Cooling System Leak Diagnosis

A real-world example of something I was trained to do at school is leak diagnosis using air pressure and soapy water. The potentially leaking system is pressurized with a manual air pump or with compressed air with a regulator to control specific pressure, and soapy water is sprayed on any potential areas where the leak could be. Radiators, charge air coolers, fittings, sealed connections, hose and line ends, are the primary culprits. That does not exclude hoses or lines themselves as they might have holes enough to cause a leak. We have done this in the school shop on things like the Charge Air Cooler on a Series 60 to find the source of a leak.

So, back to the real world example. I changed the water pump on a Duramax (more on that in another post), and after completing the installation found that the system held neither vacuum nor pressure. I pressurized the cooling system to 15 psi and sprayed soapy water all over. Eventually, I heard a fizzing sound. Crawling under the truck, I noticed that a pipe that enters the rear of the water pump was foaming quite heavily. The source of our leak. This connection has a simple dry non-metal gasket.

Off came the water pump again, and inspection of the flanges (which were straight-edged) and gasket gave no obvious hints as to why they would be leaking. I put a special silicone sealant on the gasket, reinstalled the water pump and pressurized and tested the system the following morning with no obvious signs of our leak.

Soapy water tells us where the leak is located.

Evidence of the leak on the gasket.

Reflection:

Sometimes the root cause of the problem is not entirely obvious, even when you have located and inspected where the problem occurs. Using a silicone sealer solved the leak, and we will have to leave it at that. I don't have the answer to this one, but in the end the fix was simple. Perhaps others have possible insight into the root cause? Curious minds would like to know, if so.