2006 Yukon 5.3 mobile super oil . 174,000 miles

[Woodblocker55]

I was wondering after getting ahold of previous owner. He used mobile super high mileage 5 -30
All the time . It burns a quart to 5000 miles . So I'm going use same thing . What's with rumor about if you switch to synthetic possibly the seals will leak.
Is it true ? junk yard guy said it was he said he has 3 5.3 L motors where owners stop using them because all seals started leaking after 10,000 miles on synthetic oil ..we know junk yard rumors can be just that .

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[Sam Harris]

I was wondering after getting ahold of previous owner. He used mobile super high mileage 5 -30
All the time . It burns a quart to 5000 miles . So I'm going use same thing . What's with rumor about if you switch to synthetic possibly the seals will leak.
Is it true ? junk yard guy said it was he said he has 3 5.3 L motors where owners stop using them because all seals started leaking after 10,000 miles on synthetic oil ..we know junk yard rumors can be just that .

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I don’t believe the high mileage oils really do anything. I do believe, however that going from a 5W 30 to a 10w 30 will improve your oil burning, presuming that’s where it’s going. Do you have a catch can installed ?

 

[OR VietVet]

In all the years I was in shops I heard that tale many times about switching to synthetic and then leaks popped up. I have to say that I never have seen that happen and I switched to synthetic oil on my 2002 about 4 years ago and never saw the problem on my own vehicle. IMO, if it was true, there would be a logical and mechanical reason to support that theory and it would be out there instead of the tales we all hear. There has been way enough time go by to have a truthful explanation to back up what people say.

 

[Doubeleive]

more likely that seals have simply started to leak and it's just coincidence, not a lot of people even bother to check for leaks on a regular basis much less pop the hood open and look at there engine, they drive it till it breaks and then wonder why or how did that happen????

 

[UmmScott]

I think it might be a combination of both as stated here..

As engines age and seals get older they're eventually going to leak. However, i do believe that switching to synthetic will aggravate or cause some leaks.
Here's an example.
In my job field, refrigeration compressors used to be filled with mineral oil. If a compressor went bad, modern compressors are filled with POE oil which is synthetic.
In this case, synthetic oil is a very good cleaner so as the system ran, the synthetic oil began cleaning/scrubbing the internals that were left undisturbed for years from the previous mineral oil.
The result is clogged filters, sticking valves, and leaky seals. Because the new synth oil causes the seals to swell up and leak.

Thats just an example. After all an air conditioning or refrigeration compressor is literally a small car engine (depending on what kind).

Back to the OPs point. I think you did good to reach out to the previous owner and ask what was in it. If the engine was "raised" with regular high mileage oil, then stick with it.
If it was raised with synth oil, then stick with that.[emoji106][emoji106]

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[OR VietVet]

I do get what you are saying but IMO, as I stated above, by now there should be a PROVEN reason for changing to synthetic oil will cause leaks, if in fact there is a reason. I would believe that someone somewhere in the automotive industry would have come up with a proven reasonable explanation for what is really just being thrown around like "the latest cure for hiccups".

I don't doubt your explanation but IMO the inside of an air conditioning/refrigeration compressor is different than an internal combustion engine and therefore leads to a whole other set of reasons for people's concerns.

 

[UmmScott]

The internals are the same. Crankshaft, pistons, just no piston rings and they use reed valves instead of conventional valves.

And yeah i agree with you.

I could really see it on a neglected car tho. One where the owner never changed the oil, let sludge buildup, then switched to synthetic...that would for sure cause a leaker.

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[iamdub]

IMO, Scott pretty much nailed it.

Crud builds up from using lower-quality oils, an engine (and it's seals) age, you dump in high-quality, high-detergent oils that dissolve and clean out crud. Then you have leaks. The synthetic oil didn't directly cause the leaks, it just removed built-up residues and revealed existing wear. Had that engine been better maintained, there shouldn't have been wear for the synthetic oil to reveal. If someone can blame synthetic for their leaks, then that's a testament to the effectiveness of the synthetic's detergents and they were unknowingly using the conventional as a "stop leak".

Quality conventional oils are so much better since the days of the "switched-to-synthetic-and-now-leaks" syndrome, so there really shouldn't be much of a chance at leaks if the conventional oil was changed regularly.

 

[Woodblocker55]

Well it's on order Im sticking with oil that was used for years premium conventional . I put a cam down the fill hole looks dam clean in there and after 4700 miles oil still looks clean . [emoji106][emoji6]

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[iddqd]

I use Mobile 1 10w40 and 5w30 high mileage. it's amazing. High mileage oil usually contains ingredients to make seals softer, hence preventing the leaks