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2003 Mazda Protege

Question: Why does car pump coolant out of overflow tank?

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eddiemondy, 2.0L 4 Cylinder, Thomasville, NC, February 02, 2009, 18:41
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 Rookie

My car has 110,000 mi.and I have replaced the radiator cap and had the system flushed and filled, also replaced thermostat, and overflow resovoir tank--and it still pumps coolant out the overflow and then starts to run hot. It will run fine sitting still but when you drive it, it will loose coolant untill it eventually starts to heat up. What's up with that? I recently bought the car and I have no warranty I did not notice the problem untill 30 days had passed because we did not drive the car that often. When the garage flushed the coolant system they said that it looked like it had stop leak in it. Hope you can help, love your site. --Thanks Ed

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  • Answer #1

    patrick mannion from Greg Solow's Engine Room, February 02, 2009, 19:01
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    This does not sound good. The radiator cap keeps coolant in the engine and radiator once the coolant heats up it need to expand and the radiator cap allows coolant to push a small amount of coolant into he coolant expansion tank, as the coolant in the radiator "cools down" that coolant is drawn back into the radiator through a second valve in the radiator cap. You just bought the car and it looks like someone had put stop leak in the radiator before. I suspect someone had a coolant leak and has previously over heated the car in the past. It is likely your Mazda has a blown head gasket. To test for a blown head gasket a garage will look for the presence of carbon monoxide in the cooling system. Carbon monoxide is a by produce of combustion when gasoline is burned in the engine and can only get into the cooling system if the cylinder head gasket doesn't seal well or if the cylinder head is cracked. There is a very good two stage carbon monoxide tester many repair shops have. Is there any steam present in the exhaust, or does the engine run rough when it is started or running once warmed up?

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    joecool1991, January 13, 2011, 19:50
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    My protege is doing this same thing. I think it might be the gasket on the valve cover. If there is one.

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  • Answer #2

    patrick mannion from Greg Solow's Engine Room, February 02, 2009, 19:01
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    This does not sound good. The radiator cap keeps coolant in the engine and radiator once the coolant heats up it need to expand and the radiator cap allows coolant to push a small amount of coolant into he coolant expansion tank, as the coolant in the radiator "cools down" that coolant is drawn back into the radiator through a second valve in the radiator cap. You just bought the car and it looks like someone had put stop leak in the radiator before. I suspect someone had a coolant leak and has previously over heated the car in the past. It is likely your Mazda has a blown head gasket. To test for a blown head gasket a garage will look for the presence of carbon monoxide in the cooling system. Carbon monoxide is a by produce of combustion when gasoline is burned in the engine and can only get into the cooling system if the cylinder head gasket doesn't seal well or if the cylinder head is cracked. There is a very good two stage carbon monoxide tester many repair shops have. Is there any steam present in the exhaust, or does the engine run rough when it is started or running once warmed up?

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    eddiemondy, February 03, 2009, 21:04
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    there is no steam coming from exhaust and the engine runs great both cold and fully warmed up. Is there anyway I could keep the coolant from escaping the overflow canister until the radiator cooled down and sucked it back in (A larger overflow canister maybe)?

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    Visitor, May 03, 2011, 13:17

    i have a 2002 mazda protege es and i have a foam like mix coming out of my overflow tank. I talked to some mechanics and they said it is either a head gasket or that i have a atf in my radiator.

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