Diagnosing a Hissing Sound in Your Engine

overheating engine
This overheating engine is probably making a loud hissing sound. Getty

A hissing sound is something you rarely want to hear coming from your vehicle's engine. A quiet purr or a muscly growl, fine. But something that sounds like a passel of snakes writhing under the hood often leads to a diagnosis of ill health. As with any out-of-the-ordinary sound emanating from your car or truck engine, hissing should be investigated ASAP. Left alone, things like this can come back to haunt you when that little sound turns into a big system failure and leaves you stranded on the side of the road.

The Good, the Bad, and the Ugly

A hissing sound is usually not good, but don’t panic yet. Some parts of your engine can create a hissing sounds and be perfectly normal. Your first examination after confirming that there’s a hiss someplace should be visual. The really bad hisses will be accompanied by a major release of some sort. It might be that coolant is escaping in the form of steam from a small hole in your radiator or one of the radiator hoses. Or it could be that a substantial part of your exhaust system has gone kerflooey.

Inspecting the Engine Safely

A visual inspection of your engine is the first order of business. Take your time to try and figure out exactly where the hissing is coming from. If you can locate any sort of leak from or pinhole in a hose, you'll know exactly what the problem is and can act accordingly. If you aren't able to pinpoint the source of your sound, you'll have to dig further. Without any obvious clues from a visual inspection of the engine, the next move is to attempt to pinpoint the area of the sound by listening closely to your engine while it's running. Be careful when inspecting a running engine, and be aware of any moving parts that are near you. Tie your hair back, or keep it up in a safety hat. Roll up your sleeves, tuck in loose shirts or T-shirts, and remove all jewelry—nothing should be hanging down that could get caught up in the fan belt or air conditioning. An electric cooling fan can come on unexpectedly when the engine is running. Likewise, wear heatproof gloves and watch where other parts of your body touch the engine, which, when running, can get hot enough to severely burn your skin if you lean on or touch the wrong area.

 Then you'll have another set of injuries to deal with.  

Possible Causes and Fixes

If you've determined that your engine has overheated, there are any number of reasons for this, from operating under extremely hot temperatures to low engine coolant to a bad radiator. Thankfully, most cooling system problems are easy to diagnose and fix. And if the problem is not with your radiator but with a bad hose, that's likewise an easy fix, even if you're stranded on the side of the road.

The problem could also be that your catalytic converter is plugged, In which case, check and repair the exhaust system and/or replace the catalytic converter as required.

You might also see that a vacuum line is leaking or disconnected, which is another easy fix. Just reconnect the vacuum line or replace it. If the vacuum device itself is leaking, then you'll have to have that replaced.