Fork in the road time ... which way to go??? - JeepForum.com
 
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post #1 of 14 Old 05-24-2020, 04:03 PM Thread Starter
dpl096
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Fork in the road time ... which way to go???

in December I bought a 2001 Grand Cherokee 159,000 miles 4.0 and it's a really clean vehicle, runs great - no clicking/ticking/knocking and I would like to keep it - but ..... after warming up the oil pressure is dropping to near 5lbs. Having had a 98 Cherokee that had the same issue I changed out the pressure sending unit with a Mopar oem and serviced the engine and bumped up to straight 30 weight oil. No improvement this time - darn ..... Next step I ordered a stock pressure Melling pump and pickup. Dropped the pan today and immediately realized someone else has been in there and they had replaced the stock oil pump with a Melling high volume pump and a new pickup. They were both crisp new looking and clean/no debris/clogging. .... So ....... I now this isn't as simple as an old oem pump needing replaced. Need some advice on what I'm seeing as my options ..... 1) Button it back up with the high volume pump and keep tinkering with heavier oils. 2) Button it back up with the new stock pressure pump and again tinker with different oil weights. 3) Roll in (in the chassis) new bearings and button back up with either the high volume or stock oil pump. 4) Pull the engine and do a rebuild. 5) Salvage yard engine swap. 6) re-manufactured engine from someone like Jasper.
I'm open to any and all suggestions please. Give me something to think about. I've roller in bearings before on a Wrangler and it ran fantastic and was dependable, later selling it. But that isn't always the case going that route. A salvage yard engine is always a risk - period. .... Suggestions?

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post #2 of 14 Old 05-24-2020, 04:23 PM
222Doc
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might be the Gauge. i would set up a manual one to check the real pressure.

from there its going to harder since you need to check the rod and crank bearings see if they are to far gone, plastic gauge works well for this. its not knocking, runs well? im thinking the gauge is not reading this right. lets hope.

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post #3 of 14 Old 05-25-2020, 03:42 AM
TollyWJ
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verify thats what youre actually getting with an old manual gauge. if the pressure is still that low, it IS POSSIBLE to roll in new rod bearings. you'll need to pull the pan and check the crank and make sure the rod caps go back on the rod they came off of and in the same direction. its not exactly the most graceful but if everything is in good shape BUT the rod bearings its an option.
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post #4 of 14 Old 05-25-2020, 03:42 PM Thread Starter
dpl096
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Thank you both for responding. Yes I've checked the pressure with a tried and true manual needle gauge ..... it's still uncomfortably low. I'm starting to think rolling them in is the "quickest" way if the crank is ok - as you pointed out. I did an in the frame rebuild on a '90 Wrangler where I rolled those bearings in as well and it ran strong and carried great oil pressure afterwards. I'm just not wanting to pull that engine and get elbow deep into it is my problem - being lazy I suppose. I've had local Jeep folks telling me to just drive it - that it'll be fine. I just don't know.
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post #5 of 14 Old 05-26-2020, 10:52 AM
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It would be interesting to know what the minimal oil pressure is for that engine. I had a 4.7 a few vehicles back that had the same problem. The factory spec minimum for oil pressure is 4psi at idle. I thought it was uncomfortably low, added lucas oil stabilizer and 15w-40 engine oil and ran it for a while. It never had a problem. I sold that vehicle several months ago, and I still see the new owner driving it around from time to time. Seems to be still going strong. This would be the Lazy man's attempt. If you are considering a engine swap anyway. Run it till it blows up, then swap. It could be years from now....Otherwise, roll up your sleeves, get your goggles on, and swap the bearings to know its good.

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post #6 of 14 Old 05-26-2020, 02:02 PM Thread Starter
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BIGRIGR....

Thank you for the response. I've decided to button it back up and bump up the oil to 15w40 as you did - hadnt thought of the Lucas - but I'm willing to give it a go. Were you running convential or synthetic?
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post #7 of 14 Old 05-27-2020, 12:22 AM
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Just regular conventional oil. Synthetic is only necessary if you want to extend your oil change intervals.

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post #8 of 14 Old 06-04-2020, 11:03 PM
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Just chiming in here. But I was always told that bumping up oil weight for low oil pressure could do more harm than good. The only reason you get better pressure is because of the extra resistance from the heaver oil. But in reality you are starving the top end more because of the heavey oil making it harder to push to the top of the valvetrain. Even though the pressure gauge reads better. I'd just use a normal weight good synthetic and run her the way she is. If you dont have any ticking or knocking then id say your ok. Run her until she blows. Thats just my 2 cwnts tho
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post #9 of 14 Old 06-05-2020, 12:13 PM Thread Starter
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I've decided to not monkey around with this and rebuild the engine. I believe the culprit may turn out to be the cam bearings but to be sure new bearings throughout. I am however tempted to check the compression on each cylinder now and if they are within specs then I'll leave the pistons and rings alone. At least that is my thinking today.
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post #10 of 14 Old 06-06-2020, 11:27 AM
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Cam bearings are a bit of a different situation in these engines with overhead cams. They dont really have "bearings" per say... you probably have main and rod bearings that are a little loose that are effecting your oil pressure. Or the timing chain tensioners, or an oil pump bypassing...I have heard of both the tensioners and the oil pump O-ring leaking on these engines. I have seen the worn main and rod bearings that cause it as well.

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post #11 of 14 Old 06-06-2020, 05:55 PM Thread Starter
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The only thing Im sure of is that I won't know what I've got until I tear it down. I can't help but think new main and bearings will help. If the timing chain or tensioners I'll happily change them out at well. This engine was neglected and abused by at least one previous owner and it's just a damn shame. Common sense maintenance is not too expensive if you want your vehicle to last and be dependable.
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post #12 of 14 Old 06-06-2020, 06:43 PM
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A high volume pump only masks the condition. From a wear perspective, mains, rod bearings, cam bearings all could be the problem (either separately or together). I don't remember but is the oil pressure relief valve part of that pump, or separate?

While you have it apart, plastigage the rod and especially main bearings and see if that's the trouble. If just one is bad, then try replacing that one. If they're all loose, then the wear may be more generalized and who knows what else is affected. If it's not obvious, then the whole thing would need to be opened up and checked.


Couple of thoughts:

Is there any knocking noise?

Has someone possibly replaced bearings on a ground-down crankshaft?

Back some years ago, my YJ blew a rear seal, and because the seal broke inside, it would require removing the engine and dismantling. Since it already had 250K on it, I decided to replace with a re-man. I've now got 115K on my reman and glad I spent the money. It was nice starting over with a brand new engine.

But only you can decide that.

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post #13 of 14 Old 06-06-2020, 07:34 PM
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How much does a re-man cost?
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post #14 of 14 Old 06-07-2020, 03:48 AM
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Quote:
Originally Posted by Niangua View Post
How much does a re-man cost?
Jasper is the most well known (that's what I used) but not the cheapest. The prices also seem to vary by specific engine/production number so you really will have to get quotes.

The good shops do a thorough check of the block looking for hidden flaws and give you a 100K warranty. If you decide to let their shop install it, the warranty also covers labor if there is a failure.

Advantages over having your block rebuilt:

You don't need to pull your old engine out until the new one arrives, especially if you are currently running that means your vehicle won't be laid up for weeks

They've done a lot of engines just like yours, have full fixturing and tooling

They have the tech to deeply check the rebuild block for internal flaws.

Choose an established vendor with good reputation and warranty

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