Join Date: Sep 2016
Location: Not in Boise but nearby.
The picture looks like the Donaldson hangs no lower than other parts of the engine and suspension. I've seen situations where a rock or stick flipped up and damaged things well above the lowest point on the undercarriage so if something like that happens then this filter would be at more of a risk than a stock length filter. Unless you are into rock crawling or something like that I don't think it would be a problem though. For instance I don't think snow or a rutted road would be a problem.
I am aware of the phenomenon know as pressure drop across a filter. I have a backhoe that has a gauge on the hydraulic oil filter to tell just this. There are also lots of air filters that have a little indicator that shows the same thing. I was unaware that it could be 15psi though. So I looked it up.
There is an oil pressure relief valve, called the safety relief valve, built into the oil pump. This is a last chance device which is intended to open only when the oil pressure becomes extreme. This is a common practice across the industry though not quite 100%. But......
From AllData's edition of the shop manual:
"Located in the front cover at the sub oil gallery is an oil pressure relief valve which regulates oil pressure within operating range." This is the main oil pressure regulator. It is pretty much at the end of the oil flow path. This is how the oil flows:
From the pump at the front of the engine the oil goes through a gallery on the left side of the block where it goes directly to the rear of the engine with no diversions. It then passes through the filter and cooler, meaning it again has to go to the front of the truck and back to the filter housing.
Then it enters a gallery that runs fore and aft on the left side of the engine and gets distributed to piston cooling on the left bank, bearing lubrication for both the crank and cam, and passes across to the right bank sub oil gallery via a passage from the #1 cam/crank oil supply. That is where the piston cooling for the right bank is and where the oil pressure relief valve is. If the oil pressure relief valve were to fail there would still be some pressure to the other oil users because the connecting passage isn't all that large. There would be no oil cooling to the right bank of pistons though.
Oil from the #3 cam bearing also goes up to the heads where it enters the rocker shafts and lubes the rockers.
Turbo oil comes from the #4 cam bearing oil supply and returns to the rear of the engine block.
It looks like the oiling system is the same across all models from the LLY on. The LB7 however had an additional oiling provision. Oil flowed from the rocker shafts, through a small passage in the rockers to a hole in the top of the push rods, down the push rods and onto the lifters. This oil helped lubricate the lifters which were solid, non-roller style. With the introduction of roller lifters on the LLY it wasn't necessary to have the hollow push rods so eventually they were eliminated but later engines can use either the open or blocked push rods interchangeably.
Now the question is, why does AlisoBob's truck have 15 psi more oil pressure? I see two possibilities. The first is that by coincidence the gauge or sender happened to change at the same time as his filter swap. That isn't entirely out of the question because the filter is very close to the sender for the oil pressure but I think it is only a possibility, not a probability.
The other is that in some way a reduction in pressure drop across the filter is leading to an increase in system pressure. I think this is much more likely. So then the question is, how is this accomplished?
The location of the oil pressure sensor is not given in the description of oil flow. Since it is located on the left side where oil is going in both directions it is hard to say for sure but I think it is in the gallery coming from the filter, not the one going to the filter. In that case if the filter has less pressure drop it could affect the pressure reading at the sensor. However, this isn't the whole story.
Normally the safety relief valve in the pump is set to a significantly higher pressure than the pressure relief valve that is in the right oil sub gallery. Unless something is broken, the pressure relief valve does all of the pressure control. It should be at the same pressure as all of the other oil in the system unless there is a restriction somewhere.
If the oil pump flows more oil than the pressure relief valve can dump, perhaps because the passages to the pressure relief valve are restrictive, then I can see that the pressure would increase on the sensor side of the oiling system. In the same passage that contains the pressure relief valve there are also piston cooler jets so there would be some oil flow. If the passage was restrictive and the jets flowed nearly all of the oil coming through then the regulator would have less authority on the rest of the system. The increased oil flow available elsewhere would then make for more pressure at the gauge. I think this is the explanation.
Either that or AlisoBob is actually the low life scum bag that the BITOG people would have us believe and is still trying to scam us. I know which explanation I like.
Last edited by mizterwizard; 04-09-2019 at 03:57 PM.