I bought my 2000 xj used and soon discovered that it had the infamously crappy (and cracky) 0331 cylinder head. I've swapped in a new Clearwater head, but I'm still dealing with bad oil pressure from the previous owner running on watery oil. I have 10w-30 in there now with two cans of STP treatment to boost up the viscosity, but the engine stil hot idles around-to-below 10psi. I'm thinking of dumping that all out and putting in a straight 30W or 40W or 50W. Is this glaringly stupid? I'm in eastern PA so the winters aren't too bad but will the straight weight cause any cold condition wear to the engine?

 

Mine hangs around 10 to 15 when idling & warmed up (no overheat) and just tried 20w50. I have about 150 miles on it and pressure at idle has increased to 20 plus at idle. I never had clatter or overheat problem but just did not feel comfortable at 10 to 13 pounds. I have changed sender & checked with manual gauge. I have 124k on jeep.

 

0W30, 5W30, 10W30 and straight 30 r the same vis at operating temp. The lower the 1st number, the quicker the oil flows to where it's needed at below operating temp. 20W50 is for Harley's. LOL

 

Before you get all excited with fluids - what oil filter are you running? If it is a FRAM, rip that piece of crap off and get a real oil filter. I believe Wal-Mart in the US sells WIX. WIX, NAPA Gold, Mobil1, K&N, Motorcraft, and Purolator are all quality filters.

After that I would verify oil pressure with a mechanical gauge. It's possible that the sensor driving the gauge on the dash is on its way out. From your description, however, if the PO had "water-like" oil you've likely got real damage like bearings on their way out. Upping a grade or pouring in some stuff won't be a permanent fix. I'd drop the pan and replace the oil pump, and take a look at the crank.

Stay away from straight weights if the engine isn't designed for it. Even in the warm month you'd want to let that puppy idle for 5 minutes before driving. If you WANT to, you can run a W40 (Shell Rotella is popular, the T6 5W40 apparently fares alright in the winter according to some posters). Some folks in Australia run 20W50 in their 4.0Ls but unless you're trailering across the Outback it doesn't seem very appropriate lol.

In terms of additives some guys have had luck with this: https://www.cherokeeforum.com/f2/rev...ormula-130469/

 

Wal-Mart actually sells Mopar filters # 090. I'm with salad on this.

 

^^

If the head cracked there was probably antifreeze in the oil, which eats the bearings. Running heavy weight oil may boost the pressure, but it will reduce the flow, accelerating the damage on cold starts.

 

Your point is ? I am not looking for quicker flow as I stated at idle & operating temp my gauge made me feel a little leary about pressure. My understanding is 13lbs is okay at idle & as soon as I touch gas pressure increased to 40 lbs & remains there while operating under any load. I am not a oil guru but flow was not my problem & by thinning out oil using a 0W30 or any thinner oil my pressure might drop just as they do as oil ages & thins out. Any one can chime in I love knowledge that will prolong my Jeeps life. I was under the opinion that as bearings wear you need to thicken a bit rather than thin. Harleys may use 20W50 but it also has auto applications for years.

 

Exactly what I was thinking. That's why I was thinking about putting in a thicker straight 40 or 50 but was unsure of how bad that would be for cold driving. The guy at Auto-Zone recommended 5W-50 while I heard from a longtime CJ guy to just go ahead with the straight stuff.

 

If you want an opinion based on experience, your low oil pressure is probably due to bad cam and crank bearings- your engine needs overhauled or replaced. Aside from that run what ever oil you want, because in the end you'll still need to fix the engine. Either that or we can add your name to long list of people who will try to mask the problem and pass the trouble off to the next owner.

And I think the previouse comment about using thinner oil is in relation to temp. When cold, thicker oil will take longer to build pressure. Oil pressure at the sensor isn't necessarily telling you how well your bearings are being oiled.

 

Obvious. After just replacing the previous owner's cracked 0331, I'm not looking to do an engine overhaul this weekend. I am simply looking to adjust the oil to compensate for the low pressure. Looks like there is no good answer.

 

Do what you want to. But everybody on here generally speaks from experience. Such as me who bought a Cherokee with a cracked head. Coolant in the oil. Oil pressure at 5 psi while at hot idle. Pulled my rod bearings and they were down to the copper. Nothing I did would bump the oil pressure. Heavier oil will make the weak engine work harder and possibly cause a catastrophic failure where rebuilding the engine will not be an option for you. I did a complete overhaul of my engine. But do as you please.

 

Just because one person injured their toe and it had to be amputated, not everyone needs to have theirs cut off!

Start with replacing the filter with a good one (NOT FRAM!) - even if it's already a good one, it may be defective (restricted inside when hot.) And replace the oil sending unit (they are famous for reading wrong) - then go from there!

KISS!

 

It's really a devil's bargain. You get higher pressure and a little thicker cushion with heavier oil, which may help the bearings a bit but that comes at the expense of increased wear in those same bearings and everywhere else when the engine is started.
At most I'd go for Mobil 1 15W50 until you can fix the underlying problem, instead of a 20Wsomething, and don't load the engine until it warms a bit.