Is there any advantage/disadvantage to switching from regular oil to synthetic on my 1991 420 SEL with 75K?

OH GOOD another oil thread.
Apart from the high cost i can think of no disadvantage to it.
Advantages, better for your engine I guess (no big deal to me personally), and does seem to be able to stay in the engine longer, doesn't break down as fast. Somewhat better fuel mileage. Most of the figures come from the oil manufacturers, who want to sell you this expensive stuff in the worst way, so I take the claims with a grain of salt. Myself I wouldn't bother using it unless you keep it in the engine about twice as long as normal oil, just not worth it.
Some say switching to it later in the engine life is bad, will make the engine leak, etc, which I say is all hooey.

Gilly

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I've use the synthetics and conventional, but only in my trucks. I've never seen much of a difference in either. The synthetic turns black in the 454 same as the conventional. I don't think it makes much difference in the engine.

The only area where I've heard it really matters is in the differential. The conventional is supposed to be bad or at least not as good for limited slip differentials. I don't know how true that is because I've been running plain old gear oil in all my trucks for more than ten years and they've all been limited slip.

Just my nickel

I’m all for synthetics oils, it’s all I’ve ever used in all my cars. I attempt to keep my cars / trucks until they rust apart. So I don’t have to purchase another one. Your always going to get someone that says they think it’s a waste of money and others that wouldn’t put anything else in there cars. All I can say is do the research and find out what the science behind it says. I’ve been using Amsoil forever and love it. Worth every penny.

Synthetics are designed to stay in your car longer, and to provide more protection. If you look at it, it’s cheap insurance for your engine.

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I agree - do the research. It won't yield an answer but you can be confused on a higher intellectual plane. In the mean time you can put anything you want into your car.

The one benefit I see from synthetic oils that petroleum based oils cannot offer is the wider spread of viscosity available in a single product. It allows the oil to protect under a wider variety of conditions. I run Mobil 1 5w50 in my C280, which is a synthetic. I like the fact that it flows to the top end of the motor faster on a cold start AND provides me with superior high temperature protection at the same time. Now for the E320, the manufacturer recommends the Mobil 1 0w40, so that's just what I use in it. But again, that is a larger viscosity spread than you'd ever see on a "dino" oil.

I only put 5-7,000 miles a year on the C280 so this becomes a great solution for changing the oil once a year and not having to worry if I have the right "weight" in the motor. Its always appropriate for the climate.

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Jonathan

2011 Mazda2
2000 E320 4Matic Wagon
1994 C280 (retired)

I would be incorrect to assume that a dino 20W-50 and a synthetic 20W-50 work at the same temperature ranges.

The synthetic will indeed have a lower pour point and at the same time provide protection at higher temperatures than the synthetic.

There will always be less friction with the synthetic, minimizing wear, increasing fuel economy, and making cold starting easier.

The synthetic will last longer between changes, thereby erasing the higher cost penalty and also thereby enabling you to pollute the environment less with old oil.

There is zero disadvantage to synthetics and zero reason to use nonsynthetics in the 21st century--no matter when your engine was made.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

The biggest thing that sold me on synthetic was the first time I put Mobil 1 in my 92 Jeep - about 4 years ago now I believe.

140k at the time, always had conventional. Had a heavy tap all the time, which I know is a stuck lifter. The first time I put Mobil 1 in was for the winter, 5w-30, to try it out. Yes, 5w30 in an engine with 150k - it was synthetic, I heard it would be fine.

Not only did it start easier than it ever did, I had half as much blowby coming out the CCV system in 500 miles, and the tap was gone after about 200 miles. Now I only ever hear it when it's cold and I'm straining it, like going up a hill at 50MPH in overdrive.

All of my cars have synthetic now. The Jeep has 172K, the 300M has 162K, my Charger has 44K so it should be fine of course. My mom's 300M has 101K. None burn any oil visibly, and although the Jeep has blowby it uses less than a quart per change on 10w40 (a quart on 5w30). My 300M with 162K doesn't use anything between changes, it's still on the full line when I change the oil at 4500-5500 miles.

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Syn or dino are the same when it comes to contamination.When they are contaminated they are contaminated regardless of basestock.

Dino can make it in the FSS done properly.

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1999 C280

Do a search, there are enough oil threads to keep you busy for a long time.
there are also as many opinions on which oil to use and how long. opinions are just opinions, get the facts.

synthetics flow and protect better, and can be left in longer. just because the oil gets dark doesn`t mean it needs to be changed. send a sample to a lab. and you will get a readout of what is going on in the engine.

not all synthetics are created equal, and some are not true synthetics.

Iam not a dealer or salesman and not connected with any oil co. but I use Amsoil 15w40 in my 85 300D along with the full flow bypass filter along with the stock filter. I just changed the engine over to it now that it is broken in. I noticed it ran smoother, and the temp seems to not run as hot.
I also changed the trans at 331000 miles to syn. it shifts smoother, and does not leak.

There is that fear it will cause leaks on a high milage engine. I have not had that problem.

Charlie

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Leaks are not as bad on most high mileage engines as valve noise if you use a low grade synthetic oil like 0w30.

If you switch to synthetic, try at least 10w40.

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A. Rosich
CL 500, 1998
S 500 L, 1998
E 320 T, 1995 [Sadly sold ]