i just recently put a 350 inplace of the old 305 in my 84 z28. i have a new mechanical oil pressure gauge and i get about 15-20 at idle when the car first starts. when the car is up to operating temp, the oil pressure drops to 5psi at idle and the max it will raise to is 20psi throughout the whole rpm range. i remember when i put the oil pan on the engine before it was in the car i think i pushed the oil pickup up toward the engine. i was wondering if this would make the oil pressure low and is there a way to verify if this is the cause? could i fill the car up with more oil to ensure the pickup is down in the oil or would overfilling screw somethin up or normally create a larger amount of pressure. is it common for the oil pumps to go on small blocks or do you think its time for some new bearings? any help appreciated. thanks guys.

 

the pick up should be pretty much on the bottom of the pan, with in 1/4" or so. that may be your problem or part of it but i'd suspect you have problems with the pump its self and/or the engine.

 

Was the engine equipped with a new oil pump? What was the relief valve spring pressure? What viscosity oil is in the sump? What kind of bearing clearances did you have? Did you install oil-grooved or drilled rods for loose-pin pistons? Any windage tray or pan baffles/trap doors installed?

 

sorry for the confusion. i bought the engine a few months ago and before that it was sitting in a garage for a year or more. i didnt build the engine myself, the only thing i did was oil pan gasket, new waterpump, alternator, etc. nothing with the inside of the engine. the engine was used and i dont know how many miles are on it. i didnt put a new pump on it either. im running 10w40 oil and a few days ago i put a quart of the lucas's oil stabilizer in. if i remember correctly im pretty sure the pan had a windage tray in it. the only things the engine has done to it are new holley 80457s carb, weiand stealth intake manifold and 1.5 stamped roller rockers. im not sure if it had anything else done to the valvetrain such as cam, but at idle it sure sounds like it does (either that or timing is off due to the mr.gasket TC cover) last night i put a new line from the mechanical gauge to the port on the intake. i used the copper flexible tube instead of the plastic. that didnt really seem to help very much. if anyone has any other suggestions please post. thanks alot

 

anyone know what it could be?

 

I wouldn't worry too much about the pump itself. Installation maybe, as far as the pickup being too close to the pan; or even schmutz of some sort blocking the pickup screen. But not the pump proper. They just don't fail that way. Generally they either work, or they don't.

I'd do away with the thick oil and the oil treatment. If the motor doesn't hold the correct pressure with regular 10W-30 oil, it's smoked.

I'd be more suspect of the way the motor is built, or the condition that it's in. In the former category, are things like the way the cam bearings are turned, and the bearing clearances; in the latter, bearing clearances.

Oh.... I almost forgot to mention, check the bearing clearances. Use a micrometer if a visual inspection of the bearings and crank doesn't yield a clue: don't bother with Plastigage. On a used motor the mains should be .0015" - .003", rods should be .001" - .002". Any more than that, it'll have low oil pressure, because the pump can't pressurize the system if it leaks like a sieve.

I'm expecting you'll find bearing problems.

 

I'm actually having this identical problem with my '85. I dropped in my '90 350 motor that had about 20,000 miles on it from when I bought it new from a local engine builder. When the motor was in the truck, the pressure was fine, minumum 25 psi at idle on a hot day. I dropped the same motor in the T/A and now I barley get 5psi at idle on the mechanical gauge I hooked up to test it. The only thing I changed on the oiling system was concerned was the oil filter adapter, which includes the stock bypass valve (I think) from '85. The one out of the truck had a strange adapter that used a smaller filter that ran parallel to the pan to clear the 4x4 driveshaft. I was also worried about the pickup being too high,but I was able to push it closer to the pan using a long thin screwdriver through the drain hole. Im not sure it's supposed to be that easy, but it didnt help any. Maybe there is an air leak at the top of the pickup where it goes into the pump? I'm stumped.

 

Alright- I think I have discovered both of our problems. I bit the bullet and pulled the oil pan off with the intention to replace the entire oiling system. Upon close inspection of the oil pump pickup, I found that the inside was almost completely clogged with sludge-oil. A little parts cleaner and a good rinse down with the hose, and it was good as new, pumping oil at a feverish pace. It turns out, if your oil sits in one spot exposed to air for long enough, it turns to sludge Im willing to bet my torque wrench that's what happened to Ryknow86's engine. It's just sluged. Have fun removing the pan.