Oil pump - what is the grove and the port for
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Northstar Engines and System Technical Discussion Discussion, Oil pump - what is the grove and the port for in Cadillac Engine Technical Discussion; I bought a new oil pump (List $259 but I got it for $199) - the old plastic pressure relief ...
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    Loose screw is offline Cadillac Owners Fanatic
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    Oil pump - what is the grove and the port for

    I bought a new oil pump (List $259 but I got it for $199) - the old plastic pressure relief valve is gone and a different very close tolerance lay is used with a long steel releif valve that moves side ways instead of backe to front. This improvemnet no doubt is to prevent bad things inbeding in the plastic valve and seat and keeping it open causing very low oil pressure at low RPMs. Sadly the case is still alunimmum but it appearently hasn't been a source of wear under normal conditions. Mine had some play and some signs of wear in the case and with a 142k miles it was worth the high price for a new pump.

    But I was wonder - on the back of the oil pump there is a very small groove around what I belive is the inlet port and a small whole that cut into the groove and goes back into the pump and then to a groove that goes most of the way around the case - between the two cases sections. Is this some sort of self primer, but it is on the inlet side which would mean it is sucking oil in (and air), sucking the case together? And the grove on the inlet port sucking the pump case to the block? There are no seals or gaskets used between the oil pump and the block right? What is this passage way for?

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    BeelzeBob's Avatar
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    Re: Oil pump - what is the grove and the port for

    Quote Originally Posted by Loose screw
    I bought a new oil pump (List $259 but I got it for $199) - the old plastic pressure relief valve is gone and a different very close tolerance lay is used with a long steel releif valve that moves side ways instead of backe to front. This improvemnet no doubt is to prevent bad things inbeding in the plastic valve and seat and keeping it open causing very low oil pressure at low RPMs. Sadly the case is still alunimmum but it appearently hasn't been a source of wear under normal conditions. Mine had some play and some signs of wear in the case and with a 142k miles it was worth the high price for a new pump.

    But I was wonder - on the back of the oil pump there is a very small groove around what I belive is the inlet port and a small whole that cut into the groove and goes back into the pump and then to a groove that goes most of the way around the case - between the two cases sections. Is this some sort of self primer, but it is on the inlet side which would mean it is sucking oil in (and air), sucking the case together? And the grove on the inlet port sucking the pump case to the block? There are no seals or gaskets used between the oil pump and the block right? What is this passage way for?


    You should'a just reused the old pump. It is a higher capacity/volume pump, by the way, than the new one. The new one has the piston style pressure relief valve that is slightly less prone to sticking due to debris. When the new one sticks, the oil pressure is way to HIGH and blows the filter off when cold. When the old one stuck, it had no oil pressure and you could fix it quickly by overfilling the engine and starting it. The older, original pump was a higher volume pump that was downsized later on when the piston style relief valve was integrated to reduce parasitic losses and improve fuel economy. If you like oil pressure then the older one is the choice. If you don't want it send it to Alan Johnson at CHRFAB....he is loooking for those older style pumps....LOL LOL

    The hole and groove is to route high pressure oil to the pump inlet or suction side from the pickup. It is a way of avoiding a seal or gasket on the inlet side. The pump mounts to the block with no sealer or gasket at that joint...so, if no othe steps were taken, the pump could suck air at that joint and cavitate much easier. Sucking even a tiny bit of air is terrible for pump efficiency and pump noise. Sealing it with a gasket at that structural joint would be hard. So....the anular passage and hole routes high pressure oil from the pump outlet port to that passage. If the inlet side leaks anything it will leak high pressure oil and not allow the pump inlet to suck any air. It is a "waste" of high pressure oil but the system and pump is sized for it so it is no big deal. Just a handy way of insuring that the pump never sucks air without relying on a gasket or seal at that spot. Some of the hot rodders plug that hole , continue the groove completely around the port and seal the pump to the block with RTV to get a "better" seal without the "wasted" oil pressure and instead send that extra oil pressure to the engine. It has been reported to work but I have no experience with that mod personally and cannot vouch for it. Sounds good, though. Make sure that you do not mix up the oil pump mounting bolts with any other bolts as they are a special thread pitch and length just for the pump. Make positively sure you seat the pump securely to the block by hand before tightening the fasteners. I have seen people leave the pump dangling and run the bolts in only to catch the pump cover on the edge of the drive sleeve and bust the cover on the lip of the drive sleeve.

    BTW....the wear you see on that small lip on the old pump cover is intentional. That thin lip is added as a "sacrificial" surface that can wear away as the engine breaks in to take up any runout in the drive sleeve/crank/pump mounting. Normally that lip will be very tight to the crank drive sleeve when new and it will wear on one side or the other to mate to the drive sleeve per the installed location. Normal.

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    Loose screw is offline Cadillac Owners Fanatic
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    Re: Oil pump - what is the grove and the port for

    Thanks Bbob great information and great adivce you showed the whole picture and that really helps and it is giving me a great education! Thanks for taking the time, I really do appricate it.

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    Re: Oil pump - what is the grove and the port for

    I forgot to mention, when you install the oil pump bolts, put locktite on the bolt threads so that they don't loosen. Make sure you torque them to spec with the locktite on them.

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    Loose screw is offline Cadillac Owners Fanatic
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    Re: Oil pump - what is the grove and the port for

    Locktite on the speical bolts for the pump - right, got it.
    Oh and thanks for saving me $199 the new pump is going back!

    Is Locktite used on any of the other bolts under the front cover - tensioners, chain guides, intermadiate shaft? red or blue?

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