Do Your Car Bulbs Keep Blowing? Here’s Why…

There are a million and one different things that can go wrong with a car, and only the most skilled and dedicated can pinpoint them all.

Some issues in your car can be major and require urgent attention – seeing smoke coming out of your engine would be a pretty good indicator of that – while others are more of a nuisance that you keep telling yourself you’ll sort out but you probably never will.

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Having car bulbs blowing more often than they should probably sits somewhere in between the two. It can be incredibly annoying if you’ve just bought some new headlight bulbs and then they blow within a few weeks, but it’s also potentially dangerous (and illegal) if you don’t get the problem fixed.

Here are some reasons why you car bulbs might keep blowing…

Water Intrusion

It might not come as much of a surprise that water and electrics don’t mix. Even the smallest crack or gap in your bulb fitting or socket can allow water in, and this can easily cause it to short and the bulb to blow.

Check the blown bulb for any water, as well as the socket itself. You may be able to easily repair this yourself, although depending on the seriousness of the issue, it may need more extensive investigation at a garage.

Touching the glass bulb when you replace it

Surprisingly, this is one of the most common causes of bulbs blowing, as many people simply don’t realise it’s a problem.

If you touch the glass bulb, the natural oil from your fingers will be transferred onto it. When the bulb is turned on and heats up, this oil then forms a hotspot which fatigues the bulb and can easily lead it to blow.

The same can happen if you get dirt on the bulb, so a pair of clean latex gloves is recommended when you change any of the bulbs in your car.

Mechanic changing car bulb

Loose connection

A loose connection between the contacts will not only mean that the bulb might only work intermittently, but it might actually cause it to blow.

If the circuit is not complete, then the electricity may jump or ‘arc’ between the contacts rather than simply flowing through them. This arcing produces more heat and could easily melt whatever it’s transferring into, effectively destroying the contact and more than likely blowing the bulb.

You may be able to tell if arcing has occurred because it causes small indentations called pitting.


If the bulb doesn’t sit nice and snug in the socket then it could rattle around when you drive, particularly on uneven surfaces or over speed bumps, etc. This vibration can damage the filament and cause it to break.

Voltage spike

Simply put, a voltage spike is when too much electricity is forced into the bulb, causing it to blow. This is usually the result of the alternator over-charging the battery, which isn’t usually a problem, as the battery will act as a capacitor to limit such spikes. However, as the battery gets older, or if it becomes corroded or damaged, then its ability to prevent voltage spikes is decreased.

Try checking the battery voltage using a multimeter, with the engine running at around 1200-1500 rpm. You don’t really want it to exceed 14.2 volts.

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If you don’t have a multimeter, you can check the battery by running the car with the headlights on. If the lights are dimmer than they should be or get brighter as you rev the car then you have an issue that needs looking at.

A bad ground can also cause voltage spikes or low voltage, so this could also be something to investigate.

A voltage spike will usually cause an issue for all bulbs in the car, so if you have only one bulb that keeps blowing, then it could well be a different issue.

Car bulbs

Are you simply wearing your bulbs out?

Have you considered that you might simply be wearing your bulbs out? The typical lifespan of a regular halogen bulb is around 400 hours, so if you do a lot of night driving then you could easily wear them out within a few months. And if you use xenon bulbs, then the lifespan is reduced as they burn brighter.

Obviously if your bulbs are only lasting a couple of weeks, then there’s something else at fault there.

Are you using bad quality car bulbs?

As with most things, you get what you pay for, so if you use cheap, poor quality bulbs then there’s a much higher chance that they’ll blow quickly.

Check out our fantastic range of high-quality car bulbs from top manufacturers such as Osram, which will reduce the chances of the bulbs blowing. Of course, if you have any of the other problems listed above then even the best quality bulbs might still blow.

Do you know of any other reasons why car bulbs might keep blowing? If so, let us know!