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Discussion Starter · #1 ·
I’m sure this has been discussed, but I can’t seem to find what I’m looking for. I just a 2005 TJ with 211,000 miles. Not sure what the previous owner used for oil so I’m trying to determine if I should go with a conventional or with a synthetic. And to further go down the rabbit hole, if synthetic then which one. Thanks!
 

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You will receive so many different opinions, that it will become even more confusing. If I had your Wrangler, then I would use a Conventional 10W30 oil. Just pick a Brand, because todays oils are all good.
 

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04 lj with GRTOPS half cab conversion 05 rocky mountain 06 rubicon with banks sidewinder turbo
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I’m sure this has been discussed, but I can’t seem to find what I’m looking for. I just a 2005 TJ with 211,000 miles. Not sure what the previous owner used for oil so I’m trying to determine if I should go with a conventional or with a synthetic. And to further go down the rabbit hole, if synthetic then which one. Thanks!
i run synthetic 5w40 diesel truck oil in all of mine but synthetic will leak a LOT MORE
 

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Go with a conventional and if you can find it, go with a conventional High Mileage. That will help prevent leaks from your rear main seal. And as above, synthetic engine oils tend to cause leaks. Even my BMW started leaking badly from its rear main seal on its factory recommended diet of Castrol synthetic. I switched it to a conventional High Mileage which stopped its leak within 4-5 days.
 

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'01 TJ Sport, '13 JKR
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Go with a conventional and if you can find it, go with a conventional High Mileage. That will help prevent leaks from your rear main seal. And as above, synthetic engine oils tend to cause leaks. Even my BMW started leaking badly from its rear main seal on its factory recommended diet of Castrol synthetic. I switched it to a conventional High Mileage which stopped its leak within 4-5 days.
I use conventional high milage 10w30 as well and agree with Jerry and others here. I usually just get whatever is on sale.

I do 3500 milage oil changes, which might be excessive. but I'm in a very dusty area and my TJ is mainly a trail/fun Jeep.

But this topic is like arguing politics or religion.
 

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04 lj with GRTOPS half cab conversion 05 rocky mountain 06 rubicon with banks sidewinder turbo
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I use conventional high milage 10w30 as well and agree with Jerry and others here. I usually just get whatever is on sale.

I do 3500 milage oil changes, which might be excessive. but I'm in a very dusty area and my TJ is mainly a trail/fun Jeep.

But this topic is like arguing politics or religion.
you got that right
 

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So I switched my '91 4.0L HO over to Mobil 1 10w40 synthetic high mileage at about 120K miles -- and the rear main started leaking.

After I got that fixed it's been leak free.
 

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06 TJ SE 2.4L 6spd, 79 CJ5 258ci 4spd, 83 CJ7 258ci auto
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i run synthetic 5w40 diesel truck oil in all of mine but synthetic will leak a LOT MORE
I also use the diesel oils, less detergents and additives you probably don't want anyway in a high mileage engine, quite a few legitimate studies done, I shy away from synthetic only because of high mileage engine wear, but the quality is better, so if it leaks, repair what's leaking, you wouldn't want cheaper hospital bandaging because you might bleed less, you'd want the proper repair...care first :ROFLMAO:
 

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I would never ever swap to synthetic in a high mileage engine, or swap around oil brands. This being said , I have never had an engine failure using Penzoil 10w-40 in Texas where we deal with heat more than cold of course.

also use WIX filters , a good filter as important as quality oil.
 

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Discussion Starter · #13 ·
Thanks fellas. I think the general consensus seems to be 50/50. I mostly wanted to know whether it was a definite no-no or not.

I’m also going to be changing out the rest of the fluids also. Manual tranny fluid is next. I went with Amsoil Synchromesh fluid. I just need to pick up the 14 and 17mm Allen key sockets this week. I have a 3/8 drive set, but they don’t go up that big.

Planning on doing the front and rear differentials too, but that’s going to be a bigger job so I’ll have to wait till I have time.
 

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Synthetic vs. conventional. Back in the 70s I couldn't sell one can of Mobil One. It sat on the shelf until Porsche made it the factory fill on the 911 Turbo... then it started to sell.

I always ran Valvoline VR1 in my muscle cars. When I switched from conventional to synthetic on my 2-stroke motocross bikes, it made a huge difference in piston, ring and plug longevity... it burned cleaner and left minimal carbon deposits. I could go longer without rebuilding the top ends.

I use Pennzoil 5w30 Utra Pure Synthetic in my 2013 Rubicon. I wouldn't run anything else in this POS Pentastar V6 engine.

The 4.0L HO. It's a judgment call switching from conventional to synthetic on a high mileage vehicle. I have 180K miles now and I get excellent smog check reports every two years. Valvoline VR1 has a high ZDDP content as well as Shell Rotella... both excellent conventional motor oils. However they say conventional with high ZDDP content has a negative impact on catalytic converters.

I'd rather keep my high-flow catalytic converter (outlawed now) and not take the chance of failing the bi-annual smog check...

 

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... I shy away from synthetic only because of high mileage engine wear, but the quality is better, so if it leaks, repair what's leaking ...
But, if the synthetic oil IS the cause of the leak, whether synthetic oil is better or not, to
repair "WHY" it's leaking would mean replacing the synthetic oil with conventional oil.

You could replace the leaking RMS, but, I would think that, after replacing it, if you continued to use synthetic oil, your new RMS would eventually start to leak, too.
 

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But, if the synthetic oil IS the cause of the leak, whether synthetic oil is better or not, to
repair "WHY" it's leaking would mean replacing the synthetic oil with conventional oil.

You could replace the leaking RMS, but, I would think that, after replacing it, if you continued to use synthetic oil, your new RMS would eventually start to leak, too.
I haven't experienced that. After replacing the RMS and other leaks on my 4.0L, I've continued using Mobil synthetic high mileage and its been leak free.
 
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