Finding and Fixing Leaks
I covered most of this in the Overheat Article, but I’ll cover it again here. The best way to find coolant leaks is with a cooling system pressure tester. This is a tool that you place on the opening of the cooling system, usually in place of the radiator cap, where you pump pressure into the system. Your cooling system is designed to hold pressure. If it can’t hold pressure, it probably has a leak. When you pressurize the system with the tool, the coolant will leak out where you have a pressure loss.
Most leaks are external, but sometimes there’s an internal leak. You use different testing to find these, but the pressure test will get you started. Much of this material is covered in the Solving Overheating Issues article. You might also find this video useful.
This often indicates a failed heater core. You can get another indication of a failed heater core when you use your defroster. If you find an oily residue on the windshield when you use your defroster, this could indicate a failed heater core.
The heater core is a component inside your HVAC assembly that warm coolant runs through to provide the passenger compartment with heat. It’s like a tiny radiator, and, like a tiny radiator, it can occasionally leak. Repair of this often requires removal of the dashboard and all of its components to access the HVAC unit. It can be involved and time consuming, and if you have a shop do it for you, it can be very expensive.
That said, there is a workaround. You can often bypass the heater core by rerouting the heater hoses in the engine compartment. On the firewall or bulkhead, you’ll see two coolant hoses going into and out of the heater core. If you disconnect these lines and either route them together or remove one and route it back to the engine, you have in effect bypassed the heater core. Now, doing this means you won’t have any heat, but you won’t have a leak anymore either. You be the judge in your situation of whether this is a good idea or not. It will not harm the engine or cooling system if you do this. The only reason you have a heater core is for your comfort, not the vehicle’s.
Once again, using stop leak products is not recommended. If you find you have a coolant leak, I strongly recommend you repair the leak rather than use a stop leak product. Yes, there are times those products work, but they come with a risk. If you perform the repair instead, the risk is greatly reduced if not eliminated altogether.
Sometimes you might hear a sloshing noise in your dash as you drive. While this can indicate air in your cooling system, it also could indicate a clogged AC drain if it’s accompanied by a bunch of water washing out of the HVAC when you make a turn. This sucks, but it has an easy fix. What happens is your AC’s condensation gets trapped inside the HVAC ducts. This is often due to debris clogging the drain tube in the HVAC. You can simply blow out this debris with compressed air and all is right with the world. This video shows this problem and how to fix it in detail.