14 Common Causes Of Low Engine Oil Pressure


Low engine oil pressure is something that needs to be taken care of immediately. When there is an issue with the oil pressure, a light gets illuminated on the dashboard. At this point, you need to pull over your vehicle and try to find out what caused the drop in the oil pressure. Here are the 14 most common causes of low engine oil pressure:

14 Common Causes Of Low Engine Oil Pressure

What does engine oil pressure low mean? Low oil pressure is really bad for the engine. When the oil pressure is low, it means that the engine is not getting the needed lubrication and this can lead to serious engine damage. Once you see the low oil pressure light illuminated, do not drive your vehicle until the issue is fixed. Here are the most common causes of low engine oil pressure:

1. Low Engine Oil Level

This might seem like a rooky mistake, but it happens a lot. Car owners often forget to check their engine oil level. If your engine is low on oil it can cause low engine oil pressure at idle because there won’t be a sufficient amount of oil to circulate and lubricate the engine. This can lead to serious engine damage due to lack of lubrication. I check my engine oil every 2 weeks. When you do so, make sure that your vehicle is parked on a leveled ground and that the engine is not running for at least 10 minutes.

2. Faulty Oil Pressure Gauge/Switch

The oil pressure could be just fine, but the gauge could be displaying an incorrect reading from an incorrect signal received from the sending unit. To find out if the oil pressure is low or why the oil pressure light is illuminated on your dashboard remove the switch and install a mechanical oil pressure gauge. If the reading is normal on the mechanical gauge, replace the switch/sender and this will solve your oil pressure problem.

3. Incorrect Viscosity of The Oil

Common Causes Of Low Engine Oil Pressure

This may appear like a no brainer to experienced mechanics, but the first thing to make sure of is that the engine oil being used has the correct viscosity. If the oil is too thin, you will increase the risk of metal contact in between the main/rod bearings and the engine’s crankshaft.

Always follow the recommendation made by the manufacturer. As the engine increases in mileage, for example over 150,000 miles and beyond, you can increase the viscosity slightly. If your engine required 5W-30 when it was new, you can now use 10W-30.

4. Accumulation of Dirt in The Oil Pickup Tube

This is one of the most common causes of low engine oil pressure. Sludge will clog the oil pick-up tube, therefore, restricting oil flow to the engine. Sludge is created when the engine oil starts breaking down due to heat and friction. Plus, the accumulation of deposits collected from combustion gases that made it past the piston rings.

5. Faulty Oil Pump

Another common cause of low oil pressure is excessive clearances inside the oil pump. The exact specification may vary, but there is a general rule that the oil pumps should have less than 0.003 inches space between the gears and cover and 0.005 inches clearance between the teeth and pump hosing.

With rotor style pumps, the clearance between the outer rotor and pump housing should usually be less than 0.012 inches, with no more than about 0.010 inches between the inner and outer rotor lobes. Too much clearance inside the pump will reduce the pump’s ability to pump oil efficiently which reduces the flow and pressure.

6. Oil Leak Within The Engine

A loss of engine oil can cause low oil pressure. The engine lubrication is a closed circuit and any cracks or leaks within the oil passages will affect the oil circulation. If the oil leaks due to a cracked line or worn piston rings, it leaves the system and there is just not enough oil left to lubricate the engine making sure that it is operating correctly.

7. Worn Out Internal Components: Main and Connecting Road Bearings

High engine speeds can cause faster than normal wear on crankshaft bearings, especially if combined with low-quality engine oils and longer than specified intervals in between oil changes. Excessive bearing clearances (more than about .001 inch per inch of diameter of the crankshaft journal) can cause up to a 20 percent or greater drop in oil pressure, which may in turn have an adverse effect on lubrication elsewhere in the engine (such as the camshaft and upper valve train, especially in overhead cam engines).

Having low oil pressure may result in problems with overhead cam engines with variable valve timing clearances. It’s not how these excessive clearances appear, the results are exactly the same. Excessive bearing clearances will also increase engine noise and pounding, which over time can lead to bearing fatigue and failure.

SOLUTION: The way to restore oil pressure due to excessive bearing clearances is to reduce the clearances by replacing the bearings or installing a refurbished crankshaft/new bearings kit. Installing a new oil pump or higher pressure pump won’t help because the bearings have too great a leakage rate to hold the required pressure. Installing a stronger oil pump than the old one can increase the oil flow and regain some of the lost pressure. The main problem would be still there and will cause bearing noise, wear and fatigue.

8. Contaminated Engine Oil

Engine oil contamination is something that doesn’t happen very often, but when it does, it can cause low oil pressure. The engine oil gets mixed with the fuel or coolant due to internal engine cracks or faulty seals and when it does, it is not thing its main function which is to lubricate the engine components. Decreased engine lubrication can lead to a huge repair bill. If you are noticing that you are low on engine oil, but you can’t seem to find any oil underneath your vehicle, take your vehicle to the mechanic because the issue could be internal.

9. Clogged Oil Filter

Common Causes Of Low Engine Oil Pressure - clogged oil filter

A clogged oil filter can be another cause of low oil pressure. As soon as the oil leaves the oil pump, it goes to the oil filter before reaching the bearings and oil galleys. All oil filters are creating some level or oil resistance flow. But the amount is not much, typically only a couple of pounds. But as the oil filter becomes clogged with debris, the oil restriction increases. This may reach a point where zero oil can pass through the filter. As a safety switch, the engine has a pressure relief valve located on the filter or where the filter mounts to the engine. But, that causes another set of problems.

10. Activated Engine Oil Bypass Valves

When the oil bypass valves are activated, the oil pressure will drop. As I said before, the oil filter can get clogged to a point where no oil can pass through it. To prevent the critical blockage, oil filters have a pressure relief valve installed which has a main function to open if the pressure is very high (typically 5 to 40 psi). This allows the oil to bypass the filter and keep on flowing. But the engine oil pressure will be reduced to the capacity of the bypass valve.

11. Broken or Clogged Oil Lines

If an oil line is clogged or broken the engine flow will decrease significantly and therefore the oil pressure will drop. The oil passes through a lot of small oil lines which overtime can get clogged or broken. If this is the case, you need to get your vehicle to the mechanic shop and the engine builder needs to check every single oil line and passage for leaks. Replacing or fixing an oil line isn’t very expensive, but the damage it can cause if not treated is huge. Remember, if the engine is not getting enough lubrication, it can overheat and you will be looking at a huge repair or engine replacement.

12. Clogged Oil Suction Tube

The oil suction tube has an inlet screen that often gets clogged or damaged. A clogged or damaged oil suction tube can cause low oil pressure because the oil flow is either restricted or leaking. You would need to check the inlet screen and remove any buildup that could be restricting oil flow. Sometimes the issue could be because the suction tube is not installed properly and instead of oil, it is sucking air.

13. Low Grade Engine Oil

14 Common Causes Of Low Engine Oil Pressure

Using low-grade engine oil and increasing the length of time and mileage in between oil changes will increase the risk of sludge being generated inside your engine causing low oil pressure and premature engine wear and failure. To avoid this from happening make sure to use good quality engine oils that either meet or exceed the engine manufacturer’s recommendations.

Most importantly, don’t go past the oil change intervals. The cost of frequent oil changes is cheaper than replacing an engine that failed due to poor lubrication and sludge. You could save a couple of dollars on an oil change. But, it could lead you to a $5000 bill for an engine change.

14. Weak or Leaky Oil Pressure Relief Valve

Some oil pumps also have an oil pressure relief valve. Some engines may have it on the engine block. A weak or leaky oil pressure relief valve is one of the most common causes of low engine oil pressure and happens if the valve sticks open or is held open by a small piece of debris/sludge. The relief valve is designed to limit oil pressure as engine speed increases. The valve opens when the pressure reaches a preset valve (typically 40 to 60 psi).

This vents oil back into the crankcase and limits maximum oil pressure in the engine. Too much oil pressure can be just as bad as too little. This is because excessive pressure can rupture the oil filter or even blow out pressed-in oil galley plugs in the block.

Can Engine Misfire Cause Low Oil Pressure?

There is a relation between engine misfire and low oil pressure because the sudden drop of oil pressure can cause the engine not running right and the RPMs to drop low in gear causing an engine misfire. A common cause of misfire can be oil in the spark plug and the oil could get there if there is an engine oil leak which will cause low oil pressure too. Fixing the oil leak will fix the oil pressure issue. This will return the engine to normal operating behavior and the misfire will stop.

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