Every new car I have bought has always had the statement in the owner’s manual: “Do not add anything to your engine oil, use SAE certified oils only”.
Now, there are a host of oil additives on the market-many have been sold for 70 years or more (Bardol, Oilzum, Casite, Magic Oil etc.), plus many newer brands (STP, etc.).
Obviously, people buy a lot of this stuff-yet no car manufacturer ever endorses the use of them -many actually warn you AGAINST using them.
This raises the question: are these additives worthless?
The only mechanic I ever knew to recommend them was an old guy who saw a lot of engines on their last legs (usually the rings were shot and the valve guide seals leaking)-he said that a heavy additive like STP could reduce the oil burning a bit, and prevent further cylinder wall wear. But, it would be a temporary effect at best…eventually the oil would dilute, and the blue smoke would return (and fouled sparkplugs).
These additives must be VERY profitable-most sell for several dollars for a pint or so.
Are these the automotive equivilents of patent medicines?
They’re crap. For starters, anything with solids in it (like PTFE) is double crap. Solids will be captured by the oil filter in fairly short order.
Anything that offers actual protection is offering protection you don’t particularly need. The engine is designed to work with the API-certified oil specified in your owner’s manual; you deviate from that manual at your own peril. As long as you’re changing the oil at intervals as specified in that owner’s manual, the engine will probably outlast the rest of the car. That’s been the case for three cars and a motorcycle under my ownership, none of which received oil additives, and all of which went to well over 100K miles before being I sold them; at the time of each sale, the engine was the healthiest thing about each vehicle.
Pretty much snake oil. Motor oils themselves have all of the additives they need today.
If you are really having an issue with rings and valves, the best stopgap is usually to go to a heavier weight oil.
Some further reading:
http://www.carbibles.com/additives.html
http://www.skepdic.com/slick50.html
This guy has a great site about all kinds of automotive scams. Mostly about fuel-saving devices, but there is also a section about oil additives.
Typically useless with a few exceptions. The only one I use is MMO (Marvel Mystery Oil). It’s basically a light oil with tons of detergents. I use it when I buy a used car where the oil has not been changed as often as it should have. A pint of MMO in the fresh oil will gently get rid of the sludge/deposits in the engine over the next few oil changes. I also successfully used MMO to free a sticking hydraulic lifter in an old car I had.
In addition, 6 oz of MMO added to every tank of gas on my '05 BMW completely cures a rough idle when cold. I don’t know why, but it does.
So an engine that is in good shape and has no issues needs no additives. A good additive can be useful to fix some problems though. So they are not all snake oil.
Snake oil mostly. There was one “manufacturer” (just an importer that held the EPA certs, but didn’t build any machines) of Russian motorcycles that indicated “Hyperlube” additive be used. Importation was eventually taken over by the Russian builder, and that recommendation was dropped. Hyperlube seemed a lot like STP… petroleum based molasses.
The neighbor girl once asked me to have a look at her old beater…wouldn’t turn at all, even with a jump start.
I pulled out the dipstick…actually, I tried to pull out the dipstick. Then I tried with both hands, and eventually got it out with a wad of thick tar on the end.
Seems she’d taken the “more is better” approach with the STP, and when the temps in Denver got down to single digits the “oil” got rather viscous. Took two days of heat lamps to get the sump drained. Thing was so leaky I thought it wise to avoid any flame based heat sources under there. Once we got actual oil in the pan, I had to spend an hour or so turning the crank with a ratchet and cheater pipe to force all the tar out out of the bearings etc. That was real fun in that cold I can tell you.