When you see smoke coming from under the hood of your vehicle, your primary impulse would be to think that it is overheating. There is a good possibility that this is what is happening, particularly if the weather is a bit warmer. However, what if it is cold outside or your gauges do not indicate that the car is overheating? There are quite a few answers to why car smoking but not overheating.
Smoke from under the hood does not necessarily mean there is a fire brewing. So, “where there is smoke, there is a fire,” is not a proverb you can apply in these situations. Your mechanical friends will smoke from time to time, as simple as that. But that does not mean that smoke from under the hood indicates that everything is still functioning smoothly.
Car Smoking But Not Overheating: What Smoke Means In A Car
White smoke emitted by the tailpipe is indicative of a bad head gasket or a failed internal component of the engine in the combustion chamber. When a blown radiator hose sprays coolant onto the hot engine, it produces a wispy, white smoke that resembles smoke. Smoking coolant gives off a sweet pungent smell and is oily to the touch.
Gray or blue smoke has a bitter, pungent order and usually signals burning oil in the engine. Possible reasons are seized or worn piston rings, leaking valve seals, overfilling crankcase, a plugged PCV valve, failure to change the oil, or using the wrong kind of it. Oil consumption without blue smoke or external leaks generally means the oil is burning slowly in the engine. Try using thicker or high-mileage motor oil.
Transmission Fluid Issues
Transmission fluid that has made its way into the intake manifold due to a failed transmission vacuum modulator produces thick, gray smoke.
In most cases, black smoke indicates that a vehicle is burning unburned fuel. A faulty fuel pressure regulator, faulty ignition component, faulty engine sensor, or leaking fuel injector or causes inefficient combustion, enabling raw unburned fuel to enter the exhaust system before exiting through the tailpipe. The black smoke produced by any of these situations will smell like gasoline.
On the other hand, black smoke from burned wires or an electrical failure can make the lights flicker or intervene in the process of other electrical devices. The smell resembles that of burnt plastic. With numerous electrical devices and a few hundred feet of wire jammed inside every corner of the modern-day vehicle, smoke from bad electrical connections can originate from the passenger compartment or under the hood.
In summary, different kinds of smokes give off different scents to help one identify what kind of problem they are dealing with.
The Reasons Behind Car Smoking But Not Overheating
There could be many reasons behind car smoking but not overheating. Although not serious at first, these little things can get pretty severe if you do not get to the root and repair them. The most common causes of this problem include:
Car Smoking But Not Overheating: Oil Spillage
If your car is smoking but not overheating under the hood, this could happen due to oil being outside the engine. Oil has to be inside your vehicle in its designated spots at all times. If you are not careful when filling up your car’s gas tank, oil could get access to sensitive parts. Or, there might be a spill where you are pouring oil into the crankcase.
If it is simply an oil leakage at the wrong place, not much harm is done except the production of a harsh, oily odor. You can expect this to burn off quickly without doing any long-term damage. However, if leaks are a regular thing and you keep driving without cleaning them, some plastic or rubber bits can break down due to prolonged exposure to oil.
Car Smoking But Not Overheating: A Leaky Component
This is another type of oil spillage but in this case, the oil leaks from a leaky part sitting on top of the engine. It can be a leaky valve cover gasket. You can replace this part easily for a cheap price. However, avoiding the problem for too long with exacerbating the minor leak and soon you will be dealing with a much bigger problem than what you started with.
Car Smoking But Not Overheating: The Oil Filler Cap
White smoke from under the hood of the car is a common problem in older engines. In almost all engines, the oil filler cap gives off a faint smoke, which is the remnants of burnt fuel inside the engine. Older engines generate more hot spots, creating the perfect environment for an engine smoking but not overheating.
Clogged PCV tubes or worn-out piston rings are the main culprits in this case. The timeworn rings get the pistons to tap fuel into the cylinder – a place where it burns and produces smoke. Then, the smoke gets past the rings. Smoke is supposed to be pulled back into the engine by the crankcase ventilation to be burnt again.
This process is interrupted if either the PCV valve or tube is blocked or faulty. In that case, the smoke is released through the filler cap.
Car Smoking But Not Overheating: Electrical Wires
A hot wire can also be the reason behind car smoking but not overheating. This is where you will get a strong, pungent odor from the engine that is hard to miss. It could be a challenge to trace it when the smell comes from the copper wires of the alternator. Nevertheless, a burnt alternator produces a strong odor that you will certainly notice. If this happens, the check engine lights and low voltage lights will come on.
Car Smoking But Not Overheating: Coolant Leak
If the coolant overflow tank leaks, it can cause sudden cases of steam emitting from under the hood of the car. The occasional puffs of smoke can also be the result of burnt transmission or power steering fluid. In that case, you will notice a chemical odor filling the air alongside a cloud of smoke.
Associating Smoke Colors With Problems In The Vehicle
Now that you know the common reasons behind why car smoking but not overheating, let us know what different color smokes will indicate.
Car Smoking But Not Overheating: Black Engine Smoke
Black smoke from the engine is often a mark of excessive fuel consumption. It can also be caused by a blocked air filter. If you can identify the fault early, it should be a fairly easy fix.
1. Faulty Fuel Injector
Fuel injectors supply diesel or petrol to the engine in the form of a high-pressure mist. They can get clogged with dirt or poor fuel, or leak due to wear and tear in the seals. The injector and the seals can be replaced by a certified professional.
2. Damaged Fuel Pressure Regulator
As the name suggests, the fuel pressure regulator regulates the pressure and diesel or petrol going into your car. This part can either be found inside or outside the fuel and will warrant a replacement if broken. You should have a word with your local garage if the fuel pump has to be replaced too.
3. Dysfunctional Carburetor
Older cars come with a carburetor – a component where the fuel and air mix. When this part fails to deliver adequate diesel or petrol to the engine, dark smoke will be emitted by the engine. It is important to get this issue checked as soon as you can by a professional as your car will be using too much fuel and this makes excessive emissions.
4. Clogged Inlet Manifold
The inlet manifold gives a combination of fuel and air to the engine cylinders. With a blocked inlet manifold, only a little amount will be able to enter the combustion system, causing the engine to produce a cloud of black smoke. Though this part can be cleaned at home, we suggest asking a professional to do it for you if you are not 100% comfortable with auto bits.
5. Off Ignition Timing
For the fuel to burn properly, it must be ignited at the proper time during the combustion cycle. With the ignition timing off, the engine will burn more fuel than needed. In more extreme cases, it will pump out dangerous rings of black smoke.
If you suspect your car is burning through too much oil get the engine checked by a trusted mechanic.
Car Smoking But Not Overheating: White Engine Smoke
White smoke in the engine is generally a sign of a coolant leak. A coolant leak can be caused by any of these given problems:
1. Damaged Radiator/Coolant Hose
Radiator hoses can collapse, crack or swell over time and you might be able to notice the damages by yourself by just lifting the bonnet. Fortunately, these parts are inexpensive to replace.
2. Cracked Engine Block
Engine blocks contain all important parts of the car’s engine. Extremely low temperatures can make the coolant freeze up and push against the walls, causing small cracks. Though uncommon, some portions of the engine blocks can be thinner than others due to manufacturing faults. If that is the case, those parts are more vulnerable to damage.
Try using an engine block sealer to remedy the little cracks. For the big ones, you will need professional assistance. A mechanic may have to re-weld sections of the block or resort to cold metal stitching – a complicated method that can repair damages in this case. Keep in mind that this process will be very expensive. You may find that buying a new car will come cheaper than that.
Smoke from the exhaust is not as serious as smoke from the engine. The color of the smoke clouds leaving your car’s tailpipe can help you diagnose the issue elsewhere too.
Car Smoking But Not Overheating: Black Exhaust Smoke
It is common to see cars give off black smoke from the tailpipe once the engine starts up. However, if it clears up quickly, there is nothing to worry about. Your car could be struggling with any one of these three problems if the issue persists:
1. Clogged Or Dirty Air Filter
The air filter stops unwanted debris from getting sucked into the engine. Pollutants collect in the filter with time and stop the filter from functioning properly. The filter can also get damaged in some cases. Once the debris reaches the combustion chamber, it burns along the fuel and produces black smoke.
Fortunately, a filter replacement is a rather straightforward job that you can DIY.
2. Bad Fuel Pressure Regulator
If the exhaust continues to pass black smoke, the culprit may be a faulty regulator. These devices are generally used to regulate pressure in the fuel system and can be found mounted on the fuel rail. If the regulator is not working properly, it can raise the pressure in the system and your vehicle’s fuel economy takes a hit. In select cases, the additional fuel burns as black smoke.
3. Clogged Or Leaky Fuel Injector
Fuel injectors maintain a specific level of fuel in the combustion chamber. If the part goes bad, the car might start to shake when idle. When there is too much fuel, the engine will start to burn it as black smoke. Take this as a sign to replace the parts.
Car Smoking But Not Overheating: White Exhaust Smoke
Are you seeing white smoke from the exhaust once you turn the engine on? You are saved if it dissipates as quickly as it appeared. This usually happens due to a condensation build-up. But if the white smoke remains for long after the car has been started, your engine is burning coolant leaking out of the combustion chamber. Again, this can happen due to many reasons.
1. Blown Head Gasket
The head gasket maintains a seal on the internal combustion process and prevents the oil and coolant from combining. An overheated engine precedes a blown head gasket. When the coolant moves into the combustion chamber, it evaporates/burns into white smoke.
Inspect the underside of the oil filler cap. There will be a light-brown, creamy deposit on it if oil is mixing with the water in the car’s engine. You can try to use a head gasket sealer to take care of the small cracks but a professional will be needed for the more extensive damages. Get ready to pay anything between $700 to $1,300 for repairing this.
2. Cracked Engine Block
A cracked engine block is nearly impossible to fix. The parts are essential to run a car and support a wide range of key components. Coolant can seep out through the cracks and come out as white smoke from the hotter points of the engine bay. We suggest replacing the engine block completely but you might want to consider trimming the losses and getting a new car instead.
3. Damaged Cylinder Heads
Cylinder heads are a big part of the combustion chamber. The parts can get warped from overheating and make the engine misfire. Coolant can leak through openings as a result of a lost air-tight seal. The excessive coolant will start to burn as white smoke.
As the heads have to sit perfectly with the linked parts, you will (normally) have to change cylinders instead of replacing them.
Car Smoking But Not Overheating: Grey Exhaust Smoke
A thick cloud of grey smoke from the exhaust pipe is generally a sign that the car is burning oil. Escaped (leaked) oil can burn off as ashy smoke from numerous hot points around the engine. The liquid will leak into the combustion chamber, decreasing fuel economy and eventually, wearing out the catalytic converter. The leaking can happen due to one of the two reasons:
1. Malfunctioning Valve Stem Seal
Valve stem greases the valve in combustion engines to maintain the proper ratio of air to fuel. Loose parts break the seal and allow an outlet for the oil. Repairing the problem can be complex and pricey and you might need to replace or rebuild the engine.
2. Failed Piston Rings
If greyish-blue smoke leaks the tailpipe of your vehicle when it is accelerating, take that as a sign of damaged piston rings. These components can be found in the cylinders and with a broken seal, can lead to oil leakage. An uncommon fault like this will require the knowledge and expertise of a professional to be fixed.
Car Smoking But Not Overheating: Blue Exhaust Smoke
Dark grey/blue smoke is a clear indication that your car’s engine is burning additional oil. In addition, the car may start misfiring when you rotate the keys in the ignition, or it will shake more vigorously than you are used to. As grey and blue smoke from the tailpipe can point toward the same errors, there is a natural portion of overlap with the aforementioned section. Leaks like that can be caused by:
1. Worn Pistons And Piston Rings
Pistons rely on rings to maintain an air-tight seal on the cylinders of a combustion engine. Over time as it sustains general wear and tear, the rings can start leaking oil into fuel, which burns as blue smoke eventually. Although you can see this kind of smoke from the exhaust on a regular day, it can come from the bonnet too.
Damage to the piston rings and the pistons is an extremely complicated repair which we do not recommend you take into your own hands.
2. Damaged Valve Stem Seals
Valves adjust the amount of air and fuel mixture allowed into the cylinders for combustion. Though the seals are generally made from high-strength rubber, they are prone to cracks and wear from extreme temperatures. Professionals will often use special tools to replace a valve seal.
3. Malfunctioning PCV Valve
A PCV valve (short for Positive Crankcase Ventilation valve) discharges unburned fuel and gas from the engine block. A stuck PCV valve will make the oil, air, and other gases mix inside the engine. When the engine burns this air, blue smoke will be created.
Repairing a PVC valve should not be too expensive but generally involves a replacement, not a repair.
4. Worn Engine Oil Seals
As oil moves around the engine from the tank, it depends on a bunch of seals to stop it from seeping into other sections of the air. These seals can break from general wear and tear, leading to oil burning and leaks.
If you see any blue smoke or leaked oil, get your car to a garage as soon as possible.
5. Inlet Manifold Leaks
The inlet manifold delivers a blend of air and fuel to the cylinders inside the engine. If the manifold spills oil into the cylinders, blue smoke can be emitted after it has been burnt. Sealants can be found online or at local automotive stores to temporarily patch these leaks.
6. Head Gasket Failure
Head gaskets are what seal the internal combustion process. Overheating can damage this process, allowing the oil to get into various parts of the engine. Try a head gasket sealer to resolve the small cracks but be ready to pay up to $1,300 for more extensive fixes at a garage.
Car Smoking But Not Overheating: What To Do If Your Car Begins Smoking
The first thing to do is to pull over and decide if your vehicle is safe to drive – rely on common sense and maintain caution above all. Take a look at the warning lights and gauges to measure if the engine is overheating, if the oil pressure is low, if the oil light is on or in the CEL is on.
Perform a quick visual inspection. Never put your hands on a hot engine. Wait for it to cool down and examine the fluids. However, if you notice a puddle of down under the hood, it is time to call the towing service nearby. Check out this video to learn how to diagnose leaks under your car.
Once your vehicle runs out of coolant, motor oil, or transmission fluid, it is functioning on thin ice.
Now you have the answer to why your car is smoking but not overheating. As the color and smell of the smoke is a great way to understand which components have to be checked and/or replaced, try to keep an eye out for them.
Black smoke generally indicates a problem with the fuel system, gray/white chemical smoke is a sign that you have to check the power steering and transmission, while blue smoke means you have to check the oil system of the cars.
These tools have been tried and tested by our team, they are ideal for fixing your car at home.