Originally posted by Hdbngr8:
Politely I will respond to your reply. The oil in a gas or diesel engine is not used any differently. They both perform the SAME tasks: lubrication, heat rejection, anti-rust, etc. True, the additive packages are different. Heavy duty diesel engine oil is designed for longer intervals between drains, along with some other changes that are not pertinent to this discussion. The fact of the matter is: combustion byproducts (regardless of the fuel) include acids. Let me reiterate, regardless of fuel type combustion byproducts include acids. One of the properties of engine oil is to neutralize acids over time (read up on TBN and TBA). As the service life of the oil increases it loses it's ability to neutralize. Let it go too far and the acids can (and do) damage. No, nothing like burning a hole through your block in a weeks time. It is long term wear items that suffer.
If you want to put 2-cycle oil in your car, go right ahead. I do not put diesel oil in my car. However, the next time you look at a bottle of Mobil 1, look for the latest API deisgnation and notice - right next to the SJ (or whatever the latest designation is) you will also see a C* designation for diesel (compression) engines. Oh, but according to you, that can't be!



This is basically correct. Even with little or no sulpher in the fuel (or oil), there is still a lot of acid formed from combustion. This was discovered in the 40's and was the basis for Shell oil company advertising oil with the "X" factor which kept

You missed slightly on the methods of determining the base or acid level in the oil though. TBN is total base number. A high number here shows the base reserve, or is an indication of how much more acid it can handle. The oposite side of this is TAN or total acid number (not TAB).

TBN is generally accepted as the most reliable way to tell if the additives in the oil are depleted. Although rare, it is possible to have a high TBN and still have some of the additives depleted. This is usually only an issue on extremely long oil change intervals.

On the issue of oil quality. The difference in performance between today's conventional oils (dino oil) and synthetic oil is becoming very narrow. The better of today's dino oils are very close in performance to today's synthetic oils. You can easily go 5,000 miles between oil changes on any GF-4 SM rated dino oil except under the most severe usage. And I mean the most severe, not just what most people call "severe duty" that just about defines nearly every driver. It has shifted to the point that unless the car is used in police pursuit or race track use, 5,000 miles can easily be met.

What I'm saying is that today's dino oils are very nearly synthetic oils. The base oil blending stocks are almost equilivent. In fact, some so called synthetics use the same base oil blending stocks as some dino oils (Castrol Syntec and Mobil 5000).

Prior to the latest API certification of SM, I changed the dino oil in my car every 3,000 miles. Before API changed to SM, I changed to synthetic and have been changing it every 5,000 miles. I'm going to switch back to dino oil or possibly move to dino/synthetic blend (Mobil 7500) and stay with the 5,000 mile interval.

Mobil has provided some guidelines. First, they say that if the car is still in warranty, do not exceed the manufactures oil change interval no matter which oil you use. Then they say Mobil 5000 = 5000 miles, Mobil 7500 = 7500 miles, Mobil 1 = 10,000 miles, Mobil 1 EP = 15,000 miles.

An ocassional oil analysis will also help.

If you really want to become more familiar with what is going on in the lubrication industry, hang out for a while at www.bobistheoilguy.com

Jim Johnson 98 SVT 03 Escape Limited