Why is my car blowing white smoke but not overheating?

If you start your vehicle and see white smoke coming out of the exhaust, there is a few reasons for this happening. Unfortunately, apart from one issue it means a fairly serious and costly repair.

Finding the answer to why is my car is blowing white smoke but not overheating usually requires taking your vehicle to a mechanic for inspection. However, you should not panic, if the white smoke only appears on start-up and goes away once the engine warms only. This is a typical thing almost all cars do, especially in cold weather. It’s caused by condensation in the exhaust, which goes away as soon as the vehicle reaches operating temperature.

Reasons for white smoke coming from the exhaust

  • Coolant LeakA coolant leak in which coolant is reaching the cylinder can only mean one thing…. the head gasket is leaking. When the head gasket has blown, the coolant is burnt during combustion. The white smoke being emitted from the exhaust is burnt coolant. Unfortunately, this is the most common cause of white smoke. It usually comes with other symptoms, such as low oil, an overheating engine, and low coolant level. However, if it is only a minor leak to the head gasket, it may not be bad enough for the other symptoms and not overheating yet.
  • Faulty injector – When an injector becomes defective with the injector being stuck open, allowing excessive fuel into the engine, this can be too much for the motor to burn away. The result of this is that unburnt fuel is forced into the exhaust, which can not only cause a clogged catalytic converter but also create large amounts of exhaust smoke as the fuel is burnt in the exhaust.
  • Leaking oil seals – Piston rings or valve steam oil seals can leak with age, forcing oil into the cylinder to be burnt. When oil burns, the exhaust smoke is excessive and usually has a blue tint. Although, sometimes, this can be seen or mistaken as a large amount of pure white smoke. It can be more challenging to determine the difference in diesel engines, where the exhaust gases are usually grey/white.

Does white smoke mean a blown head gasket?

The most common cause for pure white smoke is a blown head gasket. The head seals the block and head of the motor together, allowing the coolant to flow through the water jackets. When the head gasket leaks, the coolant is allowed to get into the engine internals, where it is burnt, which gives you significant amounts of white smoke.

To check if the head gasket has failed, is to check the coolant level; the level should drop as the coolant is burnt away. Another indicator is that oil has been mixed with the coolant, which will be evident in the bottle when checking the level. The coolant will be a dirty black color and have a thicker consistency. Or vice-versa checking on the underside of the oil cap will be a large amount of thick white sludge.

There are tools to help diagnose head gaskets, such as a fluid that you mix with a small coolant taken from the engine that changes color if the head gasket has failed.

What should you do if you see white smoke coming from the exhaust?

If you see white smoke coming from your exhaust and it is beyond your mechanical knowledge to repair, then have your vehicle recovered to a mechanic for inspection. It may not be as severe as a head gasket failure. An injector or fuelling-related fault could be a cheaper repair. Failure to fix the fault could lead to more damage to engine internals and a bigger repair bill.

Can I drive with white smoke from the exhaust?

Driving with white smoke from the exhaust is possible; however, the risk of damaging more components is exceptionally high. If the problem is the head gasket, eventually, the car will overheat, and it will do so within a minute or so of starting the engine, so it will not be possible to drive more than 100 yards.

An oil seal-related problem, although the car will be chucking out vast clouds of white smoke and require the oil topping up regularly, is not as bad, and the oil will continue to burn fat as you drive. More issues will follow, but a few short journeys will probably not cause too much of a problem, but the risk is yours to take.

Can low oil cause white smoke?

Low oil on its own will not cause white smoke. Low oil can cause burning in the engine, and smoke can be evident in the engine bay, but it will not be a significant amount exiting the exhaust. White smoke from the exhaust is an indication there is another issue. Read more on the subject of driving low on oil here.

Final thoughts on why is my car blowing white smoke but not overheating?

Unless you are experiencing white smoke until the engine warms up, it will probably be another issue. A coolant leak caused by a failed head gasket is the most common problem. Some vehicles are more familiar to head gasket failures than others, so it is good to be aware of this. If your car puts out a lot of white smoke, have your vehicle inspected by your mechanic, who will confirm the issue.

My name is Tom although my friends call me Tommy. Messing around with cars and bikes has always been a hobby of mine even from a young age. So I made it my day job 17 years ago. I am a fully qualified mechanic as you would expect. I've worked in all different areas of the motor trade, valeting, panel beating, engine repairs, I'm sure you get the idea. I enjoy sharing my wealth of knowledge and experience with others, which is the reason I spend a lot of time here writing for this website.

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