Chevy 5.3 Low Oil Pressure At Idle, Trouble Shooter

Low oil pressure and engine noise are often attributed to internal wear, especially on high mileage vehicles. The actual cause may be slightly less dramatic.

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Low Pressure ZoneA customer recently brought in his 2008 Chevrolet Silverado 1500, which is equipped with the 5.3L Vortec engine. The vehicle has about 200,000 miles on it and has been pretty well-maintained, with regular oil changes. The owner stated that when starting the engine in the morning following an overnight soak, he heard an engine rattling noise and the dash gauge indicated low oil pressure.

We tested the oil pressure at the oil pressure switch and at the filter, and found it to be lower than normal. We determined that the oil pressure relief valve in the pump was defective, so we removed the front cover and replaced the relief valve. Oil pressure then appeared normal. But after the engine warmed up, the oil pressure dropped below normal at idle and the engine noise (probably lifters) returned.

Raising the engine speed to above 1000 rpm causes the oil pressure to increase to about 45 psi. If the engine speed is increased even more, oil pressure tops out at about 55 psi. Given the mileage on the vehicle, I’m wondering if the lower-than-normal oil pressure at idle is due to internal engine wear. Your help would be appreciated.

Ted WilsonMilwaukee, WI

Thanks for your question, Ted. Not that many years ago, an engine with half as many miles on it as your customer’s Vortec would be a prime candidate for either overhaul or replacement, and nobody would have thought it to be unusual or premature. But there are many engines out there today that have even more miles on them, and they’re running just fine. Accumulated vehicle mileage no longer seems to have an automatic correlation to internal engine wear, provided the engine has received the necessary maintenance. So you’re welcome to conduct the other tests that are normally used to assess internal engine wear, like cylinder compression and leakdown, but I’m pretty sure the cause of your customer’s low oil pressure can be diagnosed and corrected without the need for major engine work.

Your customer’s Vortec engine features an oil pump that’s bolted to the front of the engine and driven directly by the crankshaft, via splines. The oil pump can be accessed by removing the front cover (more on this later).


You mentioned that you had already replaced the oil pump pressure relief valve, so you’ve already had the front cover off, as the valve is located in the oil pump housing. The photo above shows a Vortec oil pump with the pressure relief valve and spring removed and placed to the side.

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When the oil pump produces too much pressure, the relief valve opens and vents some of the pressurized oil back to the suction side of the pump. Too much pressure is usually a problem only if the oil is too thick when the engine is cold or if the engine speed is very high. Most of the time, the relief valve will remain closed, but a burr or other damage to the valve or its bore may cause the valve to stick open.

If the valve remains open, it will dump oil pressure all of the time, including at idle when pressure is normally at its lowest. So a stuck relief valve could cause the symptoms you’ve described (low oil pressure, noise). But you’ve already removed and replaced it. If you’re confident that the relief valve is not damaged and can move freely its bore as intended, it’s time to move on.The oil pump has a metal pickup tube attached to it, on the side of the pump opposite the relief valve. Although there are two threaded holes in the pump, the pickup tube is secured to the pump by just one bolt on the inboard side of the pump. An O-ring seals the connection between the pump and the pickup tube.Several of these engines have developed problems with the pickup tube O-ring. Some believe the O-ring may be damaged during original engine assembly, while others think the O-ring just wears out over time. Regardless of the cause, if the O-ring is damaged, it can allow the oil pump to suck air through any gaps, rather than clean oil from the pan as intended.If the pump is sucking some air, it may be able to overcome this at higher engine speeds, due to higher flow. But at idle, when oil flow is already pretty low, ingesting air via the failed O-ring could be enough to reduce oil pressure to a dangerous level.

There’s a clever test you can conduct to determine whether the O-ring has failed and the oil pump is sucking air. It involves raising the oil level in the crankcase high enough to submerge the area around the pickup tube O-ring. You can accomplish this by adding oil to the crankcase, plus raising the back of the truck to tip the oil in the crankcase toward the front of the engine.Once you’ve added oil and raised the truck, start the engine and observe the oil pressure. If it’s now normal at idle, you know that the pickup tube O-ring must be replaced. Here’s where it gets interesting, and where your creativity may come to bear.

To get a clear shot at the pickup tube, then remove the pickup tube retaining bolt and replace the O-ring, you’re supposed to remove the oil pan. Depending on the vehicle, this can be a major undertaking. If it’s an all-wheel-drive pickup, for example, you’ll also be removing the differential and basically disassembling most of the front suspension of the truck. When you’re all finished, the truck will also need a wheel alignment.

There’s nothing wrong with doing things according to the book, but there may be other ways to get the job done as well. You’ll need lots of patience, but it is possible to remove the pickup tube retaining bolt without removing the pan. You’ll have to remove the front cover, and you’ll have to use some small tools along with your wrenches, but it is possible.To avoid dropping the removed retaining bolt into the pan, pack the area below the oil pump with rags. A strong magnet on a stick should be standing at the ready near the bolt as well, just in case. With the bolt removed from the pump, remove the oil pump from the front of the crankshaft. It may take some wiggling and you may need to remove the oil pump cover, but it should clear the crankshaft. The pickup tube will stay in place in the pan. Once you’ve separated the pickup tube from the pump, you should be able to see the damaged O-ring.

Reassembly is the reverse of disassembly, as the old repair manual saying goes. Make sure you get the correct O-ring for the job and install it carefully to avoid cutting or crimping it. The pickup tube’s retaining tab is held in position by a notch in the tab and a nub that’s welded to the pickup tube. This aligns the retaining tab’s mounting hole with the threaded hole on the inboard side of the pump.

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As fate would have it, this is the hole that allows the least amount of clearance for your tools. If removing the pickup tube retaining bolt taxed your patience, you might want to take a moment for silent meditation before attempting to reinstall the oil pump and the pickup tube retaining bolt. Some folks have gotten creative with a Dremel tool to free the retaining tab, allowing it to be positioned under the outboard threaded hole. The retaining tab will do the same job in either position, so the choice is yours.


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