The Stovebolt Site Forums The Shop Area Engine Shop High Detergent; or Non-Detergent---That is the ? or is it the Answer?? blah blah...

My 1951 GMC step side has the original 228-six. It has never been rebuilt, nor does it need it. The odometer readys ca. 85,000 and it has 115 lbs compression + - 4 throughout the engine. My grandad told me "Don't use High detergent oil in that motor! It'll knock all the 50 year old dirt lose that's in it and in no time she'll start using oil! They didn't use dergent oil in that truck probably teh whole time it was driving, so unless you tear down the motor and clean it out, don't use 5w30HD oil that you just dumped in it!" DOES ANYONE HAVE AN OPINION ON THIS?? I AM THINKING OF RUNNING THE TRUCK A FEW HUNDRED MILES, DRAINING THE OIL, ADDING NEW...THEN DOING THIS OVER AND OVER ABOUT 10 TIMES. OIL IS CHEAPER THAN A REBUILD, AND I WANT TO USE HD TO KEEP IT CLEAN. OR SHOULD I JUST USE NON-DETERGETN?? ARGH....HELP.

OOPS---If you have an idea can you email me at [email protected] is quicker for me to check in my hotmail. Thanks.

kgw51gmc,

The main purpose of detergent in motor oil is to keep contaminants in suspension until you drain the oil. This is why the oil gets black and skunky...it full of junk.

A detergent oil does have a limited ability to scour internal parts, although as stated above, this is secondary. The general line of thinking is that when a rig was run on non-detergent oil, it should stay on that diet..Grandpa's theory!


If I wanted to switch to a detergent oil, I would do exactly as you have outlined above, although maybe not as many/often changes.

If you were to ask if this would lead to more oil consumption on the motor, my answer would be maybe, or maybe not.
A reasonable question would be whether the gunk in the engine from all these year of non-detergent oil is what is sealing the rings and making the motor tight.

If it were my engine, I think I would change to a oil that was more available, and offered a little more protection..a modern multigrade detergent oil.

You will probably find a million different viewpoints on this subject depending on who you talk to. Use your common sense and you will prevail.


Stuart

Stuart,
I think you are right, I just needed a push to believe in myself. I will change the oil a couple of times, get it running out on the road and see how it goes....commmon sense. Very good information and thoughts Stuart. Thanks a million. I think we can say "case closed".

Everyone has an opinion on this.

Your grandpa is right, but there are some caveats. If the engine has an oil filter, either bypass or full-flow, it is okay to use detergent oil. As Stuart said, the detergent keeps the dirt suspended in the oil, requiring a filter. Otherwise the dirt continues to pass through the bearings. With non-detergent oil the dirt settles to the bottom of the crankcase, more when the oil cools off. This is also why it is important to do a non-detergent oil change with the engine hot.

If the truck were mine and it did not have a filter, I would run non-detergent oil. Around here you can buy it at a parts store or farm store. If the truck has a filter, I would run detergent oil, as long as I could do it without grandpa finding out. Some things aren't worth the argument.

Then again, its always good to do an oil change hot, regardless of oil type. Filth will settle out eventually even in detergent oil.

I think your Grandpa was right if it does NOT have an oil filter. I don't know about it USING oil, but I always heard it could knock enough of that crud loose to clog an oil passage in less than ONE hundred miles. Then you will be rebuilding the engine.

Why not just draining and flushing the engine thoroughly before driving again? Then you can start using detergent oil.
It might not clean everything perfectly the first time, but most of the stuff that would fall off with detergent oil would certainly be cleaned away by the more aggressive flush.
There are many brands of flushes in parts stores, but I heard Kerosene or Diesel fuel was used since the olden days.

Whooaaaa!! I usually ask more questions than give answers, but I can tell you from first hand experience that you do NOT want to use any of the oil flush products. I just tried that route in a little Mazda my daughter has. We lost the lower end of the engine because a piece of the sludge was washed loose and lodged in a hole that oils a bearing. After that incident, I researched and have found very few experts who will recommend this procedure.

Yes, maybe not recommend on newer engines.

I imagine the old sixes have simpler maybe larger oil passages with less chance of getting clogged when flushing.

Please don't take my suggestion as experienced recommendation - every old engine is different and unique with sludge build-up of course.

I would take off all the covers and do a thorough visual check using common sense and good judgment.
If the sludge build up is not too bad and you feel confident, use maybe more than one good thorough flush, after you removed as much by hand as possible, where accessible.

It might reveal other problems, but better than driving around with a mystery to be revealed at typically the worst point in time, when you least want to deal with it.

Nothing scientific here,but if it has been running great all those years on non detergent,why change things?If it were mine I would stick with the non detergent.

Thanks for all the information guys. I have made a decision! This is great. I will officially stop worrying about this now. It is great to have a "panel of judges" available on my PC. Thanks again everyone.

I worked in my father's garage during the 50's.
Most cars used "single weight" High detergent oil. 30w summer and 20-20w winter. Changed often.
Some olds timers would ask for non-detergent, and we sold it from bulk drum measure. My experiance with old engines is the hard running late in their life causes oil consumption and leaks. Avoid 10w40 modern oils,and try to stay with single weight HD products.