kevtherev wrote:Some other reasons.. for those that searched and found this post
The pressure relief valve, can be yet another cause of low oil pressure if the valve sticks open or is held open by a small piece of debris. The relief valve is designed to limit oil pressure as engine speed increases. The valve opens when pressure reaches a preset value (typically 40 to 60 psi). This vents oil back into the crankcase and limits maximum oil pressure in the engine. The reason for doing so is to prevent oil pressure from reaching dangerous levels. Too much oil pressure can be just as bad as too little because excessive pressure can rupture the oil filter or even blow out pressed-in oil galley plugs in the block.
Low oil pressure may also be the result of air in the pump. If there is too little oil in the sump, air can be drawn into the pump. But this can also happen if the crankcase has been overfilled. The oil can become aerated (full of tiny bubbles) because it is making contact with the spinning crankshaft and is being churned into foam.
Sometimes the engine may become starved for oil at higher rpms because the oil is not returning quickly enough to the crankcase. The underlying cause here is usually severe varnish buildup that restricts the oil return holes in the head.
A plugged oil filter can be yet another cause of low oil pressure. When the oil leaves the pump, it passes through the filter before going on to the bearings and oil galleys. All filters create a certain amount of resistance to flow that increases with the rate of flow. But the amount is not much, typically only a couple of pounds. But as the filter becomes clogged with debris, the restriction created increases. Eventually the point may be reached where no oil will pass through the filter element. So to prevent such a blockage, a pressure relief valve located in the filter or where the filter mounts to the block is designed to open if the pressure differential across the filter exceeds a preset value (typically 5 to 40 psi). This allows the oil to bypass the filter and keep on flowing. But the engine's oil pressure will be reduced to that of the bypass valve. Replacing the plugged filter will solve the problem.
Taken in part from AA1car
With respect Kev, a lot of which doesnt apply to a wbx. Excessive bearing clearances will kill any engi e, but engine oil pumps whether two-gear, "gearotor" type or crescent gear all supply vastly more volume (and hence generate pressure) than the bearings can use.
Elevated oil temps however lead to rapidly falling viscosity, loss of film strength in the oil and loss of pressure. Repeated hot running and old oil leads to worn bearings.
Low oil? If it was worse than 60% empty and you are cornering hard or climbing 1:4 hills than maybe a wbx might tell you that it is getting thirsty, but the pickup is so low in the sump it would have to be practically running on a litre of oil.
Overfilled wbx crankshaft churning the oil? Well considering that the engine actually has very good windage and oil control thanks to the lifter housings forming a very effective sump baffle, it would have to be overfilled by maybe 50% for this to cause a problem.
I would say that for the majority of cases once old wiring, corrosion and poor earths start triggering the buzzer, the bearings are already on the way out.
They do soldier on remarkably well, I drove 250 miles on a knocking big end that sounded like an old Transhite diesel over 2500rpm (with care) and got away with it, but when they go pop...
