If gasoline and diesel are the blood that keeps a car running, then motor oil would be the equivalent of water. That greasy fluid is just as important in the everyday running of a vehicle as it would be to fuel up. With motor oil, your engine can stay lubricated, friction-free, cooled, and without excessive wear. It’s certainly a worrying sign then when you suddenly experience low oil pressure at idle.
So, why is this happening? You’ve sworn that you kept a good eye on the motor oil. You flushed and changed it when the time came, and you just had it topped up not too long ago. In that case, why is your dashboard flashing you that alarming ‘oil pressure’ warning light? Well, there could be any one of many reasons why you’re facing low oil pressure at idle. Here’s a little explainer, just to help out…
What Is Motor Oil?
Before we answer your concerns over low oil pressure at idle, we should perhaps get to grips with what motor oil is. So, what role does this fluid play in the operations of your automobile, anyway? In a nutshell, this oily liquid improves your engine’s performance and extends its longevity. It does this by preventing the many metal components in your engine (and elsewhere) from tearing each other.
That metal-on-metal contact is more than enough to break the engine in half (figuratively speaking) within mere minutes. These days, motor oil even helps your car to reduce its emissions and increase fuel economy by ensuring that the engine runs more efficiently. Motor oil is made from two key and fundamental elements – base oils, and additives.
If we’re going to think of an analogy, let’s use tea. With motor oil, the ‘base oils’ would be the water that your tea will dissolve in, whereas the ‘additives’ would be the tea bags. For the most part, the base oils – the water, in this analogy – are what perform the work of lubrication, heat absorption, and sealing your engine’s many gaskets and seals.
Base oils that are used in engine oil can be made out of three distinct blends:
- Petroleum (usually called conventional motor oil)
- Chemically-synthesized Materials (otherwise known as synthetic motor oil)
- A Combination Of Synthetics And Petroleum (referred to as a semi-synthetic mix of motor oil)
Here’s a more thorough explainer of the former two base components:
1. Petroleum (Or Conventional Base Oils)
Motor oil that uses petroleum as its ‘base oil’ is refined from crude oil. This basically comes from the same compound that goes into your fuel tank but has been refined differently. Conventional motor oil may contain elements such as sulfur, nitrogen, oxygen, and some metal components.
The latter would be nickel or vanadium, both of which are naturally a part of crude oil, and can’t be separated during the refining process. The fractional refining of crude oil can leave these elements mixed in with the rest, despite differing in structure, which can reduce the performance of the oil.
2. Synthetic Base Oils
While conventional motor oil has been refined out of crude oil, synthetic motor oils are chemically engineered to include only the best molecules. As we mentioned, refining crude oil could still leave you carrying certain components, such as a few metals, that you otherwise don’t want.
The synthesis process of synthetic oil can remove that, and is designed to exclude all contaminants or molecules that don’t belong. Its structure is pure and uniform. Its benefits include better friction reduction, optimum fuel efficiency, and better performance in high temperatures.
Now that we’ve learned more about the ‘base oils’ of motor oil, what about the ‘additives’? As per our analogy there, the additives are tea bags that add flavor. In other words, the chemicals that make up the additives in your motor oil provide additional functionality. Some examples of what additives bring to the performance and operation of your motor oil can include:
- Corrosion Resistance And Protection
- Acid Neutralisation
- Maintaining Oil Viscosity
- Detergency (or the ability to clean out the internal components)
- Dispersancy (or the ability to prevent sludge from forming in the oil, and keeps dirt or other debris suspended in the oil for removal during an oil change)
These chemicals are commonly derived from zinc, phosphorus, and boron. The hard part about these motor oils is trying to formulate the perfect mixture. That is to say getting the balance right between how many additives you’re going to add, in relation to the base oil. In all, the chemists and engineers behind these motor oils are trying their hardest to find that best-of-all-worlds blend for your car.
Why Does Your Car Need Motor Oil Anyway?
What’s just as important in our guide here on low oil pressure at idle, is understanding what motor oil does for your car. We’ve highlighted a few of them up above, but there’s so much more than your car’s engine oil has to do once it’s circulating inside your engine bay. Here are just a few of the functions that motor oil has to perform…
1. Reducing Friction
Know that your engine has countless different parts working in unison, and very closely so with one another. Without motor oil, this dance becomes mutually assured destruction, as the components – most of which are made of metal – would contact, grind, rub, and scrape against each other. The consequence of this intense friction would be having your engine fail catastrophically in an instant.
Motor oil prevents this by adding lubricant between those components, thus aiding in minimizing friction and wear. It does so by leaving a thin greasy ‘film’ over the surface of the moving parts as it swishes along. This ability for the motor oil to remain “stuck” in place on those components, and coating it after long periods of time is a crucial feature to have in most modern motor oil blends.
The “sitting still” effect can prevent wear and tear on your engine during a cold start. A cold start is a situation when the engine is cold and hasn’t been started in a while. This latter point is important, as it means the engine and its internal units haven’t had the chance to be lubricated in a long time. Studies have shown that most engine wear and damage occur during a cold start.
2. Engine Cleaning
Among the many additives that motor oil has, the ability to clean the insides of your engine is one of them. The lubrication of the motor oil can be formulated so that it would suspend contaminants like dirt or debris within the fluid itself. This is a safer alternative to just letting the particles keep sticking and adhering to the insides of the engine. Some motor oils could even dissolve these contaminants.
However, its significance remains with ‘detergents’ and ‘dispersants’. Detergents prevent debris from adhering and binding to parts, especially on those hot components such as the pistons rings or pistons. On the other hand, dispersants keep all the dirt suspended in the oil, thus making it easier to flush them out during an oil change. Additionally, it prevents the oil from turning into a thick sludge.
Your engine runs hot. Very hot. While most of the cooling of the engine is attributed to the work of coolant, your motor oil has a hand in it, too. By minimizing the friction within the engine, your motor oil inherently reduces the amount of heat that would’ve been emitted. This aids to lower the overall operating temperature of the engine, making the coolant’s job that bit easier.
On top of that, the motor oil can absorb some of the heat from the many moving parts, and then takes it away from the engine. It’ll then flow back to the oil sump, where the motor oil will be cooled. What’s interesting to learn is that lubricating the engine takes only a little bit of oil. The reason why your car needs so much motor oil in the first place is to ensure sufficient cooling of the internals.
Oddly, your motor oil also works as a pseudo-dynamic sealant in the engine. Most prominently, you can sense it in action in highly intense parts of the engine such as around the piston rings or cylinders. Here, the motor oil forms a dynamic seal, which keeps the combustion and gases sealed. This helps to avoid the hot gases from contaminating the motor oil and helps to boost performance.
While the piston rings and cylinders have numerous gaskets and seals to keep the entire section as airtight as it can be, it’s not perfect. The seals aren’t always smooth, and they will wear out after some time. These gaps are filled in by the flow of motor oil, without actually being too much to seep into the combustion chamber. Another side effect is improved fuel efficiency.
5. Shock Dampening
Try and compare the difference between falling onto solid concrete, and into a pool of water. Surely, the water would be much more pleasant on the backside, right? The same scenario is played out in the engine, where your motor oil provides a cushioning effect. It does wonders to dampen out the blow of mechanical shock that your engine’s internal components dole out by the second.
If your motor oil’s lubricating film is highly effective, it can resist rupturing to absorb and disperse the blows over a wide area. These impacts, therefore, won’t put too much wear out on a particular part or section of the engine. As the motor oil dampens the mechanical shock to its numerous bits and pieces, wear is minimized. The effect would be extending the engine’s longevity.
6. Corrosion Protection
Being a lubricant, motor oil also needs to try and prevent – or at the very least, minimize – corrosion from forming up inside the engine. Oxidation would be a natural occurrence within your engine had it not been for motor oil. Interestingly, the base oils of motor oil don’t have the natural ability to inhibit rust and corrosion. This has to be added through the use of those chemical additives.
Motor oil can be formulated to prevent corrosion in a number of ways. Either, it could chemically neutralize or remove the corrosive particles, and then scrubbing them away from the engine. Or, it can form a sort of barrier between the componentry and potentially corrosive material. In doing so, the rust won’t get the chance to bind and eat into the engine through oxidation.
What’s Causing You To Experience Low Oil Pressure At Idle?
Now that we’ve sufficiently understood its purpose in life, we can try to dive into the common causes of why your car is warning you of low oil pressure at idle. Oil pressure might seem like one of those things that you normally wouldn’t bother to check, but it’s in fact quite important. Motor oil builds up pressure when it’s circulating around the engine and is doing what it’s engineered to do.
If the oil pressure drops below its nominal level or is too low, it’s likely a sign that oil isn’t flowing. The default oil pressure does vary from one vehicle to another. Generally, however, you’d want the needle on the oil pressure gauge to be in the middle. To be more specific, when the engine is running at operating temperature, the oil pressure should fall between:
- 20 to 30 psi (or around 140 to 200 kPa) when your car is idling – this is what we’re looking for in this guide
- 45 to 70 psi (or around 310 to 482 kPa) when you’re at regular driving speeds
Your engine would be starved of oil if the pressure drops too low. Remember that the system has to pump oil through narrow channels and galleries, hence why you’re seeing pressure. Should the flow and pressure of motor oil drop, it can’t sufficiently lubricate, cool, and clean critical components like the camshaft, crankshaft, bearings, pistons, and other moving parts of the engine.
Here are some of the reasons why you’re seeing low oil pressure at idle…
1. Insufficient Or Worn Out Oil
The most common trigger for low oil pressure at idle is either not having enough oil, or if your oil is worn out. If your engine has an inadequate volume of oil, there naturally won’t be enough motor oil to create pressure with. Consequently, you also won’t have enough oil to properly lubricate, cool, and clean out the insides of your engine.
On the flip side, your motor oil can wear out and burn after some time. This happens as the lubricant is continually exposed to heat and friction, and breaks itself down. You should always keep on top of servicing your engine oil. An oil change should be scheduled every 3 to 6 months, or once every 3,000 to 5,000 miles. This would make sure that your engine is running on fresh and clean oil.
2. Too Much Internal Engine Wear
Remember how pressure is created in the oil flow? It has to flow through narrow passageways, such as through the crankshaft and camshaft bearings. As the flow of motor oil is naturally constrained, it builds up the pressure. Ordinarily, this is a good sign that oil is flowing, as it should. However, the engine’s many constituent components could wear themselves down, and broaden those gaps.
These channels become wider, and thus the oil could flow through more readily. You can notice this as the oil pressure drops, and the oil pump has an easier time trying to circulate the oil around. In this case, seeing low oil pressure at idle doesn’t necessarily entail anything wrong with the oil flow. Yet, it’s a symptom to look out for, as your engine might need repairs or part replacements urgently.
3. Faulty Oil Pressure Gauge
It might be alarming, but there’s a distant possibility that low oil pressure at idle isn’t a problem at all. Maybe, just maybe, the oil pressure gauge is broken. This can happen, and you’d be shocked to find that the engine actually has plenty of clean oil, and there aren’t any faults within the engine itself. It’s either a problem with the gauge or the sensors that feed it information on the oil flow.
Perhaps even the electrics and wiring around your dash, and particularly those feeding into the oil pressure gauge, could be to blame. In any case, it would ultimately produce a false reading of the oil pressure. You’ll have to get a technician to repair or replace the gauge. While you’re there, it might be prudent to have the oil pressure checked manually, just to make sure that all’s well.
4. Dirty Or Clogged Oil Filter
The oil filter is among the most underappreciated parts of your car. Its main role, as its name might suggest, is to filter out the motor oil. All that suspended debris and contaminants that we mentioned earlier will be trapped inside the oil filter. It prevents too much dirt from flowing inside the oil, which could leave permanent damage within the engine if it’s too much.
Normally, you’d swap out the oil filter after every – or every other, at most – oil change. Otherwise, the oil filter could get clogged up if it’s not replaced promptly. This should increase the pressure, but there’s a pressure relief valve that makes sure it doesn’t get too high. If that valve is broken, though, the engine oil might instead flow out more easily, hence reducing the oil pressure.
5. Wrong Oil Viscosity (Or Wrong Oil Type)
There are numerous types of engine oil out there with varying oil viscosity grades, and each vehicle is designed for different ones. It’s vital that during an oil change, you refer to your owner’s manual to see what type of oil is actually the best and recommended for your particular vehicle. Using the wrong oil type – and crucially, the wrong viscosity of oil – could be the reason why you’re seeing low oil pressure at idle.
The higher viscosity of the oil is naturally thicker and doesn’t flow as easily. It has its purpose, but when it’s filled into the wrong engine, it can affect the oil pressure. Depending on the operating temperature, the more thickly viscous oil may take more time to build up that pressure. Hence, why your car’s oil pressure is quite low at idle or during start-up, but could slowly increase as you drive along.
6. Overheating Engine
Having an overheating engine is a tremendous worry. Aside from all the wear and intense heat build-up in parts of your engine, you should also be concerned about the motor oil. As it aids in the cooling of your engine – albeit at a lesser degree than your coolant – the motor oil is naturally affected when the engine gets a bit too hot. This will, in the end, could result in a drop in oil pressure.
When the engine gets too hot, it causes the motor oil to thin, no matter how viscous it may be. This tinning of the motor oil prevents the pressure from rising to a more comfortable level, especially at idle. Its effects are similar as though you’ve put too low of a viscosity oil inside your engine than what it’s been designed for.
7. Faulty Oil Pump
The circulation of oil inside your engine is thanks in no small part to the oil pump. It forces the oil to flow in and out of the engine and helps your car to read the oil pressure. While this doesn’t usually happen, the oil pump can wear out and fail if not cared for, or as a consequence of too much strain on it. Should this be the case, the oil pump’s rotors could widen.
This now-broadened passageway would allow the motor oil to flow through more easily. The pump may still function perfectly fine, but the rate of flow would suffer in turn. You can tell this is an issue when the oil pressure drops below par, as it can’t build up sufficiently high enough. It might even fail to supply enough motor oil to some sections or parts of the engine.
8. Worn Out Internal Components
The engine has plenty of parts that regularly interact with motor oil. These could be the piston rings, cylinder and cylinder walls, valve stem seals, head gaskets, and so on. If these components fail – and they will when their time is due – motor oil could unintentionally seep into the engine’s combustion chamber. The engine oil will then be ignited and burnt alongside the fuel-air mixture.
A few symptoms will appear when something like this occurs. Firstly, as more oil seeps through, the overall oil level would drop, thus leading to lower oil pressure. Moreover, the burning of the motor oil will result in blue smoke being emitted from the exhaust pipes. Gasoline or diesel could also dilute the motor oil as it gets mixed, which can affect the oil pressure, as well.
Low Oil Pressure At Idle – Summary
In all, this concludes our look at low oil pressure at idle. If you notice that oil pressure light flashing at you, it’s an opportune moment to stop your car and consider your options. That warning light only flashes when the oil pressure drops below 5 to 10 psi, which is alarmingly low. Besides, fixing your low oil pressure at idle problem could be as simple as an oil change.
A flush and top-up of the motor oil shouldn’t cost much more than $100 at most workshops and is often far less. Should the underlying cause be more serious, such as a faulty oil pump or worn-out seals, it’ll no doubt cost you a bit more. But paying up for a repair bill now is significantly cheaper than total engine failure in part of ignorance, which will set you back a few grand for a new motor.
As a whole, the best way to prevent this from ever troubling you again is preventive maintenance. Following your manufacturer’s recommended service interval is more than enough to avoid having you worry over problems like this. It’s quite literally as harmless as getting your oil swapped out for some fresh grease after a few thousand miles. A fairly innocent tip, to prevent a disastrous issue.
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