Low oil pressure starves the critical moving components in your car’s engine of the lubrication and heat management they need to work properly. It can be caused by simple things like a partially clogged oil filter or something as serious as a bad oil pump.
Usually, the oil warning light comes on, but it’s possible to have oil pressure so low that it can damage the engine, yet now low enough to trigger the oil pressure warning light. That’s why it’s so important to keep an eye on your dash gauges!
Troubleshooting the cause of low oil pressure and what you can do to fix it starts with interpreting the other signs you’re experiencing.
The Importance of Oil Pressure
Oil pressure plays a critical role in ensuring that all the engine’s moving parts have the lubrication they need to run safely. Oil pressure can vary depending on the temperature of the engine.
When you first start your car the oil and the engine block are cold. The oil is thick and is slightly more resistant to flow. Assuming you have the correct type of oil in your car, the oil pump will be able to overcome this higher “Viscosity” to draw the oil up into the oil galleries. The oil pressure gauge might be slightly lower at first, but it won’t be low enough to trigger the oil pressure warning light.
As the engine warms, the viscosity of the oil lowers, and it flows more smoothly. This might cause a slightly noticeable increase in oil pressure, giving you the peace of mind that comes with knowing the engine has all the lubrication it needs to run smoothly.
How Does an Oil Pressure Gauge Work?
The oil pressure gauge on your dash display is directly connected to a special sensor in the car’s engine oil system. This gives you a basic, but not precise, measurement of the oil pressure in the system in real time.
If the oil pressure drops too low, it closes the electrical circuit inside the sensor. This triggers the oil pressure warning light to come on, letting you know you need to pull over.
Causes & Signs of Low Oil Pressure
Low oil pressure can be caused by lax maintenance habits, leading to a clogged oil filter. It’s also possible for a serious oil leak or a failing oil pump to cause oil pressure to lower to the point that the oil warning light comes on.
1. A Clogged Oil Filter
A clogged oil filter is one of the more common causes of low oil pressure. It’s usually due to lax maintenance habits, such as going too long between oil changes. However, it could also be a sign of contamination getting into the oil from something like a blown head gasket.
The oil filter’s job is to grab and collect particulate matter in the oil engine oil as it’s drawn up from the oil pan. The filter only has so much capacity before it starts to clog. This makes it difficult for the oil pump to draw up the necessary volume of oil to circulate through the system, resulting in low oil pressure.
Note
The filter can start clogging before the oil reaches its rated lifespan. Especially if you use a low-quality oil filter with a synthetic motor oil rated for more than 10,000 miles.
How to Fix a Clogged Oil Filter
If your low oil pressure problems are caused by a clogged oil filter, the easiest fix is simply to get a complete oil change. Be sure to invest in a quality oil filter that can handle the mileage rating of the oil you choose.
If you were ridiculously over the scheduled oil change mileage, you might want to ask your mechanic about an oil flush. This might be necessary to get any built-up oil sludge out of the engine.
2. Wrong Viscosity Oil
Low oil pressure is an immediate warning sign that you might have used the wrong viscosity oil in your last oil change. Each engine is engineered to run on a specific viscosity of oil. If you used one with too high of a viscosity the oil pump might not be able to pick up sufficient volume to properly lubricate the engine’s moving parts.
This will cause noticeably low oil pressure when you start the car. It might even cause the oil pressure warning light to come on.
How to Fix the Wrong Viscosity Oil
Low oil pressure from using the wrong viscosity oil is usually the aftereffect of an improperly performed DIY oil change. It’s not unheard of, especially with all the confusing marketing language surrounding motor oils sold at the retail level.
Assuming you catch it early, you can fix the oil pressure problem by draining the oil, replacing the oil filter, and giving the car a new oil change. Just make sure you’re using the correct viscosity of oil as indicated in the owner’s manual.
3. An Oil Leak
Oil leaks can reduce the volume of oil in the system to the point that it causes the oil pressure warning light to come on. This is often due to a slow leak in a seal or the oil pan drain plug that’s easy to miss if you’re not in the habit of checking your oil or looking at the floor in your garage.
The oil level in the engine gradually decreases until there isn’t enough volume to maintain proper oil pressure when the car is running. This will show up as progressively lower oil pressure on the gauge that eventually triggers the oil pressure warning light.
It could also be a catastrophic oil leak. This includes things like the rear main oil seal completely blowing out, or something puncturing the oil pan. These incidents seem to come out of nowhere.
You hear a clunk or a thud, oil rains out of the engine and you can watch the oil pressure gauge plummet until the oil warning light comes on.
How to Fix an Oil Leak
Fixing a minor oil leak that causes low oil pressure starts with finding where the oil is coming out of the system. This can be challenging if the leak is something tiny due to something like stripped threads on the oil pan drain plug.
You need to look for signs of the oil leak when the engine is running and when it’s off. Some failed oil seals will only actively leak when the engine is running and the oil pump is pushing oil through the system. There are also special oil dye tests you can use to find a particularly elusive oil leak.
The severity and location of the oil leak will determine if it’s a cheap and easy fix, that you can do yourself. Though a lot of oil leaks require a professional mechanic, and can put a big dent in your checking account.
I called several mechanics to get some ballpark quotes on some common oil leaks and their repair costs.
A leak in the oil pan drain plug can be fixed for as little as $20.
A leak in the oil pan gasket averages from $125 to $250.
Replacing a damaged oil pan ranges from $225 to $550.
The cost to replace the front main oil seal ranges from $275 to $700, with an average of around $500 for most domestic models.
The cost to replace the rear main oil seal averages from $650 to $850 but can easily be more than $1,000 in some models.
4. Oil Sludge
Oil sludge that’s allowed to buildup in the oil pump pick-up tube can gradually cause low oil pressure throughout the engine. Since it’s a slow progression you might not immediately notice a change in the oil pressure gauge.
Oil sludge is primarily caused by poor maintenance habits. The longer you let old oil circulate through your engine the more it oxidizes and particles can be left throughout the oil galleries. While the sludge is present everywhere, the clogging of the oil pump pickup tube is the most pronounced as it has to move the greatest volume of oil at one time.
How to Fix an Oil Sludge Problem
The most straightforward way to fix an oil sludge problem that’s causing low oil pressure is to perform a complete oil flush. It only takes a little more skill than changing your own oil, and usually costs less than $50.
Note
There are plenty of good reasons not to do an oil flush. In some older cars, it can cause loosened sludge to become trapped in the oil galleries. It could also weaken the patina on cracked oil seals causing them to leak when they didn’t before.
Still, if you’ve gotten to the point that the oil pressure warning light is coming on, or the oil pressure gauge is drastically low, you either need an oil flush or a mechanic’s professional cleaning.
I called around to get quotes from several mechanics on the cost of professionally cleaning oil sludge from an engine. Assuming an oil flush isn’t enough to solve the low oil pressure problem, they’ll need to perform a manual cleaning of the oil system.
A professional oil sludge cleaning can range from $450 to as much as $850. Depending on the severity of the sludge and any other components it might foul.
5. A Bad Oil Pump
A bad oil pump is arguably the most severe cause of low oil pressure. Not only can the pump itself be expensive to fix, but even a failing oil pump that’s running poorly can still cause significant engine damage.
As the oil pump starts to fail, you’ll probably notice the oil pressure gauge running increasingly low. At the same time, there’s usually a high-pitched whining noise coming from the pump itself. You might even notice the frequency of the sound getting louder at high RPMS.
A bad oil pump will struggle to keep the engine properly lubricated. The hydraulic lifters will start ticking from the lack of proper lubrication, and the engine itself will start to run hot.
Eventually, low oil pressure will get to the point where the oil warning light comes on. This is usually the swan song of the oil pump, moments after it dies.
How to Fix a Bad Oil Pump
Low oil pressure due to a bad or failing oil pump requires a total replacement. Unfortunately, this is typically beyond what even a capable DIY mechanic can do on their own.
The part cost for the replacement oil pump is usually only $85 to $225, with $175 as the real-world average for most domestic models. The problem is the time it takes for a mechanic to replace it.
The labor cost to have a mechanic replace a bad oil pump will easily add another $450 to $750 or more to a final repair bill of $500 to $900.
6. A Faulty Oil Pressure Sensor
A faulty oil pressure sensor is a somewhat rare, yet inexpensive reason why the oil warning light comes on. Except in this instance the oil pressure is fine, and the sensor itself has malfunctioned.
Inside the oil pressure sensor, there’s a spring-loaded switch connected to a diaphragm which feels the pressure inside the oil system. When pressure drops to a certain degree, the spring allows the electrical contacts to close the circuit causing the oil warning light to activate on the dash display.
This usually triggers the check engine light which will throw and store a code to help you troubleshoot the problem.
Code P0520indicates a problem with “Engine Oil Pressure Sensor/Switch – Circuit Malfunction.”
How to Fix a Bad Oil Pressure Sensor
If a bad sensor causes the warning light to come on, the sensor itself will need to be replaced. This is something you can probably do on your own with some automotive tools and a little know-how.
The cost for a replacement oil pressure sensor can range from $45 to $125.
The labor cost to have a mechanic replace it will add another $75 to $150 to a final repair bill averaging around $150.
Frequently Asked Questions
What should I do if the oil pressure warning light comes on?
If the oil pressure warning light comes on, you need to pull over and shut the engine off as soon as possible. This is a sign that the oil pressure in the system is too low to safely run the engine. Every moment the pistons and other moving parts are moving without sufficient lubrication increases the risk of suffering severe engine damage.
How does viscosity affect oil pressure?
Viscosity is the measure of an oil’s thickness or its resistance to flow. Each engine is designed to run on a specific viscosity of oil. If you put oil into your engine that has too high of viscosity, the oil pump won’t be able to pick it up and circulate it effectively through the galleries in the engine. This will starve the moving parts in the engine of the lubrication they need to move smoothly.
Viscosity is also affected by temperature. A high will be thick when the engine is cold, causing low oil pressure due to the oil pump’s inability to draw it up. As the engine warms the viscosity of the oil might flow better improving oil pressure throughout the system.
Can low oil pressure cause an engine to overheat?
Low oil pressure on its own won’t cause a car to overheat, but the heat from excess friction it produces will strain the engine cooling system. Low oil pressure might not be enough to trigger the oil warning light can expose a lingering fault in the engine cooling system. Especially if your oil pressure issues are due to an oil leak, cracked cylinder head, or a blown head gasket.
Conclusion
Low oil pressure that causes the gauge to drop rapidly or triggers the oil warning light to come on means you need to pull over as soon as possible. While it could be a faulty oil pressure sensor, it’s more likely something far more serious that could cause major engine damage if ignored.
A minor oil leak from something like a bad oil drain pan or a minor failure in a seal can slowly cause the oil pressure gauge to drop. If it suddenly plummets, it’s likely something more serious. This could be a completely blown front or rear main oil seal or something that has punctured the oil pan.
Low oil pressure can also be due to some simple maintenance mistakes. Driving too long without changing your oil, can clog your oil filter making it hard for the oil pump to maintain proper system pressure.
Also, more than one DIY mechanic has accidentally used the wrong viscosity oil in an oil change. Only to find that it’s too thick to properly pressurize and lubricate the engine’s oil system.
Written By
Jason Farrell
Jason Farrell is a certified master technician, the editor of Mechanic’s Diary in Pittsburgh, Pennsylvania. He is ASE (Automotive Service Excellence) certified and earned a Bachelor’s Degree in Automotive Technology from Pittsburg State University. With nearly 18 prior years of experience in the automotive field, he has extensive knowledge about Domestic, European, and other foreign makes and models of cars and light trucks. Jason’s experience working as a technician and service manager at dealerships, gave him the experience and know-how of most aspects of inspection, diagnosis, and repair from engine and drivability to electrical, HVAC, brakes, steering and suspension and everything in between.