I've read that synthetic motor oils promote better fuel ecomomy. How much better? Is the extra cost justified? Also, can you just switch from regular to synthetic oil without any problems? Can anyone enlighten me about these subjects?
I don't think they do provide better fuel economy, if they do the effect is negligible. However, I ALWAYS use synthetic. They provide much better resistance to break down, and have better lower viscosity at low temperatures and higher viscosity at high temperatures. If your engine is in good condition, synthetic oils will pretty much keep it that way (barring any unforseen issues, such as overheating or improper maintenance). Synthetic will also allow you to extend your oil change interval, but I do not recommend doing this. If you plan to keep your car for a while, use synthetic! The extra cost is worth it.
Just what rem83 with one addition. If you have a very old car with orgional motor and transmission and you put the synthetic in them I have found that I ended up seeing the new oil start drip out after a short while. I think the synthetic oil is thinner and cleans better but will go thru old seals after a little while of use. Now if you have a older car and just rebuilt the motor or transmission with new seals then go for synthetic oil. I some times think Auto dealers due this to older cars just so they will get a repair out of them when they start leaking out the fluids. Just my thought on this. A lot of newer cars are using synthetic oils now. Some can only use them. For better milage I don't think it would make much difference vs the cost of the oil but ya never know till you try.
The modern synthetic oils have come a long way from their founding brothers and sisters. I haven't noticed a significant change in mileage between synthetics or natural oils in my experience. I have had similar problems to what VWJunky reported with synthetic oil added to the gasoline in a 2 stroke motorcycle that I had back in the mid 1980's. A friend gave me some new 2 stroke oil to try and being perpetually broke and cheap, I gave it a try. It worked fine in the motor, but the gas line started to weep after a few weeks. This was the old neoprene hose that had a braided cotton over weave and it made a mess with black goo dripping on my motor and frame. The oil worked fine, but at that time there wasn't any hose that would hold it so I returned the unused portion to my buddy. That being said, I think the biggest problem was the chemistry of the neoprene fuel lines in 1985, not the oil, it was just so slick molecularly that it weeped through the hose.
Another alternative you might want to consider is using a parafain based traditional oil. With the wax base as opposed to an asphalt base you get an extra 15-20 degrees before breakdown as the parafin is a ring based carbon chain and when it breaks down at a higher temperture, it turns into a straight chain. The asphalt based oils are straight chains to begin with, when they break down you have serious trouble on your hands. I used Penzoil exclusively in my dragsters for that reason with good results over several seasons of racing. I never scattered a motor due to oil breakdown or lack of lubrication. Also, if possible use a straight grade of oil, say 30 weight as opposed to a multi grade of say 10W50 since the multi grade has additives that change the oil so that it will act like 10 weight when it is cold and 50 weight when it is hot. If you drive in similar outside air tempertures throughout an oil change cycle a straight weight oil will actually lubricate and cool better than a multi weight. The caveat here is that many manufacturers require multi weight oil for modern engines so if your owners manual dicatates that you must use a multi weight, don't take a chance on voiding your warranty based on my advice.
When using synthetic, the only thing I really noticed is better overall engine performance. Cleaner starts and smoother runs... I've been using Synthetics since 2000, in my Durango and now in my 300c. Both cars have performed better than specifications... Running synthetics also helps with engine tuning using the performance module...
I change oil about every 4500 - 5000 mile range to make sure I keep the engine running smoothly... Its an investment that your car would really enjoy...
I am glad I am not the only one seeing some problems with older vehicles with synthetic, thanks for the rightup Bates, very good info. I feel better about the penzoil that we are using in the Chrysler T&C since you mentioned it. With my older aircooled VW"s I had always used Castrol Strait 30wt oil and neve had a problem.
And as Bates sugested check with you manufactures warrenty and owners book to what type of oil they sugest. I know in VW land that for slect few years of the TDI with the PD motor you have to put a specific type of synthetic oil in it or it will wear out the motor. Something about very tight tollorances and engine wear. Even Radiator fluid is specific to some vehicles and can't be mixed. I have to run some crazy G12 red stuff in mine. So in short if you are unsure of anything, just be familiar with your vehicle and hand book and try and stay as close to what the manufactures say.
@bates: I wouldn't use straight weight oil in most normal use vehicles. Even if you run high weights in summer and low weights in winter, you have too much engine temperature variation from a cold start to sitting in traffic. Synthetic oil already has pretty good breakdown protection, and modern, EPA restricted engines don't see the kind of stresses that cause breakdown. For drag racing or really high performance applications, your advice seems great, but for an '09 Sonata, I think he's a lot better off with Mobil 1 or Syntec.
I agree with you for the 09 Sonata application, that is why I put the disclaimer to check the owners manual for the final word. I don't know of any cars manufactured since the turn of the century that allow single grade oil. In spite of my preference for single grade oil, I use multi grade oil in my 2000 Acura Integra that is my daily commute car, and my wife's 2005 Mazda MPV gets multi grade synthetic per the owners manual to ensure warranty coverage. My comment was more general and if it was not clear, then I appologize, I only meant that older cars that are driven in specific climates with more or less constant starting tempertures may not suffer from the use of single grade oils which tend to have slightly better break down performance due to the oil being made up more of oil and less of additives than multi grade oils, and they tend to be substantially cheaper than synthetics.
Every application is different, I was unaware until VWJunky posted above that some manufacturers vary the requirements even among the same model line to be specific to the exact engine installation. I do know that reciprocating aircraft engines mostly specify single grade oil and many Marine Diesel (boats not the USMC) applications do the same. Again like VWJunky pointed out, there are also very specific coolant requirements in some diesel applications as well. With coolants specifically designed to resist water pump cavitation which can produce bubbles in the coolant that may lead to hot spots in the engine or in extreme cases to holes in the cylinder linings as was the case with a boat that I used to run. That boat had to replace a large diesel engine because of pin holes in the cylinder linings caused by cavitation of the coolant pump which was due to the retailer not adhereing to the manufacturers requirements for coolant. The engine had also blown 2 head gaskets due to hot spots caused by aerated coolant not dispersing the heat as effectively as non aerated coolant would. The boat owner ended up having to pay for the replacement as the engine although only having a little over 4,000 hours total time (the design life expectancy was about 20,000 hours) was over 10 years old when the holes were found. There wasn't enough money in it to hire a lawyer to sue for damages with that much time passed.