What makes you think the engine designers get to recommend what oil to use?? 1957 Oldsmobile’s used 10 weight in the winter and 20 weight in the summer. Nothing has changed in 60 years…
I have yet to see or hear about any engine (that is spec’d for 5W-20) that has failed due to using 5W-20. I used 5W-20 in my Mustang that has 99k on the clock, it’s also supercharged and sees track work a few times a year. I have yet to encounter any oil-related issues.
This issue has been discussed at length on Bob’s The Oil Guy, the UOA’s confirm that 5W-20 protects at least as well as 5W-30, if not better, and has the added benefit of flowing better at startup, which is where most engine wear occurs anyway.
I have one experience that turned out poorly with regard to using oil that was not recommended.
Our store purchased a 1996 Chevy S-10 (new) with the 2.2l 4-cylinder engine. The factory recommended something like 5W30 however the store owner believed that was way too thin and that the correct viscosity was 20W50.
Within 6 months the engine was banging and clanging, sounded like someone had dropped a box of washers in the crankcase.
Did the extra thick oil cause the noise? I have no idea, but I’ll stick with something close to that recommended.
I think you could take two Jeep Wranglers, use nothing but 10W-30 in one, and 5W-30 in the other, and if both Wranglers are treated the same way, they will both last just as long. I don’t think it will make one bit of difference, except the one with 10W-30 will use more fuel.
Your Jeep has a stone age engine if it is a straight 6 cylinder. The original design goes back to before there was multigrade oil! It lately was a 5W30 or 10W30 oil engine, depending on the season. Then came CAFE!
The manufacturing precision on the engine has not really changed a lot; the seals are better now so that when using 5W20 on a very hot day it does not leak.
World engines are manufactured to the same specifications in different plants. A 4 cylinder Ford engine from Brazil is basically the same as a Ford engine made in Cologne, Germany, or Hermosillo , Mexico. The oil change intervals are a function of CLIMATE and GOVERNMENT ENVIRIONMENTAL LEGISLATION. In Europe they want long drain intervals (10,000 + miles) and they formulate a high additive super oil with 0W40 rating for instance. In the US they want max. miles per gallon (CAFE). In hot countries they specify a heavier oil to met the climate needs.
Japanese engines have tighter tolerances, but not so tight that they need 5W20 oil.
Read the rest of the posts and you will find that your questions are adequately answered.
Oh C’mon Doc, you know nobody’s operating to +/- tolerances any more. Everything now is LCL and UCL controlled.
I’d bet that the current rev of the design drawings are speced with GDT (a misnomer, since it’s actually Geometric Tolerancing and Dimensioning) and the operation is working to 3 sigma, adjusting processes on an ongoing basis based on lower and upper control limits an X-bar-R charts (can’t figure how to write this in this program).
On the other hand, this IS a Jeep…
I used Motorcraft 5W20 synthetic blend the last time and it seemed to be really thick. I think you will be OK. You can use thicker oil in OK. and it will be OK with me. I like the replies you got. (The ones I read anyway.)
If you actually wear out a Jeep Wrangler engine you would be a special person. Most people grow really tired of these vehicles after a few years and move on. You know what they are like and they are not a long term relationship.
Don’t worry.
Thanks mountainbike; as you state, manufacturing precision has increased over the years, I agree and the quality control is now better, so fewer dogs leave the factory. Having said that, a friend of mine had a brand new engine (GM V8)replaced on a Buick Roadmaster bacause it seized up.
Manufacturers usuallly do not upgrade and old design engine as it is being phased out. They may manufacture it a little better.
Last year I was given a Ford Explorer as a job car. The manual had oil requirements for the V6 and the V8 engines used in the vehicle. One was 5W20 and the other was 5W30!!! Forgot which one. The one needing the 5W30 was likely the older one with loser seals, so it needed a heavier oil to avoid leaking. It could also having the do with piston ring fit and valve gear stress.
The two issues as I see it are the CAFE drivers to 5W20 and 0W20 and the improved sealing and fit on new engines allowing 5W20 to be used without it leaking out under hot operating conditions.
New engine designs do not come along very frequently.
Using 5W20 non-synthetic under heavy loads and high temperatures will defintely increase engine wear, but OP in Western Washington state may never encounter these.
P.S. When I said “tolerances” I really meant “clearances”. Today’s manufacturing techniques allow much smaller clearances because of better dimensional control. This in turn allows a thinner oil to be used without destroying the film strength.
Just my personal opinion/observation, recommended oil viscosity is based on the climate where the engineers live and work. Could the best choice in December in Detroit be the same as the best choice in Needles in August? If they made cars in Needles maybe the recommended oil would be 20-50.
TSM wrote:
One point too with modern engines is that many manufacturers now are using the oil almost as a hydraulic fluid to operate the variable valve timing systems. I know Honda does this. I’d be wary of making a general statement recommending a weight other than what the manufacturer recommends.
How right you are TSM!
The Atlas I6 in my Trailblazer has a variable exhaust cam timing mechanism and it is sensitive to oil weight. Run too heavy and it barks about it. Let it go too long between changes and you get the same result (except now it’s sludged up to boot). A lot of engines are no longer = Grandfather’s Oldsmobile…
You make a very good point. When BMW first introduced their cars in the US, they misjudged the driving pattern of US drivers, as well as the climate. Since Germans drive at top speed on the autobahns, they specified Castrol 20W50 oil. You can guess what happens. Some hapless owner in Minnesota burned out his engine just trying to get it going on a cold winter morning.
Germany has a moderate climate, and high speed stability (at 100 mph)of the oil was the most important to GERMANS in Germany.
There was a bitter lawsuit by BMW, claiming Castrol did not meet their engine’s needs.
German car makers finally discoverd that Americans drive a lot slower, do a lot of stop and go driving and have many cold starts. The VW spec of 0W40 synthetic addresses all these problems and European oil specs are now much tougher than those rquired by US manufacturers.
Thank you TT. I’ve commented on this issue before, but yours is the first post I’ve read that confirms that it can make a difference in these systems.
Engines and trannys are getting so sophisticated now that the implications of not following the manufacturer’s recommendations can have unforeseeable consequences. I’m at the point now where even to drain and replenish my coolant for routine maintenance I stopped at the Scion dealer and got the spec coolant. The only dumb thing I did was pay extra for the “premixed”, which is only the “unmixed” with distilled water added. I was tired that day. I wasn’t thinking.
" Nothing has changed in 60 years…"
I really like that one. Take a look at a 2010 engine and a 1950 engine and try to say that with a straight face. 
I don't think there's much more than CAFE involved. I've seen some cars where one year, they recommend 10W30 (or have the actual chart listing what oil based on prevailing temps) Next year? 5W20 or 5W30 (a few Hondas have even gone 0W20 or even 0W10). No engine modifications, they just decided to go for the MPG boost. Something like a 3800 series ii v6 is nice (I have one), but it's a low-tech, pushrod V6, and they changed them from a chart (that usually recommended 10W30 unless very cold) to "use 5W30". The Northstars burn plenty of oil and recommend 5W30 on newer models. I don't think tightness of the engine, or using oil to run internal stuff (like VTech systems, VVT, or the like) are really factors here.
That said -- I do think the oil standards are quite high in recent years, and especially synthetics are quite high quality (particularly good about keeping surfaces coated even with very thin oil), i.e. a 5W20 using 30 year old standards would probably not work near as well as a modern 5W20. "bobistheoilguy.com" seems to have an ENTIRE forum related to testing, retesting, analyzing, and hashing over which oil is best, and there's nothing particuarly conclusive one way or the other regarding lightweight oils.. to me this means 5W20 is fine, as much as they've looked for trouble they'd have found it if there were any.[b]I found an article on one of the oil forums (can’t be more specific) a few years ago when my '04 Civic was new that said that Honda went from 100K+ life to 70K or so engine life when they changed to 5W-20 from 5W-30.
So to answer the OP, yes, it causes extra wear, and yes, it was to get better mileage.[/b]
Nonsense. Honda NEVER had to go to 20 weight oils. They had CAFE credits out the wazoo. They don’t sell Town Cars nor Challengers to compensate for. They did it out of environmental responsibility to research and develop the most economical package they could. With the exception of the S2000 that spec’s 5w-40 at all temps, there are millions of Honda’s out there that are just happy to deliver that Honda ZEN on 20 weights.
The OP has a 2010 Wrangler, which no longer has the old straight 6. If it’s the V6 option it’s the 3.7L, which I believe was a brand new design circa 2002, and was originally used in the Liberty. My '02 Wrangler still has the straight 6, and the manual recommends 10W30. As you point out, that engine is stone age. However, mine has 178k, runs strong, and uses no oil except for what drips out the bottom overnight. The OP’s 3.7L is a much newer, tighter engine, hence the 5W20.
I own a 2009 Tacoma 2.7L 4 cyl and while the quick reference in the owners manual recommends 0-20 and 5W-20, the more detailed section on what oil to use states in hot climates or high speed driving 5W-30 may offer better protection. I will use 5W-30 conventional oil and change it at recommended intervals (5000 mi.)
While Honda has no worries with the CAFE, might they recommend the 5W-20 to squeak out a little more MPG to advertise and compete with the other manufacturers for best in class fuel economy?
have 5w-20 in my '04 taurus. Other than being surprised that the consistency is almost that of cooking oil, it seems to work just fine. I use the motorcraft synthetic blend or the valvoline synthetic blend (max-life) and it’s just as clean coming out as it is going in. Even in Michigan where the temps are either cold (as low as -15 on some winter mornings) and hot (near 105 on some summer days) the engine seems fine in both extremes.