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Old 10-25-2012, 10:36 PM
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oil pressure loss problem

ok well i have another delema i just got done putting my motor back together and i have a loss of oil pressure when hot. motor is a 400 .30 over mild cam crank is freshly cut .10 .10 and was balanced to my pistons the pump is a new melling high volume the shaft is new cam bearings are new oil plugs are new
when i start up in the morning it goes to 60 idle driving down the road at 2k around 85. but once it warms up to about 190 hot idle it sits between 16-21
its a manual guage i have switched it with another same problem. my oil pickup is welded and sits a 3/4 of an inch from the bottom of the pan im lost i dont understand. any ideas ? my first 20 min startup i left it at 2k for 15 mins to break in the cam and ran 10-40w it did it then i noticed it on my test drive. came home saw the problem drained the oil it was a little silvery but i figured that was the rings to cylinder wall all the normal breaking in so i put my 20-50 in and a new ac delco filter and bang still does it i dont understand please help

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Old 10-26-2012, 01:22 PM
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Wouldn't sweat it

The only thing i see is that your pickup should be 3/8-1/4" above the bottom of the pan. Other than that as long as you have 10 lbs per every thousand RPM you should be fine. So at idle if you have 10 lbs your good. At high rpm or under spirited driving if your pressure falls it may be due to the pickup being positioned too high above bottom of oil pan though. Try using a WiX or Napa Gold filter. Also remember that oil gets thinner as it is heated up, hence pressure will always drop.
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Old 10-26-2012, 01:43 PM
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If your idle rpm is lower than 1000 rpm, the the 16-21 psi hot idle oil pressure wouldn't worry me at all.

My last 400 SBC went 10+ years with oil pressure just like that, and it was a 540 HP street/strip engine, with an 1100 rpm idle and 15-20 psi hot idle oil pressure.

Most SBC's I do behave similarly on the oil gauge (406's/377's and 383's).

3/4" on the pick-up to pan clearance is a bit high, but won't effect idle pressure at all, just high rpm pressure... so if pressure is fine at high rpm then it isn't an issue.
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Old 10-26-2012, 01:54 PM
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What are the bearing clearances? I use straight 50w,my idle pressure is 25 to 30 when hot.My car idles at 950.The pump is a little high in the pan as already mentioned by everyone.I dont think I would tell you to use synthetic oil as the pressure would be even lower.Nothing wrong with low oil pressure if its steady.watch your guage in the upper RPM range.I hope you carry more that 4 liters in your system.
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Old 10-26-2012, 02:44 PM
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I would not worry about it. My 406 gets 20- 25 psi at idle at 170*. I would replace the shaft ( shown last photo)
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Old 10-26-2012, 06:37 PM
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Quote:
Originally Posted by atcoscrazyest69 View Post
ok well i have another delema i just got done putting my motor back together and i have a loss of oil pressure when hot. motor is a 400 .30 over mild cam crank is freshly cut .10 .10 and was balanced to my pistons the pump is a new melling high volume the shaft is new cam bearings are new oil plugs are new
when i start up in the morning it goes to 60 idle driving down the road at 2k around 85. but once it warms up to about 190 hot idle it sits between 16-21
its a manual guage i have switched it with another same problem. my oil pickup is welded and sits a 3/4 of an inch from the bottom of the pan im lost i dont understand. any ideas ? my first 20 min startup i left it at 2k for 15 mins to break in the cam and ran 10-40w it did it then i noticed it on my test drive. came home saw the problem drained the oil it was a little silvery but i figured that was the rings to cylinder wall all the normal breaking in so i put my 20-50 in and a new ac delco filter and bang still does it i dont understand please help
This would be normal. Before getting into that let me say that the pick up being 3/4 inch off the bottom is too high it should be more like 1/4 to 3/8ths. If it's too high you run the risk of exposing it to air pick up if the oil level falls a little low.

Oils have great viscosity differences when cold but they gather in a pretty tight group when hot, I rather doubt that the differences in what you've used would be measurable on anything but lab quality sensors and instruments let alone on the rather crude gauges we run in the car. If the pressure comes up from the 16-21 at idle to about 55-60 at a 2000 then things are running pretty normally. Just fix the pick up depth. Your mechanical gauge also has a buffer in it so its resonse rate will be behind the actual changes, this is there to keep it from blowing apart. An electric gauge is usually more prompt in registering changes but introduces the probibility of electrical failures giving false data. I usually run both types and compare them, but I like old round gauges, they bring out the pilot in me making me feel safe and informed even if I'm not really.

Bogie
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