Keeps overheating, solved by replacing thermostat , bottom hose heats fine etc then within a couple of days car overheats, bottom hose stays cold. We have replaced the thermostat 4 times now (from different sources) Radiator has been replaces and the waterpump. I also notice that there is quite often a stagnant smell through the heater. I don't know if this is relevant but the previous owner totally removed the pollen filter so now just a hole there.
I thought I have read here that sometimes you have to replace the larger hoses as they can collapse. If you put a big piece of cardboard where the filter is and you never turn on the fan you might not get any stink from crud growing around the heater core or evaporator coil. I removed the evaporator coil in my truck. I had grass seed germinating in there.
I think on some of the Toyota thermostats they have a small bleed hole drilled in the thermostat. This lets the trapped air get pumped out faster. I do know on my Rabbits I had to burp the air out of the cooling system after doing any work on the cooling system.
a) There are stainless steel springs that will fit into such hoses to prevent collapse. Best is a new hose, of course, but if the radiator is somewhat restricted this is a viable alternative.
b) First, clean the drains for the heater core. There are specialists who will also de-mold the system at a healthy cost, however. One may pour a diluted chlorine bleach solution through the system with the understanding that chlorine attacks metal, especially aluminum, if allowed to rest against it.
c) If the alternative is a replacement heater core together with the removal and/or cleaning of the fan box and so forth, and you are scrupulously careful you may pour a dilute solution of chlorine bleach and ammonia through the system. This will produce Chloramine Gas (a very toxic gas that kills about anything it touches), ammonia also attacks aluminum, and this is generally a hazardous option when NO OTHER ALTERNATIVE IS AVAILABLE. Do this outside, do not expose yourself to the gas released, wear gloves and eye-protection, dilute the household bleach 3:1 and the household ammonia 2:1. Use CLEAR ammonia. Do not do this where the drained material will leach into the ground immediately, or catch it if you can. It is OK for the solution to go into storm or sewer systems, just not into the ground as (again) it is temporarily toxic. Do not drive the vehicle for at least 12 hours after this sort of treatment, but it is good to run the fan (all windows & doors open, and use a house-fan to blow air through the cabin) during the process to get the chloramine gas through the entire system. Nasty stuff, but does the trick where Lysol and other materials do not.
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