I wanted to start a thread on oil pressure related problems. Does anyone know if such a thread exists, and is it a sticky?
I'll assume for the moment that no such thread exists.
The MR2 AW11 has a simple oil pump. The pump is located at the front of the engine behind the timing wheel. It consists of two toothed rings, one inside the other. The two wheels are mounted asymetrically and are designed to squeeze oil into a high pressure output port that feeds directly into the engine block. The oil pump contains a high pressure relief valve that vents directly back to the sump. This relief valve is protective and does not operate in normal usage.
The high pressure output line runs past the oil sender unit which in turn drives the gauge on the instrument cluster. If you have any doubts, remove the oil sender and use an external oil pressure tool to read the pressure directly. I don't have one unfortunately.
Next, the high pressure line feeds directly into the oil cooler adapter. The cooler adapter is also very simple but it does have a potential flaw. In normal operation the oil is pushed through an oil filter then back into the engine block for distribution throughout the engine. However, at high RPM's a relief value opens in the oil cooler adapter which sends excess oil through the oil cooler and back into the sump. Yes, it is bleeding oil away from the engine.
The oil cooler itself is a jacket around the water coolant pipe; oil arrives at the bottom of the cooler then returns from the top of the cooler back into the sump.
This isn't a sophisticated arrangement; many of the 4AGE derivatives dispense with the oil cooler entirely.
A problem that can occur with the oil cooler adapter relates to the way in which the relief valve operates. While the relief value in the oil pump is nearly bullet proof, the same cannot be said for the adapter's relief valve. The valve consists of a spring and a piston. Oil pressure, pushing against the spring, causes the piston to retreat below the output port to the oil cooler.
However the piston may have difficulty operating if the chamber containing the spring does not vent appropriately. To ensure that oil in this chamber is vented, there are two small holes in the side of the piston. Oil trapped in the spring chamber will vent from these holes into the output port. But if these holes become blocked then normal movement of the spring is inhibited, which in turn can result in either excessive pressure at high rpm or low pressure at low rpm (most people don't notice the higher than normal pressure).
So I would recommend that if you are tracing low or high pressure problems you tackle the oil cooler adapter and the oil pressure sender unit at the same time. To do this you probably want to temporarily relocate the a/c compressor which entails removing the a/c belt, the compressor electrical connection and the oil cooler return line to the sump. However, having once done this you have clear access to both the sender and the relief valve at the bottom of the oil cooler adapter.
The oil sender is a small thread so avoid over-tightening. I use a small pipe wrench wrapped in rags to avoid denting the case of the oil sender unit. It works, although I believe there is a special tool for this exact purpose. Be gentle!
The relief valve is an 18 mm bolt (approx) on the bottom of the oil cooler adapter. Removes this and a compression washer, a spring and a piston should fall out (accompanied by oil of course). You may have to fish for the piston if it is reluctant to come out - I use a small screwdriver or a magnet to encourage it...
Inspect and thoroughly clean the piston, spring and the recess for the spring into the bolt. Debris can build up here! Make sure the two holes are completely clear and open.
If this doesn't help, the next recourse is to disassemble and possibly replace the oil pump.
Removing the oil pump requires:
1) remove the exhaust cross-pipe
2) remove the return pipe from the oil cooler to the sump
3) undo the a/c compressor (remove the electrical connection and compressor belt first)
4) undo the a/c compressor and swing out of the way (I hang the compressor from the suspension using tie wraps). Tip here: undo the top bolts on the compressor first, then the lower two bolts. Reverse the order when reassembling. Reason: access to the top bolts is made more difficult if the compressor's weight is pulling on them.
5) remove the sump (there is a splash plate between the block and sump) and be careful to avoid damaging the metal surfaces - use a blade to tease apart the gasket material and avoid using a chisel, screw driver or anything that can damage soft metal.
6) undo the oil strainer (4 bolts) and remove the splash plate
7) remove the timing belt and timing wheel on the crankshaft (you can do this without removing the engine but if the timing wheel is stuck you may want to consider removing the motor from the car)
8) unbolt the pipe for the oil depth stick
9) unbolt the oil pump (I think that's seven bolts on the front of the engine)
10) gently pry the oil pump from the block - if the gasket is metal this should be no problem, but fiber gaskets tend to stick.
11) the oil pump comes off the crank shaft. Be very careful not to damage the crankshaft in the area around the crankshaft oil seal (which fits into the outward facing wall of the oil pump). A scratch on the shaft itself will guarantee your engine leaks oil!
12) you can open the oil pump to inspect using a large philips screwdriver and you can inspect the high pressure relief valve (from the bottom) using a spring clip removal tool
13) note that a worn pump may not show obvious signs of damage. If I have a problem with pressure I usually replace the oil pump to avoid having to do this again!
When you reassemble the pump, please, please use Toyota gaskets and seals. I have lost track of the number of times I've experienced leaks due to second rate after-market gaskets and seals. Pay for the metal gaskets on the oil pump and oil strainer. You can use Toyota's gasket maker for the sump or buy a high temperature product from your local auto-store. You will need a new oil seal for the crankshaft. Toyota don't have gaskets for the sump/splash plate and the after market gaskets I've tried aren't any better than Toyota's own gasket maker goo.
Re-assembling the cross pipe under the exhaust you probably want to use new compression washers. I know some people don't bother, but they are really only one-use devices.
I'll assume for the moment that no such thread exists.
The MR2 AW11 has a simple oil pump. The pump is located at the front of the engine behind the timing wheel. It consists of two toothed rings, one inside the other. The two wheels are mounted asymetrically and are designed to squeeze oil into a high pressure output port that feeds directly into the engine block. The oil pump contains a high pressure relief valve that vents directly back to the sump. This relief valve is protective and does not operate in normal usage.
The high pressure output line runs past the oil sender unit which in turn drives the gauge on the instrument cluster. If you have any doubts, remove the oil sender and use an external oil pressure tool to read the pressure directly. I don't have one unfortunately.
Next, the high pressure line feeds directly into the oil cooler adapter. The cooler adapter is also very simple but it does have a potential flaw. In normal operation the oil is pushed through an oil filter then back into the engine block for distribution throughout the engine. However, at high RPM's a relief value opens in the oil cooler adapter which sends excess oil through the oil cooler and back into the sump. Yes, it is bleeding oil away from the engine.
The oil cooler itself is a jacket around the water coolant pipe; oil arrives at the bottom of the cooler then returns from the top of the cooler back into the sump.
This isn't a sophisticated arrangement; many of the 4AGE derivatives dispense with the oil cooler entirely.
A problem that can occur with the oil cooler adapter relates to the way in which the relief valve operates. While the relief value in the oil pump is nearly bullet proof, the same cannot be said for the adapter's relief valve. The valve consists of a spring and a piston. Oil pressure, pushing against the spring, causes the piston to retreat below the output port to the oil cooler.
However the piston may have difficulty operating if the chamber containing the spring does not vent appropriately. To ensure that oil in this chamber is vented, there are two small holes in the side of the piston. Oil trapped in the spring chamber will vent from these holes into the output port. But if these holes become blocked then normal movement of the spring is inhibited, which in turn can result in either excessive pressure at high rpm or low pressure at low rpm (most people don't notice the higher than normal pressure).
So I would recommend that if you are tracing low or high pressure problems you tackle the oil cooler adapter and the oil pressure sender unit at the same time. To do this you probably want to temporarily relocate the a/c compressor which entails removing the a/c belt, the compressor electrical connection and the oil cooler return line to the sump. However, having once done this you have clear access to both the sender and the relief valve at the bottom of the oil cooler adapter.
The oil sender is a small thread so avoid over-tightening. I use a small pipe wrench wrapped in rags to avoid denting the case of the oil sender unit. It works, although I believe there is a special tool for this exact purpose. Be gentle!
The relief valve is an 18 mm bolt (approx) on the bottom of the oil cooler adapter. Removes this and a compression washer, a spring and a piston should fall out (accompanied by oil of course). You may have to fish for the piston if it is reluctant to come out - I use a small screwdriver or a magnet to encourage it...
Inspect and thoroughly clean the piston, spring and the recess for the spring into the bolt. Debris can build up here! Make sure the two holes are completely clear and open.
If this doesn't help, the next recourse is to disassemble and possibly replace the oil pump.
Removing the oil pump requires:
1) remove the exhaust cross-pipe
2) remove the return pipe from the oil cooler to the sump
3) undo the a/c compressor (remove the electrical connection and compressor belt first)
4) undo the a/c compressor and swing out of the way (I hang the compressor from the suspension using tie wraps). Tip here: undo the top bolts on the compressor first, then the lower two bolts. Reverse the order when reassembling. Reason: access to the top bolts is made more difficult if the compressor's weight is pulling on them.
5) remove the sump (there is a splash plate between the block and sump) and be careful to avoid damaging the metal surfaces - use a blade to tease apart the gasket material and avoid using a chisel, screw driver or anything that can damage soft metal.
6) undo the oil strainer (4 bolts) and remove the splash plate
7) remove the timing belt and timing wheel on the crankshaft (you can do this without removing the engine but if the timing wheel is stuck you may want to consider removing the motor from the car)
8) unbolt the pipe for the oil depth stick
9) unbolt the oil pump (I think that's seven bolts on the front of the engine)
10) gently pry the oil pump from the block - if the gasket is metal this should be no problem, but fiber gaskets tend to stick.
11) the oil pump comes off the crank shaft. Be very careful not to damage the crankshaft in the area around the crankshaft oil seal (which fits into the outward facing wall of the oil pump). A scratch on the shaft itself will guarantee your engine leaks oil!
12) you can open the oil pump to inspect using a large philips screwdriver and you can inspect the high pressure relief valve (from the bottom) using a spring clip removal tool
13) note that a worn pump may not show obvious signs of damage. If I have a problem with pressure I usually replace the oil pump to avoid having to do this again!
When you reassemble the pump, please, please use Toyota gaskets and seals. I have lost track of the number of times I've experienced leaks due to second rate after-market gaskets and seals. Pay for the metal gaskets on the oil pump and oil strainer. You can use Toyota's gasket maker for the sump or buy a high temperature product from your local auto-store. You will need a new oil seal for the crankshaft. Toyota don't have gaskets for the sump/splash plate and the after market gaskets I've tried aren't any better than Toyota's own gasket maker goo.
Re-assembling the cross pipe under the exhaust you probably want to use new compression washers. I know some people don't bother, but they are really only one-use devices.
