The Stovebolt Site Forums The Shop Area Engine Shop Oil Pressure Question

I have a 51 Chevy half ton with a 235 out of a 55 Sedan Delivery. While driving today I noticed that the oil pressure jumped to 60 psi when driving down the road. I traveled about 2 miles. When I take my foot of the gas, the pressure drops to 40 psi. Before when driving, it always stayed at mid-level around 40 psi. When stopped, if I just tap the gas pedal the gauge jumps to 60 and then back to 40. Is this normal or something I need to look into?

Sounds like you are having some oil pump relief valve sticking,but first check with mechanicl gauge to check sender,change oil go to high detergent 5W 30 if you can get it see if that won,t clean and correct ..doc

Can the relief valve if sticking be cleaned? Would I just have to pull the oil pan to get at it? Don't think I have ever really seen one before.

A spike in pressure often indicated a blockage. As doc says, first verify the reading accurate using a known good gauge. If it does in fact spike it's time to start digging.

A couple mechanics that I know says that a 235 running at 60 psi is nothing to worry about and that is nothing for an engine like the 235. I was advised to change oil to a 10W40 and to also add a quart of Rislone Engine Treatment when I change the oil. Rislone is suppose to keep engines clean, quiets noisy valves and lifters and suppose to restore lost power. Above all, its suppose to remove sludge and other deposits and improve oil circulation. Guess I may try that when changing oil, will put in a quart of Rislone and then 4 qts. 10W40 and see if that helps. If this does not help, may just put in a new oil pump. Don't know if I can find a spare oil pressure gauge to test with.

I think your wise to go with the 10/40. I put 5/30 in a car once and it was so thin it started all my gaskets seaping

Tomco, thats what I was afraid of with 5/30, being a little too thin. I'm not sure just adding 10/40 new oil will correct the problem, thats why I am going to add Rislone. If none of this works, may just go a little further and purchase a new oil pump. I've been under this truck for the past 6 months doing this or that and was hoping I would not have to do that again due to health reasons. (I have a bad valve myself). If I have to put on a new pump, may just take it to a mechanic. Is there any kind of "Lucas" oil that would help this problem.

is your oil up to the full level line?

I think 5/30 is too thin too. Personaly I use 15/40 in all of my engines that have flat tappet cams, like your 235. The big oil companys have droped the amount of zinc and phosperous in motor oil for years because of new car emissions. It has reached the point where cam manufactures have seen an increase in cam failures. This probally won't happen to you but why take the chance with these oils that are taylored to the newer cars. 15/40 has all the good stuff older engines need. I would change the pump and not do anything to thin the oil. With the pan off you'll have a chance to clean it and the pick up screen. Hope this helps.

Sean

I have been watching this thread. I am not sure I understand what the problem is. Is 40 to 60 pounds of oil pressure a bad thing. I would pull the pan in a second if I had only 2 lbs of oil pressure...but 60 lbs? :confused:

Stuart

I don't think 60lbs is a problem either, but if the way the truck always runs changed suddenly it may indicate a sticky pressure relief valve or somthing as simple as some gasket materal that fell away from the pick up, and the pressure went up. It's hard to say but 40 - 60 lbs of pressure is great.

Sean

Most motors should have as a rule of the thumb 10 psi per 1000 rpm. So at 5000 rpm a motor should have approx. 50 psi. High Oil pressure can damage the rod bearings and especiallly at low speed. The high pressure will actually pitt the bearings and cause them eventually sieze.I would install another mechanical gauge and make sure I really had that kind of oil pressure.Most the 235's I have been around normally run 10-15 psi at Idle and 30-35 psi running down the highway

I talked to another mechanic today and he said 60 lbs. was nothing to worry about and that it really wasn't a problem. He said all the pressure is in the bottom of the engine in the pan and since it has a oil draft tube for relief that it won't hurt anything. He recommended just changing oil and putting in Rislone also. He has a pressure gauge and I will take it to him one day next week to test the actual pressure. If the pressure is actually 60 lbs., I may buy a new oil pump and clean the pan. I want everything to be right since I will probably sell this one and start another project.

A worn out pump won't put out too much pressure, it will only put out too little, so changing the pump is contra-indicated. Most 235's can't put out enough pressure to allow the pressure relief valve to open after they have reached operating temperature unless there is a blockage somewhere after the pump. Two miles is not far enough to get the oil up to operating temperature; it should take at least ten. Also the ambient temperature will have a lot to do with oil temp. I think it's colder now where you live than it has been recently.

I changed oil today and put in one qt. of Rislone. Let the truck run for about 10-15 minutes. Temp got to about 182, no oil leaks except for maybe just a very thin line trace where the head mounts to the block. At slow idle, the truck is posting oil pressure of a hair above 30, after applying rpm's, goes to 60. Truck runs and idles perfect. Maybe I just have a good oil pressure. Still will have the gauge checked when I can locate a manual pressure gauge. Pump is working because I pulled valve cover and oiler is pumping oil into the rocker arm tubes. Not as much toward the front but it is getting oil and probably will get more when going down the road. By the way, thanks to all who have replied. I apprciate it.