Differential Pressure Testing Update

[ZeeOSix]

Originally Posted By: rrounds
With such a high psid I would think it would lower the oil pressure a bit to the bearings when you start it up when its cold outside.


Only if the oil pump shoots up to its max pressure relief setting. And even then, I'm sure there is sufficient oil flow for the bearings.

Once the oil pump regulates at max pressure, then the oiling system's flow rate goes from a positive displacement scenario to a pressure dependent scenario - which could effect oil pressure at the entrance of the engine if the filter was pretty restrictive. The oil filter's resistant only reduces engine oil pressure when the oil pump is sitting at its max pressure point. Otherwise, any time the oil pump is out of pressure relief mode, all the pump's positive displacement output (volume) is forced through the filter/engine oiling circuit.

 

[dnewton3]

I should have defined what I consider to be "flutter" a bit better. I presume "flutter" to be rapidly successive, very short duration, cyclic opening/closing of the bypass valve in order to relieve the onset of the delta-p. With that in mind, I doubt it happens much if any at all.

As Jim mentions, the bypass valve will begin to "crack" open as the delta-P is entered, but it will not be fully open until a greater pressure is achieved.

I suppose in theory, one could even argue that the valve will "flutter" between the lower and upper pressures of the relief cycle, if you want to re-define "flutter" to simply mean the cyclic rapid directional change of the valve itself, so that it will "flutter" between 10-11 psi, 11-12 psi, etc ...

But I go back my comments; people worry too much about little things. If it does flutter, it's probably harmless, it almost assuredly doesn't affect wear, and it mostly unavoidable even if it does happen. It's moot.

Why worry about it? It's what BITOGers do.

 

[BlueOvalFitter]

JA, how is the testing going?

 

[Jim Allen]

Going. I have finally reached to point whereI have 15K on the (conventional) oil so I can do some testing when I have time. Which isn't now or soon. Will keep you all posted.

 

[Cooper]

Jim, just curious, is this something you will continue?

 

[CapitalTruck]

Originally Posted By: Jim Allen
The bypass will respond to fluctuations in oil pressure so if it's right at the opening pressure it may do something like a flutter as it responds to slight pressure changes (oil pressure does fluctuate a few psi in each direction).

In any case, bypass opening isn't always (or often) a complete, full opening of the valve and a total bypass of the media. It opens just enough to relieve the pressure over it's set limit so oil is almost always flowing thru the media and the partly open bypass at the same time.

I am not clear how the industry defines a bypass "event," because I didn't ask for a definition. From the context of the discussion, I interpreted it as when the valve opens to any degree and fully closes.

I hate to keep harping on my own truck... but that's the only experience I have where I can watch differential pressure in real time. When the truck starts, it flares to around 2200 rpm. When the (10W30) oil is cold, 30-40F, DP will bump right at the point where the bypass is beginning to open. The spec for the P1 currently fitted is that the bypass starts to open at 8 psi and is fully open at 16. I don't have the datalogs right here in front of me but I think the highest I have see is a tick under 10 psi... but that was a full-bore acceleration test to 5200 rpm with the oil at 45F... not MY norm, certainly. At that temp, the oil is at over 30 cSt... about as thick as 140 grade gear oil. If I drive sedately during warmup, I can keep the DP below the bypass cracking point (cracking being the point where the valve just starts to "crack" open). Remember that I am using an oil that is much heavier than spec'ed and I see cold oil pressure of 80-90 psi regularly (the oil pump relief begins to bypass at around 80 psi) even driving sedately. When I get on it cold, I have seen 110 psi or so.

What things can you do to avoid filter bypass?

1) Run the spec'ed oil viscosity, or "go thinner."

2) Use oils with better cold flow performance.

3) Drive sedately when the oil is cold.

4) Don't run the engine at high revs until the oil is fully warmed up.

5) Use a filter with a higher bypass specification (I'll leave it to you to think of the caveats that will go with that).

6) Use an oil filter with more media area (oversized, but with roughly the same efficiency as the one you are replacing) or one with high capacity, such as a fully synthetic (blown glass) type media (not a cell/syn blend).


Overall, just chill. The bypass won't open often, even if you don't do much to try and avoid it. When it does open, remember it's usually of short duration and a high percentage of the oil is still being filtered.





If I use a filter which may have a higher PSI bypass valve opening spec than OEM (despite it being from a competitor's direct cross reference) do you see any adverse effects occurring?

 

[drmax14]

Being new here I come across this thread and often wondered about bypass events on my Duramax. It has a pump relief setting of 64psi, but first start of the day the psi gauge reads around 70psi. Since the pressure sender is after the oil filter could I assume that the filters relief valve is closed due to the back pressure of the engine. Also I would guess the oil temperature to be around 60F.

 

[ZeeOSix]

Originally Posted By: drmax14
Being new here I come across this thread and often wondered about bypass events on my Duramax. It has a pump relief setting of 64psi, but first start of the day the psi gauge reads around 70psi. Since the pressure sender is after the oil filter could I assume that the filters relief valve is closed due to the back pressure of the engine. Also I would guess the oil temperature to be around 60F.


The filter bypass valve doesn't care what the engine oil pressure is at. What causes the delta-p across the filter is the oil viscosity and flow going through it, and the resistance to flow of the media. You could see 100 PSI of oil pressure on the gauge, and there might only be 5 psi of delta-p across the oil filter, which is well below the typical 12~16 PSI bypass valve setting.