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Old 11-08-2019, 05:07 PM
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High volume pump

I rebuilt my motor back in 2012 for my 1993 Wrangler 4.0. When I picked up all my parts from the machinist, he stated that I must run 20W-50 motor oil for the life of the motor. He removed too much off the crank.
I have a leak in my oil pan after 120,000 miles, and I am getting ready to replace the gasket. My question is if I instal a High volume pump, while my pan is off, will I be able to maybe run a 10w-40 to maintain good oil pressure? It would be easier to find the oil and cheaper.
Thanks

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Old 11-08-2019, 06:02 PM   #2
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I would never have paid for the machine work and made the clown pay for the crank he butchered.

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Old 11-08-2019, 06:11 PM   #3
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If it isn’t broke don’t fix it. You’ve got 120k out of a rebuild, that’s not a bad thing. I would not be rocking the boat now.
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Old 11-08-2019, 06:51 PM   #4
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Without tearing your engine apart and measuring your crankshaft there's no way anyone could answer that question.... and even then the very slight difference in hot viscosity of 40 wt to 50 wt would do next to nothing for excessive tolerances....

I suspect that it would make little to no difference to change to 10-40 now with the pump you currently have and I certainly wouldn't run 20-50 just because that bozo said so...
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Old 11-08-2019, 07:46 PM
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Yes, the crank was over cut, yes been running 20w-50 since rebuild for good pressure, yes I was compensated for the error.
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Old 11-08-2019, 09:15 PM   #6
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Give 15/40 a try an see who it works for you. Its inexpensive and available everywhere. Rule of thumb is 10 psi per 1000 rpm with an idle press of 20 to keep things happy. What are you seeing currently running 20/50 when the engine is fully warmed?
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Old 11-08-2019, 09:25 PM
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Iím seeing 21-23 psi. Not looking to go any less, only a few psi forward if possible.
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Old 11-09-2019, 01:00 PM   #8
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I'm not an engine mechanic so I'm not sure exactly what I'd do about viscosity. As stated above, "If it ain't broke....". Unless you're having slow cranking issues when the engine is cold, I'd continue with what's been working for 120K miles.

As far as a high volume oil pump, a high volume pump isn't necessarily a high pressure pump. One would think a high volume pump would also act as a high pressure pump, but that's true only until the first restriction. Think of holding your finger over the opening of a garden hose. Your finger creates pressure behind it within the hose, but once the water is past your finger, it's no longer under pressure. If you pinch the hose in the middle, you create pressure behind the pinch, but the pinch only allows so much volume beyond the pinch.
From what I read here, most posters recommend a stock oil pump. A high volume might be good on a racing engine where tolerances are kept loose to reduce friction at the expense of longevity.

If you still can, ask the fellow that built your engine for advice.

Good Luck, L.M.
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Old 11-09-2019, 04:53 PM   #9
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You can over cut a crankshaft, but you have to change the bearing caps to get the right tolerance. Different viscosity oil will not compensate for a to high tolerance in the bearing caps. It's just a disaster to happened.
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Old 11-09-2019, 05:30 PM
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If I remember correctly, the tolerances plastic gauged about .001 over What factory manual called out for.
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Old 11-09-2019, 05:46 PM   #11
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If that's the case, put 10-30 in it now and see what you get... my bet is you'll see no difference
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Old 11-09-2019, 06:21 PM
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Quote:
Originally Posted by Gottagofast View Post
If that's the case, put 10-30 in it now and see what you get... my bet is you'll see no difference
That was tried back in 2012 with 10W-40 and newer engine. Very low pressures, bad idea.
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Old 11-09-2019, 06:46 PM   #13
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Ah gotcha.... nevermind

I suspect that you have more going on than .001" excessive gap

Iirc I had an engine worn to .008 over spec that still had decent oil pressure
Now this would have been over 20 years ago so I can't guarantee that number...
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Old 11-09-2019, 06:49 PM   #14
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Quote:
Originally Posted by Scouter View Post
I’m seeing 21-23 psi. Not looking to go any less, only a few psi forward if possible.
I may have missed it, but are you referring to 21-23 lbs. of oil pressure at idle, hot? Or 21-23 above 1500 RPM? If the latter is the case, I am surprised it has lasted 120k.

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If I remember correctly, the tolerances plastic gauged about .001 over What factory manual called out for.
Virtually any internal combustion engine that runs on gasoline (and a lot of diesels) will live a long life with a couple thousandths clearance on both the rods and the mains. That being said, the factory (any one, for that matter) has a spread for the tolerances.

For instance, Chrysler specified .0015 to .002 rod bearing clearance on new 4.0 builds, with .001 to .003 as acceptable, and .002 on the mains with .001 to .0025 as acceptable. Acceptable doesn’t cut it for me. So that .001 difference reflected in the plastigage could be anything, depending on where in the spread the machinist was referring to.

I have only used two crankshaft grinders over the last 40+ years, and both are well aware of how picky I am for size and surface finish.

I don’t use plastigage, but I do mic every crankshaft, and use a dial bore gauge on every main bore and connecting rod big end prior to assembly. Time consuming yes, but no guesswork. On 4.0’s, I run .0013 to .0015 on the connecting rods, .0014 to .0018 on the mains.

So, in summary, as others have stated, it is virtually impossible to succinctly answer your question. It would be interesting to know what your max oil pressure is between 1500-4000 RPM, hot.
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Old 11-09-2019, 07:12 PM
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That would be 21-23 Hot At idle, after a good summer run, checked with a actual oil pressure gauge.

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