I'm currently using Castrol 20W50 synthetic in my 91 164 B. It seems a bit heavy for the cold Chicago winter though, and I'm wondering if anyone switches weight when the weather gets cold.

Greg

Yeah Greg,

I use 15w-50 mobil in the summer and with my 12 valve used to use 0w-50 in the winter which is thinner and obviously drops the pressure reading and sometimes on tickover,with engine hot, the low press light could flick on. This 12 valve was very responsive engine so no apparent harm was caused.
With my 24QV, i have noticed the oil pressure reading is about 1.5 bars higher than 12 valve with 15w-50, so i see no reason not to use 0-50 again this winter.
Gets down to minus 25 here.

I assume that oil consumption may increase with the thinner oil although i never checked for this.

Yup, 20W 50 will be too thick when cold. I use 5W 50 fully synthetic year round but 10W 40 fully synthetic also works fine.

I dunno about Chicago but here in Calgary we need to be ready for temps as low as minus 40 (very rare thankfully but it does get that cold occasionally and minus 30 is common). A fully synthetic oil works great for winter.

If you're a die hard dino oil fan then 10W 40 should be fine for winter. I would avoid using a 5W 30 or 5W40 dino oil as in my experience a 5W is just too thin when hot. 10W 30 works but again if you drive hard it will get too thin when hot.

Also, oil consumption will go up if you use a thinner dino oil. Synthetic should stay the same as the oil gets consumed when hot, synthetics hold up much better.

I think I'll go with the 5W50 for the winter.

The previous owner used "dino" (like that term) oil, but I want to use synthetic. So, I'm slowly weaning it in that direction in hopes it will give the seals a better chance to become acclimated. The Castrol 20W50 I'm using (or maybe it is 15W50) is a synthetic mix. When it finally comes back from the mechanic, I'll get 5W50.

Greg, I converted over to synthetic at just under 100,000 miles. I use Mobil 1 15/50 in the summer, and Castrol 5/50 in the winter. The engine is very smooth, no oil leakage to speak of, and just a little consumption - about a pint in 5000 miles. I change at 5000, oil and filter, religiously. The only seal that leaks is the o-ring under the distributor, which was seeping when I bought the car, and I just haven't had the occasion to change it yet. I think you could just switch to full synthetic at the next change, and except for the additional expense, you'll be quite happy. Cold starting will be much improved when the temps go down, and more importantly, cold engine lubrication will also be much better until the oil gets warm and distributed in the engine.
I don't believe it matters too much which brand you use, as long as the grade and weight is appropriate. I wouldn't use 5W or 0W in my car.
Move over to the new forum as soon as you can. See you there. Dennis