Flipping back and forth between synthetic & conventional motor oil

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Nov 5, 2006
Never given the thought of switching to synthetic...... much though. Just couldn’t see the expense was worth the money if one made oil changes at the manufacturers suggested intervals.

Well, a neighbor is moving and dropped off several cases of 1/2 full, 5 qt bottles of mobil1 synthetic. After consolidation, I got about 3 gallons of syn.

I understand you are not supposed to mix syn with convent at the same time. And when most people switch to syn, they switch for the life of the vehicle.

Are there any unintended consequences for running syn for a few oil changes, and once the free stuff is used up, go back to conventional ?

Would your answer be any different if I had done an LS swap, and was running an aluminum block Chevy 5.3
No problem switching up or mixing. My concern is that you were given half empty bottles. What’s really in the bottle? Who has that many half full quart bottles of oil especially high dollar oil anyway? I wouldn’t use it.
Mobil 1 has a 5 year shelf life. I actually bought a old gallon by accident once it was the color of atf when I started pouring it in. I called mobile ones tech line. They told me not to run the engine. There is a manufacturing date on the bottle it’s hard to find. There was a fresh case and a oil filter waiting at the auto parts store to replace the oil. When I got there. Great customer service. I probably wouldn’t use it.
Mixing is fine, changing back and forth is fine. You can do your own research, but that is what I've found. I agree that changing intervals is the most important part. The issue I've found through the years with older vehicles and changing to synthetic is it will find its way through oil gaskets and seals a bit easier (oil leaks).
I've been using Valvoline Maxlife synthetic blend for the last 5 years on my truck, and just switched a couple days ago to Valvoline Maxlife full synthetic (10W-30 in both cases). I've gone through and reduced my truck's oil leaks to just the upper arch oil pan or rear main (I don't know which, and it's not worth fixing the leak, to me). My truck leaks very little oil now, compared to when I bought it 30K miles and 5 years ago. I'll post up on this thread again if I start seeing new or more leaking. If so, I might go back to the synthetic blend Maxlife. Incidentally, I really like the Maxlife oils. They are abundant and inexpensive, and get good reviews from the oil nerds on Bobistheoilguy.com. I'm no oil expert, but I've had good luck with this oil in both my FZJ80 and my 2005 Honda Odyssey (205K miles on the clock so far). I tend to keep my vehicles for 10+ years, so longevity matters to me.
No problem switching up or mixing. My concern is that you were given half empty bottles. What’s really in the bottle? Who has that many half full quart bottles of oil especially high dollar oil anyway? I wouldn’t use it.

Turns out I do..... from oil changes for my BMW's over the last few years. One takes 8 quarts and the other takes 7. I buy two of the 5 quart jugs each time and when going through the garage I found a handful of 5 quart jugs that were partially full. Now that they have been found I can get a nearly "free" oil change next time. :beer:

As to the OP's question - I'd just stick with what you have been doing and get rid of the old oil, or use it in the lawnmower, snowblower, etc...
FWIW I once had a bunch of unused unopened oil of different types/brands/weights that were ?? years old, but being a cheap bastid I didn't want to toss it, so ran it for a very short time, then drained it out, replaced the filter again, and filled up again with my usual Mobil 1 which I run for at least 8-10,000 miles or one year, whichever comes first. That was 100,000+ miles ago and the routine Blackstone engine oil analyses have come back fine since, so no apparent engine damage from my short FrankenOil experiment.

FWIW Blackstone labs has run engine oil analysis on old conventional oil (unopened but decades old), and the results came back good enough to run in an engine.

Odd however that he had so many half full bottles, but as others have said,
if the oil is much over a year old I wouldn't run it for long, maybe use it
for a quick flush/drain and fill, or in the lawnmower. Either way it probably
won't hurt anything assuming it is unused and not contaminated.

This is a question for Cary, is he still around?
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I’ll check the manufacturer date on the containers. I too was suspicious. I poured them all into an empty cheese ball container, so I could see the color. All were a little darker than conventional oil, but did not look like used oil.

There is one 5qt with an unbroken seal, I’ll pour that out and compare the color with the others.

Thanks all for your thoughts.

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