Heefers replied:

My take on the matter is that there are plenty of engines out there running just fine without them. Regular maintenance and a gentle right foot is the key.

Outnabout David (SA) replied:

The bottom line is assuming that they do extend engine life is to calculate the cost over the lifetime of the vehicle vs the cost of the product. Probably not worth it if it only gains you an extra few thousand K's. At the end of the day you have to rebuild the motor anyway, just a bit sooner or later really.

The other thing is to think about how many times you buy a car these days and have to get a new motor during the time you have it (Nissan 3litre excluded)!
Modern engines last several hundred thousand kilometres so why spend a fortune you get it serviced.
Just a money maker for the dealership .

Now diffs/gearboxes/transfers on the other hand I have no problems in putting in Morey's oil stabiliser. Definitely helps meshing of the gears and will help if you run low on oil and will run slightly cooler as well. Because you don't these oils often the cost is worth it.

T-Ribby replied:

Last century I bought a low kays Mazda 323 with a "Fortron" (this one was a petrol additive, an upper cyclinder lubricant iirc) guarantee that had been going since new. This guarantee covered the life of the engine. If it blew up, Fortron would replace it. It didn't. When the garage did a recondition at about 150-180,000 (iirc) there was less than a thou wear in the bore. Good servicing or an additive that actually worked? will never know.

cheers
T.R

666toy replied:

Mostly just a rip off. Having said that i tried SLICK 50 2 stroke treatment in my Honda cr500 & found a very noticeable ware reduction within the cylinder. I used to replace rings & piston every 5 race meets slick 50 extended this to 8 or 9 race meets before there was a compression reduction so yes i believe slick 50 does work. Most of the others just increase your oil viscosity which is fine for a eng that is starting to use oil (most of these will help a little) but i am unsure as to weather the cost is worth it comparing it to just topping up the oil. If your eng is using heaps of oil it is cheaper in the long run just to have it reconditioned or replaced rather than just pouring fresh oil into it all the time . Not to mention the fine if you get caught with a smoky eng & a defect notice .
There may be some merit to using mories oil stabiliser or similar on a eng that does not get started very often eg months at a time (due to the sticking effect of mories has to prevent dry start up) but a daily or even weekly driver will have no issues here (oil does not get away that quick).
Regular oil changes @ 5000klm is your best defence against ware (regard-less of what some company's say) use a good oil eg. VALVOLINE SHELL CALTEX MOBIL etc. & quality filters .
For vehicles that are left unused often try to run them once a month at least & still change eng oil every 12 months or 5000klm which ever comes first.
Hope this helps...666toy

gonebush SA replied:

we swear by good oil and Nulon oil treatment. I know not many of you out there are going to believe me but i swear this is true, we own a VN commodore that has just done 760,000 we have owned her for 12 years and the motor has never been touched and she still runs like the day we bought it. it has always had treatment in it and was serviced every 10,000 ks until she reached around the 400,000 and now it's every 5,000 and all this time it's been on LPG
yes it mightn't be the treatment that has given us such a good run but for an extra $10 a service we aren't about to find out.