Engine Lubricating Oil

[Guest Bob Call]

OK, is there an oil company chemical engineer out there that knows lube oils?

My question is are "detergent" oils truly detergent or are the additivies dispersing agents? It has been my understanding that the additive is a dispersing agent that keeps particles in suspension to keep them from settling out and forming sediment in the crankcase oil pan and sludge deposits in other parts of the engine where oil puddles.

Some people say don't put "detergent" oil in an old car as it will break up the sediment in the oil pan and circulate it in the oil. Is this possible if the additive is really a detergent? Is this possible if the additive is a dispersent? I'm thinking that the term "detergent oil" was created by the marketing department to make motorists want to buy it to keep the inside of their engines sparkling clean, when in fact the additive was to keep contaminants in suspension so they would drain out in the oil at oil change time rather settling in the oil pan.

Let' hear from a Shell, Chevron or Exxon chemist and give us the straight story on detergent oils.

[Rusty_OToole]

I have been hearing this old wive's tale about not using detergent oil or multigrade oil in old cars for years.

What these pundits forget, or don't know, is that detergent oils date back to the late 40s if not earlier, and multigrade oils to 1951. So if your car was made since the end of WW2 chances are it has used multigrade, detergent oil all its life.

Likewise if it is a prewar car that has been rebuilt since the 1940s.

I know when I worked in a gas station in the sixties, the default choice for all oil changes was 10W30. I don't remember using anything else except for VW beetles which specified single grade detergent oil because the multigrades of that day would not stand up to the elevated temps of the air cooled motors.

We did sell straight 30wt bulk oil from a drum but the only cars that used it were worn out oil burning clunkers.

Edited May 1, 2011 by Rusty_OToole (see edit history)

[Guest Bob Call]

Rusty, glad to hear you agree about the old wives tale. Common sense tells me that the hard packed sediment in an oil pan requires a strong solvent to break up and motor oil is not a solvent. I know from experience that cleaning engine parts with kerosene or diesel fuel does little to sediment in an oil pan and both are strong solvents. You have to get in there with a scraper and brush to get the gunk out.

I worked in my uncle's service stations in the 50's and like you said most people requested 10W30 for an oil change. We sold bulk 20W and 30W "non-detergent" for the oil burners at 10 cents per quart served up in those glass bottles with the pour spout tops. Back then a complete engine overhaul at 40,000 miles was common. Probably due to the quality of metals used in rings, valves, bushings and bearings rather than the quality of the lube oils.

Edited May 1, 2011 by Bob Call (see edit history)

[broker-len]

I have a 4 cylinder plymouth the engine is rebuilt----I started using straight 30 and found that when at driving speeds the oil pressure was as recomended 30 to 40 lbs at Idle the pressues went way down I think the multi holds a more even presure I do use a zink additive in both my 30s cars bobnroman@yahoo.com