Mixing Engine Oil

[Hawk]

Mainesail,

I take it the double oil change really cleans it out. Can you expand on the merits of the double change.

[Ron Hill]

Hawk : My experience is that after a single oil change you start up the engine, check the oil and you'd never know that you just changed oil !   I remove the engine (for other reasons) drained the oil, started the engine (after it was back in the boat) and the new oil "look" lasted only about 25 hours before it was pitch black again. 

Bottom line is "It's the nature of the beast" that diesel oil gets really black if you leave it for 100 hrs.  That's why diesel oil has a "C" rating so the suspended particulates do not damage the parts that it is lubricating.

[Hawk]

Thanks Ron. Do I take it that you also perform a double change once a year?

[Mike and Joanne Stimmler]

I don't want to speak for Ron but in my experience the oil turns black after the first engine use no matter what. My oil pan was rusted out and even after I changed it out, the oil was black after the 2nd use. So, botom line is, as long as you change it on a regular basis, black oil is OK.

Mike

[Jeff Kaplan]

guys here's the deal, in lay terms and not getting overly technical, in a diesel engine, when you change the oil and then start and run the engine, the oil will turn black in just a short period of time. this is because  carbon, black,  is produced when the diesel fuel is combusted in the cylinder heads. some of it gets washed down onto the cylinder walls and eventually, the carbon sticks to the cast iron block.  it is the oil that lubricates the cylinders and cleans the carbon deposits from the block. if the oil does not turn black, the oil is not doing its job. also, as mentioned above, you will never get all the oil out of the pan, so the new oil will mix with whatever was left behind...jeff

[Ron Hill]

I would NOT recommend changing to synthetic oil in an older engine.  Infact most experts (not your local mechanic) recommend that you use regular oil thru the 25 - 100 hr break in.  Then you switch to synthetic oil - NOT later on. 
As someone mentioned in a previous post, you'll incur oil leaks if you switch to synthetic in an older engine or transmission.  Be-where !!