What's the best oil?

[FABombjoy]

Our normal go-to oil is Castrol 20W-50. If you are the typical low mile driver and change it every year/3000 miles it should be fine. This is the official company recommendation.

Serious questions:

1: Which official company?
2: Why not use 10w-30 per Volvo's 1984 TSB? I feel like that carries a lot of weight (ack, pun) behind it. The TSB claims the revision is to lower deposits, although that may not be a significant issue with modern oils, but the improved fuel economy, power, and stability of having a lower viscosity spread would seem worth the switch.

[content22207_2]

viscosity spread

The way multi-viscosity oils work:

Base oil is the lower viscosity number. A 20W50 oil is based on 20 weight oil.

Higher viscosity number is achieved with coiled polymers that unwind as they heat up, making the base oil act like thicker oil.

The bigger the difference between viscosity numbers, the more dependent the oil is on these polymers for the higher rating. As those polymers break down, the less able the oil is to reach a thicker state. Single biggest threat to multi viscosity polymers is physical -- they get ground into pieces ("viscosity shear"). Multi viscosity polymers that are broken into pieces can't thicken the oil up as well as intact polymers.

Bill Robertson
#5939

[mr_maxime]

Any recommendations for people who drive over 3k miles per year? I'm assuming its just the same but at 3k intervals.

[content22207_2]

Change your oil every 3,000 miles (or less -- I use 2,500 mile intervals). Oil and filters aren't prohibitively expensive. Changing the oil is one of the cheapest things you can do to a car.

Bill Robertson
#5939

[sdg3205]

I had the oil talk with Wolfgang of the DeLorean World Tour when they were in Vancouver. They run synthetics in their cars, and not just because of the distances they have to travel before an oil change is possible. If your DeLorean leaks oil now, it will still leak oil with synthetic. You probably wont notice an increase in the amount of oil leaked. I switched my 220,000 mi Jeep to synthetic and the slight leak at the valve cover did not get any worse.

We know little of synthetics in DMCs because its rare. At less than 2000 miles per year, even I have a tough time justifying it.

Castrol 20w-50.

[David T]

Any recommendations for people who drive over 3k miles per year? I'm assuming its just the same but at 3k intervals.

I see no problem going to 5,000 miles or once a year, which ever comes first. Oils are made so much better now than in the past, the PRV isn't working all that hard, and the motor holds 6 qts so it never gets overheated and breaks down. Changing it more often is not necessary and wasteful. Always change the oil filter when changing the oil.

[DMCVegas]

Mobil does not recommend synthetic in this engine probably because they have not tested it.

I think that James Espy had a story about this where Mobil was talking with DMCH, and they came back and advised against it's use for some reason. He probably has the details on that.

Otherwise, no one is going to have a solid answer about this question. Asking questions about what brand or type of oil to use is like asking which religion is best to follow...

Anyway, I use 20w50 in the summer, and drop down to 10w40 in the winter when it gets much colder in Vegas. The difference during cranking on cold mornings was obvious, and those weight recommendations in relation to temperature are in the Owner's Manual. If you're not a year-round daily driver, you probably don't need to drop down to the lighter weight.

[content22207_2]

2: Why not use 10w-30 per Volvo's 1984 TSB? I feel like that carries a lot of weight (ack, pun) behind it. The TSB claims the revision is to lower deposits, although that may not be a significant issue with modern oils, but the improved fuel economy, power, and stability of having a lower viscosity spread would seem worth the switch.

IIRC the TSB was due to excessive camshaft wear. I'm traveling at the moment, but will check when I get home.

IIRC TSB was dated November 1984. It applied retroactively to all PRV's.

Bill Robertson
#5939

[FABombjoy]

Asking questions about what brand or type of oil to use is like asking which religion is best to follow...

I agree completely and normally steer clear of oil threads as they tend to be a parade of N=1, brand loyalty, and thinly-veiled MLM conscription schemes.

Scientific interests are why Volvo TSB is so interesting. Volvo used a wide variety of PRVs for far longer and would have had access to scientific testing and a large sampling of statistical data regarding oil-related failures. If feel like if I have to take the word of DMC or Volvo I would side with Volvo.

[mluder]

My understanding is that the issue with synthetics is they are very consistent at a molecular level when compared to traditional. This is why they tend to show leaks more often especially in older cars.
I used to run Pennzoil 10W-30 and recently changed to Castrol GTX 10W-40 on my last oil change... Now my previously leak free engine is dripping oil everywhere. Needless to say I will be going back to Pennzoil on the next change. (Or maybe try the Castrol 20W-50 as Dave suggested)

Of course that's my story - your experience may vary.

Cheers
Steven