it is hot. The real reason for changing the oil when it is hot is that any suspended particles or contaminants might settle at the top or bottom of the oil in the pan, and circulating hot oil will ensure you get the most of those contaminants out.

There is no reason for you to burn your hands on hot oil. Replace your drain plug with a valve like one of these. I use these Fram kits on all of my vehicles. I even have one on the manual transmission of my car. They make the job a lot easier and you will never have to replace another crush washer.

In the end, whether the oil is hot or cold probably won’t make much of a difference. I seriously doubt changing the oil while it is cold will make a difference in the life of your car.

I’ve always changed my oil cold (I warm it up a bit in winter). In 40 years I’ve never worn out an engine, even after hundreds of thousands of miles. Cold has always worked great for me. If the engines never wear out, I’ll keep doin’ what I’m doin’.

You dad’s logic is good, and his is a common philosophy, I simply offer my own philosohy and its results.

Yes, run the engine a bit first. ( on our Cessna 172 airplane , 50w oil, this was a must.)
Then get out your implements to do the work.
Then test to see the temp of the pan and drain when it cools down below “burning your hand”.

I change hot,its what the manufacture recommends. One other thing,many manufactures are going backto canister type filters (BMW never left). You should always open this canister to aid the flow of oil out of the engine (helps the canister empty also).

Like MB’s personal experience of never having engine problems changing cold,I have never had drain plug problems removing hot drain plugs,anecdocal evidence both experiences.

How long do I let the oil drain? I drains for however long it takes me to walk to the parts counter and get a filter and walk back.

Over time things change, very true of oil. Go back to your father’s early days and perhaps oils were single grade. In the 40’s and 50’s cars used 30W oil commonly. I don’t know if lighter weights were used in winter, but likely not less than 20W was used in winter. With those old style single weight oils having them not got more oil to drain out. Cold 30W oil is like a thick syrup.

Then came the multi-weight oils which started in the 60’s. 10W30 was most common but a lot of folks used 20W40 in warmer climates. These oils drain better cold but still might be somewhat thick.

Now most cars use 5W oils and they are very liquid at moderate temps. In the middle of a Vermont winter perhaps changing the oil when warm is still a good practice. I let the motor cool off for an hour or so before changing the oil or I’ll do it cold. Changing the oil on “hot” motor isn’t easy when you are a DIY’er crawling around the car. Changing oil on a hot motor is easy when you have the car on a lift.

Honestly, I’m unaware of any evidence or data whatsoever that it matters. The important thing is that you do it, whether hot or cold. There is tons of evidence that doing it regularly will help the engine last for many, many miles.

Oldschool’s post brought up a thought that I’d like to add, however. Whichever you choose, you need to develop standards for yourself. For example, I always use a 10" wratchet with socket to remove the plug, and a “stubby” box-end wrench to install it. That prevents struggling on removal and prevents overtightening on installation. I have an “oil change kit” with tools I bought just to change oil, including replacement nylon plug washers.

And I never ever ever force the plug or the filter in. It should start and screw in very easily by hand. The “stubby” is only to snug it up. If it won’t spin easily, find out why before proceeding.

I also use disposable latex gloves, and wipe everything clean as I proceed including the mounting surface for the oil filter gasket. My oil changes are like surgical operations. I usually don’t even get the tools dirty.

Hot or cold, the important thing is that it gets done.

Almost, but not quite. Hot oil is thinner than cold. A multi-grad oil, lets say 10W-30, has the viscosity of a 10W single viscosity oil at a specified ‘cold’ temperature, and it has the viscosity of a 30W single viscosity oil at a specified ‘hot’ temperature. This is very different from what you said. All oil decrease in viscosity as they warm, it’s just that the multi-grade oil decreases less than a single-grade oil.

Nobody used to think about safety in the past and burns were “yer own lookout”.

I don’t see why you can’t change it cold or cool. The oil is filtered when the engine is running and the oils are much better quality these days. Warm up a lawn mower before changing oil. I would like changing oil if I could get to the drain plug and the filter from the front of the vehicle. Life could be easier for all of us.

That seems contradictory to me. If we were talking about single viscosity oils, would hot 30 weight oil be thinner than cold 5 weight oil?

Actually, since we are talking about a hybrid, is hot 20 weight oil thinner than cold 0 weight oil?

Bottom line: It don’t matter. Now let’s spend our energies on more productive topics.

“The way multi-viscosity oils work, they are actually thicker when they are hot.”

Not exactly.

10W30 means the oil when cold with act like a 10W oil and like a 30W oil when hot. It will be thiner when hot, but not as thin as a 10 W oil would be.

I have always changed my when it is warm to hot. Currently I use a Pella oil extractor so I don’t need to get under the car. Makes life easy.

I’ll make up some numbers that show how this works:
Oil weight/‘cold’ vis/‘hot’ vis

See, they all get thinner when they heat up, but the 10W-30 decreases less (50%) than the straight weight oils (90%).

How does this work with 0W-20 oil? Is hot 20 weight oil thinner than cold 0 weight oil? Wouldn’t this be an exception to the rule that hot oil is always thinner than cold oil?

We are talking about a hybrid, after all, which probably uses 0W-20 oil.

…and I appreciate the education. I guess I really didn’t understand how multi-viscosity oil works.

It works the same way, a 0W-20 oil will get thinner as it warms up. I know of no liquids that increase viscosity as they heat up. Might be some, somewhere, but they’re not on the shelf at Walmart!

Here’s a plot:

My understanding is that a hot change is better for removing any sludge in the pan: both because the sludge is of a lower viscosity when hot, and that the corresponding fatser emptying of lower viscosity oil encourages the sludge to drain. Also, I would think that isoluable particulates would be more likely to be suspended in an engine that’s just been run.

I wear a rubber glove to prevent burns and soaking my hand in oil. Also, rather than try to catch the drain plug to prevent it from dropping in the drain pan, just stretch metal mesh over the pan and let that plug drop!

If there are “suspended particles” in your oil, hot or cold oil changes are the least of your problems. Any particle large enough to “settle out” as the oil cools is large enough to have been trapped in the filter. When you change your oil, if you get 90% of it out, you did good, hot or cold…