Mobil one on an extremely high mileage engine?

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I have searched for this, but I didn't find anything on it.

Can anything adverse happen if I started running synthetic on an engine that has 250K kilometers on it already?

I'm not sure what the car has been running previously, I'm assuming regular dino 5W30.

And if there's no bad effects, what would be the right one to run, 5W30 or should I go 0W40 ( keep in mind I'm in up north )?

Thanks in advance!

Synthetic is fine. Run it if you feel the cost is acceptable.

If you start the car in very cold weather (-20 F or lower is my mark), then I'd get 0W-40. Mobil 1 5W-30 is pretty good, but the 0W is better when it gets horribly cold.

There is a continueing debate that some full synthetics may tend to slightly shrink old seals. Those that have a high level of Group IV base stock are the only ones that might be effected. This includes Mobil 1.

I switched to full synthetic at about 190,000 miles. I had a very slight leak prior to the switch. It seems to be about the same.

When I switched, I also moved from 3,000 mile oil change intervals to 5,000 mile oil change intervals. On the 3,000 mile oil change interval, the oil is still full when changed, and even now it still show full at 3,000 miles. Using a 5,000 mile interval, I need to add about 1/2 quart at 3,500 to 4,000 miles.

It is my belief that you can switch between synthetic and dino any time. That is also what the oil companies publish. If you are concerned, you may want to try either a high milage synthetic (Valvoline Max-Life full synthetic) or try a synthetic blend instead of a full synthetic.

Thanks for the reply guys...

My only concern is developing leaks that I don't have at the moment. And that concern is especially with the 0W40 grade.

Maybe I'm better off to run 5W30 to be on the safe side?

no need on the 0 weight. I have had 5W30 mobil one in mine and it starts fine with out plugging it in (no head bolt heater) and it has seen -40+(F) below numerous times....on a very bad battary at that.

Originally posted by elraido:
no need on the 0 weight. I have had 5W30 mobil one in mine and it starts fine with out plugging it in (no head bolt heater) and it has seen -40+(F) below numerous times....on a very bad battary at that.

Ok thanks for the info.

Originally posted by elraido:
no need on the 0 weight. I have had 5W30 mobil one in mine and it starts fine with out plugging it in (no head bolt heater) and it has seen -40+(F) below numerous times....on a very bad battary at that.

Yes, there's a need for the 0 weight. The thinner oil isn't just to make it crank easier, it's to reduce wear on startup.

And what's -40+(F)?

I have to reluctantly add to that old story about switching to synthetic oil and leaks develop.

Just switched our 98 to synthetic (Wal-Mart ST 10W30 Higher mileage Vehicle Formula) at 125K miles about two months ago. Previously, had mostly dino 5W30, except the wife said she had bought synthetic a couple of times way back when she took it "in" for oil changes. I'd done almost all of the changes other than a few since we bought the car at 28K almost 5-6 years ago.

Oil pan gasket now leaks like a sieve.... This sucker isn't just seeping, it's marking its territory!

I added a bottle of the Valvoline Max-Life additive. Slowed it down a bit, but it still leaks.

Have ordered a new oil pan gasket and will replace it in a few weeks..

Steve

Aren't you happy to know you have a bad gasket, and you can get it fixed, instead of having so much sludge floating around that it plugs leaks?

Originally posted by Auto-X Fil:
Aren't you happy to know you have a bad gasket, and you can get it fixed, instead of having so much sludge floating around that it plugs leaks?

That was old thinking. Current thinking is that certain synthetic base stocks tend to shrink some seals and gaskets, especially if other things are not blended in to mitigate that factor.

I may get flamed for this, but my shadow's got 192k miles on it. I've been running regular (non-synthetic) 20W-50 in it, and it has GREATLY reduced the burning/smoking and leaking problems it was having...
that's just my experience, I'll disappear now

Originally posted by Auto-X Fil:

Originally posted by elraido:
no need on the 0 weight. I have had 5W30 mobil one in mine and it starts fine with out plugging it in (no head bolt heater) and it has seen -40+(F) below numerous times....on a very bad battary at that.

Yes, there's a need for the 0 weight. The thinner oil isn't just to make it crank easier, it's to reduce wear on startup.

And what's -40+(F)?

-40 and below (why I wrote it that way I don't know). And trust me, the 5 weight oil is good enough for extreamly cold starts. I have had a the stuff sit in its bottles over night when it is that cold and it is still EASILY poorable when I change the oil.

Originally posted by Big Jim:

Originally posted by Auto-X Fil:
Aren't you happy to know you have a bad gasket, and you can get it fixed, instead of having so much sludge floating around that it plugs leaks?

That was old thinking. Current thinking is that certain synthetic base stocks tend to shrink some seals and gaskets, especially if other things are not blended in to mitigate that factor.

Actually, Jim, the "shrinking seals" thinking is from about 1972, which I think predates the sludge theory by a good 20 years, at least. Back then, there was a real problem with shrinking seals, which was quickly remedied by the oil makers. Problem solved.

You telling us it's back? What happened? Did the guys at Mobil lose the recipe? Or did the gasket-makers change everything without telling anyone?

Originally posted by RogerB:

Originally posted by Big Jim:

Originally posted by Auto-X Fil:
Aren't you happy to know you have a bad gasket, and you can get it fixed, instead of having so much sludge floating around that it plugs leaks?

That was old thinking. Current thinking is that certain synthetic base stocks tend to shrink some seals and gaskets, especially if other things are not blended in to mitigate that factor.

Actually, Jim, the "shrinking seals" thinking is from about 1972, which I think predates the sludge theory by a good 20 years, at least. Back then, there was a real problem with shrinking seals, which was quickly remedied by the oil makers. Problem solved.

You telling us it's back? What happened? Did the guys at Mobil lose the recipe? Or did the gasket-makers change everything without telling anyone?

You (RogerB) are indeed correct, the only oils nowadays that would have trouble with shrinking seals are the extremely high-end ester only (group V) oils like Motul 300V, some ELF brands, and maybe redline. To be fair though even the deposits on seal problem should be a thing of the past soon. The current crop of SM rated dino oils are so good I doubt they would ever sludge in a 3000 mile interval. For an older contour that probably saw SJ rated group II basestock oils though, sludge on the seals is a real problem (especially if maintenance was shady) and switching to Synthetic could show the problem (kind of like ripping the scab off a scrape or cut).

Wal-mart brand synthetic motor oil....