The exhaust manifold is usually a single pipe that delivers exhaust fumes from cylinders to the outside exhaust pipe. Exhaust fumes are dangerous because they carry the colorless, odorless poison called carbon monoxide, and a leaking exhaust manifold may allow carbon monoxide into the cabin of the vehicle when the vents are open. Fumes are dangerous, but when they’re seeping out, they also reduce the efficiency of the vehicle. Here are four signs to look for when you suspect a manifold leak.

1. Cracked Pipe

A cracked pipe in the exhaust manifold rigging is a sure sign that it is leaking. This rigging is underneath the car; thus, in order to check the piping, you will have to put the car on a lift. Once the piping is in full view, check for cracks, and if any are present, it’s time to take your car in for repairs.

2. Volume of Noise

If there is a leak, you will often hear an increased noise volume near the engine when you start the car. Keep in mind that there is a gasket that mediates between the engine block and the actual exhaust manifold piping. Like the piping itself, this gasket goes through the stress of a constant heating and cooling cycle. In other words, if the crack is not visible in the pipe, an indicator of a bad manifold could still show in a blown gasket.

3. Hard Acceleration

Step on the accelerator and listen for noises that seem out of place. Sometimes you can detect the sounds of the exhaust fumes leaking through, but the problem with this technique is that it can be difficult to distinguish these noises from that of a normal engine.

Noises with the engine can be the result of many other car problems, so it can be hard to know whether this indicates a manifold problem or not. This method should likely be used only to try to confirm your suspicions after you’ve already found another warning sign.

4. Sputtering

If you hear sputtering, then you know that there is a leak somewhere. Again, check the other symptoms to distinguish an engine manifold leak from other leaks. If this happens in conjunction with any of these other problems, then you know what you’re dealing with for certain.

5. Exhaust Fumes

Even though carbon monoxide is odorless, other exhaust fumes are not, and if your manifold is leaking, these odors will be stronger than normal. If your car seems to be producing more noxious exhaust than usual, it may be time to schedule an appointment at the repair shop. Take care when testing for this that you do not endanger your health inhaling too much carbon monoxide.