Just bought my first diesel. The manual says to change oil every 7500 miles (schedule B..worst case driving). Why can a diesel go 7500 and a gas engine only goes 3000 between oil changes?

 

The oil change interval depends on the manufacturer. Some recommend as many as 10,000 miles.
After break-in I change at 5000 miles. It's easy to keep track of.

 

My guess would be a diesel goes twice as far between changes, because you have twice as much oil in the pan to wear out.

 

I would guess two reasons...

First, the Cummins holds about 12 quarts.

Secondly, it is my understanding anyway that diesels don't have the same hydrocarbon combustion byproducts that gas engines do, and as a result diesels tend not develop acids in the oil as quickly from blow-by gasses in the crankcase.

 

What did you change it at the first time?

Just wondering. I have 3300 on, I was going to wait until 5K, then step up to 7500.

I changed my 2nd Gen religiously at 5,000. The more I read, I probably could have gone longer with no issues.

 

Diesel-spec oil is refined to hold far more contaminents/combustion byproducts in suspension, and of course we have twice as much of it!

 

I did first oil change 2500mls
Next at 10,000 - I will continue at 7500 intervals and fuel at 10,000mls.

 

Todays cars oil changes aren't at 3k and haven't been for sometime now.

 

My wife's Honda is 5K. In a non-dusty environment, I would bet an analysis at 7500 wouldn't be any different.

 

After my first change at 7800, I sent a sample to Blackstone Labs. They said everything was fine, and to do my next after 5K more to help speed up break in. From the way they worded it, I could go longer than 5K between changes once it's broken in, imo.

 

As one poster said, gasser haven't been 3000 for a long time. Dealers and oil change places will tell you 3,000, but, consider, they are in the business of selling service, oil changes among them. They'd like to sell you an oil change every 100 miles!!! I go by what the owner's manual says. After all, those are the guys that designed and built the vehicle as well as provide the warranty. They should know what's needed. Have you actually been changing your gasser's oil every 3,000?

 

A general rule of thumb was to change oil at least with the seasons. Based on that thinking, shops and manufacturers probably said that since the average (?) mileage per year is 12-15K, every 3 months (quarterly) or 3000 miles (1/4 of avg mileage/year) would get everyone on the same page. Of course, for those of us that drive in excess of 3K a month, that logic just doesn't work...

 

I run nothing but synthetics in anything with a motor. They do not break down like a mineral oil, so I have no problem going a long time between changes on some of my engines.
I changed my oil the first time in my truck at 500 miles, then 1000, then 2500, 5000, 10,000, at 15,000 it got synthetic.
During break-in, it's not the oil going bad, it's the extra solids floating around in it that bother me. Yes, the filter is supposed to catch it all, but the metal shows up in the oil when you drain it. I consider early and frequent oil changes to be long term insurance. Maybe it's not necessary, but it sure can't hurt.

 

You can get 12-15k oil intervals on a gasser.

Use Redline synthetic, I use it on my 93 GT and I change the oil every 12k, I still change the filter every 3-4k and then top off of course.

 

i change mine every 5,000