Motor flush on oil change requires cold engine?

[Por_sha911]

Originally Posted by VenezianBlau 87

Multi vis oil is thinner when cold, "W" winter at 0 deg. F; thicker when at 212 deg. F. (the second number---such as with 5W-30)

I don't think that is correct. Oil change in the summer: the new oil pours very quickly. In winter (the same oil) pours much slower. It is thinner when warm.

[Rawknees'Turbo]

Originally Posted by VenezianBlau 87

Multi vis oil is thinner when cold, "W" winter at 0 deg. F; thicker when at 212 deg. F. (the second number---such as with 5W-30)

Originally Posted by Por_sha911

I don't think that is correct. Oil change in the summer: the new oil pours very quickly. In winter (the same oil) pours much slower. It is thinner when warm.

The second number in the xW-xx indicates the rate of thinning when heated - the higher the number on the right the more resistant it is to heat related thinning (it does not actually thicken when heated).

[VenezianBlau 87]

Quote from Amsoil link:
"...we can simply say this: most oil sold today is multi-viscosity. The first number refers to its viscosity, or resistance to flow, when cold (e.g. 5W). Think of the “W” as standing for “winter.” The lower the number, the faster the oil will flow when cold, meaning a 5W-50 oil will flow faster at startup than a 20W-50 oil. Multi-viscosity oils use chemicals called viscosity index improvers to allow the oil to flow differently at different temperatures. For example, they allow a 20W-50 oil to behave like a 20-weight oil when cold and a 50-weight oil when warm."

https://blog.amsoil.com/should-i-run-multi-weight-or-straight-weight-oil-in-my-muscle-car/

Rawknees: "the higher the number on the right the more resistant it is to heat related thinning (it does not actually thicken when heated)"

More than resists thinning as it becomes more viscous or thicker than when cold. I don't think the difference is easily observable as Por_Sha claims. I'd swear hot oil of the same rating is thinner based on observation but it's not.

[GH85Carrera]

If it is this bad, no cleaner or magic crap in a can will help.

When my original 305 in the El Camino had 300,000 miles of regular use, and regular oil changes the oil was so clean that when I did an oil change, it was hard to see the oil level on the dip stick as it was almost clear.



I took the old 305 apart just because I was curious. This is the innards of the engine after 300,000+ miles. The rings were worn, and the valve guides were worn out. It ran just fine, but I hated the smoke, and $1,700 fixed it with the new 350.

[T77911S]

Originally Posted by speeder

The only motor flush I would ever do is add a quart or two of ATF and drive a few hundred miles before draining it. Having torn down more engines than I can count, the only place I ever see appreciable amounts of sludge is in the oil pan.

If you wanted to really clean the insides of the engine, the best way would be to shut it off hot and let it sit for hours, then drain it and drop the oil pan. Clean the oil pan in your parts washer until it’s spotless inside, rinse it with fresh water and let it air dry before reinstalling it. There is always some real crap in the pan that does not drain unless the engine has been maintained like Air Force One.

I always change oil hot but I do it on time and let it drain for a very long time. The bottom line is that it takes a long time for all of the dirty oil to drain into the sump and if you just shut it off, you’ll never drain it all. The absolute best way is to drain it cold and remove the pan if you are trying to get the dirt out.

i have seen sludge in the valve train/cover also.

i just bought an 08 535i that needs turbos.
when i drained the oil it did not look good. looked like it had water in it.
i sent the oil off and sure enough it did. water NOT coolant. most likely from short dirves and condensation build up. the engine wear was good.
anyway. i was going to remove the drain plug and pour a qrt or two of new oil in it and let it "flush" out anything sitting in the pan.


i did look up engine flushes. i have "heard" you can use kerosene, even kerosene with no oil. but naa. not worth it. i dont feel good about it.

i did one on a 280z when i was a kid. add a qrt tot he oil. get it hot and drain.
let me tell, even though it was mostly oil, it was a "good" parts cleaner. i dropped something in the pan and when i got it out it was clean.

[A930Rocket]

When I pulled the valve cover and the oil pan on my 05 330, both were clean and tinged gold. ~165k on the clock. I change the oil before every track weekend. So, probably four or five times a year.

I’ve only owned it a couple years, so I don’t know the previous history, except T77911S flogging the snot out of it at the track!😂

[flipper35]

Originally Posted by Bob Kontak

I did have an early 2000's Passat with a 1.8 Turbo in it. It would throw the oil pressure light and I used the anti sludge stuff to no avail. Still would say it was starving.

I just used a thinner oil. No problem for 10k miles or so then my kid took the car out.

I had an issue with starvation under hard acceleration so I went thicker and it helped it not slosh out of the pan as bad, but I finally just got a baffled oil pan.

At the local shop a tractor was brought in and they could not drain the oil as nothing cam out when they took the plug out. Then the mechanic stuck a screwdriver in and it stuck in the goo. Turns out it had used a bit and the owner kept topping off with Slick 50.

[speeder]

those are pretty clean but my 1980 Scirocco w/ 32k miles takes the case. Here is what it looked like under the valve cover after sitting for 20+ years:



The other thing that you want to look at when buying a used engine, (or a vehicle but it's harder to see assembled), is the coolant passages. Nothing tells you more about the maintenance history and prognosis going forward than that. And the oil passages, of course.