Switching to synthetic at 80,000?

[mattluttrell]

Switching causes gum or leaks? This sounds silly. I mean one rumor says it creates gunk. The other rumor says it removes gunk.

When I buy a used car I run an oil flush and immediately switch to full synthetic. I've never had an engine burn oil or even leak. (Aside from the common BMW leaks)

Read about the gunk that can clog in the heads causing valve noise. Read about the cam bearing issues. This will make you want to flush and get to a 0W or 5W synthetic ASAP.

The only crime I can see would be not cleaning your engine and running synthetic.

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[Slow5.0]

Well some cars like 0W oil like 96 Probe GT that uses HLAS for lifters and reason why there is better oil from from those tiny holes in HLAS. Other example, 94 Mustang GT with 302 and aftermarker roller rockers will make noise on summer on 90f on even brand new RR and boy good luck with 0W or 30W. It will run smooth with 50wt but you have to watch out for winter season if that oil is left in engine and 20f outside temp. Even Optima Red Top will have hard ime starting
Other example is using Rotella T6 synthetic 5w40 on semi truck diesels like Cummins ISX. It will need 1gal every 5k miles after first 10k miles on even on healthy engine
On the other hand using Rotella T5 15W40 on same Cummins ISX engine wont need any oil till 15k

 

[Wake]

Oils are better today than 30 years ago in their cleaning properties. I think that's where the problem originally started when you ran synthetic through a sludged up motor the oil leaks would appear that the sludge used to plug.

I don't think anything of switching a high mile engine to synthetic today. After pulling the top enf off a 120K mile hot running motor (80's emissions) I was a true believer in synthetic oil. Not a bit of sludge in the head pockets or lifter valley. And no oil leaks.