Oil suggestion: High Mileage Jeep Grand Cherokee

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Florida
I've already got a separate thread with oil suggestions for my vehicles, but I wanted to make a separate thread here just for my Jeep. Little background: It currently has 280,400 miles, and I recently replaced the rear main seal and oil pan gasket, so there's no significant leaks. Actually haven't observed any significant oil loss either. It runs like a champ, although the fuel efficency isn't so great overall, it's good for what it is. Has 245/70/16 tires, lifted about 2" with an Old Man Emu/Bilstein 5100 shock combo that's popular with Jeep guys. Not the highest lift, but a great ride. Added some wheel spacers and the Jeep sits as I feel it should have from the factory, and I average about 14.7 mpg per the overhead computer. Not the most accurate gauge, sure, but the gauge read 17 mpg with stock tires at stock ride height. Currently I have Valvoline MaxLife 15w40 with a quart of Mobil1 HM 10w40, and a bit of Lucas oil stabilizer (yeah I guess that stuff is [censored] now!) and I feel like it may be a bit too thick for my Jeep. I do like the idea of the added protection though. So my question for you guys, is should I go ahead and run a 5w30 HM Synthetic like Castrol? Maybe go for an extended performance Synthetic? Or just stick to Syn-blends like Quaker State defy or Valvoline MaxLife? Rotella T6 has been the most recommended, but I don't have any sludge or leaks, so I wonder if I can get by with a 5w30 weight to improve efficiency. I'd like to hit about 15.5-16 mpg, but I don't want to sacrifice protection. I've read the Castrol Edge oils run a little thicker, and I know they have a nice gold color to their oil, which is nice laugh haha I think the Pennzoil Plat may run too thin, however the Euro spec 0w40 may be nice for my Jeep, considering I don't have any oil leaks or significant oil burn off. I'm still learning the jargon around here (yes after 7+ years lol) but I think I understand that a thin Xw40 weight may be comparable to a thick Xw30 weight. Thoughts??
 

Nick1994

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A 1" taller tire shouldn't make the mpg go down 2.3 mpg. I've got a little bigger size tires on my Jeep and if I drive it slow it is pretty good on gas, almost 22 on the highway. I'd just use a 5w30 as long as the oil pressure is fine and it isn't consuming.
 

Dumc87

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Originally Posted By: Nick1994
A 1" taller tire shouldn't make the mpg go down 2.3 mpg. I've got a little bigger size tires on my Jeep and if I drive it slow it is pretty good on gas, almost 22 on the highway. I'd just use a 5w30 as long as the oil pressure is fine and it isn't consuming.
Actually installed a new oil pump when I did the rear main seal. Well that's key, if I drive slowly, I'm sure I can net much better fuel economy lol I had a Jeep Grand with the 4.0, lifted about 6.5" on 31" tires (didnt look as odd as it sounds lol) and I averaged 13-14mpg mixed. --- I went with the Valvoline MaxLife 15w40 to make sure I kept things clean, but I realize that a good robust Synthetic, especially Edge HM, would probably do just as well at keeping things clean while improving efficiency a tad.
 
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Chicago, IL
I don't think you'll gain much just dropping down to 30 weight without changing anything else. As you already pointed out it's a combination of things that leads to noticeable mpg increases (ride height, wheel size, etc). But heck... only one way to be sure. We had a 5.9 at work in a Ram that got fed 30 weight bulk Valvoline. That thing towed daily, got sold with 250k still running fine. So I'd say your good to go.
 
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Arkansas
any HM 5w30/10w30/10w40 should be satisfactory. I would probably go for a thicker 5/10w30 and call it a day. Maxlife or Castrol high mileage 5/10w30 would be a great choice here. However if you want more data you will need to do a VOA/UOA on the different combinations over a couple of oil changes to see what works for you!
 

Dumc87

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Originally Posted By: gomes512
I don't think you'll gain much just dropping down to 30 weight without changing anything else. As you already pointed out it's a combination of things that leads to noticeable mpg increases (ride height, wheel size, etc). But heck... only one way to be sure. We had a 5.9 at work in a Ram that got fed 30 weight bulk Valvoline. That thing towed daily, got sold with 250k still running fine. So I'd say your good to go.
I'm sure to actually get 17 or 18 mpg, I'd have to regear to 4.11 gears, full synthetic diff fluid, new ATF fluid, highway tires, and a freer flowing exhaust lol
 
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Kalifornia Kollective
Originally Posted By: bubbatime
Maxlife 10W40
Yeah, that's where I'd go too. Skip the Lucas. Run an oversized filter if you have the clearance? That'll be a bit more overall volume and extra filter area never hurts off road. You never know when something will come loose and you'll get dust in it... To many miles for 5W-30 IMHO ... When's the last time you serviced the tranny? How bout the rear ends? Have you put a high flow CAT on it? Done anything to the exhaust? My guess is that the CAT is somewhat blocked. The O2 sensor is getting tired. The cam chain is stretched so it's valving 2~3* retarded. All this adds up to loss of mileage and some power. Question is, do you want to spend the $$ to get it right ... First thing I'd do is go through the ground side of the 12 system. All the connections have crevice corrosion and minor salt bridging. Nothing is reading correct voltages. They are all off by 0.1~0.3 volts. Makes no difference in a carb'd points system. Makes a world of difference with a digital system. Go get new HD battery cables with clamp-on ends. Before you install, solder the crimped-on lug through the bolt hole. You'll need a propane torch. Install with a dab of grease under the bolt head and some Never Seize on the threads. Add a new #8 wire with soldered lugs from the battery (-) pinch bolt to the radiator support. Add another from the battery (-) pinch bolt to the alternator mounting bracket. And then from there to the firewall. Hood hinge bolts work great. That will put all the engine sensors and the ECU on a level playing field with a real common ground for a true zero reference. You may get you mileage back just doing that ... smile
 
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Just curious, what is the oil pressure at a warm idle? A vacuum reading at idle would tell you things too. What you are looking for isn't worth putting into a old jeep.* Be happy it runs and don't expect economy out of a jeep, any jeep. * better gears tuned to HP and tire size. Lift and associated hardware aren't helping MPG and engine performance either
 
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Originally Posted By: Dumc87
1998 Jeep Grand Cherokee 5.9 +280k - Maxlife 15w40 Thoughts??
3 thoughts on this: First, keep doing what you are doing, or Second, the 5.9 (360cid) was run on a 30 weight for many years. If it doesn't leak any, then go ahead and try the 5w30 in your favorite brand and see how it does; and Third, the mpg you quoted is pretty good, that's known to be a thirsty engine....I agree that the oil won't make much of a difference, but it might especially if you go to a 5wXX vs the 15wXX you have in there right now.
 
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Dumc87

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Originally Posted By: Kuato
Originally Posted By: Dumc87
1998 Jeep Grand Cherokee 5.9 +280k - Maxlife 15w40 Thoughts??
3 thoughts on this: First, keep doing what you are doing, or Second, the 5.9 (360cid) was run on a 30 weight for many years. If it doesn't leak any, then go ahead and try the 5w30 in your favorite brand and see how it does; and Third, the mpg you quoted is pretty good, that's known to be a thirsty engine....I agree that the oil won't make much of a difference, but it might especially if you go to a 5wXX vs the 15wXX you have in there right now.
That's where my thought-line is. If the 5.9 leaked, then I'd say the 15w40 HDEO oil is justified. However, the thing runs great! Eventually I'm going to have to appease my curiosity and run a 5w30 weight. I figure 3K intervals would be best, considering the mileage and ease of an oil change. Maybe 5K with a full syn.? The idea of an oversize filter could work, but I'm not sure what's a step up from the SuperTech size ST16 (that's the only PN oil filter I remember lol)
 
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Mahzurrah!
The 15w40 is overkill IMO but a good 10w40 would be just the ticket for that old warrior, like the Maxlife 10w40. Upsize filter is the PH8A equivalent if you want it.
 

Dumc87

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Originally Posted By: KCJeep
The 15w40 is overkill IMO but a good 10w40 would be just the ticket for that old warrior, like the Maxlife 10w40. Upsize filter is the PH8A equivalent if you want it.
Made me want to call her 'ol Jeep Wayne laugh Yeah, not too funny now that I wrote it .... lol
 

Dumc87

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Looking up some various cars the PH8A fits, and looks like 93-98 Ford Rangers use that size. Pretty cool! Should be able to find a multitude of brands that way.
 

Dumc87

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Went by the local WalMart that's been clearing out Bosch DP filters, and found a D3500, which cross-references with a PH8A, for $2.81 laugh Bought the last three I saw. Now they have a bunch of 3334's. Not sure what PN those are for. Got some Castrol Edge HM 5w30. Will top off with my Mobil1 jug that's actually a mix of new leftover oils; M1 HM 10w40, PP HM 5w20, Valvoline FS ML 5w20 and 7-11 conventional 10w40, considering the new oil filter will be a little bit bigger than the normal one.
 

Dumc87

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Originally Posted By: Dallas69
Just run 10-40 Maxlife or any namebrand oil. Don't use Lucas or any additive, you don't need it.
I want to test out the 5w30. Nothing against Valvoline ML 1040, it's actually a logical oil for my Jeep, but if I can run a full syn HM 5w30, that'd be pretty sweet
 

Dumc87

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Originally Posted By: car51
PYB 10w30 or even 5w30 Pennzoil "GOLD" blend.
Hmm, why Pennzoil over Castrol for my application? I do really like how the PPPHM 5w20 "feels" in my Matrix. No idea if that's just placebo or factual though lol I have a jug of PPPHM 10w30 ready to go for the Z and PPPHM 5w30 for the Matrix in Summer (Florida gets pretty toasty in June & July LOL)
 
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