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Old 04-18-2006, 04:47 PM
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chevy small block possible low oil pressure?

Recently I have rebuilt a Chevy small block 283ci, and I'm wondering if I am having an oil pressure issue or if I should not be worried?

At cold idle, the oil pressure is about 65psi which seems right, however as the engine warms up the oil pressures drops substantially. When the engine is fully warmed up idle oil pressure is 5psi or lower, at 3000rpm the oil pressure is about 30psi, at 4000rpm the engine MAYBE has 35psi.

The engine is still being broken in and only has 500 miles on it. The engine is .060 overbore with a 262 comp-cam, and 327 heads. I don't have the clearances with me but I believe they were in spec. I'm using generic 10w30 for the break in process.

If there isn't a problem let me know, but I'm guessing their is, and will kindly take any ideas and suggestions on what it could be. Tonight I'm going to change the oil filter to see if that makes a difference but other than that I do not know what else to check, so all ideas are welcome.

Thanks,
Evan

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Old 04-18-2006, 04:50 PM
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Change the oil and filter (do not use a Fram filter) and let us know what transpires.

tom
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Old 04-18-2006, 05:15 PM
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Doc here,

Mechanical or Electrical Gauge?

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Old 04-18-2006, 05:19 PM
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Electrical. Their "may" be a problem with it but I don't think so because cold idle seems right then goes weird from there. However I have found a problem with the oil temperature guage as the sender wasn't right for the guage. The reason for that is this motor has been swapped into a '75 Porsche 914 so there have been some interesting things.
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Old 04-18-2006, 05:29 PM
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Doc here,

That was going to be my next question..

Was the resistance value of the sender matched to the resistance value of the gauge..but it sounds like you covered that..

I don't remember, on that engine, and I could be wrong, but wasn't there a "Shuttle" of sorts in the oil Filter casting that acted like a Check valve (one way oil flow)?

If so, Could that be sticking slightly open when warm?

Try the oil and filter first, Then if you have one, a known good gauge..(just in case) ..then see if there isn't a check valve in the oil filter/pump line..

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Old 04-19-2006, 01:02 AM
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Well I took off the filter and went to put on the new one and.... I bought the wrong one . However, when I took off the old filter the oil was really dirty while the oil from the dipstick looks brand new. So maybe the problem is just a clogged filter, but I'm still not sure. I'll post another update when I get the right filter tomorrow.
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Old 04-20-2006, 11:26 AM
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Changed the oil filter last night. It turns out the engine has an screw-on adapter for a ford oil filter... Anyways, changing the oil filter had no discernible effect, at best, oil pressure increased a couple of psi, at worst, didn't change anything. At fully warm idle oil pressure still looks to be between 0 and 5psi.

There was no check valve that we could find, there was a rubber check valve on Ford the oil filter though. At the moment we do not have another oil pressure gage to test ours against, but I am almost positive ours is good. Talking with my father who helped me build the engine, one of the clearances was .003 which is large but in spec.

So.. Now that I know the oil filter isn't the problem, what could the problem be and what are things I can do to bump up the oil pressure?
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Old 04-20-2006, 12:08 PM
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"Recently I have rebuilt a Chevy small block 283ci"

"one of the clearances was .003 which is large but in spec."

There's a possibility that during the rebuild something was not in specs. A bearing perhaps. So when the engine is cold, it has the right pressure but as the engine warms up the clearances on something might be expanding beyond tolerances creating excessive oil flow in the area. Which will decrease oil pressure.

Last edited by simple71; 04-20-2006 at 12:26 PM. Reason: bad english
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Old 04-20-2006, 12:37 PM
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you never mentioned what kind of oil pump you have which might be important if its a high volume pump which would reduce your oil pres. reading.not knowing that info,it doesn't really look bad accept the idle pres..it should be 10-15 with a regular oil pump using 10-30.
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Old 04-20-2006, 12:53 PM
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If it were mine...

Id go out and get a mechanical oil pressure gauge. Electric gauges, in my personal experience, are not quite as accurate.

If possible, ditch the oil filter adaptor. The small block chevy oiling system is excellent. While the adaptor may function just as well, a factory setup would make me feel better.

If all else fails, switch to a heavier weight oil. 20w-50 in a small block isnt unheard of. Be nice to it till the oil is good and warm!
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Old 04-20-2006, 12:54 PM
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Quote:
Originally Posted by GoneNova/406
you never mentioned what kind of oil pump you have which might be important if its a high volume pump which would reduce your oil pres. reading.not knowing that info,it doesn't really look bad accept the idle pres..it should be 10-15 with a regular oil pump using 10-30.

I don't know what the oil pump is, I'll try and get that info later today. However even if it is a high volume pump and reduces the pressure is that good or bad? And also I can spin the engine to 5000+ and the oil pressure never really goes above 35psi once it is fully up to temperature, is that acceptable saying it might be a high volume pump?
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Old 04-20-2006, 01:08 PM
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if its just a normal high volume pump it will pump more oil but the guage won't show that as any more pres..so yes its perfectly normal.for a normal pump your pres.'s are fine accept for the idling pres..at start up it would be high then drop when warm but at idle you should get 10-15 lbs. with a regular pump and 35 for the road is ok.especially with 10-30.it would be a higher reading if you put 20-50 in but 10-30 according to the motor guru's and racers is better.i have switch my way of thinking also in that respect.if you were to take your pump out in the future you can add the spring fromchevy #3848911 for $5-$10 that will give a normal pump approx. 65-75 lbs..melling pumps are color coded springs,plain yellow and pink or 40-45,55,65-70 which should be about the same as chevy or the white spring from mr. gasket.if you contact melling they will set you up.they did me.i had to pick it up at jegs but i got it.

Last edited by GoneNova/406; 04-20-2006 at 01:19 PM.
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Old 04-20-2006, 03:18 PM
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I also might be looking at getting a new oil pump, does anyone have an recomendations? This car will be daily driven, autoX, and some track days. Motor will be spun to about 6k depends on when power drops.
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Old 04-20-2006, 03:40 PM
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Quote:
Originally Posted by simple71
"Recently I have rebuilt a Chevy small block 283ci"

"one of the clearances was .003 which is large but in spec."

There's a possibility that during the rebuild something was not in specs. A bearing perhaps. So when the engine is cold, it has the right pressure but as the engine warms up the clearances on something might be expanding beyond tolerances creating excessive oil flow in the area. Which will decrease oil pressure.
When this low oil pressure condition exists in a hot engine I always suspect large main bearing clearances. Like simple explains a wide clearance gets wider with heat, in addition oil temps is very high causing thinning of the oil causing the pressure to drop.

Pull the bottom end apart, locate and tighten up the loose bearing clearance and the problem goes away.
.
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Old 04-20-2006, 04:47 PM
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I agree with JohnyR17. Try a mechanical gauge. My wife's Vette idles at high pressure when cold, then drops with temperature, but it's always about 10 - 20 lbs higher than you are reporting. The high volume pump is simply a longer (axially) pump. This makes the cells of the pump defined by the teeth larger, hence it simply pumps more oil. But the relief pressure is governed by the spring, and adding oil into the flow path at pressures below the relief pressure should not cause oil pressure to drop. If anything, below the relief pressure, oil pressure should increase if the pump is pumping more into the system. If you try a mechanical gauge, and nothing improves, try 20-40 oil. It should get better. I think I read the engine was pretty fresh. If the 20-40 doesn't make a dramatic difference, I'd pull it and go looking for the problem.

Just one man's opinion.

Pat
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