there's at least one other known pressure-relief valve...
used in the AAH/AFC engines in the cylinder heads that regulates oil pressure in the lifter oil gallies in each cylinder head.
And there's another one under the valley pan tho I can't tell from the diagram if either are addressed via it's circulation layout.
One things clear... these engines have a lot of in-line oil pressure reliefs going on. Way more than any other engine I'm personally aware of. Great when they work... a potential nightmare if/when any one fails. And everything mechanical will fail.
Re: there's at least one other known pressure-relief valve...
Good call! I never think of the two valves in the head. You can't tell from the picture, but the hex part of the valve is connected to the rest by an extremely thin bit of metal - so thin, in fact, that you're just as likely to twist the head off and have a nice smooth hole in your head than remove the valve. Nice. The valve on 30v engines has a Torx head embedded in the valve body instead, much nicer.
So: oil pressure relief valves:
- 16 bar (232 psi) in oil pickup assembly
- 11 bar (160 psi) safety valve, only opens at high RPM and cold engine temp; AFC only
- pressure relief valve, *cough* in the oil pump
- now in the engine; there are the pressure valves Mance mentioned, one on each head. Those control top-end oil pressure.
- there are two oil check valves in the steadying chamber (under the valley pan), but those don't really do much in terms of pressure control; they just keep oil in the lifters when you shut the engine off.
There's also some pressure control done by the head gasket - each one has a finely-tuned obstruction to oil flow that maintains oil pressure in the engine block when the oil pressure relief valves are open.
OK so im a little confused...I have an AHA (99 2.8 A6) do i have a relief valve?
here is my problem: when the engine is cold the oil pressure is perfect through the RPM range ( checked with mechanical gauge) but when the engine gets to normal operating temp the oil pressure drops at 1500-2000 rpm then shoots back to normal. It has a new oil pump and full Syn oil in it, and a OEM Mann filter.
run some seafoam in your oil for about 200 miles, about 1/3 of a can
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