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Thermostat has been replaced. Sorry, forgot to mention.

Can you take a picture of the substance and upload it to a picture hosting site and send us the link?

Sorry, alas no. It has been cleaned out. What I can tell you is that it is sort of pasty and was not mixed in with the coolant but rather collected around the rim of the radiator cap and was coming out in bits when flushed. It was quite white.

From your description is sounds like oil in the coolant. Since you had it cleared out, you'll have to see if there is a reappearance later. If there is, you'll have to do some investigating.

Are the coolant hoses to the heater core hot when the engine is at operating temperature? Have you tried back flushing the core? Make sure you use Toyota Super Long Life coolant (pink).

I believe we may have found our answer. Apparently coolant, if old, can create a residue - silicate (though we did a flush and replace about a year ago). I think this is what the white chalky, pasty substance was we found that seems to be gumming up the heating core. It might also account for why there is heat when it runs on straight water and not with coolant. My concern is this. If we replace the heating core, frankly after flushing three times with little or no help doesn't seem to be working, my fear is that there is still this old residue still floating around that would clog up the new heating core. I'd welcome thoughts.

That weird. Your coolant system should be using Toyota Super Long Life Coolant which doesn't have any silicates in it.


COOLANT TYPE: In order to avoid technical problems, only use "Toyota Super Long Life Coolant" or similar high quality ethylene glycol based non-silicate, non-amine, non-nitrite, and non-borate coolant with long-life hybrid organic acid technology. Do not use plain water alone.

Yep, we get that now, of course too late. I am still wondering about how to make sure all the silicate is out of the system before replacing the heater core or how to get all the silicate out of the heater core so we don't need to replace it.

You sure it is silicate, because toyota super long life isn't susposed to have any silicates in it. Not really sure how you would go about getting that out without multiple flushings. Did you remove the heater core hoses and try backflashing the core out? Your hoses should be hot for the core to work. Maybe you have air pockets trapped in the coolant system.

You sure it is silicate, because toyota super long life isn't susposed to have any silicates in it. Not really sure how you would go about getting that out without multiple flushings. Did you remove the heater core hoses and try backflashing the core out? Your hoses should be hot for the core to work. Maybe you have air pockets trapped in the coolant system.

No hoses are not hot, though today after an hour's drive, there is some improvement in heat. It's certainly not fully back but probably about 40% better than nothing but still a way to go. Once heated up you can turn on the head and it will be hot for a couple of minutes until it cools off again.