by Craig Woodman
New car gasoline engines image by Christopher Dodge from Fotolia.com
Gasoline engines use an intake manifold to deliver a fuel-air mixture to each cylinder for combustion. The intake manifolds used to be made of cast iron. The biggest problem with cast iron is that it is heavy. Aluminum and plastic are the most widely used materials today. Intake manifolds can leak in two ways, either through a coolant leak through the intake manifold gaskets or an air leak in the manifold outside of normal air passages. Air leaks can affect engine performance, while coolant leaks can lead to engine failure.
Inspect the intake manifold where the ducts or tubes join the engine. Using the flashlight, look for signs of refrigerant leaks. They show up as wet spots or spots around the runners in minor cases. In severe cases of coolant leakage, the manifold parts are wet with coolant or there are pools of coolant. Coolant can also run down the front or rear of the engine, depending on the severity of the leak. If you’re not sure if the intake manifold is leaking or if a leak is coming from somewhere else, take a closer look.
Add the coolant leak test dye to the radiator filler cap. Replace the cap and start the engine, allowing it to warm up completely. Turn off the engine and let it cool down so you can comfortably work around the engine. Put on the yellow glasses and shine the UV light around the areas where the leak is involved. You will be able to see the dye in the coolant as a bright green, wherever it drips. With a close inspection, you can determine where the bright green tinted coolant is coming from.
Attach the spray tube to the nozzle of the carb cleaner can. Starting the engine. With the engine running, spray carburetor cleaner in short, gentle bursts around the area where the manifold passages meet the engine. Wait a few moments after spraying and listen to the engine running. If the engine speeds up or changes its performance, you probably have a leak at the intake manifold gasket. If you don’t notice any changes, back up the runners, pausing after each spray. If the engine speed changes, there is probably a crack in the manifold. Also check the area between the manifold and the throttle body.
- If you have access to a diagnostic smoke dispenser, you can perform an intake manifold test by placing the nozzle inside the throttle body and filling the manifold with smoke. Watch for smoke coming out of gutters or cracks. Some smoke machines use an ultraviolet dye in the smoke. You can easily see it under UV light.
- Be careful when using carburetor cleaner near a hot engine. A hot engine or loose sparks can cause a fire. Have a carbon dioxide fire extinguisher handy. Keep your hands away from all moving parts while testing a running engine.
Articles will need
- Carburetor Cleaner Can with Spray Tube
- Cooling System Leak Test Dye
- Ultraviolet Leak Detection Light
- Regular flashlight
- Glasses with yellow lenses