mikeringland Posted February 18, 2011 Share Posted February 18, 2011 I have a 350 in my Monte that was rebuilt by an engine shop back in '04 by the previous owner of the car. By the looks of the receipt, it looks slightly above a stock engine, but nothing too crazy. Anyway, for the last couple years if I am driving the car on a warm or hot day, when I come to a stop at a red light or park it after its been running a while, my oil pressure dips down to about 5psi. When I start the car up cold its about 55psi and when I accelerate about 60psi. Once the car has warmed up it remains steady between 20-40psi. It just seems when the car has been driving for a while, combined with a summer day, the oil pressure can drop to nearly 0psi while idling. I do have some piston ring wear due to some blue smoke that comes out when I first start it and I checked the plugs I installed last year and they have a black coating on the ends after only driving the car about 1000 miles last summer. I use 20W-50 oil which the previous owner advised me to use. Do I need a new oil pump, or is it some other sort of problem? And, if it is the oil pump, so I go with a standard pump or a high flow pump? Quote Link to comment Share on other sites More sharing options...
Mikstudie Posted February 18, 2011 Share Posted February 18, 2011 The blue smoke is most likely a common problem with a SB chevy,Valve Stem Seals, will cause blue smoke on start up and fouled plugs. Oil pressure thing,if you said it was about 10+- at idle and 35+ while driving I would say no big deal. 0 is a little low,could be oil pump,or just what we call a loose motor. I had a 350 that was 5psi at idle and 35+ off idle and drove it that way for 90k miles. How many miles are on the rebuild? And are you sure it's a rebuild? Any ticking at idle? Quote Link to comment Share on other sites More sharing options...
mikeringland Posted February 18, 2011 Author Share Posted February 18, 2011 Yeah the motor was definitely rebuilt. I have a detailed receipt from an engine shop. Looks like it was bored .030 over, that makes it what a 355? I have a Comp Cam card that has specs on it such as: duration at .050 Intake 212, Exhaust 218, and tappet lift: Intake 256, Exhaust 268. It has an Edlebrock aluminum intake and a Holley 670 CFM dual fuel feed carb on it. I'm no engine expert but that carb has always seemed too much for that motor. There's no ticking at idle, other than this oil psi issue, the motor runs very strong. If I were to venture a guess I'd say there's about 10K miles on the motor since the rebuild. Quote Link to comment Share on other sites More sharing options...
stangeba Posted February 18, 2011 Share Posted February 18, 2011 Have you verified the pressure with a known good gauge? Quote Link to comment Share on other sites More sharing options...
Machtuck Posted February 18, 2011 Share Posted February 18, 2011 I have had this issue as well with sbc's. Even ones that I raced. There are two things that are probably evident from what you describe. You have a STD vol oil pump and the mains are on the loose side...say .0025-.0035. What is your idle rpm? This sounds simplistic but the rule of thumb is 10 psi per one thousand rpm. If your idle is low, your Current psi is representative of this rule. I see no reason to be concerned as long as it increases quickly with throttle input and you hear no funny noises. Consider a new gauge as well as these may be even slightly erroneous through time. Quote Link to comment Share on other sites More sharing options...
Mike 57 Posted February 18, 2011 Share Posted February 18, 2011 Yeah, I agree, probably built with "racing" clearances. You could bump up the idle a bit. If the pressure is consistent I would drive it and and keep an eye on it. Sounds like it has been like that if the prior owner used 20/50. Quote Link to comment Share on other sites More sharing options...
mikeringland Posted February 18, 2011 Author Share Posted February 18, 2011 The idle in Park is about 1100 RPM and in Drive about 700 RPM. The gauge is an aftermarket one installed by the previous owner. When the pressure dips down to 5psi, the original oil "dummy light" on the dash also comes on. So I'd say with both the gauge and the dummy light, the pressure seems true. Should I bump up the idle some, and to about what? Also, does that dual feed carburetor seem excessive to you guys, or am I wrong? Quote Link to comment Share on other sites More sharing options...
Mikstudie Posted February 18, 2011 Share Posted February 18, 2011 I would say the carb seems a bit too much. I have some pretty good HP coming out of my motor and I tried a large dual feed carb and it ran like crap (over kill) and on a side note to guys looking at exhaust,I tried the 3" pipes and again ran like crap (over kill). Unless you have big time HP dont over think your exhaust or carb, I run headers,2 1/2 ext pipes,flow masters,2 1/4 tails you need some form of back pressure to even out what your motor takes in and what it puts out...JMO!!!!! Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted February 18, 2011 Share Posted February 18, 2011 Does it do this after a fresh oil change also, maybe the oil breaks down a bit when it gets a little older. check to see if the oil is thinning out an bit maybe to much fuel running through the engine and not burning completly also smell the oil to see if theres any fuel in there. Just another thought. Quote Link to comment Share on other sites More sharing options...
Mikstudie Posted February 18, 2011 Share Posted February 18, 2011 Does it do this after a fresh oil change also, maybe the oil breaks down a bit when it gets a little older. check to see if the oil is thinning out an bit maybe to much fuel running through the engine and not burning completly also smell the oil to see if theres any fuel in there. Just another thought. Good thinking!!!! Quote Link to comment Share on other sites More sharing options...
JOHNA01374 Posted February 18, 2011 Share Posted February 18, 2011 I wouldn't be too concerned about the oil pressure at idle IF this motor was running 10-30. I've had a couple of SBC's run 5psi at idle due to how I built the motor but they all ran 10-30 oil. With 20-50 in the motor I would expect to see at least 10psi on the gauge at idle and 50 to 60 psi driving unless the motor is really loose. I'd verify the pressure first (different gauge) then consider having the motor looked at. One thing that I would look at is the type of oil filter that is on the car. In a pinch I bought a Fram filter and used it. About 500 miles after the oil change I noticed the motor seemed to have low pressure. After banging my head against the wall for 2 days and getting ready to pull the motor I swapped the oil filter for a WIX and problem solved. I cut the Frma open and the media inside had collapsed. Gotta love their quality control Quote Link to comment Share on other sites More sharing options...
mikeringland Posted February 18, 2011 Author Share Posted February 18, 2011 Honestly I don't think the oil itself is a problem. I usually change the oil twice a year, once in April and then in late July. I only drive the car like once a week to a local car show or just go out for a drive here and there. I only drive it between the months of April and October. When it comes to the filter, I use a Bosch filter that I think is a good quality oil filter, compared to Fram or STP which are total crap. I probably put only about 1000 miles a year at the most on my car. Quote Link to comment Share on other sites More sharing options...
snomobeelr Posted February 18, 2011 Share Posted February 18, 2011 I had same type of issue. My oil pressure dropped but drove it for a while. I puuled the motor (not for that reason) when I pulled the pan turns out the Sump/Screen was coming out of the pump and tilted down. Quote Link to comment Share on other sites More sharing options...
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