High volume oil pump?
02-23-2016, 09:39 PM
#16
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Year: 2004
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Engine: 2000 4.0
. Push more flow and the pressure goes up. A 20-25% increase in flow should give roughly a 50% increase in pressure. The other thing to keep in mind is that you need a certain amount of oil pressure to "float" the crank and camshaft... when the engine is running the shafts don't actually touch the bearings; they're floating on a film of oil that's being pumped into the bearings. If the pressure is too low to support the shaft, it contacts the bearings and you get more wear. Another way to look at it is filling a pail that has a hole in it. A small hole and you can still keep it full if you pour it in as fast as it's running out; a larger hole and you have to fill it faster to keep it full. That's where/why the high volume pump should help.
FWIW, I'm a mechanical engineer for a company that makes hydraulic components... while engines aren't my specialty, I do understand fluid flow and pressure.
FWIW, I'm a mechanical engineer for a company that makes hydraulic components... while engines aren't my specialty, I do understand fluid flow and pressure.
An engine with open sleeve bearing relies on hydrodynamic pressure. The speed and rotation of the crank/cam journal create a wedge of oil that the bearing "skates" on. The pressure in an automotive lubricating system is simply dead head pressure or reserve pressure. That pressure instantly goes away once it inters the journal. That wedge of oil however can have a hydrodynamic pressure of over a thousand PSI.
02-24-2016, 01:32 AM
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Read his post #7 he has pressure. His gauge is programmed to drop to zero around 4-6 psi. Pressure at hot idle does not mean a whole lot...while it is alarming to look at it don't mean oil has quit flowing. As long as his lifters stay pumped up he has oil flowing. His pressure at highway speed is good so his bearings cannot be that bad....maybe worn a little but if spread though several bearings that could affect pressure. Accumulatively his bearings could be still within tolerance! With the head crack it is usually the cam bearing/bearings that take the hit.
02-24-2016, 05:44 AM
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Year: 2000
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If your an engineer then surely you understand that you CAN NOT build pressure to "float" the crank. To do this you would have to have a closed bearing with seals on each side to contain the oil (hydrostatic).
An engine with open sleeve bearing relies on hydrodynamic pressure. The speed and rotation of the crank/cam journal create a wedge of oil that the bearing "skates" on. The pressure in an automotive lubricating system is simply dead head pressure or reserve pressure. That pressure instantly goes away once it inters the journal. That wedge of oil however can have a hydrodynamic pressure of over a thousand PSI.
An engine with open sleeve bearing relies on hydrodynamic pressure. The speed and rotation of the crank/cam journal create a wedge of oil that the bearing "skates" on. The pressure in an automotive lubricating system is simply dead head pressure or reserve pressure. That pressure instantly goes away once it inters the journal. That wedge of oil however can have a hydrodynamic pressure of over a thousand PSI.
Hah! Maybe we should just fill our radiators with motor oil, then a coolant leak won't dilute the oil and fry our engines (just kidding).
02-24-2016, 08:45 AM
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Well, up to a point. High pressure is actually resistance to flow, which is not good. That's why 40W is not good. Too thick.
Incidentally, oil pressure is mainly developed in the cam bearings.
A high volume pump is also not good. The oil needs to move slowly enough to pick up and carry away heat from the bearings and other components.
Edit: on Tuesday morning, I talked to a long-time mechanic. He said a high volume pump and/or replacing crank & rod bearings won't help the oil pressure. He agreed with me that oil pressure is mainly a function of the cam bearings. He said to change your oil now and put 50 weight in in and run it until you can rebuild the engine properly. Take his advice if you want to. It is the cheaper way out for now.
Incidentally, oil pressure is mainly developed in the cam bearings.
A high volume pump is also not good. The oil needs to move slowly enough to pick up and carry away heat from the bearings and other components.
Edit: on Tuesday morning, I talked to a long-time mechanic. He said a high volume pump and/or replacing crank & rod bearings won't help the oil pressure. He agreed with me that oil pressure is mainly a function of the cam bearings. He said to change your oil now and put 50 weight in in and run it until you can rebuild the engine properly. Take his advice if you want to. It is the cheaper way out for now.
Either rebuild or leave well enough alone. Your engine is being lubricated just fine with the standard pump.....even more so with less restriction/low pressure.I think you're fine.
I'd put a mechanical gauge in so you can see the real pressure and then stop worrying. There are plenty of later-year XJ's out there running very low oil pressure readings with no ill effects.
If you want to clog things up with cholesterol in a can, that's your call. Pretty much all engine and lubrication experts agree you shouldn't thicken the oil merely to get the numbers up. Some folks do anyway and love the results. YMMV.
I'd put a mechanical gauge in so you can see the real pressure and then stop worrying. There are plenty of later-year XJ's out there running very low oil pressure readings with no ill effects.
If you want to clog things up with cholesterol in a can, that's your call. Pretty much all engine and lubrication experts agree you shouldn't thicken the oil merely to get the numbers up. Some folks do anyway and love the results. YMMV.
Read his post #7 he has pressure. His gauge is programmed to drop to zero around 4-6 psi. Pressure at hot idle does not mean a whole lot...while it is alarming to look at it don't mean oil has quit flowing. As long as his lifters stay pumped up he has oil flowing. His pressure at highway speed is good so his bearings cannot be that bad....maybe worn a little but if spread though several bearings that could affect pressure. Accumulatively his bearings could be still within tolerance! With the head crack it is usually the cam bearing/bearings that take the hit.
Another in agreement in general on all these quotes on engines on a whole. But even more so for the OP's 4.0 no need for a HV or HP oil pump and have saw then cause problems with stock engines in the past (no experience with 4.0's) but they should be no different same principle.
The additive decals you see at the racetrack on a lot of cars, they do not use any of them. But if you race in a series and they are a sponsor you have to run one of them and where they tell you to place them even. That entitles you to part of the contingency money with how you place.
02-24-2016, 08:54 AM
#23
Another in agreement in general on all these quotes on engines on a whole. But even more so for the OP's 4.0 no need for a HV or HP oil pump and have saw then cause problems with stock engines in the past (no experience with 4.0's) but they should be no different same principle.
The additive decals you see at the racetrack on a lot of cars, they do not use any of them. But if you race in a series and they are a sponsor you have to run one of them and where they tell you to place them even. That entitles you to part of the contingency money with how you place.
The additive decals you see at the racetrack on a lot of cars, they do not use any of them. But if you race in a series and they are a sponsor you have to run one of them and where they tell you to place them even. That entitles you to part of the contingency money with how you place.
4.0/2.5 distributors are weak and cannot handle the additional stress of HV or HP pumps.
You will notice wear/stress on the drive pins, also, gear failure and shaft wear are common, as your will read on Jeep sites quite often.
Also, no mention here of the fact that lifters fail, or begin to fail, at 6lbs of pressure.
Since I'm a 'snake oil' salesman.............just waiting on all the over educated engineers to point this out.
Edit to add- thinner oils are 'wet' and bleed out easily. Lucas is 100% pure petroleum, not an 'additive' in the snake oil sense, it does force the oil to cling to the metals longer, slowing the bleed of worn bearing for a time......not a fix but may gain you time.
Last edited by Jeep Driver; 02-24-2016 at 09:02 AM.
02-24-2016, 03:41 PM
#24
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.not a fix but may gain you time.
02-24-2016, 04:38 PM
#25
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But the "additional stress" is offset by the reduced back pressure on the pump, reducing the torque it takes to drive it...
02-24-2016, 05:22 PM
#26
Case in point.......posted just minutes ago.......
https://www.cherokeeforum.com/f2/new...y-4-0l-222659/
02-24-2016, 05:39 PM
#27
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The input torque on the pump drive shaft is equal to the output torque produced by the back pressure (i.e. oil pressure) on the pump gears. Less back pressure, less input torque, less load on the distributor shaft.
The fact that Mopar offers a high volume pump says they believe the distributor drive shaft is strong enough to drive it, even at the maximum pressure, which I'm not achieving.
What does that have to do with oil pump drive torque?
The fact that Mopar offers a high volume pump says they believe the distributor drive shaft is strong enough to drive it, even at the maximum pressure, which I'm not achieving.
Case in point.......posted just minutes ago.......
https://www.cherokeeforum.com/f2/new...y-4-0l-222659/
https://www.cherokeeforum.com/f2/new...y-4-0l-222659/
02-24-2016, 05:47 PM
#28
The input torque on the pump drive shaft is equal to the output torque produced by the back pressure (i.e. oil pressure) on the pump gears. Less back pressure, less input torque, less load on the distributor shaft.
The fact that Mopar offers a high volume pump says they believe the distributor drive shaft is strong enough to drive it, even at the maximum pressure, which I'm not achieving.
What does that have to do with oil pump drive torque?
The fact that Mopar offers a high volume pump says they believe the distributor drive shaft is strong enough to drive it, even at the maximum pressure, which I'm not achieving.
What does that have to do with oil pump drive torque?
The distributor drives the pump. Has everything to do with it.
The gears are larger on the HV pump, cogs of the gears are longer to move more oil.
It does cause more stress.
You are seeking HV at idle, the HV pump may offer you that at idle but your engine spends little time at idle.......thus the trade off.........solving one problem and creating another.
I studied this some time ago, every article I read was against the HV pump in most cases, specifically in the 4.0/2.5
02-24-2016, 07:49 PM
#29
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The distributor driveshaft drives the pump, but nothing in the linked topic suggests that the bearing failure was related to the oil pump.
In a healthy engine with good oil pressure already, I agree that a HV pump is unnecessary and possibly harmful. But in an engine that has 20psi oil pressure at highway speed when hot, that's a different matter... and if it increases that 20psi to 30psi, that's still less stress on the distributor shaft than a stock pump at the 75psi relief pressure.
The gears are larger on the HV pump, cogs of the gears are longer to move more oil.
It does cause more stress.
You are seeking HV at idle, the HV pump may offer you that at idle but your engine spends little time at idle.......thus the trade off.........solving one problem and creating another.
It does cause more stress.
You are seeking HV at idle, the HV pump may offer you that at idle but your engine spends little time at idle.......thus the trade off.........solving one problem and creating another.
10-09-2016, 07:27 PM
#30
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HP Oil Pump
Well...I hope you folks are wrong about the HP pumps....I've installed 4 of them, 3 in 4.0L XJ's and one in my Comanche. No problem whatsoever. The only one of those 4 vehicles with an oil pressure gauge was my '87 Waggy, it bumped the oil pressure 15lbs. No problems yes, but if the distributor TAS, I guess I will know why.