Technical Detergent oil VS non detergent

I know the basic properties of both oils, but I want to present a scenario. I have a 1938 model flat six motor that runs really well. The oil in it is very black. I know that the car has been run in more recent years { maybe 20-25 years). I do not know if the motor has ever been apart, or if maybe has had a rebuild. I am thinking that if the motor has never been apart, it is packed full of dirt and oil sludge and I don't want to wash all this sludge loose with a detergent oil and ruin the motor. I know that since 1938 it had lots of non detergent in it, as that was the norm back in those days. If the motor is reaonably clean inside, then I would certainly use modern detergent oil. I would like to hear some of you guys' thoughts and observations on this topic.

 

Can you find non-detergent oil in your area?

 

I stick to non detergent in my old flat six.. Never had anything else in it. Why switch? If the oil's black, change it out and keep on truckin....

 

If it runs "really well", I think that the pan should be removed, all of the sludge and gunk manually removed and everything washed down. The pan can then be re-installed and filled with detergent oil to finish the clean out. If it doesn't already have a bypass filter, I'd install one.

Back in the day, we'd fill the crankcase on a junkyard engine with 50/50 kerosene and motor oil and run it for 10 or 15 minutes, drain it, and refill. Some of the engines ran better while most had no change. I don't remember every clogging one up and blowing it up. I think that mixture has more aggressive solvent properties than detergent oil. Back then, they also sold "Motor Flush" specifically for doing this.

 

The way I was taught is that, if there is an oil filter, use detergent. The oil carries the filth to the filter. If there is no filter, use non detergent. You want the filth to fall out and be drained from the bottom of the pan. On an old engine of unknown virtue, I run it with new oil 'till it up to temp and drain that out and refill. A bunch of crap will come out of most of them, detergent or non. Mike

 

If it's not smoking, then it can't be too long since it's been worked on...take a look at the oil pan bolts, are they caked with decades of crap? or can you see the hexes clearly?

If it's been apart some time, then I'd just go ahead and run modern oil in it and not worry about it. If it's been together forever, maybe you should drop the pan and take a looksee. If it smokes a bit (blue oil burning smoke), then pull the pan and head and put some new rings in it, and lap the valves, pretend it's an old fashioned overhaul.

 

Whenever I drag home a new victim, I will do a Seafoam treatment followed by the dripping water to clean out the upper stuff, then drop the oil and refill with good detergent oil and a good filter. As soon as the new oil shows color (sludge) change it again- repeat as necessary. Usually after 3 or 4 times, the oil stays fairly clean. Trick is to get the crud out as it's slowly removed

 

Slow and easy conversion would be my choice. Run it up to temperature and drain, refill with NON detergent. Drive and monitor the oil condition (color). The black color you are seeing is due to the contaminants being held in suspension, which is a good thing.
Resist the temptation to switch to detergent oil in one change... As long as nothing changes in the way it runs (or burns oil), I would (after about three closely spaced NON detergent changes) settle into just using NON detergent oil. Introducing detergent oil or "engine flushes" (Seafoam, kerosene, solvent, etc.) will just dislodge crust and crud, and probably do more damage than good.
If curiosity is endangering your cats' life, at the most, drop the pan and look it over, clean it (and the oil pump intake) and button it up.
If it ain't broke, don't "fix" it!

 

Yes it is contaminants- but all those contaminants are going thru the bearings etc. That's why I change it quick, when it just shows a little color, not black with goo. Each change, it will take a little longer to show color as it slowly cleans

 

I've done this with an old clunker engine to find out if it's usable. Jack the car up with the sump plug facing downhill and place a small blower heater so that it's heating the sump. When the sump is good and warm pull the sump plug and watch the sludge drip. I did it this way rather than send the sludge through the engine by starting it. Once the oil and sludge stopped exiting I put the plug in and filled with elcheapo oil and new filter and fired it up. I ended up doing about 50,000 miles over 3 years with that engine. Yes, I drove around town for a couple of days and changed the oil for a better quality once I was happy with it.

 

That’s a good idea too .
Like Denny posted on using kerosene .
In the old days here ,,,it was common to drain and refill with straight diesel fuel .
Run for 10-15 minutes,,,,,,idle only,,, maybe a little higher,,,,,,,but no load .
Then drain and refill with oil,,,,,usually much better after that .
Cleaned the ring grooves too ,,,,,rings sealed better after that .

Tommy

 

I would check my engine design. flathead V8 has sludge traps in the crankshaft. Detergent oil would possibly loosen something you don't want floating around in your engine.

 

The old 8N etc tractors have a large drain plug with a screen attached to keep debris out of the pump inlet, and it's big enough to reach in there with a clean rag and get the stuff that's accumulated around the screen- is a "B" engine the same way? Great idea, an extra protection- as long as one changed the oil and cleaned the screen as you were supposed to

 

I’d pull the pan. Gasket and a bit of scraping and cleaning seems easier and more cost effective and less time consuming than frequent oil changes and monitoring.
I assume it also has side covers for valance adjustment? Pop those and have a look.

 

I never start an old engine without changing the oil first. If it looks really bad I pull the pan and clean out the goo and clean the oil pump screen. I usually wipe down all the inside I can get to with clean old rags to get every bit out that I can. We used to do the kerosene or ATF trick when we worked on used car lot clunkers. It worked pretty well. I would also pull the side plate(s) off and clean out the valve chamber. If the oil is full of thick goo check for water leaks into the crankcase. Re-torqueing the head bolts before starting it is a good idea, too. Tighten in the proper order, very important.

 

I'd pull the pan. If not, switch to detergent oil, no reason you can't change the filter a few times on the same oil change. Does that have an oil filter ?

I've done motor flushes, pulled valve covers and cleaned all top end crud manually, half 50wt, half naphtha, ran it until it got hot. Lucky it didn't plug the pickup. It didn't hurt it, but I'd take a more conservative approach now. Half quart of trans fluid added the day you're gonna change oil is a better plan

 

All very interesting reply’s and I have nothing to add, but a question. When did detergent oil come out?

 

The last couple of old engines we tore down had a lot of sludge in the pan.
Cleaning a pan was regular maintenance.
I thinks I’d drop or look inside the pan.
The old rule of thumb I was taught is detergent if it has a filter. Non-detergent without an oil filter.

we’re about to build a flat 4 willys. Has the bypass oil filter. I’ve wondered if either is ok due to the bypass system.
I have 2 flat willys. engines one with a filter. One without. The amount of sludge in the non filter pan was much more than the filtered engine.

on a side note, a good PCV set up has a lot to do with how clean an engine is.

 

???

 

Does the motor even have an oil filter on it? Is the oil filter a bypass filter?

You list a 38 Chevy in your profile, I thought that by 38, Chevy didn't have flathead 6 motors?

 

I don't know the definitive answer to that, I think it was kind of a rolling introduction, but according to the attached slides, in 1953 the API created a new classification of engine oils called MS (for Most Severe) which were detergent oils. This means that some detergent containing oils may have been out before the API recognized it and created a classification. Certainly they would've been available after that in '53. Then in 1970 the API created the "S" engine oil classifications that they are still using today, but they went backwards and created classifications for the older types of oils as well. So the SA, SB, SC service classifications were all obsoleted by the time they were created. It's kind of strange the way it happened, but prior to 53 I don't think there were any official classifications at all, then in '70 I think they were just trying to tidy up some loose ends. SA, SB, SC, etc oils may still be available some places, but we can't get them around here. Not only that, but the API cannot certify any of those oils as the tooling needed to run the tests no longer exists. So it's a buyer beware situation, you really don't know what you're getting, you have to trust the brand you're buying. Anyway, see the attached, it might help.

 

Yes sir. It took some looking but I found plenty of it at Tractor Supply.

 

Thanks. That is kinda the way I am leaning.

 

There's an assumption here that only non detergent oils can form sludge..That's not true .Any engine can run detergent oil and be a mess inside because of driving conditions and or lack of maintenance..

 

Yes, I pretty much grew up on the old late 30;s and 40;s Chevys and still enjoy tinkering with them. And yes, they are overhead valve 6 cyls. However the car I am referring to in this post is a 1938 Dodge that I bought a few months back, All the Mopar 6 cyls were flathead up til about 1960 when the slant 6 came out.

 

Speaking of detergent oil. Remember the TV commercial late 60’s-early 70’s where the guy cleaned his hands with motor oil to show how it would clean your engine? I forget with Brand the commercial was for.

 

My uncle Joe opened his Standard Oil station in 1927 and closed in September of 1974. The rule there was no filter or just a bypass filter you drained 1qt of oil and added 1qt of kerosene. Ran it for 10 or 15 minutes and drained it while good and hot. Got refilled with new non-detergent. All neighborhood cars never any problems. Never lost an engine. Canister or spin on oil filters got detergent oil and a new filter.

 

I habitually pull the pan on every engine that come to me.

It gets cleaned, and then I run modern detergent oil. If there is no filter, it gets one, if possible.

I have done this to over 100 engines on the last 40-years. Zero oil related failures. Several made it over 300,000 miles.

 

Years ago I thought I should be a big shot Packard guy, had a 29 short sedan, and a 30 medium phaeton. In our local club we had an old guy who was a Packard dealer mechanic until they folded. Highly respected man, in his retirement years the national club would pay him his hourly shop rate to drive the Tow rig and follow them on big tours. He told me, if you switch to detergent, "change the oil after dark" ! Meaning, frequently. Reason is, he explained, the detergent will loosen up all the dirt that once was resting peacefully, and once you loosen it up it likes to embed itself into the soft metals like aluminum, and bearings. Bearings under pressure may wash it thru, but often the first to die is wrist pins, which are not pressure fed on old motors, only splash. Sure enough, both my motors had wrist pin knock. Not necessarily a death sentence, I drove a White tandem axle dump truck with a 250 cummins for 10 years that was knocking when I got in it, they said it had been knocking for years before that, wrist pin knock they figured. I bought it from the company when they got rid of it, used it a couple years, sold it to a farmer who used it a couple years, who sold it to a company that exports junk to mexico, and it is probably still on the road. 1968 White