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L16 question


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Behind oil filter. Steel ball with small spring behind it. In the extremely unlikely event of the oil filter plugging up the full gallery oil pressure of 45-60 lbs would easily push past this valve so the engine wouldn't starve for oil. This oil would be unfiltered, but still, the oil in the pan has already been constantly filtered previously anyway so better than none, right?


If replacing, pry out with screw driver and press in new one.

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  • 1 year later...

I know I'm digging up an old thread, but I just read in the manual that all this valve does is return the oil to the inlet side of the pump to reduce pressure from above 60psi.


I also was previously under the impression that in the event of the filter plugging up(or high pressures due to cold start, excessive oil pressure, etc..), this would allow unfiltered oil to enter the bearings. This is a concern of mine, because I'm building a new engine, and I don't want to have to worry about this. I was told to plug the relief, but that doesn't seem like a good idea either. What I just read was that it is there so that pressure doesn't build up and push out the oil galley plugs.. if it's just returning the oil to the inlet side of the pump, then I won't worry about plugging it. If the manual is incorrect, and it sends unfiltered oil to my bearings, I'll plug it.


Also, if this is true, then it seems like shimming your oil pump for higher pressure is a fruitless venture, unless of course you block this relief off.

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No. You are right.


There is a pressure regulating valve in the oil pump. It looks like a small piston (some are round like a marble) with a spring behind it. Oil pressure compresses the piston against the spring and if sufficient, will push it back to expose an opening to vent oil back to the inlet.


There is a relief valve behind the oil filter. It's job is to bypass oil if the filter should plug. A plugged filter is highly unlikely if changed regularly and a quality filter used. If it plugs from something else the motor is in trouble anyway. Unfiltered oil is better than no oil. Also the oil in the pan isn't going to be excessively dirty as all the oil is constantly being filtered and returned to the pan hundreds of times a day. Racers pry them out and tap and plug the hole.

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