Looks Like, Smells Like, Tastes Like

Low winter rating to support cold starting

High HTHS viscosity to protect critical parts

Solid amount of ZDDP, not exceeding API SG, is a must

Moly and boron anti-wear additives are a definite plus

A strong detergent package is important

Conventional PCMOs

Synthetic PCMOs

Conventional HDEOs

Synthetic HDEOs

So far we’ve built up a pretty good picture of the sort of oil we want to put in our Jeep engines:So, which oils fit the bill? Let’s ignore the religious war of conventional vs. synthetic and magic hand-waving and just look at the numbers.Unfortunately, some numbers are not published by all manufacturers. Much of this data was collected via independent Virgin Oil Analyses from generous users on forums and companies like the Petroleum Quality Institute of America. As a result, some numbers are taken from typical production values as reported by the manufacturer, and other are taken from tests performed on a given batch. HTHS is missing for most of the conventional PCMOs because oil nerds aren’t really interested in them. Likewise, Mobil appears to not like publishing cold-cranking simulator results.This list is by no means complete; just a few that popped into my head. If someone would like to see another oil compared drop me a line and I’ll do my best.So much for every oil being the same! By now the real differences between HDEOs and PCMOs should be readily apparent. One of them probably tastes just like Buckley’s. Also, most of the PCMOs listed to not meet the ACEA A3 HTHS minimum of 3.5, which is specified in overseas 4.0Ls.Considering modern technology, one would assume that to meet API SN-RC and ILSAC GF-5, new additives like moly and boron would be good replacements for ZDDP. Apparently some companies don’t even bother adding them!Castrol GTX 5w30 and Valvoline Premium 5w30 I would run only in a lawn mower I hated. They have the lowest ZDDP of any lubricant in this chart, no moly or boron, and their detergent package is very low. On top of that, Castrol GTX is at the very limit for being a 5W rating, which is a good thing as I don’t mow my lawn past October. Valvoline’s product sports a very low TBN, apparently keeping alive the notion that oil changes must be done every 3000 miles.Quaker State and Pennzoil’s 5w30s appear are what modern conventional PCMOs should look like. The viscosity data hint at different refining process or VII levels, more research is required to figure out what the real difference is. Pennzoil appears to have a superior additive package with a higher TBN, and would be a good choice in other engines.MAG1’s 5w30, in some regions sold as Walmart SuperTech, actually appears to be a pretty good product, as far as this category goes, anyway. It has the highest level of zinc, reasonable detergent, and a chunk of moly. The TBN isn’t very good but considering the cost of this oil is not a huge deal.As far as the SN oils go, there are some unexpected differences evident between the synthetic and conventional PCMOs. ZDDP additives are tuned for more zinc with less phosphorous. As well, most of them have moly and boron to make up for lower zinc levels. This is very good news for owners, and I suspect another reason that more new cars specify synthetic oils.Once again, Valvoline seems to be leading the way with a deficient additive package. This is remarkable as the MaxLife formula is marketed as a “high mileage” oil – yet contains no modern anti-wear additives, and none of the zinc required by older engines. It also has a low TBN so it won’t even last that long. Curiously this oil is rated API SN, though is inferior to the other SN oils in almost every way.Quaker State’s Defy is another “high mileage” oil that appears to fall short of the mark. It too is lacking in the zinc department, but this is a real mystery on account of its API SL certification. Why is it only SL while it meets the SN limit for phosphorous? This raises some questions as to the quality of the rest of the oil. At least it has some boron and moly. Not a totally useless oil, but I’d definitely buy Pennzoil conventional before picking up a jug of QS Defy.Mobil 1 High Mileage 10w30 is the only oil I have in this chart that actually appears to be designed for use in use in older engines. It has a pretty good chunk of zinc as well as moly and a whack of boron to back it up. Additionally it is on the high end of what is permissible for a 30-weight. The large detergent package, thicker oil, and reasonable TBN make this a good candidate for leaving it in longer in an engine from a dirtier time. This oil obviously violates the SM and SN limit for phosphorous so is certified in the SL category. One can only hope that it meets the rest of the SM and SN spec.Castrol Edge Syntec 5w30 is a pretty solid oil that would be a good choice for an extended OCI. It has a very high HTHS for a 30-weight and the TBN shows quite the alkaline reserve. Oddly this oil has double the amount of magnesium than calcium, which will have two effects: This oil focuses on more on suspending contaminants than cleaning them, so would not do as well as other oils to clean up an already dirty engine. However, low calcium will let the ZDDP go farther before it degrades.Pennzoil Platinum and Mobil 1 5w30s seem to take the cake in this category. Mobil 1 is probably made from better base stocks and sports superior cold cranking. Both have excellent TBNs and, as far as SN goes, good anti-wear packages. Although Pennzoil has a better ratio in the ZDDP formulation, Mobil 1 has more moly and boron to make up for it. Between these two oils we are seeing for the first time a significant difference in the cleaning package: Pennzoil is heavy on detergent, and Mobil 1 has a much more balanced approach with a whack of dispersant. Mobil 1 will be more effective in keeping contaminants suspended in the oil so that the filter can clean them up. Of these two oils, Mobil 1 appears to be better suited for running an extended OCI. For a standard OCI, the Pennzoil is likely priced much better.Curiously Mobil 1 Extended Performance 5w30 is basically a watered-down version of Mobil 1 5w30 in a more expensive bottle.Now we’re starting to get into the good stuff. The first thing I’d like to point out is that all of these diesel oils are also certified by the API for use in gasoline engines. Any oil listed here with API SM passes modern wear, performance, and seal compatibility tests, but as they are all outside of the Xw20 and Xw30 range, phosphorous limits do not apply, making them ideal candidates.Most of these oils are 15w grades, meaning they are not suitable for winter use in our engines, although acceptable for summer and mild climates.MAG1’s Walmart-branded SuperTech oil again impresses with superior cold cranking performance and the strongest ZDDP in this category. The high flash point and good cold-cranking results hint at a high quality base stock; I would not be surprised if this was a blend. Although the TBN is a little flaccid this is a very good oil for the price.Mobil Delvac Super 1300 15w40 is pretty similar to the SuperTech. Although it has lower zinc, it has more moly and boron. A better detergent package and TBN mean it will go further than the SuperTech.Rotella T Triple Protection (T3) is interesting. It has great zinc, does alright when it’s cold, and a huge slug of detergent. The 15w40 beats its 10w30 brother in anti-wear protection, both in HTHS and zinc, moly, and boron, and overall is about on par with the SuperTech for anti-wear. However, the 15w40’s phosphorous content is abnormally high – nearly a 1:1 ratio with zinc! While it does have the anti-wear properties our engines need, it compares poorly to other oils as it will shorten catalyst life with little benefit. Despite this it has a serious wad of calcium which supports its use as a cheap way to clean up a dirty engine. It is an excellent conventional HDEO but there are better options for a mixed fleet.T3 10w30, while lacking in moly, is a reasonable oil. It’s pretty thick for a 10w30, and with a higher TBN it would be well suited for extended use. A decent zinc/phosphorous ratio is supported by lower calcium. However, the 10w30 variant isn’t as strong as other oils in terms of cleaning up and may not be the best choice for a dirty engine. I should mention that although this has higher levels of phosphorous in 10w30 grade it is still able to be certified as API SM. The reason for this is that it is primarily an HDEO, not a PCMO. When a “C” designation precedes an “S” designation, as in CJ-4/SM, the “non-critical” side kicks in. This oil would be able to achieve API SM with up to 920 PPM of phosphorous. The reverse would not be true if it was rated SM/CJ-4.Chevron Delo 400 LE 15w40 is actually my favorite oil in this category. It’s a little thicker than the other 15w40s but has the best additive package overall. With lower phosphorous for better catalyst life while keeping zinc over 1000 PPM, this is very much in line with API SL/SJ requirements that half of XJs adhered to. A healthy dose of moly and Texas-size slug of boron should produced results similar to or maybe better than higher levels of zinc. Why buy fancy ceramic additives when you can get it in this oil for less? A balanced detergent/dispersant package rounds this oil out nicely. I will be switching to this oil once weather permits.Overall it’s easy to see why classic car owners prefer using HDEOs. The additives are simply superior to PCMO, and in some cases the additives in conventional diesel oil out-perform synthetic gas oil – but you pay much less!Now we get into the really good stuff. As far as our engines are concerned, synthetic HDEOs are the cream of the crop for all seasons and climates. They easily meet or exceed the requirements we set out earlier for both viscosity and additive characteristics. In general synthetic HDEOs have a lighter HTHS than their conventional brethren, providing a fuel economy advantage, but with a higher quality base stock still providing superior film strength.Shell Rotella T5 is again an “interesting” oil. The 10w30 variant is a synthetic blend, and aside from the obvious implications it appears to be identical to its conventional T3 10w30 brother.T5 0w40 is sold up here as an Arctic Blend. It is a full synthetic. It has fantastic cold weather properties and an excellent HTHS, especially considering the 0w rating, but is a little lacking on the additive side. The calcium is quite high which will impact the practical performance of ZDDP. This oil is clearly from a previous generation as supported by the old CG-4/SJ rating. Apparently this oil is being retired and a new T6 0w40 is taking its place, however I couldn’t find any data on the T6 and T5 is still on all of the shelves. Perhaps I will revisit this in a few months.The Mobil 1 oils, once again, are very similar. Unfortunately no CCS results have been published for these two so I cannot make any comparison or speculation as to their cold weather performance, but the reader can assume it is certainly adequate. Delvac 1 ESP 5w40 has a much higher flash point and much lower pour point so is likely a better base stock. Turbo Diesel Truck 5w40 has the weakest ZDDP of the bunch, and not much in the way of moly to show for it. Delvac 1 ESP at least has more ZDDP, in fact the zinc levels place it the third highest in our entire survey, making this a very good choice. Delvac 1 has lower calcium which will let the ZDDP perform better than TDT in a flat-tappet engine. High dispersant will keep particulates suspended for a long time. With a good filter this would be a great oil to run. TDT, with more detergent, may be better suited to an engine with sludge potential, such as frequent starts and stops from city driving. This is also suggested by TDT 5w40 marketed to consumers with diesel-powered pickups, and Delvac 1 ESP 5w40 marketed at on-highway trucks.Valvoline Premium Blue Extreme 5w40 is essentially designed for Cummins diesels. It has a stellar level of zinc and a nice dose of moly and boron, much higher than Shell Rotella T5 and both of the Mobil oils. The slightly lower HTHS will provide ample protection but giving a fuel economy advantage over the 3.9 and 4.0 candidates. The most notable feature is the incredibly massive wad of calcium detergent. While this is very typical of high-performing HDEOs from previous generations, it will have massive impact on ZDDP in flat tappet cam engines. It’s worth pointing out at this point that the majority of heavy duty diesel engines have been using roller cam followers for a very long time – earliest I’m personally familiar with is the Detroit Diesel Series 71 from 1938 – so this isn’t a problem in the intended market. While this is undoubtedly a quality oil, I do not recommend it for use in any flat tappet engine like our 4.0L.And so we come to the last in the lube lineup: Shell Rotella T6 5w40. This oil behaves very well in the cold, of all HDEOs compared it is second only to T5 0w40. At extreme lows it actually performs better than most 5w30 conventional oils. It’s lighter than any other 40-weight HDEO at 40°C and 100°C, giving it a fuel economy advantage, but with a strong HTHS that provides better film strength than either Mobil synthetic HDEO or Valvoline PBX. Rotella T6 has the second-highest level of zinc of any oil in this chart, but throws in a respectable wedge of moly and boron to increase lubricity and protection anyway. This oil has an extremely powerful detergent/dispersant package that will clean the engine very well and actually keep it that way. The lower amount of calcium means the ZDDP will accomplish a lot more than Rotella T5 or Premium Blue Extreme, and the zinc vs. calcium ratios are above any conventional HDEO in this lineup. Combine this superior additive package with an excellent TBN and this oil will be a solid performer for a very long time. The only down-side to this oil is the high level of phosphorous, but given the other qualities this is forgivable: In a Jeep I’d much rather the engine be as reliable as possible, so if I have to replace an emissions part a year or two earlier than with another oil, then so be it. For older XJs, this oil still falls within the original API SF-SH limits for phosphorous, and is very similar to what these engines were originally designed to use.For the Jeep 4.0L, Shell Rotella T6 is the most ideal oil to run. It provides the best balance of engine wear protection versus fuel economy, and is the best suited to provide the most reliable performance in all situations.The price isn’t that bad either – 5L jugs come on sale for $34 every 4-6 weeks placing it at around $6.20/L, compared to my normal price of Pennzoil 5w30 at about $4.60/L, Quaker State 5w30 at $5.40/L, Mobil 1 at $10.23/L, and Royal Purple at $11.84/L.