purchased a new Melling oil pump for my 1.6 Miata. The factory one had a fancy washer in the waste gate that has a tapered hole in the middle to restrict the flow of oil out of the opening. ( regulating the oil pressure?) And the new one has none. Would adding the washer to the new one raise the oil pressure enough to go through with installing it? From what I have read about the upgraded ones is that the difference between them is the shim. It increases the tension on the spring and the hole slows the oil from exiting the gate increasing the oil pressure... The second picture is the factory shim.
The relief valve only controls Max pressure and typically has no effect after the engine is at operating temperature so there's no benefit to shimming the spring.
In reply to APEowner :
That's always been my understanding as well. I've never figured out the logic in shimming the relief valve.
The only time the spring should work is at higher RPM thus causing higher oil pressure. It acts as a relief valve, letting out the excess oil pressure. So the factory one has that washer to help regulate the oil flow.
As APEowner said, you're likely not reaching the relief valve pressure when the oil is at operating temp.
The washer is something for the spring to sit against, nothing more fancy of a purpose than that.
MyMiatas said:
The only time the spring should work is at higher RPM thus causing higher oil pressure. It acts as a relief valve, letting out the excess oil pressure. So the factory one has that washer to help regulate the oil flow.
The oil doesn't go through the spring, it's dumped back into the intake side of the pump when the valve opens and, as I said above that's unlikely to happen when the engine is at operating temperature.
After debating about it. One would have to come to the conclusion that the forums that I came across about this subject may have been a misleading topic. The actual pump that is driven by the crankshaft should only put out the desired pressure it was design too. The higher the RPM the more oil flows through the system (at cooperating temp). I saw the washer in the old one and none in the new and that began the debate. Thank you for the reply.
MyMiatas said:
After debating about it. One would have to come to the conclusion that the forums that I came across about this subject may have been a misleading topic. The actual pump that is driven by the crankshaft should only put out the desired pressure it was design too. The higher the RPM the more oil flows through the system (at cooperating temp). I saw the washer in the old one and none in the new and that began the debate. Thank you for the reply.
The oil pump puts out (for our purposes here) a fixed amount of fluid per revolution. The pressure comes from resistance to flow in the engine. The bypass is to prevent pressure from getting too high.
Hot thin oil has lower pressure because there is less resistance to flow. Likewise a worn out engine has lower pressure because less resistance to flow. The same amount of oil will be moving through the system. (technically more volume at the lower pressure because the pump will get a little more volumetrically efficient at lower output pressure...)
It seems the thinking here is that the relief valve acts like a wastegate and is regulating oil pressure across the RPM range, while the situation is more like you're running a tiny turbo and the wastegate rarely opens at all...maybe the situation varies by engine model but there's a lot of this "relief valve regulates normal oil pressure" thinking out there. I've been guilty of it, since I had my 4AGE's oil pump shimmed, my thinking was to compensate for the pressure drop of adding an oil cooler system. I actually found a table of oil pressure increase vs. shim thickness for a 4AGE somewhere when I did this, but I'm having a hard time finding any results from people experimenting with it now...
In reply to GameboyRMH :
The regulator does not open until it reaches its relief pressure. If you only have 10psi oil pressure at idle, you could shim it until the spring is coil-binding and you would still have 10psi.
But are there any engines that could reach relief pressure at full operating temperature at higher RPMs? If so, shimming the pump could be having something like the intended effect on some engines, which might've lead to the misconception that it's a generally effective way to get an oil pressure boost.
In reply to GameboyRMH :
Almost all engines generally hit relief pressure by 3000-4000rpm or so depending on factors.
Oil pressure is a function of how much resistance to flow there is in the oil galleries. The pressure regulator merely sets an upper bound on the oil pressure. If the regulator maxed out at 60psi at 3000 before shimming, you still will have 60psi at 3000 after. You'll just continue building pressure at higher speeds until it hits the new pressure.
I had a BP engine that had the oil squirters blocked off and one of the higher volume pumps that came from a VVT engine. Ridiculous cold oil pressure, close to 90 psi IIRC. Never saw that when the engine was hot.
On the top of the 1.6 engine block there is a oil passage that is part of the main line. It has a plug in it that has a tiny hole that the oil passes though to get to the cylinder head. That small hole certainly would cause the oil pressure in the block side to stay at a certain point. Forcing some to where it needs to be, the crankshaft.
The valve didnt work like I was picturing it operating. I pictures it having a area that it open to dumping oil out the hole that had the spring and valve in it, back into the oil pan.
Here is a picture of the cap that opens when it is too high in pressure. As you can see the shiny spot is where the oil is fed back to the pump area instead of out the hole with the spring
