Just because some of you guys (and me at times) dis-agree with Bob doesn't mean his posts are a waste of "bandwidth". Lets have a little brotherly love for one another. I for one love to exchange information and take people to task on thier ideas. I at times am thinking wrong.. and at times others are. Oil and cooling are both areas of engine maintainence that are important and I've noticed that popular opinions seem to be accepted as "fact" when it's not.
I'm not trying to pull a trump card here.. But I was a FEAD & cooling engineer for Ford for 6 years. I build my own engines from time to time as well. (a top dollar 800hp sc & nitrous'ed 5.4L on the stand right now)
Now for oil and cooling...
40-50% of the combustion heat goes out the exhaust. This is the single most important thing you can modify to aid in cooling a engine. People *most of the time* don't know this or simply over look it. If you got multiple holes in the bucket... plug the big one first.
20-30% is done by a wet cooling system.
Here is a quick lesson:
When the coolant is not moving (which is a majority of the time) air bubbles form (boiling) on all the ultra hot casting surfaces. Mostly up around the combustion chamber areas. This makes heat transfer into the liquid less effective. For many decades this was just accepted and not addressed.
This is why we (OEM cooling engineers) have started using De-gas bottles as standard equipment on modern cars. It does two things. It helps make the liquid coolant more effective and it helps us to reduce the amount of coolant needed to do the job. (weight and cost savings) There are other things we could do to even further this line of thinking. But that's still not cost effective as of yet. (precision cooling)
20-25% is done by the oil. Oil temps generally climb as a motor runs. (Unless you have a coolant or external cooler)
5-10% is disapaited into the engine room air and transmission casting.
Now for oil alone.
Oil has to not only lubricate but it has to carry away heat. The better it lubricates.. the less frictional heat is created. The better it can disipate heat, the longer it takes to heat the oil in a global sense. Point being that oil break down is two parts.
1) Heat will break it down and make the additives less effective, or even non-effective if let go too long. A full synthetic oil is superior in this. As for one brand over the other and many many miles? I'm not sure and don't really care because of a more important and overwhelming issue.
2) Debris! The oil suspends debris of all sorts as it makes it's circut through the engine. All kinds of metal, carbon, fuel, sand, and water are put into the oil. The oils job in part is to suspend this junk and carry it to the filter.
Here is my major beef with leaving a oil in a engine for more than 10k miles.
The filter only does it's job down to a certian partical size. (measured in microns) The things that don't get trapped go back into circulation and in a small measure aid in being an abrasion on parts that are under high loads.
This is a scientific fact that you can't change. Maybe one brand over the other is better at having it's additives not get depleted.. but that's only part of the problem.
Here is what I do for my cars. (We have 4) It's my opinion that a bang for the buck balance needs to be figured out by each person.
On the three daily drivers we have I run 10w-30 mobil 1 and a Pure-o-later *pure one* or motorcraft filter. I simply use my judgement on the type of miles I've driven, I smell the oil, and I put it between my fingers and try to feel how much grit it has. (try these.. you'll see what I mean) Smell and feel are most important. When feeling it, don't just rub your fingers around. Put a lot of pressure on the oil and feel how slick it is compaired to new oil. Try it.
On the ranger, the oil gets pretty dirty pretty fast. I'll now be changing it in the 6k to 10k mile range. Just depends on what kind of driving I've been doing and how hot it's been
On the caddy I run it up to 10-12k miles. Its a northstar motor, gets dirty very slowly, and has a higher capacity than other cars. (7.5 quarts)
On the 94 pontiac (daughters car) I change it about every 4k miles. She *only* drives 6 miles a day and the oil gets dirty very very quickly.
On the Lightning I changed it ever 2k miles. SC and spraying nitrous blows combustion residue past the rings much more than a regular car.
Now with the new tolerances I'm running I'll switch to a straight 30W with zinc in it and change it about every 2 times out to the track.