Like all we do is chase down coolant leaks. Maybe that has something to do with weather patterns and large swings in ambient temperature. It may also relate to how well customers take care of their vehicles, how often they take them in for service, or the replacement parts they use. Either way, these repairs need to be made, and finding out the cause needs to happen quickly and accurately.
Sometimes that’s not too hard to do if the leak is obviously coming from a blown hose, corroded fittings, or a loose clamp connection. A thorough check of the engine, radiator, and remaining hoses and fittings is still a top priority, but getting that main problem fixed is usually quick and easy.
That is, as long as the parts are available. I ran across a low-mileage Cherokee recently that should have been a cake job. It needed a new radiator due to internal clogging and major external fin corrosion, thanks to PennDOT’s road deicing brine solution. However, it ended up taking two days and required me to graft together an upper radiator hose out of two “almost right, but not quite” hoses.
Although it was an original, stock 2000 XJ, it turned out to be one of the rarest combinations ever made by Chrysler: a left-hand-drive, 2-door, 4-wheel-drive, 4-cylinder, manual-transmission model with air conditioning. In fact, production numbers on this setup were so low that neither of the most well-known hose manufacturers makes a replacement.
Then you have those leaks that seem to come and go, because that’s exactly what they do. I’m referring, of course, to tank leaks that show up only when conditions are right. About 90% of automotive radiators today are made of an aluminum core with plastic side tanks that are crimped together with a gasket during manufacture.
However, that crimp connection can only be made so tight. Too tight and the tank can crack; too loose and it leaks. This means the gasket has to take up the difference. Very small crimp leaks will sometimes come and go with ambient temperature and stop leaking much of the time when the system warms up. These nuisance leaks may only drip once in a while, but the gasket will eventually succumb to cycling and corrosion, requiring replacement of the radiator assembly.
If the tank is completely blown due to excessive system pressure, you’ll have to check for a bad radiator cap, debris causing restricted coolant flow, or even a blown cylinder head gasket.
Sneaky Leak
Sometimes these elusive small leaks take a bit more detective work to find. Take, for example, the heater control valve that leaks only when it’s in the OFF position. This is something technicians don’t always think about checking, since the position of the valve is often not the determining factor.
The one we repaired was vacuum-operated and leaking through the shaft seal, but only when the valve was in the OFF position, not allowing coolant to flow through the valve to the heater core. Since the valve’s default position is ON (OPEN) when there is no vacuum applied, such as when there’s a system fault or if the engine isn’t running, the leak never showed up during a pressure test. A pressure test can only be done with the engine off, relatively cold, and when the system is not self-pressurized.
The reason it’s so difficult to find some of these come-and-go leaks is because coolant dries up, and we need to use something that will stick around long enough to enable us to find it. This is where dye can really help.
It’s Just Another Way to Dye
We’re all familiar with using A/C dye to help detect current or future refrigerant leaks. It’s easy to use since you just have to add the right amount and type of dye to the system, let it circulate so it mixes well with the oil and refrigerant, and then search for a leak using a UV (ultraviolet) light. It may not show every kind of leak, and sometimes dye takes a while before you can see it, but once you do, it’s a positive indication of where the leak is located.
But using dye isn’t limited to A/C systems. Various dye formulations exist that make it possible to dye many other fluids.
Keep this in mind if you consider reusing recently drained engine coolant: if it’s been sitting around for several hours exposed to the atmosphere and not covered, much of the water component may have evaporated, which concentrates the mixture. Contrary to popular belief, even some of the glycol will evaporate, albeit at a much slower rate, changing the concentration level again.
If you’re planning to reuse coolant, for example after recently flushing and refilling a system with a new coolant mixture, it’s best to pour it into a clean, used-coolant container immediately after draining to retain its consistency.
Also, make sure to filter or strain the coolant before reuse and measure its freezing point with a refractometer.