Going between Conventional and Part Synthetic Oils

[porschpow]

I noticed that I put in Part Synthetic Oil (Castrol GTX high mileage) 10W 40.

NOW I DON'T WANT THIS TO BE ANOTHER OIL THREAD, but im a little concerned.

I didn't mean to swtich, didn't read the label. Is it ok to switch back to Conventional (like regular oil Castrol GTX), or should I just stick with what I have now???

[91waggin]

Won't hurt anything. I wouldn't change it early now that you've put it in there, but you can change back at the next oil change without any harm.

[sly]

+1 just run with it. switch back at the next change.

[mobydick]

+2. You'll be fine. The only time it would be a concern, I've heard, is when you run a high mileage oil like Max Life. Once you start on it you need to keep using it. Or so I've been told.

[porschpow]

thats what this castrol is, its Castrol GTX high mileage

Should I stick with Synthetic, or just continue on with conventional?

[mobydick]

thats what this castrol is, its Castrol GTX high mileage

Should I stick with Synthetic, or just continue on with conventional?

Honestly I couldn't tell you one way or another. I run mobil 1 high mileage 10w30 in mine and it runs great. I would check out www.bobistheoilguy.com for more info in it. Those guys are nuts about oil over there.

[kishy]

As a general rule, as long as you're using oil that meets the specifications otherwise, synthetic/conventional or any mix of them is not a problem. I had concerns before running synthetic that more had to do with understanding the best way to cut down on the cold engine chatter you get on a cool morning...in my case synthetic cured that chatter. I switched from full conventional 10W30 to synthetic blend high mileage 10W30 to synthetic 10W30 and now I'm back on the blend high mileage. I intend to continue switching around too based on cost (and using the full synthetic in the winter), since this is one of those things where the exact product you use isn't what matters as much as how often you change it.

Where there is a potential issue is high mileage oils that contain "seal conditioners" or "seal swellers" which may result in unpredictable seal and gasket life if you switch to a non-high mileage oil afterwards...seconding the suggestion for BiTOG without a doubt, there's a lot of good reading to be done there.

[marquisman]

Going from a high mileage conventional to a synthetic, probably will cause external oil leaks. Friend of mine did this to his chev 305. Its one oily bitch. Even the valve seals leak lol.

[kodiak]

I also suggest that you check out bob is the oil guy website and forum none of us here are tribologists (as far as I know) and really cannot give you the correct answer. Knowledge of and experience with a failure does not guarantee knowledge of the cause of the failure.

Sent from my '85 Lincolin Town Car

[91waggin]

Scott sez: "Oil is oil. Keep it clean, keep it full."

I like synthetics because I've seen the kind of shape an engine that's had synthetic its whole life looks at 300k miles and it's very impressive. But that's just me. Plenty of people have gotten 300k+ miles out of various engines with dinosaur oil.

[marquisman]

The switching over is where people have concerns. If you are starting with a fresh engine, now would be the time to use synthetic. Its usually just best to stick with one thing and keep it regularly changed.

[gadget73]

If you switch over and it starts leaking, that seal needed replacing anyway. My Mark VII was switched at 180k. I replaced the original cork valve cover gaskets at 225k. The original intake gasket was done around 240k. Each were replaced when it got up to 1 quart every 3000 miles of loss. Its at 245k now and the only leak it has is the crappy oil drain plug gasket that leaks just enough to piss me off. I run 5w30 in it too, so its not like its living on road oil to keep it plugged shut.

[porschpow]

I will talk to the oil guy and see what he says, but thanks for the input

I was always taught if you go synthetic, don't go back, cause that is when the problems start

[GrandestMarquis]

I've done a lot of reading on this in the past. Bottom line, you should be fine to run it then switch back. From everything I've read the whole "switching causes seal leaks" is no longer really an issue. It was when full synthetics first came out a looonnnnggg time ago. Since then the specs between the two have become compareable. I have switched back and forth, mixed synthetic and non if I needed to top something off, and I even run marvels in older cars the last 500 miles before draining. Never had oil cause a leak. Like said above, if it leaks it was already bad.

FYI, I run Mobil 1 20w50 in my merc because it has a higher zinc level and is better for flat tappet motors. Oil manufacturers actually removed zinc or at least cut back because of roller motors having less friction. So for anyone running older flat tappet motors, pick something properly formulated for longevity.

[cld783]

i've switched back and forth and even topped off with synthetics a few times. i cant tell any difference and never had a problem. i think its probably best to stick with conventional 10w30 and same brand if possible.