Finally changed to "high mileage" oil

I'll sooner call myself obsessive than expert, fluid mechanics isn't really my subject, normally this is where I wait for my machinist to correct me.

You know Dan it's funny I just checked and on my recent Alfa engine overhaul I intended to use 10w40 like a good stubborn know-it-all but sure enough I couldn't find it anywhere from a brand with enough ZDDP so I settled for Shell Rotella T1 15w40. Engineers man, I'm sometimes better at giving advice than following it. Granted if I can find 10w40 I would be happy to switch, but that's only because I feel better following the factory sticker and I'm only barely still young enough to be doing an engine overhaul in my "spare time" now. My professional mentors suggest when I'm done that I will soon find myself with no time to do another one for a long while... better safe than sorry then.

Solid A+ for NAPA they have all the best stuff.
 
I thought it was good to have shiny metal flakes in the oil....they help seal up the leaks and freshen up the bearings, kind of like that "Scrubbing Bubbles" cleaner. At least that is what my friends sister's ex-boyfriends father told me.
 
10w-30 was recommended by the manufacturer and people still use 10w-30 ,but did that same manufacturer recommend 10w-30 for a higher mileage worn engine of TJ age? Do they recommend 10w-30 "high mileage oil "with additives to keep the seals pliable? Or do they really not care about older high mileage because they are in the business of selling new vehicles and maintaining those newer vehicles through dealerships?

Recommended is for newer engines not high millage worn engines and that is what many experienced mechanics will tell you when you ask their opinion on what oil to use. Some modern and high tec engines require and demand thinner oil because of there design but the TJ 4.0 is not one of them.

15w-40 for a warmer climate should be more of a norm, If 10w is good to go for a cooler climate cold start up then 15w will make no difference whatsoever to a cold start up in a warm climate re damage.

If you have a perfect high mileage 4.0 with no wear then you are lucky, if you can rebuild your 4.0 the first sign of any wear then again you are lucky.

I read that the first Synthetic could cause some seal shrinkage and some hardening of seals but that was in the 1970,s and does not relate to modern synthetics, the difference is 10w-30 synthetic is thinner than 10w-30 conventional and the reason the RMS can leak with synthetic, up the thickness of the synthetic and more than likely the RMS will leak no more than it did or did not with conventional.

Maybe some of the Knockers of using above 10-w 30 especially in a hot climate should actually try a higher viscosity for themselves after all oil and a filter is cheap and they may get a pleasant surprise, If not change it back to 10w-30 its really that simple and at least you will have had the personal experience, same with using a higher viscosity synthetic does it stop/slow RMS leak that is showing after using 10w-30 synthetic?
 
I switched to 'high mileage' conventional oil as a preventative measure and immediately developed a leak, has not stopped leaking a day since the change over :ROFLMAO::ROFLMAO:

so there's that
 
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I generally run 5W-30 high mileage year-round. I'll probably end up dumping the same bottle into my new 2021 car as well.

I've been really tempted to try a good 0W-30, but it seems the blends are either not high mileage or not as long lasting.
 
back in the day, whenever i switched a first gen Saab 900 over to synthetic (this was in the 80s/90s, the engine would immediately develop a HUGE front main seal leak. four times i went through this. the front main seal was on the back of the engine (because Saab) with about one inch of clearance against the firewall to get it out. Huge PITA but i thought it was worth it, and probably was, as conventional oils back then were awful compared to what we use now.
 
Westtown Willy said:
I switched to 'high mileage' conventional oil as a preventative measure and immediately developed a leak, has not stopped leaking a day since the change over :ROFLMAO::ROFLMAO:

so there's that
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Yep, changing oil type and viscosity can absolutely cause a leak. Anybody that suggests otherwise hasn't been reading this whole thread or all of the others that talk about the same thing. Just switch back to what worked or pick another brand next time. It's just like the lifter tick, there is no one shoe fits all approach. I really do enjoy when people post a little reality check now and then.
 
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