Flush engine oil when changing oil viscosity?

[denea]

Driving a 2007 Volvo S40, 2.4i gasoline engine (b5244s4) with 100k miles / 160k km on it (if not tampered). Bought the car 2 years ago and I have to idea what did the previous owner do with it, besides that he was using 5w-30 oil. I'm currently using Castrol Magnatec Professional 5w-30 A5/B5 and there is a "slight" oil consumption of ~1 liter per 6k miles / 10k km.
The official Volvo engine oil documents say that for temperatures over 90F (32 Celsius) 0w-40 oil is recommended. Over here (Eastern Europe) during summer the temperatures go up to 98F (37 celsius) and winter often down to 14F (-10 Celsius), so I'm thinking of using 0w-40 all year around for better protection and maybe it will solve my oil consumption issue as well.
Should I do and engine oil flush when changing viscosity from 5w-30 to 0w-40? I will probably use synthetic Shell 0w-40 or Castrol Edge 0w-40 A3/B4, depending on the price.

 

[kschachn]

What kind of "flush" and what problem are you hoping to correct with it?

 

[Astro14]

There is no need to flush the engine when changing viscosity. Unless you have a specific problem, there is really no need to flush it at all.

That said, Volvos of that vintage are notorious for plugging up the PCV system at about your mileage. A flush WILL NOT FIX that problem. No chemical will. A new PCV system (known as a flame trap), along with mechanical cleaning of the oil vent passages will.

If your oil consumption increases, and/or you start seeing leaks, start with a Complete Flame Trap replacement.

In the meantime, just change the oil.

 

[aquariuscsm]

Delete.

 

[aquariuscsm]

Should I do and engine oil flush when changing viscosity from 5w-30 to 0w-40?

Absolutely not.

 

[Leo99]

What kind of "flush" and what problem are you hoping to correct with it?

I'm guessing he means to flush out all the old oil and start afresh with the new oil.

And no, the old oil remnants can mix with the new.

 

[wpod]

What would there be to gain?

 

[Jimmy_Russels]

What would there be to gain?

Maybe the OP is misleading. It's not a "I installed 5w30, ran that for 10min, but now want 0w16". It's more like "I have this old used engine oil in the engine, should I flush it out?".

A lot of old oil will come to the pan when the engine idles for about 10sec w/ drain plug out.

 

[Oildudeny]

Just drain and fill up with your new brew and change filter by the next oil change all the previous will be washed away

 

[OVERKILL]

A lot of old oil will come to the pan when the engine idles for about 10sec w/ drain plug out.

I'm sorry, what? You are actually advocating running an engine with the drain plug out?

 

[NormanBuntz]

With that odometer mileage, I believe an engine flush could bring unwanted issues. Just make your change and use a quality filter.

 

[fsdork]

A lot of old oil will come to the pan when the engine idles for about 10sec w/ drain plug out.

OP, do not listen to this advice.

Also, as others have said, don't worry about flushing the old oil out. The amount left behind in the engine before you refill it isn't worth worrying about.

 

[totegoat]

If you are concerned about remnants of the old oil, do a follow-up oil/filter change at a sooner interval than usual.

 

[mahanddeem]

A lot of old oil will come to the pan when the engine idles for about 10sec w/ drain plug out.

What?
The last I would do in my life is to run an engine with oil pouring from the buttom

 

[wpod]

Maybe the OP is misleading. It's not a "I installed 5w30, ran that for 10min, but now want 0w16". It's more like "I have this old used engine oil in the engine, should I flush it out?".

A lot of old oil will come to the pan when the engine idles for about 10sec w/ drain plug out.

Why would one see an advantage to run an engine without oil ?

 

[OilReport99]

Should I do and engine oil flush when changing viscosity from 5w-30 to 0w-40?

The best "flush" will be the 0W-40 you're planning to run, depending on the price.

 

[blufeb95]

Solvent flushes shouldn't be done unless there's a problem that you're trying to fix, and doing a back to back oil change as a "flush" to get rid of the small amount of 5w30 that will be left in the engine would just be a waste of oil.

 

[denea]

Thank you for the answers, really helpful to see so many quality opinions.
I was thinking of a "flush" as the liquid you pour in the engine to clean it from sludge or whatever else, because maybe the viscosities were incompatible so I'd need to get rid of all the 5w-30 ... turns out there is no such need.
Will also definitely clean the PCV as Astro14 mentioned!

 

[viscous]

doing a back to back oil change as a "flush" to get rid of the small amount of 5w30 that will be left in the engine would just be a waste of oil.

That is known as a FVOC:

DIY Oil Particulate Test, SVOC vs FVOC

Several months ago I think someone mentioned on this forum about using paper stock and oil drop test to view the cleanliness/particulate concentration of used oil. Attached is a photo of two samples I obtained. In the past I would just pull a dipstick and look at the oil, which is very thin...

www.bobistheoilguy.com

 

[OilUzer]

Forget the flush, with "Winter often down to 14F ..." , I would consider 10W or even 15W if burning some oil or at least I would experiment with as long as it meets the other required specs.