Oil pressure

FATKENYAN23

MEMBER
GMC C1500

Hi, my 1992 GMC Sierra K 1500, with a 5.7L 350, has 209,116 miles on it, this summer I decided to rebuild the motor because it was running rough, always had low oil pressure and would mis-fire in the winter. I pulled the engine, and took it apart down to the block. I cleaned the heads, put new bearings in and added a high volume oil pump. I put it all together and put in back in the truck. I put 10W-40 oil (a thicker oil, to give it more pressure) because it is a 4x4. It blew the gasket around my oil filter right off the engine so I shut it off and put another filter on. The filter was a STP S3980, then the second was a Fram PH3980. I was able to tune the values and put the value covers back on. I was able to drive the truck about 1,426 miles before I blew another filter gasket off the truck. Now I have put a total of 3,059 miles on the engine since the rebuild. I can not even start the truck without blowing an oil filter gasket right off. I asked around if anyone knew what to do and the GM troubleshooter said to check my lines running to the radiator from the oil pan. They were criss crosses and I switched them to the normal position. The the factory elbow that you screw the oil filter onto, I replaced. I thought maybe the threads were loose. I put on another filter started in up, this time with 5W-30 oil. I blew off a filter, this time a GM filter. So I crawled under changed it with another filter (GM also) and tightened it with 1/4 turn using oil filter pliers. I started it up and it blew another filter gasket. When you start the truck the gauges say the truck runs at 1000 rpm and the oil press is just above 60psi. Then you hear a pop and the pressure drops to 0psi. This happens in a matter of seconds, while in park. When I could still drive the truck, (just after the rebuild) the pressure would be way above 60psi and as the engine heated up it would drop down to 1 tick above 0psi. I an getting very frustrated with this, all in all I have put 34 oil filters on in 3months and gone though 142 quarts of oil ranging from 10W-40 to 10W30 to 5W-30. I bought a regular oil pump and I plan to replace that. What should I do?

2 Replies

MERLIN2021

MECHANIC
17,250 POSTS

The pressure relief valve on the pump is stuck. If you are lucky it's s crew you can remove near the oil filter, either see if you can clean it or replace it.

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Saturday, November 24th, 2007 AT 4:25 PM

PEAR69

MECHANIC
1,482 POSTS

You should understand what makes pressure in your engine first before you go installing a high volume pump in it. A high volume pump, is just that, A HIGH VOLUME PUMP! This DOES NOT mean you will always get a higher oil pressure.
An oil pump is a positive displacement pump, meaning that it only moves a certain amount of oil from one place to another. AN OIL PUMP DOES NOT CREATE OIL PRESSURE! Oil is incompressable, it is a fluid.( Air is compressable ) The ONLY thing that creates oil pressure- is the resistance in the oiling system! The oil passages, oil galleries, BEARING CLEARENCES (very important!), Bends in the oil lines and the oil filter. When the oil pressure gets too high, a releif valve, held back by a spring, releives some of the pressure caused by the " resistance", in the system.
So, with all that being said, YES- it is most likely the spring is stuck on your releif valve--however--if the spring is too stiff this could cause your problem also. What caused the sticking spring? Do not take this the wrong way, and I do not want to panic you, but if the spring is not the answer then the bearing clearences are too tight, or the oil passages are clogged or something like that.
As an engines' bearing clearence gets old and loosens up, the oil pressure (or resistance) goes down. If the oil passages are clogging up, the pressure ( or resistance) goes up. High oil pressure is just as bad or worse than low oil pressure.
BTW-- the rule of thumb is 10psi of oil pressure for every 1000 rpm's. Street motors rarely ever get above 5500 to 6000 rpms. So 60 psi is way more enough pressure. The nascar motors at Daytona run between 60 and 70 psi because of there tight clearences. These motors are trash after 700 miles or so. Also BTW, run 10w30 fully synthetic oil. Oil must flow. Oh that's another subject>>> Good luck and I hope this helped you. Let me know how you make out and what you find.