Finding and Fixing Leaks
As mentioned earlier, you can have a vapor leak as well as a liquid fuel leak on a gasoline engine. From as far back as the 70s, auto manufacturers have incorporated evaporative emission systems on their vehicles. They do this for a couple of reasons. The first is to reduce hydrocarbon emissions from the vehicle. The second reason is to save fuel. Evaporating fuel is a fuel loss, plain and simple. The more fuel that evaporates, the less you have in the tank. You might be surprised at how much fuel can be lost just by leaving your gas cap off.
For this reason, manufacturers have sealed the fuel system and created a mechanism that stores evaporative fuel emissions in a charcoal canister. When certain conditions are met, this sequestered fuel vapor is routed back to the engine to be burned in the combustion chamber. The system is somewhat complex in its operation; it involves a set of sensors and solenoid valves to help direct and control the flow of the evaporative emissions in your vehicle. When there’s a failure in the system, it usually sets off the check engine light. Some modern systems even have a separate light just for a loose gas cap. If you see this light come on, check and tighten the gas cap as necessary. This should reset the light if you’ve sealed everything back up. If you still have an issue, you might need to take your vehicle in to find the source of the leak. In the meantime, you might try replacing the gas cap. I recommend an OE cap if you go this route for best results.
No matter what, you don’t want to ignore these leaks, especially if you have emissions testing in your area. A check engine light for an evaporative emission failure is an automatic fail of an emissions test. In addition, it takes time for the system to reset itself even after you repair the leak. It might take weeks to meet the right conditions in order for your vehicle to run the self diagnostic test on the evaporative emission system. Yes, you can force the system to run the test early, but this might require a proprietary scanner capable of running the test on your vehicle. Aside from the check engine light on your dash, you will likely not notice any difference in vehicle performance. However, you might smell the fuel leak. This might aid in finding the source of the leak. “Just follow your nose,” as Toucan Sam says, but in this case, you’re not looking for breakfast cereal, you’re looking for fuel leaks.
Not all evaporative emission leaks are external, however. Sometimes a solenoid goes bad and the leak is internal. To find these leaks, it’s good to have a smoke machine and a service manual that shows the testing of the different components of the system. I often get asked if the DIYer can fix an evaporative emission problem. My answer is, not often. Every once in a while someone gets lucky and replaces the right part based on something they read on the Internet, but most of them replace part after part to no avail. Without the proper testing equipment and information, you’re kinda flying blind. In addition, even if you manage to fix the leak, it might be some time before you can verify the repair due to the length of time the system needs to run its self diagnostic, as mentioned above. If you don’t have the proper testing equipment, you might leave evaporative emissions work to a professional. I don’t often say that, but in this case it might actually save you money. Ignorance can get expensive.
Diesel fuel is closer to oil than it is to gasoline. It too has a distinctive odor, and also feels slick between your fingers like oil does. Diesel is not as volatile as gasoline, but you still need to address a diesel fuel leak sooner rather than later.
Diesel fuel works best under pressure. Diesel engines use this high pressure in their fuel systems to atomize the fuel when it’s injected into the combustion chamber. This is the heart of the system, really. If there’s a loss of pressure or there’s air in the fuel system, the engine won’t run. So if you have a diesel fuel leak and your engine won’t start, repair the fuel leak, bleed the air from the system, and try again.
In addition to the fuel tank, fuel lines, and fuel filters, diesels also have a fuel distributor. This distributor sends fuel to the correct cylinder at the correct time. You could say the fuel distributor is the brains of the operation when it comes to fuel delivery on a diesel engine. That said, the fuel distributor is another possible leak source. In addition to leaking externally, it can also leak internally. If this happens, it can cause the engine not to start or run properly. Also, diesel engines can have external fuel pumps or more than one fuel pump in their systems. These fuel pumps are also potential leak sources. The fuel system on a diesel is very important to its operation, so any leaks you find in the system should be addressed ASAP.
You might notice that you have a water leak into the passenger compartment or cargo area of your vehicle when it rains or gets wet. Lucky you. Water leaks can be very difficult to track down. I’ve dismantled entire vehicle interiors in the past in an effort to find a pesky water leak. Hopefully it won’t be that way for you. Some of the most common water leaks I find are from the windshield. Often when I find a leak of this type, the windshield has been replaced at some point. Sometimes they don’t get sealed properly and you get a leak. To verify this, you might have a friend use a garden hose on the suspected area while you sit in the vehicle looking for the source of the leak. In fact, this is how you would verify and track down just about any water leak. At one shop where I worked, we had a shower head rigged up to a garden hose on a long pole. This way we could look for leaks on our own instead of needing two people for the job. A garden hose and some duct tape would accomplish the same task.
In addition to a leak at the windshield, I have seen where the area under the windshield has rusted away, causing a leak. This is REALLY hard to find, mainly because you need to remove the windshield in order to verify a leak of this type. If you find this, you’ll have to repair the body damage before reinstalling the windshield to eliminate the leak.
Vehicles with water leaks have often been in collisions. Sometimes things get missed or not repaired properly at the body shop. So if you have a water leak and recent body shop repairs, you might look closely at the work that was done, or bring it back to the place that did the work. Either way, vehicles with collision damage are always suspect.
Sunroofs or moon-roofs are also suspect. They often have drain tubes that lead down the roof pillars that are supposed to gutter the water in the sunroof tray away. Sometimes these fail or get clogged up. When this happens, you get a nice cold shower when you make a turn. It’s not refreshing at all, trust me. You often need to remove the headliner to access these drains. Consult your service manual on this before you tear into it. This can keep you out of trouble when you tear apart your vehicle’s interior. I’ve often cleaned clogged drains with a bit of compressed air once I access them.
Lastly, if you park your vehicle under a tree, you might consider parking someplace else. Leaves and debris from trees often cause of these obstructions, not to mention the issues this debris can cause to the HVAC system.
I’ve also seen occasions when a tail light fixture was the source of a leak into the cargo area. On many vehicles, a gasket under the tail light assembly is used to seal the trunk or hatch area. When these seals fail, they can cause a water leak into the cargo area. Replacing these gaskets often repairs a leak of this type, but once again, if the vehicle has been in a collision, it might never seal correctly if the body was not repaired properly.
Door and window seals should also be inspected if you’re looking for a water leak. Any damage to a weather seal can allow water to enter the passenger compartment. It’s a good idea to inspect these seals if you have a water leak into the passenger compartment.
I’m not proud of it, but on some of my own vehicles with water leaks, I’ve drilled holes in the floor pan to give the water someplace to go. Like I said, I’m not proud of it, but it worked. If you run into a water leak that you can’t fix or are not willing to fix, this might be your option. Just a couple of small holes should do it. Just be sure you’re not drilling into anything important before you commit.
If you see water dripping under your vehicle and you have the AC on, don’t worry; this is normal. As your AC operates, condensation is created inside the HVAC unit. This water is collected and drained from the system through a drain tube under your vehicle. Remember the discussion about water in your dash? On hot, humid days, you’ll see a lot of water coming out of these drains. Do not be alarmed; this is normal. Also, if you have a van, SUV, or other vehicle with front and rear climate control, you might see water dripping out from more than one location. This is due to the multiple AC evaporators in these systems. Once again, this is normal and nothing to be concerned about.
I think that about covers it for leaks. As I’m sure you’re tired of hearing by now, consult your vehicle’s service manual before you do any repairs. This can clue you into any important service procedures for your vehicle. Here’s a video that might help you find the service manual for your vehicle.
As I said in the power steering section, you can use a piece of clean cardboard under your vehicle overnight to help identify the fluid that’s leaking, as well as its source. Also, if you need to clean up a spill or leak, kitty litter does an excellent job. Just leave it on there for a day or so before you sweep it up so it can absorb the leaked fluid. You might even do a little dance on the kitty litter once you have it in place. This aids in the absorption of the leaked fluid. Just don’t get too happy or you’ll have a puddle of goo and a bunch of kitty litter everywhere to clean up. Otherwise, good luck finding and solving the leaks on your vehicle.
Written By EricTheCarGuy
Edited By Julie Hucke
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