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Q: No heat, coolant level on 1993 Toyota Previa

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I have only cold air blowing from vents unless I am accelerating. Recently, I had basic maintennance done ... oil change, fluids checked, radiator flushed, etc, Then the heat was warm ALL the time ... but only for 2 weeks. Now its cold except when accelerating. Shouldnt there be coolant in the reservoir tank, up to the "cold line"?? Should I add directly to the overflow tank? Anything specific I should check or monitor, or is this out of my league?
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There is most likely air trapped in the cooling system. top up the cooling system the reservoir is the highest point of the cooling system. The cooling system is a sealed system and should not drop in level unless the cooling system has a problem or leak. Perhaps bring it back to the shop that has done all the recent work and have them pressure test the system for leaks and or get them to bleed the air out of the system.
unless you have a leak.. check the thermostat, it could be it needs to be changed, also if you change the thermostat and it continues to blow cold air....worst case scenario is heater core is bad.
After experiencing some overheating, I recently self drained & flushed my 1993 Previa's radiator and reservoir tank with interesting results. I noticed something was wrong when my temperature needle moved to hot, my radiator reservoir tank was full and remained cool, and the heater did not normally come on to heat inside the van. I think the hot coolant was not flowing past the heater core because of a blockage in the cooling system. So I guessed the reservoir was the bottle neck keeping the system flowing.

First, I removed the top plastic air duct intake cover. Then I removed the radiator reservoir tank. After unscrewing the bottom radiator drain plug to drain coolant, I ran a yard water hose (with on/off hand grip for control) from the top radiator inlet hole and flushed out the old coolant.

The interesting part came when I completely cleaned and flushed the coolant reservoir tank with a the yard water hose. I noticed that one or two of the three inlet/outlet nozzles had been clogged with debris and/or coolant sealant. So I cleared the reservoir's thin nozzles with a Q-tip and thin ice pick or screwdriver. It appeared that the reservoir tank had been clogged which made the cooling system inefficient, especially during warm weather with the AC on.

To flush out the old coolant from the engine, I ran the yard water hose from top radiator hose with the engine one for about 1 minute. Eventually I saw old water/coolant flush out from the hoses that connects to the reservoir tank (which had been removed.)

After 45 minutes of draining, cleaning, flushing, I hooked everything back up and refilled the radiator with fresh coolant. Be careful when removing the hoses... the nozzles, nipples, or hose connection tips can easily be broken if the rubber hoses are pulled the wrong way.

For now it seems the radiator is keeping cool. If your temperature needle is showing up hot past the middle mark, try flushing out the reservoir tank to make the cooling system more efficient. It may be clogged because 3 of the 4 holes are very small and can easily get clogged with old coolant, debris, dirt and/or sealant.
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