Yesterday I did my second coolant flush in 2 years. When I opened the radiator cap it had a yellow residue almost like rust around the cap. My reserve tank had alot of deposits as well. I changed both the upper and lower radiator hoses as well as the thermostat during the flush. The thermostat also had some of this yellow deposit around metal part of the spring.

I want to know what's your opinions or try to diagnose the cause of this deposit. I am using Toyota Red, distilled water, and my previous setup I had put a bottle of water wet. The car has approximately 150k miles.

 

Questions...

1. Have you experienced any detonation or pinging?
2. Have you pressure tested your cooling system to ensure there are no leaks?
3. Has your car been running hot during any length of time?

 

No to all three. I think its my radiator just rusting.

 

It's calcium buildup and that is coming from somewhere, most likely contaminant in the coolant system. Did you use de-ionized, distilled, or regular water last time you serviced the system?

 

I used distilled water last time and also this time around. I was told that distilled water doesn't have the chemicals to cause a chemical reaction and ultimately lead to products such as calcium deposits. Right now I'm looking into replacing the radiator b/c the barb fitting on the tranny cooler broke.

It also seems as if my heater is hotter now. I believe that there were some blockage before and the new flush cleared the passages. The interval changes were about 30k miles