Something to ponder regarding oil pressure

S10Vette

Member
Pretty sure everyone would agree on what the normal oil pressure range should be although perhaps differences of opinion on the minimum acceptable on an older engine.

Another question that has come up is regarding how long it should take for pressure to come up at the gauge, and that has been covered also.

So what I got to thinking about is that the pressure gauge is at the end of the loop so to speak as is best practice for locating a gauge. What is different though from (almost all) automotive applications is that the oil line tees off to the (partial flow) oil filter.

So in reality, aren't we measuring to a large degree the flow resistance through the oil filter on the return? To illustrate, if you disconnected the line to the filter would not the gauge read nearly zero psi ? Likewise if you plugged the line then you would be reading the pressure that the relief valve (assuming it could handle the flow) was controlling, with all other return flow to the pan going past the bearings, etc.

I wonder also if a badly clogged filter would potentially increase the pressure reading at the gauge ?
 
The orifice in the filter is a small "leak to sump" vs. all the other "leaks" past the main, rod and cam journals.

Typical thought is that 15% (give or take) of the oil pumped passes through the orifice and filter, leaving 85% to lube the bearings and timing gears and POSSIBLY lift the relief valve a bit if the pump is real good and all the bearing clearances are "in spec".
 

So of course, [u:8df514d2ad]after[/u:8df514d2ad] posting this I found other related discussions. So, the main answer is that the filter center tube has a restricted orifice size specifically to ensure enough "backpressure" in the system. Obviously something to take into account if converting to a "spin on" filter and that has been covered.
 
(quoted from post at 14:48:59 12/31/16) Pretty sure everyone would agree on what the normal oil pressure range should be although perhaps differences of opinion on the minimum acceptable on an older engine.

Another question that has come up is regarding how long it should take for pressure to come up at the gauge, and that has been covered also.

So what I got to thinking about is that the pressure gauge is at the end of the loop so to speak as is best practice for locating a gauge. What is different though from (almost all) automotive applications is that the oil line tees off to the (partial flow) oil filter.

So in reality, aren't we measuring to a large degree the flow resistance through the oil filter on the return? To illustrate, if you disconnected the line to the filter would not the gauge read nearly zero psi ? Likewise if you plugged the line then you would be reading the pressure that the relief valve (assuming it could handle the flow) was controlling, with all other return flow to the pan going past the bearings, etc.

I wonder also if a badly clogged filter would potentially increase the pressure reading at the gauge ?

Pressure is pressure - the gauge is reading the pressure going through the bearings regardless of what other factors are controlling it. It's a bypass filtering system so the oil filter has little if any throttling effect.

TOH
 
(quoted from post at 12:42:47 12/31/16)

Pressure is pressure - the gauge is reading the pressure going through the bearings regardless of what other factors are controlling it. It's a bypass filtering system so the oil filter has little if any throttling effect.

TOH

However if you disconnect the line to the filter and relieve that restriction on the return I believe the pressure in the system and therefore to the bearings would also drop, correct ? Obviously the lines of course are small enough that there is [u:e523d18696]some[/u:e523d18696] restriction on that flow.
 
The oil filter hole is about .060 and the pump can supply enough volume through the large main galley to keep that and the .003 / .008? exits supplied with volume . If you forget a rear oil galley plug then the pump can not supply enough volume .


It is an interesting concept .though , they make a water manifold system for your house so you can flush the throne and not burn someone in the shower .
 
However if you disconnect the line to the filter and relieve that restriction on the return I believe the pressure in the system and therefore to the bearings would also drop, correct ? Obviously the lines of course are small enough that there is [u:128d6efb3d]some[/u:128d6efb3d] restriction on that flow.

Easy enough to prove / disprove . Before your next oil change , start her up and have someone watch the gauge while some else disconnects the oil inlet line .It will make a small mess but it would take a while to even get 1/2 quart low .
 
(quoted from post at 18:15:50 12/31/16)
However if you disconnect the line to the filter and relieve that restriction on the return I believe the pressure in the system and therefore to the bearings would also drop, correct ? Obviously the lines of course are small enough that there is [u:8db77ccceb]some[/u:8db77ccceb] restriction on that flow.

Easy enough to prove / disprove . Before your next oil change , start her up and have someone watch the gauge while some else disconnects the oil inlet line .It will make a small mess but it would take a while to even get 1/2 quart low .
rops mine from 25# to 20#. Would likely drop more, but the brass flare fitting ID is only 0.177 inch. Filled my 1 pint catch bottle in 5 seconds. 25 seconds if catch at filer outlet.
 
(quoted from post at 17:45:12 12/31/16)
(quoted from post at 18:15:50 12/31/16)
However if you disconnect the line to the filter and relieve that restriction on the return I believe the pressure in the system and therefore to the bearings would also drop, correct ? Obviously the lines of course are small enough that there is [u:5e29eb1b4c]some[/u:5e29eb1b4c] restriction on that flow.

Easy enough to prove / disprove . Before your next oil change , start her up and have someone watch the gauge while some else disconnects the oil inlet line .It will make a small mess but it would take a while to even get 1/2 quart low .
rops mine from 25# to 20#. Would likely drop more, but the brass flare fitting ID is only 0.177 inch. Filled my 1 pint catch bottle in 5 seconds. 25 seconds if catch at filer outlet.

That's good info . I am rebuilding the 8n and will add a spin on filter ( I already have a nice remote housing ) I will save myself some time and stick with an .060 office and not play around with different sizes .
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top