# ?? for Mechanic



## stillfish (Dec 5, 2005)

I dont know where to post this, so its here.. I have a Mercury Villager and the Heat only works when i drive, and when i come to a stop it blows cold then warms back up when driving. My fluid is fine and it dosent overheat, the previous owner had the radiator flushed.. I was told that when this happens all the crap in your engine gets flushed through and gets stuck in your heater core which causes fluid restriction. Is this true??


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## 2SloSHO (Jan 23, 2008)

stillfish said:


> I dont know where to post this, so its here.. I have a Mercury Villager and the Heat only works when i drive, and when i come to a stop it blows cold then warms back up when driving. My fluid is fine and it dosent overheat, the previous owner had the radiator flushed.. I was told that when this happens all the crap in your engine gets flushed through and gets stuck in your heater core which causes fluid restriction. Is this true??


Could be, or it could be as simple as an air bubble in the system. Id start with double checking for air in the system......

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## stillfish (Dec 5, 2005)

This happened to my 2001 chevy truck, and the heater core was full of crap which restricted coolent flow in the heater core. Flushed out and the heater coremand worked fine..


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## glockman55 (Mar 9, 2006)

Sounds like an air bubble in the system.. try bleeding the air out.. is there a bleeder screw on you goose neck..or google it..


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## bigcountrysg (Oct 9, 2006)

Water pump is going bad. It does not push water at stop or idle, but will push the water when driving or revving up the engine. I have seen it a few times on vehicles.


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## Farmers (Jul 12, 2012)

Water pump I have changed one before impeller looked like Chinese throwing star nothing left to move water


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## vanj85 (Jun 23, 2011)

Or it could be your thermostat is sticking open, not allowing you to actually get warm coolant to your heater core. Any air bubbles would be purged out throw the over flow resivoir tube after a few time of heating up, as long as you coolant level looks good i'd rule that out. Your heater core could be plugged, unhook both lines from core by fire wall blow air from a compressor through it and see if theres a lot of gunk that comes out the other side, I usually zip tie a plastic garbage bag around the outlet end to catch the coolant and rust.


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## jrockfishhunter (Nov 4, 2011)

Thermostat sounds stuck open to me would check that first

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## tjstebb (Jun 5, 2006)

Do you get heat if you sit still and hold engine throttle at around 2000 Rpm's? If you get heat stopped and holding engine rpm. Then it's probably the water pump. Usually if a T-stat sticks open the coolant never heats up so you never get heat driving or sitting still. I've changed a lot of water pumps for this same symptom. 

Tjstebb


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## bigcountrysg (Oct 9, 2006)

If it was summer time and hot outside, then I bet your engine temp would raise while stop. But when you start driving again it would come back down. 

If it was a thermostat problem, then you would barely have any heat or no heat at all. 
Because when the thermostat fails it fails open allowing the coolant to flow freely. There for it does not get warm.


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## Nodakhtr (Jan 15, 2013)

I would take the thermostate out and see if that makes a difference first, that would cost you nothing.

Sometimes those thermostates will only open partially when really hot. Watch you temp gauge, if that themostate is not opening and you have 180 degrees the hot water is not getting to the core.


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## Joel/AK (Jan 12, 2013)

With the engine up to temp, touch the heater hoses. Are they both hot, 1 hot, or both cold. Start eliminating things. If only one is hot, its your heater core, if none are hot than its not moving coolant. 


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## averageguy (Jan 1, 2008)

Joel/AK said:


> With the engine up to temp, touch the heater hoses. Are they both hot, 1 hot, or both cold. Start eliminating things. If only one is hot, its your heater core, if none are hot than its not moving coolant.
> 
> 
> Posted using Outdoor Hub Campfire


 Try above.. Also, some cooling systems have areas that are higher than the cap or fill jug. If air gets trapped it will not purge itself and has to be pulled out using a vaccum tool made for this purpose. This usually happens when the system has been emptied for some type of service, like changing a water pump, thermostat or heater core. My bet is a plugged heater core. My buddies brother changed his water pump, thermostat, radiator and purged the air out and same thing, no heat sitting still or moving slow. Pulled the heater core out and blew out what looked like mud with the air hose. Put in a new one and he had heat.


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