2000 SR5 this morning had no heat. I checked and the coolant is really low. No apparent leaks. Doesn’t seem to be coolant in the transmission, Engine has been running fine, no hesitation or white exhaust however I do remover thinking I could smell coolant yesterday. Thoughts?

 

If your coolant overflows (i.e., from bad radiator cap), or there is a hairline crack in the system that coolant or steam escapes while you're driving, trace of coolant leak may disappear/vaporize as soon as you drive. You may smell coolant vapors as you drive.

 

OK. I'm going to get coolant this morning, refill the radiator, start it, look for bubbles in the tank, then let it run. It's 4 degrees here and everything is covered with snow. I'm hoping that if I let get warmed up a leak will show up in the snow. Guess we'll see.

 

If you have rear heat there are lines to that, heater control valve and hoses from that to the back of the engine, hoses to the oil cooler if you have one, coolant line under the throttle body, water pump, hoses at the radiator and thermostat. Gonna assume you'd notice if it was the heater core. To find one of my leaks I carefully stuck the camera down in places my eyes didn't fit and took pictures of the small id hose ends until I found the one with the coolant-colored residue.

 

 

A couple of possibilities. A while back the upper rad hose was changed out, I'm wondering if there wasn't an airlock somewhere in the system that finally made it's way out and when it did I was low on coolant. The system pressure tested ok, however the radiator cap looked like crap so I changed it out for a new Toyota cap. At 200,000+ it was probably done anyway. Hopefully that's all it was.

 

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no heat is a symptom of low coolant? I had to put half a jug of 50/50 in mine but ive had to do that every few months. 99% sure it is because i have a small head gasket weap.

 

Before I replaced my motor the old motor had a mysterious coolant leak. Went through two years trying to figure it out, had no coolant in the exhaust or bubbles in the rad, even replaced the rad and cap. It wasn't until I looked at rebuilding the motor did I find the culprit. There was a hairline crack in the cylinder wall (I think #3), that was weeping coolant into the cylinder. In the very beginning it was just a small amount but it got worse to the point where it was beginning to water lock the cylinder.

If you can't find the coolant leak anywhere external to the engine, then chances are it is internal.