When choosing an oil, do you look for one that stays cleaner longer, or one that gets dirty and cleans the engine? Or does it matter? What does everyone think? I think that one that gets dirty and cleans the crud out of the engine would be the best.

 

Are you serious?
Maybe I'm a bit stupid but I always thought the oil turned black from heat, friction, wear and breakdown. I never thought of oil as a cleanser of the engine I thought the black was something that couldn't be avoided.
Recently (last summer) I rebuilt my engine and the guy helping me told me that I would not have black oil again. I checked it the other day and sure enough it was black and 1 quart low. Bummer. I have changed it a few times since the rebuild, and its not the original stuff.

 

I think it all gets down to the detergents in the oil. The question I was trying to ask was do you want an oil that picks up all the scum in an engine and holds it in suspension, so it can be removed, or an oil that doesnt get dirty, and thus lubricates better? Feel free to make any argument you like, I'd like to hear different reasoning on this!

Edit: It is my understanding that most of the darkness of oil comes from blowby, if this is wrong, let me know that too.

 

Exactly what is blowby and would I have it already with a fresh engine? I've heard of it but can't describe it. How can it be avoided. I looked inside my carb last week I was getting an intermitent stall and it was pretty dark inside but thought it was from an incorrectly adjusted carb,plus the plate under the carb was upside down for a while and was giving me fits trying to find my vacuum leak. As a result it was running like crap. Fixed the stall tho, my fuel pump came apart on one of the valves inside the pump.

 

Blowby is where a small amount of combustion gas gets by the rings, carrying with it carbon. This gets the oil dirty. When the rebuild was one, if they didnt use new rings, you will have just as much blowby as it had before the rebuild. The rebuilder probably figured that since he cleaned all the sludge out of the oil pan and the valve covers, that the oil wouldn't get dark anymore. Well, it does. Something else to think about, is what thermostat are you running? The oil needs to get good and hot to get all the moisture out of it (something else that blowby carrys with it.) Just think of it this way: If the oil is getting dirty, that much more scum is not getting deposited in your engine!

 

It used to be that we checked for blowby by taking out the PCV valve and checking to see how much oil smoke/exhaust was coming out (of the engine, not the PCV) - in an engine with good compression there should be very little at idle, though if you tweak the throttle and rev it up a bit you'll probably see a small amount. In an engine with bad rings you'll see some smoke even at idle, and in an engine with *really* bad rings (like the 302 in my Lincoln) you'll see a ton of smoke. It's tough to explain just how much you should see - it's sort of something you learn through experience.

Anyway, that's how us rednecks used to check for blowby - if you want to get fancy and have some patience you could run compression tests and that sort of thing.

LK

 

gasoline is the main contaminater of oil besides blowby??
I think thats how it goes if I remember correctly. Check if your choke is to rich along with other things that get to rich since the stuff that doesn't burn properly is building up somewhere in the motor.

 

I don't like the idea of crudy oil running through my main bearings, as crud removal is good in some areas but other crud should stay in it's place. But I think that problem has to do more with engine flushs rather,not what normal oil can pick up. I like to see dirty brown that almost looks somewhat new in a thin pour when any oil comes outta one of my motors. If the oil got almost black or something I'd probaly think something is up to no good.

 

Good Question but its a two part question, You get what you pay for, if you buy a bad grade of oil you'll have to change it more frequetly than you would if you would buy a good grade of oil regardless of the filter you use. Its also a question whether or not you use a conventional oil or synthetic and the additives they contain to give them thermal and oxidative stability. I'll stop here before I write a whole page.

 

Be happy that your oil turns black. As you've guessed, this is due to carbon-based particulate material held in suspension in the oil. Having these particles in suspension means that they are available to the filter for removal from the oil. Standard spin-on oil filters remove carbon particles down to about 25 microns, which is about one-thousanth of an inch (1 micron = 0.00003937 inch). Since your engine's minimum bearing clearance is about 20-thousanths of an inch, the sub-1/1000th residual carbon in your oil doesn't really pose any threat to its longevity or reliability. That's why one commonly sees engines go hundreds of thousands of miles between rebuilds when their oil and filter are changed regularly.

Running your oil hot enough to boil off the water and the tiny amount of unbrunt gasoline that slips by the rings is important, too. Water can form acids in the oil, which obviously aren't good for the engine, and gasoline helps break down oil into polymer chain lengths that don't have good lubrication qualities, resulting in unwanted engine wear.

Finally, if you simply don't care for the dark color of your engine's oil, try adding a bypass filter, which can take out particulate material down to about 1 micron. These can keep your engine's oil looking fresh and new for months. Probably the best known DIY bypass filters are from OilGuard

Stan