I'm referring to the volvo shops and other euro indi shops here in southern california. I don't know if this goes the same in other states, but all the shops I've been to use 20w50 year round. here's my understanding. 20w50 has a higher viscosity and is mainly used during the summer. the volvo manual states different oil weight for different seasons. I remember some shops saying that 20w50 is better for older cars or high-mileage cars because the higher viscosity reduces wear. I remember getting 20w50 even in cooler seasons. I've noticed here on the board many bricksters use 10w40 or synthetic. so, big question, is 20w50 ok for winter? it's been cold here, like around 60-65F. my last oil change was with 20w50. I'm due for a change, and I might do it myself and put in valvoline 10w40. but then I need to do a pcv service, so I might just end up throwing some cash to a shop for an oil service plus a flame trap service since I'm a bit wary of doing the latter myself.

"...it's been cold here, like around 60-65F..."

I love it! Spoken like a true Californian.

I have license to tease you, as I'm from California also. And yes, you're right, my local indy mechanic encouraged 20-50 also. But then we were dealing with 115 deg summers (although the winters did get down into the single digits out on the high desert).

The one time I got lazy and took the 960 in for an oil change while I was still living in SoCal, the guy wanted to use 20w-50. In the 960 in January! When I told him to use 10w-30 he started arguing with me. They wouldn't "warentee" the work and made me sign a waver. They had already drained the oil and so I couldn't just take off and go somewhere else. I had to stand there and watch him to make sure he didn't use 20w-50.

Now I use Mobil 1 5w-40 in the 960 and 240 with 5k mile intervals year round. I live in the Bay Area so freezing weather is not an issue.

Certainly a topic for discussion, where many opinions flare.
In general, I would agree with the comments presented here for using 15W-40 for hot/summer and 10w-30 for winter, EXCEPT for the addition of the engine type. This is the rule for later B230F low friction engines. If we're talking about the older B21F, and even older B20F, I would recommend 20W-50 for those engines for hot/summer, and 10W-40 for winter. Having had 140's with high rpm performance in my shed for years, I used 20W-50 all year and even ran well in -10 deg on VT ski trips.
Taking it a bit farther, the later LH 2.4 FI seems to behave well with lower viscosity, like 10W-30 dino oil and 5W-30 syn. The temp/fuel compensation for choke and even running can be less than adequate even in hot climates like Dallas where I live. They are close tolerance engines, and if in good shape, will be better with low viscosity oils all year.
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'89 245 Sportwagon, '04 V70 2.5T Sportwagon

and some places just hate radial tires, and some like "Marvel Mystery Oil", and some put ATF in the gas tank.

Because it's fine to use down to about freezing. I like it fine if its summer here.

Just change it very often and it doesn't matter what you use. I change minimum every 3 weeks. Use what is cheapest.

These days I have 10W30 ($5.00 gallon) in for mornings that are significantly below freezing.

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Stef -- 1981 wagon B21A SU M46 317000km

I am really surprised that your local 'Volvo' indie shops are using the 20/50. Every Volvo manual I have seen says to not use anything thicker than 15/40, with 15/40 reserved for high speed/high temp duty. Some of the dealers around here (Va.) used the 15/40 up until about 10 years ago, and then most switched to 10/30 year round. I use 5w/40 synthetic year round in my 240, only because my son is now driving it full time. Used to use 10/30 year round. The 5/40 is a more robust oil, so the maintenance schedule can be a little more flexible, and he is one of those folks that thinks a gas pedal is an on/off switch. Not a variable speed device. Definitely severe service.
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'94 940 150k, '86 240 170k, '72 142 KIA, '70 144 KIA, '69 144 RIP

This is usually one of those 'hot-button' topics - along with what brand of brake pads or what brand of shocks to use - so I'm a little surprised that there hasn't been a lot more discussion. Anyway, here goes...

20W50 is on the heavy side unless you are pulling an Airstream Classic across the Nevada desert in summer. 15W40 is the max I would use, but normally it would be 10W30/10W40 for spring/summer/fall, 5W30 when the winter is in full swing (Canada, eh.).

Dino oil SAE rated at 10W40 will flow the same hot or cold as an SAE 10W40 synth, but the real difference IMO is the higher temperature capability of the synth and the lower tendancy for coking. Regardless, I still change the synth every 5000km, because, well, dirty oil is still dirty oil.

I wouldn't say the heavier oil necessarily reduces wear; in fact, the very opposite may actually be true, as the oil takes longer to reach every part, and may be difficult to reach into the smallest of areas (such as piston skirts) on a well-maintained or low-mileage 'tight' engine.

The heavier oil will cause extra drag on the engine in general and also put extra strain on the oil pump and pump drive in particular. I had a timing belt jump on a car (not a Volvo) when I drove from the warm west coast to a winter resort, due mainly because of a loose belt (i.e., neglect) but made worse by the 20W50 I was still using at the time and the extra strain it put on the intermediate shaft (which drove the oil pump and distributor).

What the heavier oil can do is help reduce oil consumption (rings/valve guides) and piston blow-by on high-mileage, loose engines.

But in the end, no matter what shop you choose, if you don't like their default 20W50 viscosity, they should put in whatever you ask for - but you do have to ask.

I tried it once and it was too thick. The oil never fully warmed up, which you can tell beacuse under the oil cap is a milky color. I'd stick with 10w 30 in the winter and 10w 40 in the summer, unless its warm al year then just 10w40.

20w50 needs worked pretty hard to get into its operating temp, thats why a lot of the times it say "racing" or something like that on the bottle.
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Zack Silver 83' 242Ti (221k)

Here, the specialty shops all use 15W40, and the dealer uses Pennzoil. Apparently that's what Volvo recommends. Most seem to use the same oil year round.
I run 15W40 in summer and 10W30 in winter. 15W40 is a bit heavy for areas where you will encounter freezing temperatures. 10W30 seems to be a better choice but still fine for warmer days or long trips where the oil warms fully.
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Rob Bareiss, New London CT ::: '87 244DL/M47- 234K, '82 245T/M46-182K, '89 244DL/AW70- 212K Not too distant past: 86 244DL 215K, 87 244DL 239K, 88 744GLE 233K, 88 244GL 147K, 91 244 183K

Hmmmm... why did no one in the North East note... that Ugly Duck should be raw dog slapped for mentioning 60 ish as cold!!!!