The water level on my 91 accord got really low due to a crack. When the car starting getting hot I stopped and realized water was really low I filled it up and for about 6 miles every thing seemed normal and then all of a sudden the Heater went from hot to cold and temp. guage started rising. What would cause that. Note that I had not change the radiator fluid since I got the car in Oct.93. Might the sludge in the bottom of the radiator clogged the thermostat or what
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Re: My heater went from hot to cold
Either you have a air pocket in the cooling system or the engine got to hot and hurt the head gasket .while engine is cold check level if low fill up slowly if full start car with radiator cap off is coolant spews out of radiator then look to the head gasket remember coolant should me cold!!
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An air bound heater core can cause this. A thermostat issue would cause it to overheat quickly (stuck shut) or cause the engine to take a long time to get up to normal operating temperature (stuck open).
Try this after the car has sat over night and is COLD.:
Top off the coolant RESERVOIR to the COLD MARK with a 50/50 mix of coolant and water when the engine and coolant are COLD. Replace the reservoir cap.
NEVER open the radiator cap when hot!!
Open RADIATOR cap - WHEN COLD - and top off radiator with the same 50/50 mix of coolant and water to just under the inner lip of the filler neck.
Start engine, turn heat to HOT and FAN to HIGH.
Watch the coolant level in the radiator. Maintain the level of coolant as close as possible to just under the filler neck lip. It is expected to fluctuate up and down as the thermostat opens to flood the radiator - and be pulled into the engine block. The more variation in the high and low indicates a fair amount of coolant has been lost. After the engine has gotten hot, you should feel hot air coming from the heater. Check the radiator level once more, top off and replace the radiator cap.
If still no heat, there may be a clog or restriction in the heater core hose. A cooling system flush should fix this, but can cost a few bucks at a Jiffy Lube or similar.
If you're losing coolant - that could be an indication of a leak (see puddles where you park?) due to a bad hose clamp or hole in a hose ($) or a bad gasket ($$$) or cracked engine block ($$$$). Look for white "smoke" (steam really) in the exhaust after the engine has warmed up to indicate that the coolant is entering a piston due to a gasket or block issue.
the first thing i would do is check the coolant level when the engine is cold. When the coolant level gets low enough the first thing to stop working is the heater. If the coolant level is good than I would suspect a plugged heater core.
If the thermostat where stuck open you would notice that the temp gauge would read low. If the water pump was not working correctly the vehicle would be overheating.
Sounds like the water pump is cavitating . Replace water pump. Check coolant level also. Open the bleeder valve usually located on thermostat housing to remove air from system. close valve when coolant is present while filling. close radiator cap and top off recovery bottle to correct level. These engines are prone to overheating, do not let temp gauge get in the red.
It is possible that the coolant is a little low causing the heater core to get "air locked" Check your coolant level. There could also be a problem with your water pump not able to pump correctly due to a worn or corroded impeller. This will usually cause the heater temperature to fluctuate widely with engine RPM. There is allways some fluctuation caused by RPM, but if it is a large fluctuation, it usually means low water pump output or possibly a partially clogged heater core.
Feel the hoses going into and out of the heater core. They should both be hot. There may be a 20 or 30 degree difference in temperature, but both should feel very hot to the touch. If one is really hot and the other just feels warm, the heater core is probably clogged. If you have access to an infrared thermometer, taking the temperature of the hoses is the best way to check this.
If both hoses feel "Warm" at idle and get really hot when the throttle is cracked open for a short period (20-30 Seconds ), the water pump may be the problem.
If the car is hot and the heater blows cold air your thermostat is stuck shut or your radiator is really low on water/antifreeze check when engine is cold hasn't been ran like overnight take off the radiator cap and if it is low add so antifreeze/water if heater still blows cold air or water level is ok your thermostat is stuck shut and needs to be replaced.
Check you coolant level could be low or your thermstat could be messed up or your water pump could be going out. Worst case blown headgasket or cracked heads. On most cars when you turn the heat on it pulls heat out of the radiator. On most cars when you turn the cold ac on it pulls cold coolant from the radiator to use. Many cars today are coming with systems that are separate.
Sounds like a thermostat sticking. Some things to do. First check coolant level is up and moving. Second (most likely), change thermostat. Very easy fix for backyard mechanic. Make sure to put thermostat in so water flow is correct direction. Look for arrow on side of thermostat. Next, is belt to water pump loose. Another easy fix in most cars.