convince me to run 15w-40

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Jan 13, 2003
collierville, TN
Im sure yall have seen my posts regarding the oil for the 4.0L in my jeep. Running 10w-30 in the winter and 20w-50 in the summer gives me good pressures but id like to find something that i can use all year and the 15w-40 has been coming up alot. There are post about clogging up the Cat, hurting bearings b/c the tolerances are too tight, and other issues that would go along with a heavier oil. The temp currently outside is 15 degrees farenheit and that is about the coldest it gets but in the summer we routinely get 100+ degrees with very high humidity and it makes for very crappy engine conditions (as far as power and wear/tear). I already ordered a bottle of auto-rx and have about 1500 miles until my next sched. change and will drop in the auto-rx when i have about 1K to go and would like to start putting in the 15w-40. My only concerns have been pressure (low when ive been driving for a while and its hot outside- above60 farenheit), and a slight rear main leak. Ive been running dino. Lemme hear your opinions. Manual calls for 10w-30 for my climate. This is a rebuilt engine. Thanx
"Hurting bearings because tolerances are too tight" I find interesting. 15W40 would be regarded as an average viscosity here along with 20W50 (Shannow what do you think?). I've run 25W70 in the past in my Mazda 626 turbo (626 GT in the U.S) and with 200,000kms on her still runs like new. Dyno operator even commented on how good it was last Saturday. I've just trialled 10W30 CAFE oil for the first time and never again. Rattly top end etc tells me it ain't doing the engine any good. 5/10W40 would be my choice over 15W40 if your in a colder part of the U.S though.
I've seen many motors clock up 150,000 miles on dino 20W-50 (valvoline and castol), starting in Canberra winters (around 20F) in the mornings. Used to run 25W and 30W stuff when I lived there, and didn't wreck anything.

Hell, we used to drive to the snowfields, ski all day, and drive home without worrying about summer and winter oils.

I don't think a 15W is gonna kill anything given your climate.
It sounds like the 15w40 Schaeffer blend would be perfect for your situation. It's cold weather performance is excellent, it has a CCS viscosity at -25C of 4877 (and at -15C it's 1775!) and it has a borderline pumping temp of -25F. So for your area you'd have no problems at all with this oil even on your coldest morning.
I'd have no problem running a 15w-40 in this motor year round down in Tennessee. I would use one like the Schaeffers S7000, 15w-40 that has excellent cold pumping characteristics. My second choice would be the Delvac 1300, 15w-40. George Morrison @ AVLube can tell you more about that stuff - he's a site sponsor.

I'd put in the 15w-40 when the temps start to warm up a bit in March/April and see if you are satisfied with the cold weather performance. Then you can decide if you want to run it next winter. The commercial, 15w-40 engine lubes are of higher quality than the gas engine stuff, since these engines are run until overhaul @ 750k-1000k miles. Due to this, trucking companies can really tell what product is working the best.

My daily driver is a very basic 1990 Toyota 2WD pickup with the classic 22R 4-cylinder engine. I bought it used in 1992 with 38,000 miles on it. It currently has almost 130,000 miles on it and ALL I'VE EVER PUT IN IT IS SAE 15W-40 motor oil. The rest of the truck is going to disintegrate before the engine goes out. In Tennessee, you should have no problem. Now, if I lived in some place that was really cold, I'd being using a lighter grade in winter but in California it has been no problem.

Originally posted by darrenc:
The motor is extremely robust—it has six mains.

Are you sure it doesn't have seven main bearings? The only domestic inline six I've ever known that didn't have seven was the old Chrysler slant-six, which was based on the earlier flathead six from the 40s.
I run the Schaeffer's series 7000 15w-40 in every thing I own. 98 Ford F-150 with a 4.2 L v-6, 97 Saturn 1.9 L I-4 , John Deere diesel tractor, 15 hp 4 stroke outboard and several one lung yard machines.

No problems at all. In-fact it was 18*f this morning and both the Saturn and Ford started right up.
yes it does have 7.. The rebuild was due to a hydrolocking situation that still is under suspicion. I broke the rear axle and the oil had been freshly changed in addition to new air filter... A few weeks later the axle was fixed but now the engine was toast... The oil was milk and the filter was a different make/model and had visibly been soaked. Shop denied everything and once that was replaced i had to replace the transmission and tcase- the entire drivetrain in other words and this place kept denyin everything. Ive now become the only one to work on the jeep (well my friends help) but the engine died at 77K in an unexplained death... Cost me 1 year of part time work that i had saved to get it all fixed. Sorry for the story but thats how a 4.0 will die- WATER
The 4.0 is not a high-tolerance engine, even from the factory. It is actually pretty loose and sloppy, but not know to be oil burners. The motor is extremely robust—it has six mains. 15W-40 is a great oil for this motor. I’m surprised you had to rebuild. The 4.0 has a reputation for being nearly indestructible. They are weepers and leakers though.
Highney. Yuck. I'm looking at a tranny myself. Already did the diff...bad carrier bearing. T-case is good thought. My Select-trac and 4.0 are about the only thing on my ZJ that seems durable. DM really needs to get it together with QAQC.
Shannow before I learnt something about oil and mainly from here I used Penrite 'Turbo' now called HPR40 in my Mazda Turbo even in winter and a lot of time at the snowfields. Its 25W70. 200,000kms up as of last week and seems like new. I wouldn't run 25W70 now or xW30 either after recent trial of 10W30.
I have been using Rotella 15-40 in my Areostar for about 4-5 years. I use it year-round. The van has about 127000 miles on it now, started using it at around 40000 mile.I change the oil every 3-4 thousand miles and I still do not have to add any oil between changes, and thats in michigan weather.

Originally posted by mebanditws6:
Hmmm 7 mains How many for the 318 Dodge? I know it has 2 bolts per main cap but not sure how many mains.

V8s genrally have 5 main bearings. Here's a rule of thumb: Take the number of crank journals and add one to get the number of main bearings.

However, Pontiac made a 301cid (4.9 liter) V8 in the early 80s that had only 3 mains.

[ January 25, 2003, 11:32 AM: Message edited by: G-Man II ]
thanx widman! I dont have any specific noise other then the diesel like chatter that the I-6 will give ya even on the showroom floor. You didnt have any issues with the 15w-40 after the lifter issue was dealt with? How was your pressure compared to the 20w-50 (hot and cold please) and also Did you have any leaks or adverse affects? Thanx
4 years ago I bought a 93 Grand Cherokee with the 4.0 liter engine and 50,000 miles on the odometer and a little lifter noise. Without even thinking it might want anything lighter I put Delo 400 15w40 in it but the lifter noise continued. I upped to 20w50 Group I for 2 years, including driving at -10C and +58C until I could smuggle in a new set of lifters, then went back to Delo. Just sold it with 80,000 miles on it.
With the 20w50 i saw morning pressures above 80. The 15w40 was more like I like, around 65-70 psi. Don't really remember the pressure warmed up one vs other. I kept in in a town at 6300 ft above sea level where morning temps ranged between -2 and +15 C year around, and afternoon temps often passed 40C. Drove it a few times to the mines and places at 18,000 feet above sea level and a coupleof times to here (1200 ft).
Only other problem with the early version of that engine is the weakness in the valve springs and the clips that hold the valves in place. When I replaced the lifters I replaced the head and valves with a (used) 96 or 97 model with better springs.
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