Synthetic motor oil vs conventional

[Cragelarson83]

So i keep trying to search 4 threads that are up-to-date like from at least 2015. So what my question is is if synthetic motor oil will actually give you better gas mileage and better performance. I know that there's been discussion on synthetic being for lazy people that don't care about their mileage intervals. I'm a person that is going to change my oil every 3000 Miles regardless and since synthetic motor oils aren't much more than conventional motor oils anymore my question is what are people's experience as far as having a high mileage motor with at least a hundred seventy-five thousand on it and switching to synthetic motor oil. Did it cause your engine to have more engine oil leaks because of the detergents and everything in the motor oil did it give you better gas mileage did you see any bad things happen as far as engine performance or knocking and Ticking when switching to synthetic motor oil. I don't know if this thread has talked about. If so I can't find it searching since the search isn't working and I have to use Google. I have tons of questions that I wanted to ask but I don't want people to say oh there's tons of threads about it so use your search. I have searched and read pages and pages and pages of Google threads from this forum in a lot of times I don't get the answers. So I don't want people talking down on my post because they say the threads or any here and I need to search when I actually try so if my future posts or something that has been talked about then just direct me to that post so I can read it because I'm failing in finding the information that I want. Thank you so much this form is awesome and I just have questions that I would like answers to.

[deevergote]

The only reason to use synthetic in an engine that does not require it is to extend the oil change interval. 3000 miles is overkill for any oil, unless you're driving hard or in extreme conditions. 5000-7500 should be fine with a quality conventional oil. 10,000+ for a quality synthetic. Synthetics don't cause leaks. They merely find them. They generally run thinner than conventional oil, so if you have a leak the synthetic oil will flow through it more freely.
Horsepower and mpg gains from synthetic oil, if there really are any, would be minimal. Undetectable, even.

[F22Chris]

Deev, I just saw a commercial for annual interval oil from Mobile1. Its good for 20k miles according to them.

[Fleetw00d]

They generally run thinner than conventional oil, so if you have a leak the synthetic oil will flow through it more freely.
Horsepower and mpg gains from synthetic oil, if there really are any, would be minimal. Undetectable, even.

Synthetics are engineered to "run thinner" at low temperatures; that is the viscosity doesn't increase as quickly with reducing temperatures as much as conventional oil so it flows more easily at low temperatures allowing oil to be pumped to the engine after a cold start to reduce the time the engine runs "dry", reducing wear. They are also engineered not to thin as quickly at higher temperatures so that they provide better fluid film thickness, again to reduce wear. Also, because of the way they are engineered, they resist breakdown and sludging better than conventional motor oil which allows for the longer change intervals.

Here is just one article (from AMSoil) I found that attempts to explain the differences: http://www.upmpg.com/tech_articles/motoroil_viscosity/

[hiptech]

What a coincidence I've been contemplating switching the 93SE over to synthetic for sometime. Not because of any of usual discussions concerning mileage, change intervals, etc. but rather I because I buy the Mobil 1 5W-30 on sale @ Costco for the other 2 cars and it seems silly to stock a 2nd oil type.

But I keep talking to my indy Honda mechanic about it and his opinion about fluid changes is interesting if nothing else. He believes it's never good practice to make a major switch on any fluid on a car as old the 93SE since it's still has all the original engine, tranny, etc. In fact when we discuss changing brake fluid his advice is to use a turkey baster and draw out fluid from the to reservoir and only replace that much. If you do this over the course of a week at a time you will eventually replace it without causing any leaks... strange I know. But I do trust him and respect his experience and knowledge.

Since I've only used Castrol GTX 5W-30 since day one I'm hesitant to risk changing it but part of me wants to try out his gradual approach method but not sure it's a good idea to mix 2 brands and types of oils until I can achieve a slow changeover?

Anyway I caught this YT video from a podcast called "Savagegeese" whose reviews are very frank (if you catch my drift) and feel he has a valid point concerning oils in general. Personally I think he's onto something...

https://www.youtube.com/watch?v=ASAdkJydBFU

[deevergote]

There is absolutely no risk in mixing oils. Hell, you could use half conventional and half synthetic if you want. No risk at all.

Brake fluid is another story. You can't mix certain types of brake fluid.

[wagon-r]

Brake fluid is another story. You can't mix certain types of brake fluid.

Which is one reason to always drain the brake fluid and refill.

Frankly, if it were me, I'd find a different mechanic.

[deevergote]

Agreed. The conventional/synthetic thing is an old wives' tale. A mechanic that buys into that is probably not terribly knowledgeable.

As for brake fluid, there should never be a reason to mix anyway. Replace dot3 with dot3.

[Fleetw00d]

I don't think the turkey baster method is going to change enough fluid, particularly at the calipers and wheel cylinders, because there really isn't too much mixing like engine oil, transmission fluid, or power steering fluid. It is easy enough to bleed at each wheel to flush clean fluid through the system (at least back to the wheels). The problem is that brake fluid absorbs water which makes it tend to boil at a lower temperature creating vapor bubbles that interfere with proper application of the brakes; the high temperatures occur under heavy braking at the calipers and wheel cylinders, not at the master cylinder.

[F22Chris]

@hiptech
Maybe if you use a baster, and then bleed. That sounds right. Do it in 20 minutes versus the span of a week. There's no reason a leak would develop from bleeding unless you break something.
Synthetic oils are more stable at high temperatures, more fluid at cold temperatures, have friction modifiers, and have better cleaning abilities. That's probably why that tale started.. "I changed to synthetic, and now my rear main seal leaks!" - probably due to the synthetic oil taking the crap off the crank built up for 20 years.

[deevergote]

For brake fluid, you don't necessarily have to remove ALL of the old fluid. You can mix old and new. Just don't mix types. Drain the master cylinder, refill with fresh fluid, bleed at all 4 corners until it's clear, making sure the master cylinder reservoir doesn't go dry. Once all 4 corners are clear, fill the master cylinder to the fill line and you're done.
Replace your brake fluid with the same thing that came out... which should be DOT 3. You can use DOT 4 or a 3/4 hybrid. DO NOT, however, attempt to use DOT 5, as that will cause a system failure. It does not mix with 3 or 4.

[F22Chris]

Difference in 3 and 4 is boiling point. 5 is silicone based.

[deevergote]

Right.
And for 90% of CB7s (those that don't see heavy track duty, do heavy towing, or drive on extremely steep roads), DOT 3 does the job.

[Cragelarson83]

Thank you for clearing this up for me. Years ago i was a assistant manager at a quick change oil shop. I was always told that synthetic would make the motor feel smoother and restore a little lost hp from sludge and buildup. I ran Valvoline full synthetic high mileage this oil change. I'll probably switch it back to conventional. I do have minor oil leaks in the common areas such as valve cover, tube seals and distributor o-ring. I have all the new gaskets that I'm waiting to put in when i do the a6 cam, intake manifold, black box....etc. I'm mainly trying to get the best gas mileage i can. I'm gonna search the forum for answers about what to do before i start a new thread. I'm sorry if stuff i ask has already been answered in the past. I promise i try to search before asking anything. This forum is freaking awesome. Thanks guys. I'll be posting updated pics of my 93lx soon. It's came a long way.

[deevergote]

No problem! We don't mind answering repeat questions, as long as it's clear that some effort has been made. It's hard to sift through 14 years of information, and many times the information you find doesn't fully answer your questions. As long as advice is appreciated, and those giving it aren't abused (as in, relied upon with no effort to search first) pretty much anyone here is more than happy to help.