2 oil pressure reliefs?

[ed1380]

I know there's one on the ofh then what is this? Its right by the oil pump on the front cover. Is it another pressure relief?

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[19Eclipse90]

The pipe plug is just a plug for a machined port. It plugs the gallery that links the oil pump to the gallery transferring oil from the pump to the oil filter housing.

The ball plug on top of the housing is for the feed to the rear balance shaft. Although the front cover is different than a 6-bolt (different plumbing/appearance), it's the same idea. On the number one main bearing there is a hole where oil feeds in from the main oil gallery (in the picture in the first linked thread, post #2, approximately at 10:30), just like the rest of the main bearings. The number one main is different, however, in that it has a second hole (approximately at 1:00) that feeds oil to the rear balance shaft, which provides lubrication for the shaft bearing (towards the passenger side) and both the drive gear and rear shaft bearing surfaces in the oil pump cover.

These have some good visuals that may help you see how the oil flows behind the front cover, as well as the lubrication system diagram (which is just like the 2G except for the external oil cooler bit) that clearly shows the feed for the rear shaft:
OFHs Oil Flow Pathways For The Engine (Questions)
How to rebuild your 6 bolt front case

 

[ed1380]

is that all it does? When I had the front case and oil pump off it looked like there was a spring and piston inside like an oil relief.

I'm asking because I'm having oil pressure problems after a rebuild. it ran fine for 30 minutes in the garage but halfway down the road I lost pressure. towed it home and installed a pressure gauge. started it and oil pressure was 40psi. everything seemed fine. I shut the engine off. everytime after that it would hit 20 psi then drop below 10. almost as if some oil pressure relief gets opened.

 

[19Eclipse90]

There is no relief valve there. I feel like the 2G diagram would indicate an oil pressure relief valve if there was. ASA doesn't list anything of the sort in that area, either, though they do list the "plug". And of course there is this age old thread that says the same thing: oil pressure relief valve?

Here's some things to think about:

• What purpose would an oil pressure relief valve serve at that point? Most of the oil is going through the main gallery on the opposite side of the engine and up into the head by that point.
• Where would the oil "relieve" too? That area is enclosed by the front cover, block, and oil pump casing. So unless it blocks (partially or fully) the passageway back into the front cover, thus hindering oil flow from the front main, it wouldn't actually be relieving anything, just "checking" it to regulate pressure -- at the same time making the rear balance shaft bearings and oil pump drive gear bearing suffer and potentially increasing the pressure on the front main.

Additional piece of info, the 6-bolt oil pressure relief valve begins to open at/around 78psi. All 4G63 engines use the exact same components so I'd assume it's about the same pressure for 7-bolts.

 

[ed1380]

thanks for the clarification