ok. so this is the second engine that is doin this. when cold, the engine carries about 30psi of oil. when hot and in gear. it carries about 18. after driving it hard, it will drop to about 5psi in gear at idle. then when i give it some gas it will go to 20psi. after its warm, it wont go past 25 psi no matter how fast i turn the motor. there isnt a whole lot of oil in the line (goin to my gauge). there arent any kinks. after running it hard, and leaving it in gear at an idle. the gauge will read about 5-8psi. then it will slowly drop to 0. no matter how hard i run the engine, it wont go past 20-25 psi when its warm. both engines doing this were rebuilt. im wanting to say try a different gauge. but the other engine spun a bearing. so maybe the pump is actually bad? i was running 10w-30, when i replaced it, it smelled like gas and was **** thin. im now running 10w-40 and it seemed to be a little better. i havnt smelled the oil yet, but if there is gas getting in my oil,,, what would be the most common cause? im goin to do a compression check, if that checks out ok, what should i be looking into? intake gasket? both engines were rebuilt by others, not myself, so it is possible they reused the pumps and they were worn. please help!

Thanks Anthony

 

I assume you have the carb setup now? What are you using for a fuel pump?

If there is gas in the oil this can kill bearings after a while. Make sure you get this taken care of. If you run a carb the fuel pressure needs to me regulated down to around 5psi. To much more than that can overflow the needle/seat in the carb and the raw gas goes into the motor. The car would run like crap to,or it should.

Did the oil pressure sensor ever get replaced? I had a 79 T/A once that suddenly had low oil pressure. Turned out a piece of teflon tape on the treads of the sensor got into the sensor hole. Air bubbles in the oil gauge lines are normal.

You can always drop the pan and replace the pump if you find out it's old or defective.

 

It's normal for the oil presure to drop off some when the motor warms up. But not be able to get over 25psi when warm is something I'd be concernd about. Same thing with the 30psi when cold. Most of my motors will get around 60-70psi when cold, then drop off to 45psi. When idling I usually see 30psi.

When the motors were rebuilt was the stock pump used? Or a high volume/high presure (Hv/Hp)? Were the cam bearings replaced? Do you know what the oil clearances were?

I've seen motors that were freshly rebuilt, but the cam bearings weren't replaced, that had low oil presure.

I'd take a guess that maybe the relief spring in the oil pump could be shot.

As far as the oil smelling like gas, most likely the rings. Does the motor smoke any?

[Edit: I just re-read the original post, so disregard the paragraph about the bearings/clearances.]

 

no abnormal smoke. no abnormal smells or sounds. im carryiing about 6psi fuel pressure. its a mechanical pump with a 670 street avenger. that i still dont have dialed in yet. its got an off idle stumble, but after that it rips the tires from the street. ill have to do a check on that spring in the pump, changing to a harder 1 will cause the relief to open only when more pressure is applied right? like i said, i had the same problem with 2 different engines. the first engine only had 1200 miles on it. when i tore the other engine apart, the oil pump had the pickup welded. so it had some work done. would a small oil leak cause the pressure to drop? maybe when the oil gets thinned out from the heat, its not as viscous? and that with a oil leak(its still full) could cause the pressure to drop?

 

anyone?!

 

What color are your spark plugs? If your carb is setup right they should be a golden brown. Im thinking lean with the off idle stumble. Too much or not enough fuel will cause your oil to get soaked with gas. There are too many variables the best way for you to go is to get an Air/Fuel meter. That will help alot better than an internet forum.

 

It would have to be a pretty bad leak to cause a pressure drop and even then it will have to be from a pressurized passage,not an intake or pan leak.

 

Based on your original post you are using a mechanical gauge right?

Did you ever verify if there was fuel in the oil?

 

now i have a new issue. we ripped the intake and heads off, replaced the gaskets, turns out the torker II intake that was on it was warped and thats what was creating the problem. Now its like the secondaries arent opening, goin to check that today, im sure it will be running lean because i didnt check the vacuum and i put a 4.5 power valve in it....but now that i dont have a vacuum leak, thats probly a little to much. so it probly does run lean. before i changed the gaskets it would run strong. after its got ***** till about 3krpm then its gutless. it was burning antifreeze and gas was in the oil. the off idle stumble is gone and im using the green 290 carb cam (24cc) and a .035 discharge nozzle. and it seems to work good. so i think the power valve is my problem now..... back to the oil pressure, it still bleeds off after im rough with it, or i drive for a while. im ok with 8lbs at idle in gear, but never goin past 25-30 when the rpms are high is my concern now. maybe just maybe, a couple more oil changes will clear that up. this by the way is in a 78 camaro, with a 80-85 350. would anybody happen to know if i could drop the pan to change the pump? or is pulling the engine a must?

carb issue is figured out, installed the 6.5 pv and adjusted the carb linkage. it wasnt getting full throttle. is all good now...but oil pressure?

Anthony

 

Id pull the engine myself. But it can be done without pulling the engine. If you had the same problem with the engine prior, why did you use the same oil pump on the new engine? Oil pumps cost about 20-50 bucks which is cheap insurance for what you have invested. Stay away from the high volume pumps; the stock pump is more than efficient, unless you are racing your car. I have a stock volume pump and no matter how hard i drive my car the oil pressure is never as erratic as what your describing. Its either the pump or the guage. Is the guage mechanical or electric?

 

spark plugs are great. not to light, not to dark. i dont think much gas will get into the oil now. nor will antifreeze. like i said i changed the head and intake gaskets. im just tryin to figure out if and what is wrong with the oil pump.

symptoms.... at cold start idling about 1500 its 25-30psi.
when idle drops to about 900, oil pressure is 20-25.
in gear while warm at idle, it is 19-22.
after drivin for 10 minutes, hard or not. it will stay about 8-10. then when revved up it will hold 20-22. no matter what i turn the motor to rpm wise, it wont break 25-30 psi. after sitting in gear idling for about 30 seconds when the engine temp reaches 170(165 my t stat) it will hold 8 and slowly bleed off to 0. then it will begin to run rough. and want to die. so i turn it off.

im debating, change the pump and pickup(got a $32 z28 pump from jegs) which is supposed to be 10% more flow and pressure then stock, and a pick up for my car. or take it back and install a high pressure spring in the pump... either way, the pan has to be dropped and pump removed.

 

its not the same pump, they are 2 different engines. the other engine threw a rod. i didnt build either of these engines. the gauge is mechanical. i just picked up a melling M55A z28 pump, and im reading the casting is thinner and they fail. so im goin to take that back, get a stock replacement pump, put a high pressure relief spring in it, and hopefully that will fix it. if thats what i need to do.

 

If the vehicle is for the street just leave the stock spring in the new pump. High volume pumps take more horsepower to drive. The stock pump creates more than enough oil pressure for street use. If you dont believe me pick up a Small Block Chevy performance book. Install the new pump and try a different oil pressure guage. If the new gauge and pump does the same thing then the pump is not the issue.
Sounds like your pressure is fine. Too much bearing clearance? As oil warms up it thins out, if you have too much bearing clearance the warm thin oil will bleed through bad bearings. That would explain the loss of pressure you have when the engine is at operating temp causing the engine to run rough. It also explains why your pressure never gets above 35 psi. Hopefully its not bad bearings and the pump is the issue.
Did you get the engines from the same builder? If it is bad bearings and you got both engines from the same builder, go else where.

 

i have the same setup with a mechanical fuel and a holley 670 street avenger.. i actually just whipped my rod bearing due to loss of pressure about a year ago.. my oil smelled like gas as well. it was due to the floats being over full it was dumping gas.... if your gonna change the pump check the pickup clearences.. my original oil pan was actually bent a little and almost created a little suction on the pickup.. could be a factor.. also the guages cause make a difference

 

its gradually getting better. i have a high pressure felief spring waiting to go in. i added a half of a quart and that seemed to help a tad. maybe it is a hp/hv pump. ive tried different gauges, the outcomes the same. stll bleeds off. but its carrying about 12-15lbs now. and when its cold, it hits about 50. im gonna do a couple more oil changes and make sure i dont lose any oil. then let you guys know. thanks for the help!