synthetic vs regular oil

[wowie]

The 98 Legacy I recently bought is due for an oil change. It has 136,000 miles. Anybody have an opinion on whether to stick with the Castrol I've always used in my 90 Legacy or to go with synthetic? I've heard something like Mobil One synthetic can get you slightly better mpg, true or false? Any other reasons for switching or staying?

[Setright]

Mobil 1 will protect better and give a slight increase in economy and power. The debate on whether it's worth it or not will never finish.

 

I run Mobil 1.

 

You might want to get the "High Mileage" Mobil 1 - not in the economy sense, but for engines with lots of miles. This will guard against the oil leaks that can come with switching to a synthetic.

[86subaru]

you can go farther between oil changes, i use amsoil or royale purple , i have noticed alittle more seeping of oil around the cam -covers ,than before but after a few miles it has stopped , ihave 191,000mi on my 88 d/r 5sp wagon, i have only added 1.5 qt in 5500mi ,as far as better mpg i did not get any better

[Setright]

Yeah, Mobil 1 will last 6-7k miles easily.

[1 Lucky Texan]

Yeah, Mobil 1 will last 6-7k miles easily.

 

Yep. I try to keep to a 5-6K schedule, but I know i have some 'overhead' with Mobil 1. Certainly plenty of folks have gotten great service out of 'dino' oil and modern oils will last much longer, in modern engines, than ever before. I am just in a position where I can afford the xtra protection.

 

Also, do not be shocked by how much darker synthetic appears at the drain intervals. It isn't due to the extended time as much as synthetic's ability to keep 'varnish' in suspension (solution?) better than refined oil. Otherwise it gets left behind on internal surfaces.

[charm]

I saw a commercial for Mobil 1 extended (or something like that) says it has a longer change interval. According to the commercial it was nearly what Amsoil claims to get. Anybody have any info on this stuff?

[1 Lucky Texan]

I saw a commercial for Mobil 1 extended (or something like that) says it has a longer change interval. According to the commercial it was nearly what Amsoil claims to get. Anybody have any info on this stuff?

 

I would tend to believe it, I just choose to be cautious and stick close to the manual's recommendation. I do not believe 'average' drivers need to change dino oil every 3K either. But I would never tell someone they were wrong for doing it.

 

Check www.bobistheoilguy.com for some interesting discussions based mostly on UOA (used oil analysis). That is probably the best way to determine the longest acceptable drain interval for any oil. It has a lot to do with acid buffering ability, viscosity changes, fuel contamination, etc. And will be different for different cars, mileages, driving conditions, etc.

[cookie]

I don't really see any difference between it and the Mobil 1 I run in my BMW. I plan to run it another few thousand miles and get Blackstone Labs to analyse it to give me some idea waht is going on with both the oil and my typical 2.5 piston slap.

[NoahDL88]

Subaru builds and tests their engines with Castrol, logic would dictate that for maximum life and dependability Castrol would be your best bet.

[nipper]

It really depends upon what makes you feel good. In subarus I have never used synthetic oil and always had them last over 200K. Other people have used synthetic oil and got the same thing. The oil may last 6000 miles, but if the owners manual says a filter change at "x" miles, you still need to do that filter change at "x" miles.

 

 

nipper

[friendly_jacek]

Subaru builds and tests their engines with Castrol, logic would dictate that for maximum life and dependability Castrol would be your best bet.

 

The only problem with that theory is that the "factory tested" Castrol SH has little in common with the SM-rated Castrol now.

 

But seriously, the margin between the current regular and synth oils is smaller than ever. Today's regular oil would be called synth blend or semi-synth just a few years ago.

 

On the other hand, one should distinguish between heavy duty engine oils (API: SL/CI-4+), performance engine oils with high HTHS (ACEA: A3, VW 505.00 and similar), and the light duty oils optimized either for gas saving (ACEA: A1, API: SM/GF-4) or long life (ACEA: A5).

[Setright]

Yes, yes, but Castrol buys their synthetic basestocks from....Mobil !

[mikkl]

The 98 Legacy I recently bought is due for an oil change. It has 136,000 miles. Anybody have an opinion on whether to stick with the Castrol I've always used in my 90 Legacy or to go with synthetic? I've heard something like Mobil One synthetic can get you slightly better mpg, true or false? Any other reasons for switching or staying?

 

I would stay with what has been used in the new car. After all these miles on standard oil, a switch to synthetic oil may cause your oil consumption to increase. Rubber seals swell in the presence of oil and after many years will begin to loose the ability to change size, permanently deforming and relying on the swell for sealing. Changing oils, particularly to synthetic, can signficantly reduce the swell, permitting leaks and additional consumption past the valve seals.

 

I had a car with 80K miles that I switched to a synthetic oil. My consumption went from one quart in 2000 miles to 4 quarts in 400. Switching back to conventional oils returned the engine to the earlier level of oil consumption.

 

In my experience, a switch to synthetic oils should be made when the engine is new.

 

By the way, I've also seen changes in oil consumption by changing brands of standard oils. Once the seals have accomodated to a given base package of additives (a specific manufacturer), they will work best if they stay with the same oil--at least in my experience.

 

mikkl

[edrach]

I would agree with most of what you say except don't change to synthetic on a new engine until 10K to 20K miles. Give the rings a better chance to seat with the dino oil; starting with synthetic might never allow the rings to seat properly.

I would stay with what has been used in the new car. After all these miles on standard oil, a switch to synthetic oil may cause your oil consumption to increase. Rubber seals swell in the presence of oil and after many years will begin to loose the ability to change size, permanently deforming and relying on the swell for sealing. Changing oils, particularly to synthetic, can signficantly reduce the swell, permitting leaks and additional consumption past the valve seals.

 

I had a car with 80K miles that I switched to a synthetic oil. My consumption went from one quart in 2000 miles to 4 quarts in 400. Switching back to conventional oils returned the engine to the earlier level of oil consumption.

 

In my experience, a switch to synthetic oils should be made when the engine is new.

 

By the way, I've also seen changes in oil consumption by changing brands of standard oils. Once the seals have accomodated to a given base package of additives (a specific manufacturer), they will work best if they stay with the same oil--at least in my experience.

 

mikkl

[swc7916]

I do not believe 'average' drivers need to change dino oil every 3K either. But I would never tell someone they were wrong for doing it.

 

It may not be necessary, but I change my oil and filter every 3k because my cars cost me a lot of money and additional cost of frequent oil changes is pretty cheap insurance. I figure that all oils are good and if I'm going to run it for only 3k miles and then throw it away, why not just get whatever's on sale?

[klrskir]

I run Mobil1...You can hear "the difference" best during a cold start.

[blitz]

As money gets tighter for average working stiffs (present company included), the semi-synths are going to be the preferred choice, not because of a perception that they offer the best value, but because they actually offer the least wear (except in arctic starting).

[bulwnkl]

The 98 Legacy I recently bought is due for an oil change. It has 136,000 miles. Anybody have an opinion on whether to stick with the Castrol I've always used in my 90 Legacy or to go with synthetic? I've heard something like Mobil One synthetic can get you slightly better mpg, true or false? Any other reasons for switching or staying?

 

I have experienced zero increase in mileage in any vehicle from Mobil-1 synthetic (or any other synthetic) since my 1990 Honda CRX. Current SM/GF-4 oils (at least in 5W20, 5W30, and 10W30) are friction-modified and are just as "slippery" as the M1.

 

Some have mentioned seal problems and leaks if you switch to M1 at this point. If you want to go to M1 and this concerns you, run an Auto-RX treatment first. That's your best shot to avoid any such leaks.

 

Personally, I'd stick with the dino at this point, but neither choice is "wrong."

[marty yandle]

It really depends upon what makes you feel good. In subarus I have never used synthetic oil and always had them last over 200K. Other people have used synthetic oil and got the same thing. The oil may last 6000 miles, but if the owners manual says a filter change at "x" miles, you still need to do that filter change at "x" miles.

 

 

nipper

 

My local Mobil Oil Change place has Mobile1 filter that's good for the life of the oil. Marty

[Snowman]

My local Mobil Oil Change place has Mobile1 filter that's good for the life of the oil. Marty

 

Not to be a party pooper, but did you ask them what makes it so special? Unless there is some huge difference in size or design, I would tend to believe that it's just slick marketing.

[cookie]

for heavy duty use that release additives slowly over the life of the filter, they are supposed to also have more filtering area for long life. I've never used them myself.

[nipper]

My local Mobil Oil Change place has Mobile1 filter that's good for the life of the oil. Marty

 

For the cost of what an engie goes for, I would rather change the filter at recomended intervals, then take the chance. ALso the better question is who makes the filter for them, as I doubt mobile is in the oil filter business. Some filters arent worht the powder and shot to blow them to hell, others are great.

 

nipper

[teasdam]

Autozone here carries Mobil filters (which cost something like $11 a piece) but I've never found them for my '03 outback 4-cyl. I'm still using OEM...besides my dealership is always sending me buy 2, get the 3rd free coupons.

 

(edit: Oh...I just got what you said nipper...yeah, it'd be nice to know where those Mobil 1 filters are coming from and see if you're just paying for the name.)

 

Along these lines...I also changed the diff fluid on both ends with Mobil 1 and it increased fuel economy by 2-3 mpg. It doesn't take long to get your money back on the investment at $3/gallon for gas.

[nipper]

Found this link

 

http://www.corolland.com/oil-filters.html

 

http://minimopar.knizefamily.net/oilfilterstudy.html#m1-301

 

ive read it before, its interesting, if not completly scientific. The writer says that Champion makes Mobil One filters

 

nipper

[wowie]

Thanks for all the info.

The mechanic who worked on the car before I bought it put in a semi-synth from Chevron. I don't know what was in there before but I think I'll go with 10-30 Castrol for now.