Toyota Repair: Gunk, upper radiator hose, plastic jug

Question
Hi Ted,

Yesterday evening I drove my 1995 Camry (179K miles) about 16 miles one way to my home. When I shut off the engine, I heard a tapping sound under the hood. The sound was coming from the radiator overflow plastic jug. The jug was completely full to the neck of the jug.

When the overflow jug stopped making that noise, then the upper radiator hose started making a gurgling like sound. I turned on the key to check the engine temp which was at normal operating temp.

The next morning (nine hours later) the overflow jug level dropped from completely full to just above the word Low on the jug. (The word LOW is above the low level line on the jug.) Next I checked the radiator which was full up to the neck. The underside of the radiator cap was covered with a brownish/orangish colored gunk. I wiped off that gunk and also took a picture of the radiator cap and radiator neck so you can see the gunk if you wish. Every few months when I remove the radiator cap it has gunk on the underside.

The same morning I checked the radiator I drove 9 miles to work at about 25 to 45 miles per hour. The engine temp never when above normal. At work I popped the hood. I did not hear any gurgling sounds but I noticed a bubble or two rising from the bottom of the overflow jug in the coolant to the top of the jug.

My 1995 Camry has 179K miles and a 4 cylinder engine. I replaced all the small hoses in November of last year and put in new Peak fluid. I did not replace the thermostat though. The last time the thermostat was replaced was in June of 2009 with a NAPA thermostat.

Ted, should the overflow jug be completely filled to the top when the engine was only driven 16 miles? What was causing the tapping sound in the overflow jug and the gurgling sound in the upper radiator hose? What about the gunk on the bottom of the radiator cap and this also appears in the bottom of the overflow jug?

It has been YEARS since the motor was flushed or maybe I never have the engine flushed. The local Toyota garage does not recommend flushing the engine due to the mileage and age of this 1995 Camry 4 cylinder. They said a flush could create engine problems. What are your thoughts on the gunk, the sounds in the jug and the upper radiator hose noise, and flushing the engine?

Thanks Ted!

Answer
It sounds like it could be a leaking headgasket,the filling and draining of the coolant bottle indicates that there may be air in the system, the head gasket can be checked using an inexpensive chemical test kit available at most autoparts stores, if the headgasket checks out ok then I would go ahead and have the system flushed, it may also be a good idea to replace the thermostat and have the radiator tested to see if it's partially clogged.