Oil Changes: Hot or not?
 

In high school auto shop class I was taught to change the oil when the engine is warmed up. That was 25 years ago, and synthetic multi-weight oils like Mobil1 flow pretty well when they are cold. I'm not trying to start another oil debate but I just want to know if there is some other benefit to heating the engine before changing the oil since it is much easier to do it when it's cold - especially if my car is already on jack-stands for other work in my garage. I hate starting it when it's in the air for some reason.
I doubt most shops take the time to warm up the car first but what the h3ll do I know...I'm not a mechanic.

better results/quicker hot, easier to do cold

Hot. When I had my Boxster or Turbo in for an oil change -- this at the local Porsche dealer -- the engine was always warmed up. I had a data logger in each car that recorded engine telemetry that I could look at later and there was a 15+ minute idle time during the oil service..

More recently when I had a trip logger installed with a cell phone connection I could check the car's progress during service. I'd see it moved from the parking lot to the service bay -- I could tell which bay and therefore which tech was doing the service -- then see the car sit for 15+ minutes with the engine running. Later I'd see the car move from the service bay to the wash bay. Often I'd email the SA to let him know the car was done before he knew it was done and tell him where it was parked so he could put the paperwork and key in the car (locked) for me to pick up after hours.

The factory manual calls for the oil to be up to some minimum temperature when changed. The oil drain time is given, and the amount of oil to be added to the engine is given. Then the oil level is checked to be sure the digital reading agrees with the amount of oil put into the engine. Thi is when the digital oil level system is checked to confirm it is working correctly.

When the engine up to temperature -- hot enough I can check the oil level -- when I've changed the oil in my Turbo the fresh oil comes up to temperature very quickly and I can confirm the oil level is good after just a short post change engine idle time. In fact the oil comes up to temperature so quickly it gaveme barely enough time to pick up my tools and clean up a bit and by that time the engine is hot enough I can check the oil level.

Hot also means the oil is stirred up and all the contaminates are dispersed through the oil so the maximum of contaminates are removed with the oil.

Not sure why you balk at running the engine while the car is on jack stands. Often when I visited the Porsche dealer and its service department a tech would have a car with its engine idling on the lift and sometimes high enough in the air to allow him room to be under the car if he was looking for a leak or even listening for a noise.

Just leave the transmission in neutral/Park while the engine idles.

Cold so you don't burn your mitts. There is a lot of oil that doesn't come out in the valve covers and gallerys anyways.

warm if not hot. it's a better "drain". is this not the conventional "wisdom"? it's a couple of plugs lol.

Well, a better drain? Maybe. As I mentioned the oil is certainly not stratified if drained hot. The engine is designed so that there are no catch basins so that if the car is reasonably level (and even if it is not that level, but say with the rear of the car off the ground with the car backed up on ramps) the oil will still drain down into the pan (or crankcase in the case of the Turbo).

But it is a faster drain hot that's for sure. The Turbo drain time is IIRC 20 minutes hot. If one wanted to drain the oil cold not sure how long a drain time cold equals a 20 minute drain with the oil cold. An hour? Two? Maybe overnight? My sources do not give a cold drain time.

Then there is the need to bring the oil up to temperature so the oil level can be checked to confirm the system is working right after the correct amount of oil has been added back into the engine.

It really doesn't matter. There is so much oil that doesnt drain out regardless of if you do it warm or cold... try disassembling one on a stand after draining fluids before pulling it out of car. It drips for days...total oil capacity is 12.5L, refill amount for oil changes is 8.75 with filter change.

^^^^ THIS

If you've ever had one on the stand, you'd know that it leaks oil and coolant for DAYS. It makes no difference hot or cold. If oil only drained when hot, how well do you think the new stuff would come out of the bottle? And I've never thought, "you know, the oil was cold when I drained it, so there's still some left in the engine. I'd better reduce how much I put back in by half a quart." It just doesn't happen like that. It gets the exact same amount going back in, hot or cold.

Thank you all for the replies. This is exactly what I was looking for. They all make sense and the bottom line is, it may be slightly better to work with a warm engine but doing it at room temperature is fine (In California...maybe not so much in Minnesota this time of year).
I change it about every 6 months (about 1000 miles) so it doesn't really have time to get too dirty.

Well, it does matter as the drain interval (hot) is given and then the amount of oil to add back in is given then the engine is started and the digital oil level system is checked to ensure its reading is correct agrees with the known quantity of oil added after a known quantity of oil was drained.

By draining the oil cold the amount of oil drained is not what the factory expected so the amount to add back in could be wrong. So the check of the digital oil level system is compromised. Also the factory has taken into account how much oil remains and by draining the oil cold and removing less oil this ratio of old oil to new oil is upset.

It is for reasons such as this back and forth about something like draining the oil cold or hot I so distrust owner serviced vehicles. But servicing is like oil selection. If one decides to ignore what the factory has to say on the subject then he can service the vehicle any old way and use any thing to justify his servicing.

For my cars, including my Turbo, I prefer to adhere to the factory in this regard. I see no reason to use my vehicle as a test platform to see what I can get away with.

I always keep a couple empty Mobil1 5L containers in the garage. I drain the oil tank, engine case, turbos and oil filter housing cold, then pour the contents into the empty containers from my last oil change. Then I know exactly how much to put back into the filler neck. Cold out = cold in. At that point, after warming up I can check the gauge and see what needs to be added to get a perfect fill every time. Not trying to "get away" with anything...far from it. I change the oil on a far earlier schedule than the factory calls for.
If we all followed everything Porsche recommends no one on this forum would have over 450 crank HP :) Their specs are like the Bible or the Quran; once you begin preaching to the letter of the text people get turned off pretty quickly.

all that other stuff doesn't matter. drain the two plugs, swap the filter ( i never drain the turbo's ) add 7 qt's, start the car and wait for engine temps to be "normal" and "check oil". you'll probably need another 3/4 qt.. max 1 qt ( rare ).

if ya havent got the oil "drain and fill" procedure figured out by now? lol.

I have done mine both hot and cold. The only difference is hot it will most likely splash all over when you pull the tank drain, and cold I let the main crankcase drain for an hour. Same amount of oil comes out both ways. Only thing I noticed is to do the filter first so the oil in the filter housing can drain down into the crankcase and out in to the pan.

You simply put the amount that comes out, back in. This is quite literally the simplest basic maintenance out there. Get it in the ballpark and check the oil, add as necessary. Just like any other car. The factory service manual even states the amounts to add are approximate and to check it to ensure you have the right amount of oil and adjust accordingly. Some cars use more oil than others and no one has ever added oil to the reservoir prior to draining the oil to make sure the starting point for draining the oil is consistent.

The reason the factory specs are to drain it hot is because when the car comes in for service, the car is hot from being driven in 9 times out of 10. If the spec was to do it cold, then owners would have to wait a long time for their cars to be serviced and no one wants to leave a car overnight for a simple oil change. The car and the oil does not care one way or the other.

If the oil level indicator goes wrong, it gives a clear fault- oil level indicator failure in red in the center display.. it isn't a mechanical thing that can get knocked out of calibration, it isn't something that is capable of being recalibrated- it either works or it doesnt. It's like your gas gauge- do you feel the need to check the calibration of that whenever you add fuel>

If you think the overwhelming majority of dealership techs are doing anything different, well...

only to add: dealers NEVER drain the turbos. lazy like me.