i just recentaly built a sbc 400 1973 and when we did the break in i had about 45 oil psi and now i was crusing around today and saw that it had gone down to about 15 and when i got on it it doesnt move. should i change out my filter? im only like 40 miles if that on the new motor break in.. should i be worried guys? and im running just plain old 5w30 with summits zinc additive

 

Have you changed the oil and filter yet? If not, do so.

It isn't likely that it is a clogged oil filter. Oil pressure sending unit is the #1 cause. Then you get into things such as stuck open oil pump relief valve, bad bearings, other mechanical stuff.

What does the oil pressure do at idle?

 

I would drain the pan and look for metal in the oil. You may have chewed a bearing. Did you replace all the bearings? Was the block machined, clearanced? If it was machined, where did the machinist set oil clearances? It may have been setup to run heavier oil than the 5-30. Did you replace the oil pump with a high volume unit?

 

idles at 15 psi. motor only has like 20 miles on it so no i havent changed the filter. i will drop the oil out at work to look for metal...i hope to god thats not the case. ill also test the sensor to double check its functioning.

yes all bearings were replaced the mains were .20 and the rods were .10 i believe. yes block was machined .60 over on a sbc 400. no deck milling. or align hone. yes it is a high volume oil pump.. thanks for quick replies

 

No line hone....

Like said above check the sender unit. what was your pickup to oil pan clearance? Was the pickup tube pressed in or given a tack to hold it in place?

Its usually something simple. Hopefully not a missing galley plug somewhere (doubt it)

 

nope we didnt line hone it. and i took the sensor out and put a mechnical one in and presto! 75 psi oil pressure and increasing as i hit the gas, yaaaaaay no blown motor haha. so i didnt have a new sensor right away so i put the old one back in and then it started having problems running and we think we addressed it. does the computer by chance have a safety kill switch where if the oil pressure is to low or to high itll kill the fuel pump? i think thats what happened to me and we just put a paper clip in the connector to drive it home. just making sure that a new oil sensor will fix everything

 

I'm having same exact problem at first start up oil pressure is around fifty and stays high for 5 min or so then it starts to drop. When I pull to a stop oil pressure is at 15 and falls to zero and will stall . Also kinda hear something like a electrical motor running. Just rebuilt motor. Help please

 

i would say change the sensor but im not sure im going to change the sensor on mine tonight and see if it helps

 

so the sending unit or what ever oil sensor it is thats on the more bottom side of the block not the one by the distributor looks brand new so im not replacing that but i am goingto replace the one behind distributor. i also am replacing exhuast sensor wich looks like its the original and i happen to break the knock sensor off while i was under there. man my luck....

did you set tps and iac when you were done rebuilding? i didnt but i think im going to asap prob fri. i didnt know you had to reset them i figured computer resets with battery disconected. anyway good luck mani know i sure could use some

 

no i didnt reset them, i cut those things off! my new block i pluged the knock sensor cuz i have a vacumm advanced HEI distributor, and for the iac i have a carb on it now so those were all useless to me.

 

man if i only had a carb this would be so much easier . oh and if it wasnt auto either that be great. ill be switching over to a five speed as soon as the race season slows down. i spend all my money on track time and tires in the spring and summer and fall and winter money goes into the cage.

 

ya but my oil sensor was above the oil filter im not sure which sensor your describing

 

On my motor there is two oil sensors. A sending unit an then a the sensor switch