Is 10W40 oil okay or should I put 10W30 into the 4.0?

I personally wouldn't sweat it at all. Lots of people use 10w40 in higher mileage engines
 
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Jerry Bransford said:
I prefer 10W-30 in most climates but 10W-40 won't hurt your engine at all.
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Ok that sounds good we have around 100 degrees Fahrenheit here so 10W40 is probably a good option, my dad used from the beginning full synthetic oil should I stick too with it or switch too a half synthetic or even conventional Motor oil. And what do you think about Mobl1 my dad used it also from the beginning. For my next Oil change should I put 10W30 in or should I continue with 10W40 i think my dad used it also for a longer time period.

Thanks for your help, here in Austria nobody knows something about Jeeps and if they know something it's not right
 
LennartfromAustria said:
Ok that sounds good we have around 100 degrees Fahrenheit here so 10W40 is probably a good option, my dad used from the beginning full synthetic oil should I stick too with it or switch too a half synthetic or even conventional Motor oil. And what do you think about Mobl1 my dad used it also from the beginning. For my next Oil change should I put 10W30 in or should I continue with 10W40 i think my dad used it also for a longer time period.

Thanks for your help, here in Austria nobody knows something about Jeeps and if they know something it's not right
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If that is what your Dad has been using and it’s been doing well with it then I would continue using the same. You won’t have any issues. If you want to switch for some reason that’d be fine as well. I wouldn’t worry too much about it. 10w30 or 10w40 will both get the job done and you’ll never realize any problems either way…
 
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LennartfromAustria said:
@Jerry Bransford
I have another question, I bought a serpentine belt with 2000 mm and my TJ no AC with Power steering has a 2004 mm belt. Is it ok too use the 2000 one?
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If the 2,000mm serpentine belt goes onto the pulleys without issue I’d run it. Just over an 1/8” usually won’t make a difference, usually…
 
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I swapped to Magnatec 10w40 last change and its night& day difference and that's in a Perth winter!
When I bought my TJ a year ago I did an oil change with "as recommended" 10w 30 mineral and it rattled and struggled through the Perth summer heat that's because its possibly ran its entire life "other than factory" on 10w 50!
This Australian Summer I am defiantly going 10w 50 Penrite, 10w 30 is way too thin for a hot climate, do some oil research on availability of viscosities to different countries as I have and you will realize the possible misguidance. 10w 50 will not hurt or affect a TJ,s performance in Summer, in fact it will thank you very much :)

if you have an oil change in a chain garage you will get 15w-40 from a huge 44 gallon drum!

I challenge @Jerry Bransford to try 10w-40 magnatec and I would almost guarantee he will be using 10w-50 in the CA summer, :)
 
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