why would you lose oil pressure at high rpm???

Question

Hi i have a 355 chevy motor that loses oil pressure at high rpm between 5000-6000 rpms oil pressure goes up to 60 lb's then drops to 20 lb's. It's fine at low rpm durnig normal driving it runs about 40 lb's at 2800 rpms. ANY BODY KNOW WHY??

Answer 1

As others have said, you are starving for oil at high RPMS. I assume that you aren't a fool and have the right oil level. If this is happening only when you accelerate or turn, you may be able to solve it by building a baffle into the bottom of the pan. Another alternative is to install an Accusump. If it happens at all times, you may be able to find a deeper pan, allowing an extra quart or two.

One more possibility, and that is that the oil is foaming at high RPM. This could be caused by the oil itself...try switching to a synthetic. Do you run an oil cooler? If not, the oil could be thinning out due to high temps. It could also be caused by water mixing with the oil, usually from head gasket leakage. You can determine this with oil analysis if it isn't obvious on examination.

Answer 2

I'm going to guess it's a high volume oil pump. Because you are pumping such a high volume of oil, you may be starving the pump at high rpm's. It has pumped most of the oil out of the pan and up to the heads and there isn't enough oil in the pan. The pick-up sump also may be too close to the bottom of the pan, which would prevent it from pumping the proper amount of oil, or it may not be deep enough in the pan, and is sucking air when the oil level drops. Check the depth of the sump in relation to the bottom of the pan to make sure it's right. A deep oil pan and sump might be a good idea, too. A pan that kicks out to both sides at the bottom will allow extra oil without the clearance problems of a deeper pan.

Answer 3

A few possibilities. One is that the pickup for the pump is too close to the bottom of the pan and can't suck up oil fast enough. Two is that there is something blocking the pickup. And three is that if it is an older engine, the oil return holes are blocked and oil can't get back to the pan fast enough. My bet is on #1 if it's recently been rebuilt. When installing a new pump most people braze or tack weld the pickup in place to prevent it from falling out or down.

Answer 4

Oil pressure is only supposed to be at about 4-6 PSI idling,, Lousy oil pump.. any cracks in oil galleys, leaks between the pump and the block, theirs lots of reasons for really low oil pressure but you have a fairly new car so unless your engine was built incorrectly im not gonna bother listing all the other crap, check your oil pressure and it should be around 4 psi or so at idling, dont be alarmed. Oil grades affect the flow, running thick oil or to thin of oil will affect the pressure, look into it.

Answer 5

Is it breaking up at the higher RPM, if it is, you may be floating the valves if you have the hydraulic lifters in there, you may need to go to a roller rocker, if you haven't already. If you are set there, go with some of the oil pan ideas, you could overfill the oil pan a little bit, and see if that helps, if it does, go with the larger oil pan with baffles.

Answer 6

You may be starving the oil pump.. I'd check the accuaracy of your dip stick [no pun entended] and make sure you have the correct amount of oil.
Also for high rpm use a windage tray and pan baffling is good to have...

Answer 7

Oil starvation

Due to one of three causes:

Not enough oil in the pan
clogged pickup
blocked return lines

Answer 8

buddy you ever heard of pumping the pan dry. If the engine was built proper ith the oil drain back holes added this would not happen.Tear engine down and enlarge ans add oil drain back holes..I know this due to the fact i worked where we built Hooter National race engines.

Answer 9

Maybe the oil gasket is damaged and the pressure is leaking form there, try replacing them.

Answer 10

if loss off oil pressure could be one o f 3 that i can think off but from ur info my guess would be that the cam shaft bearings r worn