Apologies but I really don't think that is the case...
they are not gonna waste money putting something in that can do no good job becasue of one of the other ingredients. they'd just save $1 per quart and not put it in in the first place
detergent is designed to keep particulate contamination suspended in the oil so that a good spin-on filter can remove it.
just like washing clothes..... the water looks dirty, the detergent kept the small contaminants suspended. only the big clods of mud and that dollop of ketchup you dumped on the front of your shirt are floating at the bottom.
a low detergent oil allows it all to sludge in the sump. The natural effect in a low or no detrgent oil is to allow it all to fall to the bottom, which is fine provided you set your pickup depth as per the manual. This was the standard when engines were low rpm things and turbos and cam variators etc didn't need to be oiled.
nothing wrong with this if you stick with this kind of oil.
However a swap to a higher detergent after years of low detergent oil will stir it all up and you brand new filter will be full of crap within 500 miles.
each oil has zddp package designed to work with the other additives in the oil.
Heat and friction causes the ZDDP, or components of it, to chemcially bond to the surfaces. i.e a bit of iron reacts with something in the ZDDP package to make a new compound on the surface of the part, that is slippy and protects the part. you can't see it, you can't taste it, you can't scratch it off with your thumb nail... chemistry happend.
it can be worn off, but the detergent doesn't wash it off.
same idea as leaded petrol and exhaust valve seats:
chemcial reaction occured at the seat and valve interface, that stopped the valve repeatedly welding istelf to the seat, that protection wore off, but it couldn't be washed off.
much like you can't wash off anodising on an aluminium part with water, but you can wear it off.
you can't wash rust off iron but you can grind it off
etc
too little ZDDP causes wear
too much ZDDP causes things to stick, it can mess with clearances, cause things to sieze, makes hydrulic lifter pistons sticky (never pump up) can cause lifters not to spin in bore etc etc.
I wiped my cam due to too little ZDDP could also be I wiped my cam due to too damn much ZDDP.
Adding an additive to an oil that has already been carefully formulated to do a specific job in the first place is a lottery..
you have no idea of the impact of the additive on all other constituents in the oil
cheap old style single weight mineral oil with an anchient spec...well ok but anything you can buy today....i'd be wary
you may end up with just the right amount of ZDDP but have totally screwed the viscocity modifiers
or converted a medium detergent oil to a low detergent oil.
but then again you might not have....whats in the additive?? (trade secret) over and above the zddp content?
whats in the oil.....Trade secret unless the ingredient in question has some kind of health impact or the SAE stipulate it must be on the label.
some additives i'm sure are good some are no more than a bottle of diesel with fairy dust in.
if you buy oil sensibly for your flat tappet 50+ year old engine
you probably won't have an issue.
use the additive with cheap running in oil for break in, its a basic mineral oil, by all means add the zddp bottle of magic, its in there for 20 minutes + 500 miles while everything gets its last and most important polish.....
...then just switch to something good with the right formulation for the rest of the life of the engine.
Dave
