I have intermittent heat - sometimes hot, but almost always cool even when engine is warmed to normal level. A/C is fine and cold. Coolant level is fine in radiator and in reservoir. No puddles. No white smoke or fouling of engine - runs fine. No milk shake looking oil - oil looks fine. I have been losing antifreeze for months. A quart a week. My mechanic seems unable to track it down. Here is what we have done: No puddles or leaks of fluid inside vehicle front floor Pressure tested cooling system - OK No leaks in radiator New thermostat installed Coolant test pack used Chemical test for carbon monoxide in coolant was NEGative Have flushed system Have had oil change and other fluids checked After new thermostat was installed last week, the heat worked normally on one day. (I don't need it much right now) It was 47F this AM and I only got heat for about 2 minutes of a 20 minute drive. Temp gauge reads normal. It overheated once befopre thermostat change but was low on antifreeze at that time. Coolant added, and this has not recurred. I am seeing ALL kinds of ideas online but want to know what we should target next. My mechanic also advises not to use anti-leak products for head gasket, etc, and we have not looked that far. Thanks for any help you can offer! I have sunk a bundle in this car so cheap checks would be cool. ;)
Sounds like an air pocket in the coolant system. Those can be a pain, some cars have bleed valves to help. If there is an air pocket, it will seem to be full of coolant, but when the air pocket gets to the heater core it gets stuck there and guess what? No heat, because you won't get any heat unless hot coolant is in the heater core. Old fashioned way is to open the system and keep pouring coolant in at operating temp with heat on full until all the air is pushed out. If it has a bleed valve that can be helpful. Have seen this problem on many vehicles.
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