Mysterious Coolant Leak


I have a 2006 Outback that has been leaking coolant since the day I bought the car. 27K miles, and I’ve had to fill the reservoir twice (from well-below “Low” to just below “Full”). No puddles, no stains, no evidence of a leak anywhere, but I can smell the coolant when I roll down the windows or when I exit the car, particularly on longer drives on very hot days (can’t smell it coming through the vents though, so I assume this rules out a leaking heater core). The temperature gauge never indicates the car is running hot. I’ve had the car pressure tested 4 times, most recently using the “overnight” method, and the emissions have been checked too. Oil looks good/not cloudy as well. I’m stumped. Any advice out there?


I had a 98 Windstar that used to lose about a pint a month, more so in the winter months. It was never confirmed, but my mechanic thought is was leaking from the gasket between the aluminum radiator and the composite side tanks. In the winter the gasket would contract and there would be a slow leak. After I had it a few years just prior to a coolant change I put about half a bottle of Bars Leak in the radiator. After I flushed and changed the coolant to get rid of any Bars Leak in the system, the van didn’t lose any more coolant for the remainder of the time I had it. The van was still running well at 8 years and 98k miles when I sold it.

On the other hand, my 2000 Blazer’s coolant level started dropping right after I changed the coolant. I told my mechanic about it at the next oil change, he noticed a few drops of coolant in the oil as the last of it drained out. It turned out to be the intake gasket (common problem on many GM vehicles of this vintage). I took it to the dealer who verified my mechanic’s diagnosis. Left unrepaired, coolant in the oil would destroy the engine.

Correct me I’m wrong, but can the dealer/mechanic put some dye in the cooling system and use a black light to trace the leak.

Good luck, keep documentation on all the attempted repairs for when your warranty runs out.

Ed B.


Filling the reservoir twice in 27,000 miles is not a big leak. Probably not large enough to drip on the ground. It is likely seeping somewhere and evaporating from engine heat before getting a chance to drip onto the ground.

I think you or someone will have to crawl under the car to have a look around for evidence of seepage. Since it’s been going on for so long there should be a trail of dried coolant somewhere. Of course, the front end of the car will have to be lifted and jack stands used for safety. Until someone does an actual inspection, everything else will be just speculation.


The only thing I would add is that what 1961 suggested it may be internal leak and that could damage some expensive parts. You should have the oil checked for coolant and the coolant checked for oil.


just to give my cheap opinion.

sometimes water pumps develop a leak through a small weep hole around the shaft of the pump.

it is usual that if the pump is weeping through the hole, the pump is about ready to go.
it is possible that your pump has a weep, which is evaporating as fast as it weeps.

i had one on my old F250, and i only noticed it when i was digging under the hood, looking for a fuel leak in the carburator. all the little nooks and crannys were bright green, but there wasnt enough to make it to the ground!


Thanks for the advice guys. Someone else had previously suggested checking the water pump/weep hole, so I guess that’s next on the agenda.