IJ.;1994245 said:
10/60 and the 10/70 I'm now using isn't heavy at low temps, I don't understand the reasoning behind the "it's only providing pressure and not flow"... :nono:
Ian, in the case of a 7M, where is the extra flow coming from? Simply showing more pressure does not equate to more flow.
Don't misunderstand me, an increase in pressure
can mean an increase in flow if you have a variable flow pump. However, a car engine like the 7M (and other belt-driven oil pump ICE engines I know) the oil pump doesn't flow any more oil, no matter what grade oil you put in. The amount of flow through the pump is a relatively fixed constant for a given RPM. The pump turns x RPM for x RPM of the engine and puts out x volume flow. No oil changes that. What changes the oil getting to your bearings is the flow that's redirected through the relief valves both in the pump and the filter bracket. The reality is that in factory configuration the 7M LOSES oil flow as pressures increases. The pump will output X amount of flow and redirect Y and Z flow away from the bearings as soon as the reliefs open up.
If you shim the oil pump AND remove the factory filter bracket relief, under some circumstances, sure you may get more flow (high RPM, oil flowing through the engine easier than through the relief).
Let's try an equation(variables only, not concerned with constants for simplicity's sake):
Vf= Volume flow at pump gears (Proportionate to RPM since the pump is direct driven assuming the pump is a closed system)
Vb= Volume flow at bearings
Vpr = Volume flow at pump relief
Vcr = Volume cooler (filter bracket) relief
Pg= Gauge Pressure (beginning on oil circuit)
Pfb= Pressure at the final bearing (we can't measure this)
Ov= Oil viscosity
Bc= Bearing clearances
Pl = Pressure loss/gradient from the main oil channel to the bearing surfaces
We start with Vf. Vf cannot be increased by any means I've ever seen no a 7M. You'd have to re-gear the oil pump to have a different gear ratio. In this scenario Vf is a fixed constant at a given RPM.
This is roughly what you have:
Vf = Vb + Vpr + Vcr
Rewritten:
Vb = Vf - Vpr - Vcr
Vb is what we care about. That's the game. Maximum flow (with sufficient pressure) to the bearings.
To increase Vb, you need to decrease Vpr or Vcr or both. You can eliminate Vcr by installing a full flow oil cooler. Vpr you can decrease by shimming the pump.
So what about Pressure?
Pg = Vb*Ov/(Bc + Pl)
Bc is changed by your bearing clearances and Pl is an unknown. I think Pl is significant. If Ov goes up we have more pressure, but we do not have more volume flow to the bearings.
Remember, the pump flow does not depend on the oil viscosity at all.
Pfb = Pg - Pl*Ov
Pfb matters, Pg doesn't. Pg is what you see on the dash. Pfb is what keeps the motor bearings alive. For Pl to be zero the oil passages would need to be the same net diameter, length and straightness (curves introduce restriction). Looking at the 7M oil passages I dont know how you could argue they are equal. A couple poor bearings will be at the end of the oil passage and see pressure losses that are
directly linked to the viscosity of the oil used.
You can use a pressure drop calculator to estimate the drop across a given length of straight pipe, but the net result is that the pressure drop increases as oil viscosity increases with a 1:1 ratio compared to the increase in pressure seen by raising the oil viscosity. This is to say the bearings are going to see roughly the same pressure with different viscosity oils. Despite your gauge pressure, I think the bearings see roughly the same pressure. That increase in pressure seen on the gauge is GONE due to increased pressure losses by the time the oil gets where you want it.
Another function of the oil is to pull away any contaminants from your engine and to pull heat away. An oil does this best by flowing easily and quickly. Again, the only way to change the VOLUME moving through the motor is by shimming the pump and eliminating the oil filter bracket relief AND by revving past the point where the pump relief used to kick in. Without both of those modifications, the pump flow is relatively fixed. I submit a heavier oil does this job of heat transfer and contamination wash worse than a lighter oil because you will be REDUCING oil flow, even if your pressure reads higher.
Again, in factory configuration, the more oil pressure indicated on your gauge the LESS volume of oil you have going through your engine bearings. Best case scenario, you only lose a little volume in flow to the relief valves and the extra viscosity protects the bearings enough to avoid damage and you don't notice a difference. Worst case, you lose volume flow through the relief valves and the pressure at the bearings is now too weak to perform it's job or to properly pull heat and contaminants out of the engine.
IJ said:
If this were the case it would come with huge warnings NOT to use it in anything other than modified engines... (bit of a clue it's factory spec for some BMW engines)
It's Engine Oil not Single 140 gear oil...
Any factory engine could be designed to run heavier 100C viscosity. The manufacturer would recommend whatever fits their clearances best. I understand heavy oil is factory spec in some engines. The 7M is not. Yours was built for more clearance. Many here still use heavy oil on a stock motor which is spec'd for 30W oil.
nathaninwa;1994249 said:
It might be engine oil, but already said in the thread, theres members putting 20w/50 just to see more oil pressure, but the very thing there trying to fix, is actually causing more problems. Information is key and reading is the best thing we can do. Oils have come along ways. I switched machine shops this last time around, and one of his questions when talking about oil clearances, what oil are you going to run.
If the pump didnt have a bypass, then yes, constant flow, but with a bypass installed, flow is never really known.
Yes and yes (except it's not just one bypass, it's two!).
