What You Should Know About Engine Vacuum Leaks


It doesn’t happen often in newer cars but all cars can develop “vacuum leaks.” It’s a situation where a hose or engine gasket has failed and outside air gets pulled into the engine while its running. This can create all sorts of problems, some of them being significant but most just leading to poor engine performance. In general, fixing a vacuum leak is something that you leave to your mechanic but they are worth learning about. You never know when a mechanic is going to say to you, “you’ve got a vacuum leak that I have to find.”

Where’s the vacuum?

Vacuum is generated when an engine is running. Internal combustion engines suck in atmospheric air, spray gasoline into it, ignite it, then blow it out the tailpipe. It is during the first part of this process, the sucking air in part, where a vacuum is created. Long ago, engineers knew that having a source of engine vacuum was useful. You can use it to activate things (such as heating systems), to power things (such as power brakes,) and to monitor engine conditions (such as air/fuel ratios). It’s a pretty useful power source that engineers commonly use.

Problems occur when the vacuum of an engine is disrupted by a leak. This can happen when gaskets fail, plastic parts break or when vacuum hoses get old and crack. At David Stanley Dodge of Midwest City, a local Chrysler, Dodge, Jeep, Ram dealer in Midwest City, OK, they say sometimes it happens when someone simply dislodges a hose when repairing another issue under the hood.

The symptoms

Vacuum leaks can cause a myriad of problems with a car. To start with, you may have engine problems that are immediately obvious. Things like hard starting, misfiring, rough idle and stalling are all possible when you have a vacuum leak. You may also have less obvious problems such as poor fuel economy, poor acceleration, or just the check engine light on. Although it is rare, if the vacuum hose was damaged or unplugged on your vacuum brake booster, you may even find that your brakes don’t work very well.

Fixing it yourself

In most cases, it is best to have a mechanic troubleshoot a vacuum leak but if you want to take a crack at it. Here’s a few tips:

First, open the hood and look at all the vacuum hoses routed around. If you have an older car, you may find one that has slipped off its coupling or has cracked. Underneath the hoods of most cars today is a plastic sticker that has a diagram of the emissions control system. It will show where all the emission hoses are routed. This is a good map to follow when looking for problems with vacuum hoses because emission hoses are often at fault.

The next thing to do is start your engine and listen. Although engines aren’t exactly quiet under the hood, sometimes you can hear a vacuum leak because it emits a distinct hissing sound. This is usually one the first things a mechanic will do when they suspect an engine leak.

Get a Pro

Honestly, if you don’t find any problems and you still think you have a vacuum leak, it’s time to have a professional mechanic look at things. They not only have the tools (like a car lift) to look all over a car, they also have the experience to know where leaks occur in particular makes and models.


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