are they safe? are they worth using? do they really do what they're advertised to do?
Trust me, they work. I burned up the valves in a Buick many years ago from adding carburetor cleaner at every fill up. Oops! When you pay for a fuel injection cleaning they use a pressurized can as part #1 and then they hand you a bottle of fuel injector cleaner to add at your next fill up. They should also clean the throttle body as part of this service. The oil additives are most helpful for neglectful people or neglectful or rough use of the car. For example, towing a heavy trailer is extreme service and I've seen new p'ups use or burn a quart a day of regular oil when they should have been using a heavy 15w40 or added something like STP to the oil. Good Luck!
Additives are a waste of money and are not recommended. The only thing I would do is possibly switch to a high mileage oil but even then I would only do so if the car was leaking oil. Changing it every 5000 to 7500 miles is sufficient for normal use. Severe use calls for every 3000 to 3750 miles. I own a 1996 Accord LX wagon and change the oil every 7500 miles as per the owner's manual. There has been problems in the past with using synthetic oil and then switching to conventional oil causing oil leaks due to damaged seals. This problem should no longer be an issue with modern oils but since you have an older car, IF the former owner used synthetic oil I would continue to use the same oil so as not to take any chances.Fuel treatments won't hurt anything. I have used them once or twice in my life and consider them a waste of money as well.
they are safe, for the most part. as a rule of thumb, put a bottle of fuel injector cleaner in your tank at every oil change. we pay a lot for gas, but are getting less detergents. a lot of fuel additives are primarily kerosene that's been modified chemically. Use something like Techron or Seafoam, Gumout or Redline's complete fuel system cleaner. the oil additives, they serve a purpose, if you need them. some will thicken oil to increase compression if you have that problem, others are designed to stop leaks from the seals, sometime they work, but it depends on the leak. there's an additive by Lucas, called oil stabilizer, it works very well, I use it mainly in the summertime because our california sun is so blistering hot, and I sit in traffic quite a bit, I let the oil stabilizer do its magic. it makes the oil morestickier", so it adheres to the parts better (and longer). It also helps rejuvenate the rubber seals so they won't leak. My car has 174,000 miles, and I have never replaced a seal or gasket yet. what's your car doing or not doing? that depends on what addtive you should or shouldn't use. a lot additives out there I consider snake oil. essentially they have to work somewhat, but some are more potent than others, and yes, I've tried them all.
