QuestionMy dad and i recently rebuilt my 1275 engine. everything new. head, pistons, rings, oil pump... everything. im in the military and dont have him here to help. when i start it, it runs great with a psi of around 60, as im driving it will start to decline after 5minutes. after 10 minutes it is at 15 psi. then when i stop at a light its at 5 and will sound like crap and stall out. but when i get it started back up it hesitates. what could the problem be? how can i go about checking it? and what do i need to replace haha. thank you.
AnswerHi Joseph. I get the impression that your engine has been rebuilt carefully, using all the right components. The fact that you can get 60 psi on a cold engine is a good sign, but it worries me that the pressure drops so quickly as it warms up.
You should get at least 40 psi when cold, possibly as high as 60 on a new engine. Once warmed up, you should get a steady 40 psi whilst driving, dropping to 20 psi on tickover.
I do have a few thoughts:
1) What oil are you using? Modern oils are too thin for your engine. You need an oil to 20W/50 specification (unless you live in Alaska). When cold, a thin oil will give good pressure, but this will quickly drop as it warms up.
2) When building the engine, did you fit a new oil pressure relief valve? Also, did you remember to re-seat the valve? It is located under a large dome-headed nut towards the rear of the block, low down on the left side. Underneath the nut you will find a spring-loaded plunger. Remove the nut and the spring, and then extract the plunger. If it looks old, with a wear ridge around it, then fit a new one. To seat a new plunger, slide it into the block, insert a suitable length of steel rod, and give the end of the rod a `bop' with a large hammer. If you have a LHD car, then access may be difficult because of the steering column.
