csaxon

I've been using Mobil I since 1974, when the can said it was good for 25000 miles! Then the car dealers screamed that no one would come in for service and they wouldn't honor warranties unless the suggested oil changes were done according to the car service manual. So, Mobil took the 25000 mile guarantee off of the can and said to follow manufactureres recommended oil changes.

The original was a 5w20 which was pretty thin. I put it in a 1974 mercedes 450 SL and drove year round with it in Georgia. The problems I had were that the oil was so thin and slippery that it found its way out of the smallest of cracks in valve cover seals, etc. Secondly, because of its thinness, the dual camshaft chain tensioner wouldn't hold pressure until the car was running so you would get chain slapping and it actually wore some groves in the head. I still use Mobil 1 in all of my cars and I just sold the 450SL 30 years later which runs like new and never had an engine problem.

The problem with putting it in an older engine that has been using conventional oil is that it is an aggressive cleaner. So, seals and gaskets that have swollen and varnished/ sludged over may begin to leak as the crud dissolves.

I should mention that the reaon I first used Mobil 1 in 1974 was that I flew jets and the engines turned at over 14000 rpm and exceeded 850 degrees C. The oil the technicians put in the engines was a version of Mobil 1.

girvan

And so much for the myth that all kinds of leaks will be caused by switching: I treated my wife's inherited and much neglected 100K mile Toyota to Synthetics. The nasty oil drips went way after a few days and now after 3 changes the underside of the engine and transmission is totally dry. The black grunge in the filler hole and dipstick is also gone. Perhaps the oil dissolved away the dirt lodged in the oil seals?

I’ve yet to see this mysterious article that keeps getting referred to on synthesis oil shrinking seals/expanding seals/causing leaks (pick the most convenient one). Which bar was it written in? Don’t we think the guys who formulate the oil know a thing or two about looking after seals, and don’t we think that with 3 times the profit margin to play with they might actually be able to look after seals better. Sorry if forgot the other bar stool theory that they deliberately swell the seals so that if you convert back it will leak.

persian451

so what steps should I take in switching from conventional to synthetic?
I got a 91 LS400 with 179k miles.. running 20w50 oil

if synthetic is soo good, why is it a hassle to switch?

modelaford

Total BS on the engine starting to leak oil with synthetic. No 1, if you had synthetic in it its whole life it would not be an issue. your seals are most likely hard as a rock due to age and heat. now full synthetic takes like 500 degrees more heat and the seals stay soft. Some 20 years ago when the full synthetics first came out they had a problem with leaks due to the oil did not contain Seal Swell a special additive to keep the seals pliable. You can accomplish the same thing by putting 6 oz of brake fluid in the crankcase, it will act as seal swell and if the seals are not actually cracked it will make them pliable again and you will not have to replace them. Usually when a seal starts to leak there is a reason and it cannot be blamed on the oil. Sorry about the long post.

LexFather

Synthetic oil molecularly bonds to the engine, therefore under initaial startup there is lubrication at the joints. Whereas with regular oil, the car has to have the oil go through the system. Synthetic oil can also stand more extreme temperatures than conventional oil.

parula

The more I learn here and elsewhere only convinces me more to use synthetic and nothing else.

The few pennies it costs me to put the best into my $35k car is well worth it, and it probably pays for itself anyway with a little better mileage over 5k miles - why would anyone use anything else??

Leets

Cuz in my honest opinion synthetics are a waste of money. The big difference between synthetics and regular oil is that synthetics are more stable over a longer period of time. This means that, theoretically, you could keep synthetic oil in your car for nearly twice the time you'd keep regular oil in. That brings up the question, though, as to why the heck would you want to leave any oil in your car for more than 3K miles? Sure the oil will still be good beyond that point, but how efficient is it going to be at cleaning your engine? Plus, your oil system does not rely solely on the oil... let's not forget the filter. Filters are only efficient when they're not clogged with material. Therefore, if you're changing your oil around the 3K mark then there's no point in spending extra money on "long-life" oil. As for the lubrication issue, yes synthetics (if they're functioning properly) do adhere better due to their smaller molecular structure, but that doesn't mean that regular oil doesn't adhere to the metal. If you're looking the ultimate in protection, your best bet is a top of the line oil additive (no slick 50, Z-max, or STP... they're junk). You're money is much better spent on a good additive. Plus it's usually cheaper to purchase regular oil and the best oil additive than to just purchase synthetics. As for blends... you might as well just buy regular oil and give the cashier two dollars more per quart than it rings up as. Blends often contain too few synthetic additives to actually make a difference. And finally, yes you can mix synthetics and regular... just never, never, NEVER mix different weights.