Dropping oil pressure

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Echomirage

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no one rents a mechanical oil gauge, but i bought a cheap little 2in mech. gauge for $18. now, where is the sender on a 96 454? haynes manual only shows the V6 and 350, being above the oil filter. where is it on a big block?
 

SAATR

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I do not remember, to be honest. I would look above the oil filter housing and behind the distributor as those locations are fairly common on small blocks. I don't remember if the oil galleys are the same on SBC and BBC.

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grampadirt

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On a big block(at least my '95)it's next to the vibration dampner,driver's side.I piggy-backed the mechanical & the dash gauges with a couple of brass fitings so I could have both.Also,I didn't like the plastic tube that came with the gauge so I bought a bendable copper tube kit.That round black tube looking thing is the dash gauge sender.

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Echomirage

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ill check this weekend. i bought the gauge just to test the factory one. im hoping its just the sender, so ill replace that if needed.
 

CarolinaOBS

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i don't have a big block but i had a similar issue, had sludge in the pan and it caused oil pressure to drop, down to below 10psi, even when tested mechanically. Dropped the pan, sludge had killed my original oil pump. Cleaned the sludge out (probably caused by a leaky intake gasket). Swapped in a new melling high volume pump, problem solved. Holds 60lbs driving down the highway now. My suggestion, test pressure, if still bad check for sludge!
 

Echomirage

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On a big block(at least my '95)it's next to the vibration dampner,driver's side.I piggy-backed the mechanical & the dash gauges with a couple of brass fitings so I could have both.Also,I didn't like the plastic tube that came with the gauge so I bought a bendable copper tube kit.That round black tube looking thing is the dash gauge sender.

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i dont have a sender there, but i do have a plug in the exact same location. the haynes books says, when removing the pan, to disconnect the oil pressure sending unit 'on the side of the block', and nothing else. its very tight around there, and i dont see anything directly on the block that looks like the picture.

could i unscrew the plug i have, which is in the exact same location as the pic, and use that for the mech. gauge test?
 

Echomirage

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ok, guess that plug works. i installed the mech gauge, and it seems to be working. it does definitely read different then the dash gauge, though. at warm idle, the dash reads about 20. the mech reads 10 or less. at speed, dash reads above 20, mech reads 20ish, maybe 25. i took it for a short ride, and didnt get the complete drop like i did before, so im thinking its the sender after all?

now it is a cheap little gauge, not a top of the line autometer, so im hoping its trustworthy.

is the 10lbs or less at warm idle a concern?

also, there is no oil in the clear plastic tube leading to the mech gauge....should there be, or does it read the air pressure reaching the gauge? if theres supposed to be oil up to the gauge, do i have to bleed it?
 

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ok, guess that plug works. i installed the mech gauge, and it seems to be working. it does definitely read different then the dash gauge, though. at warm idle, the dash reads about 20. the mech reads 10 or less. at speed, dash reads above 20, mech reads 20ish, maybe 25. i took it for a short ride, and didnt get the complete drop like i did before, so im thinking its the sender after all?

now it is a cheap little gauge, not a top of the line autometer, so im hoping its trustworthy.

is the 10lbs or less at warm idle a concern?

also, there is no oil in the clear plastic tube leading to the mech gauge....should there be, or does it read the air pressure reaching the gauge? if theres supposed to be oil up to the gauge, do i have to bleed it?

Don't worry about the air in the line. The oil pressure and air pressure will be the same. Good tools are worth spending a bit of money on, especially when they are used to take critical measurements. Given the discrepancies between the two gauges' readings, I would want a third, known accurate measurement.

The <10psi warm idle could be an issue. Minimum spec on the 5.7 is 5 or 7 psi at hot idle. Not sure about the 7.4. If you are only getting up into the 20's going down the highway, then there is definitely an issue. Get a better gauge and verify what you see. Plenty of actual test gauges on Amazon for the price you paid for that one, and lots that are more expensive, of course.
 

Ironhead

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I just went over the entire thread, and could not see how many miles are on this engine. That would be useful information when diagnosing mechanical condition. You were going to pull the pan anyway, and I think this is something you should do.

Lubrication of bearings is all about oil flow, not pressure. Low pressure just indicates either that the pump is not flowing enough oil, or that the bearing clearances are too big, leading to a lack of resistance to flow.

A clean sump and pickup, clean oil filter, enough oil, and a good gauge. That should be the starting point to determine if there's a problem here. If you get 25 psi at normal rpm hot, I think your engine is ok.
 

grampadirt

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Thought I'd throw this in...cold start in the morning.
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