is it normal for oil pressure to fluctuate?

Question

I have a 94 GMC2500. I noticed that the oil pressure gauge will rest just outside of lower red zone (but still in the green) when idling, but jump to the middle of the gauge when the the truck is moving.

i just had a jiffy-lube oil change a couple of weeks ago.

Is this normal for an older vehicle (over 100k mi) or should i be looking for a leak?

Answer 1

Normally the oil pressure in a small block Chevrolet will be 20 - 25 lbs. at idle and 40 - 45 lbs. when the RPM's are above 1000. For now, the first thing to check is the oil level and make sure the oil filter is dry and tight. If the oil pressure gage has no numbers, the hydraulic lifter will clatter like heck if the oil pressure is too low at idle.



I dislike fast oil change shops because they make too many mistakes! Their biggest one is when they change the oil filter the old gasket is left on the cast-iron oil filter mounting pad. Sooner or later you'll have a serious oil leak at the filter gasket area.

Answer 2

How Does Oil Pressure Work?

1. There are many things that affect oil pressure. If the oil has not been changed at regular intervals and left for extended periods of time, it begins to produce sludge. This sludge, over a period of time, also hardens into a hard cake or ash type of material and will clog up many of the oil passages in the engine. It can block the oil pump screen preventing the oil pump to pick up sufficient oil, the oil filter from flowing at the right rate and even the return holes in the cylinder head. The cylinder head under the valve cover is where most of the caking results and can stop the oil from returning to the oil pan.

2. If the engine is low on oil, insufficient oil will be picked up by the pump and the vehicle will have either no oil pressure or fluctuating pressure. Fluctuating oil pressure shows up when the vehicle decelerates or stops. All the remaining oil will move to the front of the oil pan and expose the oil pump pickup tube.

Conditions of Pertinent Parts

3. If the vehicle has a bad oil pressure sender, it will result in unreliable pressure indications. If the vehicle was ever inadvertently run out of oil there could be significant wear in the engine resulting in low oil pressure. The condition of the oil pump and tightness of the bearings are factors affecting oil pressure. Oil pressure can be compared to a large diameter fire hose that has a small nozzle. All the water being pushed out the small nozzle creates tremendous pressure. Open the nozzle to close to the same size as the hose and the pressure is greatly reduced. Like a fire hose, the oil pump puts out volume and pressure. The tighter the bearings in the vehicle the higher the oil pressure--just like having a small nozzle. The more the bearings wear due to dirty oil, mileage or running out of oil, the lower the pressure. One more thing that can reduce oil pressure is a crack in the crank shaft at one of the bearing journals

Diagnosing Oil Pressure Problems

4. In diagnosing the cause of low or no oil pressure, first check the level and condition of the oil. If it is very low and dirty it will need to be changed. The filter must also be changed. For now, just to test the engine and see if that is all of the problem, fill the oil to the proper level. If the oil was extremely dirty then the valve cover must be removed to see just how dirty or how much caking is on the heads. Once the valve cover is removed if there is a lot of caking remove it be chipping it loose on the head with a screwdriver and vacuum it out with a shop vacuum. The oil pan will also have to be removed and cleaned and the oil pump screen cleaned or replaced. If there was little caking in the valve cover stop there and replace the valve cover.

RulingOut Bearing Problems

5. Start the engine and immediately check the oil pressure with the engine cold. Listen for knocking noises in the engine. Tap the gas pedal quickly a couple times bringing the RPM to about 2,000 and see if there any noises as the engine is accelerated. If so, there is a bearing problem, which requires major engine work. To proceed further would be futile. If no noises are heard get out of the vehicle and with the engine running open the oil filler cap on the engine and see if there is oil flowing to the valves. You may need a flashlight but oil should be seen on the valve rocker arms and the bottom of the head. If no oil is seen flowing there is definitely a pressure problem.

Diagnose Pump Problems

6. Buy or borrow and external oil pressure gauge. With the engine off remove the oil pressure sender and insert the end of the external gauge. Start the engine and observe the gauge. Watch the oil pressure when it is cold and when hot for differential readings. If the oil pressure is low to start with and the engine has no apparent knocking noises the problem is very likely with the oil pump. The oil pan must be removed and the oil pump and screen replaced. If the oil pressure is high and after a few minutes it drops to zero the crankshaft is bad and has a crack in it. If the oil pressure is high to start and when it warms up never drops below 10 pounds at an idle then the oil sending unit is bad and needs to be replaced.

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Answer 3

Pressure Fluctuation

Answer 4

Yes, every engine will have oil pressure fluctuations related to engine speed. And an engine with 100k miles will have a little more fluctuation, since the bearings are worn more than an engine with fewer miles. As long as the oil pressure doesn't drop off completely you should be okay. Also remember, pressure doesn't necessarilly mean lubrication. Pressure means restriction, and if any oil ports are plugged you'll show high ("good") pressure and still lock the engine up. As long as the pressure gauge isn't in the red zone on either end you're fine.

Answer 5

it is normal to have a lower oil-pressure when idling,but by accelerating the gauge must show higher level

of pressure and remember,if there was a leak,you should see it on the ground under the place where the

leak was happening.

Answer 6

its not a leak at least not that you could aee. oil pressure is rasised as rpms increase. why? oil pressure is the result of oil being forced thru the engines various bearings and tiny passages. at idle the oil is being pumped at lower volumes similar to turning on you garden hose at a trickle. when reved up the flow is increased as it would with a hose turned higher. that tug you get from a garden hose on high is water pressure! if your hose was pushing that water thru a pressure nozzle it would attempt to pull even more!

Answer 7

Its normal for mostly every engine, remember the oil pump spins faster when the engine is moving faster.

Answer 8

it,s natural for the oil pressure to be higher while your on the road then it would be sitting and idling.