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Conventional to Synthetic switch


Hawkeye

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I have a 93 4.0 with just over 185,000 miles. Don't know where I heard it but heard years ago that it's not a good idea to switch from conventional oil to synthetic because of seals. I have been using a synthetic blend high mileage for quite some time. Is it true that there could be a problem with seals when switching oil?
 


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rusty ol ranger

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At 185,000 i wouldnt, youll begin burning/leaking oil, or worsen the condition if its already doing it
 

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1st, the Motorcraft synthetic blend is an excellent oil and given the part of the world you live in, there is only a small advantage to a full synthetic.

2nd, if you use a full synthetic high mileage oil, you should not expect to have seal issues. The original synthetics like Mobil1 did not have enough seal conditioners for old seals so they would often start leaking with the full syn oil in an old vehicle. So, they responded by creating a high mileage version of the full syn oil, and I have not heard of leak issues after switching to the high mileage full synthetic oil. For example, the 09 Ranger I recently acquired has been switched to Mobil1 high mileage 5W30 and it has not developed any leaks.
 

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fastpakr

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Switch any time you like.
 

rusty ol ranger

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Switch any time you like.
Google it. What i said is pretty easy to find across all kinds of forums. Ive even had it happen myself. Its even been covered here years ago. Has something to do with thinner molecules or better flow/cleaning properties.
 

rusty ol ranger

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Screenshot_20201009-084958_Samsung Internet.jpg


Take that as you will..."finding an existing leak"....ok well if its not leaking that bad with dino oil then you switch and it gets worse...then maybe the synthetic didnt cause it but it sure as hell aggravated it.

Screenshot_20201009-085329_Samsung Internet.jpg


So do what you want OP, but i wouldnt. Rather the synthetic causes the leaks/burning could be debated all day...but it will uncover symptoms that wernt there with the dino oil.

I do run a synthetic HIGH MILEAGE BLEND in my 460 and 2.9...both leak with dino oil anyways and the blend hasnt sped it up much. But thats a blend...and neither have 185k.
 

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Rusty, feel free to google 'switching between synthetic and conventional'.

In the mean time, here's an article to help you out:

Synthetic oils causing leaks hasn't been an issue since the 70's. But that's probably why you weren't aware of the change.
 

rusty ol ranger

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Like many myths, this one is based in fact. Early synthetics were made of esters, which were harder on seals, especially those made of neoprene. However, synthetic oils have come a long way since the early 1970s, and they're much nicer to delicate seals. But while synthetic oil won't create a leak, it will find one. Its streamlined molecular structure has no mercy for cracked or otherwise marginal seals. The oil and its additives may even clean deposits from the engine, which is good -- unless those deposits are acting like spackle on questionable seals.
Right from your article. So answer this...if im running regular oil and my rear mains not leaking (regardless of why), i change it with some fancy synthetic, then it starts dripping...isnt that synthetic causing the leak? Thats exactly why i wouldnt change to full synthetic on a high mileage engine.

Sure it may "clean" stuff and thats what making it leak...but a leak is a leak.

Its also not hard to envision the "better flowing synthetic" slipping past valve guides and rings that were perfectly finr sealing out dino oil, and causing oil burning.

So yes.....whatever pretty picture the oil companies wanna paint to screw you out of 15 bucks for a qt of oil is fine...but if its not losing oil with dino....and then it starts when i switch to synthetic...then yes. The synthetic started it.
 

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Yes - a leak is a leak.

If a leak was already there, it will be found. This isn't complicated.
 

rusty ol ranger

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Yes - a leak is a leak.

If a leak was already there, it will be found. This isn't complicated.
If theres no oil coming out of it its not a leak is it?

So yes...synthetic can cause a leak.
 

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Hawkeye, about how long have you been using the semi synthetic oil? If it has been a few years, I would say that any leak that develops is probably just from age, not necessarily from synthetic oil.

Honestly, I would just continue to use what you are using. If you put a good deal of mileage on the truck, perhaps consider shortening your oil change interval.

I know myself that I usually change my oil every 6 months or 6000 miles, whatever comes first. Usually every April and October.
 

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I don't have a dog in this fight....

I see the Motorcraft synthetic blend on sale for less then $20 a jug... I would just stay right there if it were me. You can also buy a Motorcraft filter for less then $4. That will keep your engine happy.
 

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I don't have a dog in this fight....

I see the Motorcraft synthetic blend on sale for less then $20 a jug... I would just stay right there if it were me. You can also buy a Motorcraft filter for less then $4. That will keep your engine happy.
:agree:
 

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There's not nearly as much difference between synthetic oils, and the 'dinosaur' oils as you might think. Synthetic is still just oil - it's that all of the oil molecules are closer to the same size. That is accomplished by distilling the oil after going through the refinery process (cracking). Advances in refining brought conventional oils closer to synthetic in the late 90s and I think there were in fact some lawsuits flying around, as memory serves, between the "original" synthetic producer(s) and some of the newer stuff, but the courts upheld oil companies claiming "synthetic" no matter how they got it. Anyway......

Oil isn't just oil. There's "stuff" in it to keep the integrity of the seals good, among other things. Remember Valvoline coming out with the "Max-Life" oil? They just added a lot more of whatever is good for the seals to regular oil (at the time, they probably have a synthetic blend too). That stuff works. I made the mistake of putting Mobil 1 in my 68 Bronco back in the 90s, and it proceeded to leak like a screen door on a submarine..... oil EVERYWHERE! Changed out to Max-Life and the only things that leaked after that were the steering box and front pinion seal, neither of which of course had engine oil.

Anyway, when my 97 started leaking at the rear main seal (250,000+ miles) I started dumping 4 quarts of the usual Mobil 1, and a quart of Max life in it, at each change. That helped, a little. But of course the RMS needed replacing and that got done when the transmission was rebuilt.

You can mix different brands and even weights. Weights on oil are just an average of the viscosity of everything that's in the bottle. Big molecules, small molecules, etc. Mix 0-20 and 10-40 half and half, and you end up with 5-30 or thereabouts. Even with "full" synthetic, there is some "regular" oil mixed in, to help keep the additives in suspension. The reason your oil comes out thicker when you change it, than when you put it in, is that the lighter molecules in the mix tended to burn out before the heavier molecules. Unless you have a carb running way rich in which case the oil has a lot of gasoline in it......

Bottom line, oil is oil, and people who think that synthetic is some magic creation are flat out wrong. It's just a more consistent bottle of the same size oil molecules - plus whatever additives the manufacturer sees fit to put in.
 


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