Mobil 1 says 5000 miles, but I wouldn't go over 3000 with any oil. And I am leary of 25,000 mile oil changes only because if something "happens" you got "whatever" in there for 22,000 extra miles... ya know, water contamination or whatever. I use Mobil 1 with a Motorcraft FL-820s and have no problems, and don't mind spending the $25 every 3 months or 3,000 miles....it's better than $4,500 in one big lump sum for a motor. Just out of curiosity, why are you going with an AC/Delco filter??

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Okay, after jioning a few days ago, and reading all the post about synthetics, I have this sudden urge that makes me think that I have to go synthetic...With 88,000 on my engine, I worry about it causing leaks, as I have read some post here that make it sound as if synthetic my in fact cause leakage when you switch over.
Is this true?
If I do switch,(which I think I am) I am going to do a flush before addign the new synthetic and filter.
Will the flush cause leakage, or cause it to burn oil?
Last question, When I change over to synthetic,(99% sure I will use Mobil one, with a AC Delco UG Filter) at what intervals should I change it? I am used to changing at 2500 miles (both oil and filter)

Thanks for all tips!

 

I had a leak on my last truck with Amsoil. Same truck didn't leak with Mobil 1. The leak wouldn't start until the oil had about 3000 miles on it, but some of this Amsoil is supposed to last 20,000+ miles.

I agree with Sycoholic. I don't want ANY oil in my engine for 20,000 miles! You have to change the filter anyway.

As a note, looking through my owners guide on my '95 it states only to use API certified oils (Amsoil is not). It also states that if synthetics are used, you must maintain regular change intervals.

Personally I never got any increased mileage or performance with synthetics. I don't have a problem with them and they do lubricate better IMO, but with so many engines with LOTS of miles using nothing but conventional, I don't see that it really helps much.

 

I used to test motor and trans. fluids for an independent research co. a few years back, the bottom line is this: if your changing your oil every 3k, do not waste your money on synthetics. They were designed, in part, for extended drain intervals. The very small gains you will see in mileage and cooler operating temps do not justify the added expense unless you are going to or over a 6k drain interval. Yes, they are more than safe up to about 9k, with no filter change in (normal) driving. In reference to causing leaks, I have seen trans. fluid attack seals way more often than crankcase oils. Hope this helps.