View Full Version : changing to syn oil

10-18-02, 08:03 AM
Is there any reason I can't change my other cars (1995 fire bird and wife's 2000
Neon) to syn oil? It would mean less oil changes, might save a few bucks. Would
the seals still work? I would hope/think so.

10-18-02, 08:18 AM
How many miles on it?

10-18-02, 08:45 AM
Sothpaw, I would do it along with a certain criteria. Your engine has less than 50k miles, no oil leaks and under 10 years old.

I changed to synthetic Mobil 1 after I purchased my '79 with 49k miles on it. It didn't have any noticable oil spots under the car.

After changing to Mobil 1 the only difference I notice was new oil spots under the car everytime I parked the car.

I wanted to do this for the same reason, so I would only change the oil once a year since I normally would only put 2k miles in that period.

I switched back to regular 10W-40. Didn't think I need lighter weight than that since the car sits in a heated garage during the winter months here in Colorado.

Just my experience.


10-18-02, 09:04 AM
I don't see how you'll save any money. Most "experts" recommend you still change it at the same frequency, or only slightly longer.

10-18-02, 09:11 AM
I think that the actual synthetic oil will lubricate significantly longer than the regular oil, but it's the oil filter that will have problems after 3000 or so. I think some members here change the filter but not the oil after 3K.

10-18-02, 11:03 AM
yes, I would change filter every 4000 or so but that's easier and cheaper than doing
the whole thing.

1995 firebird: 85k, just bought this year with 71k.

2000 Neon: She got this new, has 42 k on it now. Well maintained.

10-18-02, 11:22 AM
Broke in my 300M on regular oil and changed to synthetic at 2,500 miles. Perfect

10-18-02, 12:12 PM
I switched my Vette over to synthetic at 133000 miles - it had been run on dino for at least the previous owner's tenure. Didn't notice any MORE leaks, but the valve cover gaskets leaked a little worse. Switched to synthetic early on my Subaru (~10k miles) and it leaks more oil when old than our other car with the same engine, slightly less mileage, and dino oil. However, I got better gas mileage (esp. when the engine is cold) and it's not enough leaking to be concerned with. I do change filters twice between oil/filter changes.

10-18-02, 12:17 PM
I switched all of my cars over to Mobil 1 5w30, 90 Vette (has 125,000 miles), two 73 Vettes (one 50K miles, the other unkn but over 130K), '00 truck, and my lawn mower.

Don't be worried about changing, go ahead, your engine will thank you.


10-18-02, 12:46 PM
The common thread that most of these posts are alluding to is the propensity to develop oil leaks after the switch to synthetics. The main difference between synthetics and dino oil is that the in the former oil, molecules are all a consistent size (and very small), thus reducing engine wear. The latter is an amalgamation of molecular sizes. When one switches to sythetics in a higher mileage car after use of dino, any small gaps in the seals that normally would not allow the dino oil to seep through due to larger molecular size, may now allow the smaller, more uniform sized sythetic molecules to pass. Thus, you may notice oil leaks when you had none before. This is the only downside. From all info that I have seen, reduced engine wear is the main benefit of sythetics as all oil wears out in a similar manner with similar driving conditions in the same engine--it does not offer any prolonged oil life. Should you notice any leaks, simply switch back to dino-based oil. I would give it a try.

The Car Whisperer
10-18-02, 05:29 PM
I tried synthetics in my older cars including my Vette. Too many oil leaks for me. I switched back to regular oil. I have had lots of cars, both new and old, always changed my oil and filter every 3000 miles and have never had an oil related problem with any of my cars.

10-19-02, 07:18 AM

No longer oil life with syn. oil? Can you name your sources, I'd like to read that. I wouldn't
make the change if I still had to do oil and filter every 3 k mi.

I'm not planning to keep the firebird too long; Neon is another story. Might be worth it to
protect the engine a little better.

--Maybe small molecular size explains why my vette leaks a little oil, huh?

10-20-02, 03:52 PM
My sources are just the general data reported from various places such as Motor Trend and Road & Track. Especially the former as their "Tech Tidbits" and "Technical Correspondence" have discussed this subject a few times. Unless someone out there has seen, heard, or read otherwise, all data point to decreased wear as the main benefit for syn oils. For my money and the expensive engine in my car, that is enough for me to shell out the extra bucks for the syn oil.

I would suggest you check out this page (http://www.prod.mobil1.com/index.jsp) from Mobil regarding their suggested use and benefits of their syn oil. Now I am sure that their lawyers had some say in this, but basically, even Mobil recommeds that you keep to the cars oil change schedule. As most manufacturers don't specify different change schemes for syn vs. dino oil, then it can be read that no extra life is inferred with syn oils.

One must keep in mind that the main reason that oil is changed is because of what is pulls out of the engine (e.g. water, contaminants from incomplete combustion, wear particles, etc.). Hence, you should still change it just as often.

10-20-02, 09:23 PM
Kfehling, actually the filter will control water and contaminants. The reason you change dino oil is because the additive package breaks down and the oil no longer protects to the temperature it was designed to. Synthetic oils don't use anywhere near the same amount of additives and so they don't break down as quickly (esp. at high temps) and so they will protect for longer between changes. Just keep changing the filter...

Consider this: for most cars today, under normal driving conditions with normal oil, recommended change interval is 7500 miles! Granted, a lot of us don't drive under 'normal' conditions, but if the manufacturer thinks dino oil can last that long, then certainly synthetic will. I can provide scans from owners' manuals, btw, to support the 7500-mile interval.

Not having an engine that took Mobil-1 from the factory, can someone look up what their owner's manual says the change interval should be on an LT-1 Vette?


LarryK 87
10-21-02, 12:39 PM
well actually some manuf. do specify differant intervals provided you run a synthic oil, Porsche, and Caddy's just to name 2 ( 7500 mile interval ) Mobil 1 still recommends 3000 with their super-syn oil, and Amsoil anywhere from 7500 - 25,000. The other statements ie: small oil leaks after converting also has some merit, BUT if the synthetic had been stuck with in all likely hood the oil leak might have disappeared. One of the many advantages of todays synthetics is their abaility to clean the engine, and this may sometimes result is small leaks, as the seals ( and engine )become cleaned, and reconditioned, the leak is generally re-sealed ( assuming no carbon etc buildup was simply blocking an existing leak).

U.S. is the only primary place with a 3000 mile oil change interval, the same oil's and vehicles sold here, has a 6000 mile interval in europe.

Any good synthetic will actually save you money in reduced oil changes AmsOil, RedLine, and Royal Purple. Of course i am a bit biased towards AmsOil !!!
But i do run it in my '87', with 92K and my 97 Intrepid with 147K, no oil leaks in either vehicle ( and the Intrepid was changed over at 90K, ran dino oil from the day i bought it with 21K on it)
Of course as mentioned in earler posts The filter is of major concern, but the oil plays an important roll as well, i would not attempt to take ANY dino oil to the 10K to 15K mark under any circumstance, but i would with a synthetic ( also included in the Dino catagory would be the Dino/synthetic blends ie castrol etc )


10-21-02, 06:31 PM
I do not run synthetic in my 94 Camry V6; I just don't feel justified in spending the money on that car like that. I bought it with 74,000 miles and have used regular dino oil until today with it's 130,000+ miles. Haven't had a problem with anything yet. Toyota actually allows 7,500 miles between oil changes under "normal driving conditions", whatever that means! LOL.

Hib Halverson
10-21-02, 11:39 PM
Originally posted by sothpaw
Is there any reason I can't change my other cars (1995 fire bird and wife's 2000
Neon) to syn oil? It would mean less oil changes, might save a few bucks. Would
the seals still work? I would hope/think so.

In the Firebird and the Neon, the use of synthetic oil has no issues.

Best is Red Line 10W30. Good is Mobil 1 10W30. With Red Line you can go to some pretty amazing extended drain intervals. With Mobil you can go a little bit for extended drain interval but not as much.

I've used Red Line 10W30 Engine Oil in all my late model vehicles including the 95 Corvette. With the 01 Camaro and the 99 Blazer that get driven a lot, I change the oil every 16,000-18,000 miles but I change the filter every 3000-4000 miles. I back this up with spectographic oil analysis which shows these intervals to be acceptable. I've been doing that for about the last 10 years.

The cars that don't get driven a lot, I change the oil every two years or 10,000 miles, which ever comes first. I change filters every 4000 miles or so.

With my two older cars (65 and 71) I use Red Line SAE30 Race Oil. They get changed about every two years.

Do not use Red Line's Race Oils in engines with catylitic convertors.

10-22-02, 09:16 AM
A while back I accidentally changed to Mobil 1 15w- 50 on my 7-series BMW with 173,000 miles on it.

Don't even ask how you do that "accidentally." You had to be there.

Anyway, the only thing I've noticed since is a slight reduction in oil consumption, not an increase, and the several minor leaks haven't gotten any worse. It went from using a quart every 1000 miles to now using a quart about every 1300 - 1400 miles.

I've changed everything else I have over to Mobil 1, including a 24-year-old Bronco, the '89 Corvette, an '86 Suzuki, and an '01 Explorer 4.0L SOHC.

No problems with any of them; slightly improved hot idle oil pressure in the L98. I've extended the oil change intervals slightly, up to what the manufacturer "recommends" instead of the 2000 mile intervals I used with Castrol 15w - 50.

I surely would not use the "sewing machine oil" grades of synthetics, the 5 weight and "0" weight oils, in any kind of high-preformance machine, though. Those are intended solely for milking the last little bit of fuel economy out of an engine at any cost, and when the cost is a rebuild, it's too high!


10-22-02, 11:03 AM
Your Bimmer oil consumption probably got less because you switched to 15w base stock oil (I'm assuming your BMW uses 10w30 normally like my co-workers' do).

Now, I do have to disagree with your 5 and 0 wt comments. A multiviscosity oil will protect as if it were the higher number, but flow when cold as if it were the lower number. So a 5w30 protects as well as a 10w30... PROVIDED that the additive package that makes it multiviscous is intact. And that's where synthetic shows its advantage over dino. There are MUCH less additives needed to make a synthetic multiviscous and the package does not break down anywhere near as quickly.

Check this web page. The author is reasonably unbiased from a marketing perspective and is a racer.


10-22-02, 01:43 PM
I'm gonna move this to General Tech seeing as how it is not directly associated with the C4 model Corvette, but any car. ;)