what is the symptons of bad radiator cap?
08-28-2014, 04:59 AM
#1
Racer
Thread Starter
what is the symptons of bad radiator cap?
My car is a 2005 m6 and on my way home my water temp started to rise when i got home it was 259F.
My fan is working and i have never had any problem befor.
It looked like the water reservoar was empty so i open the cap --> very bad idea, I swear it was water in there.
Can this be a bad radiator cap?
the water was not boiling until i open the cap.
that can the boiling problem be? bad cap?
My fan is working and i have never had any problem befor.
It looked like the water reservoar was empty so i open the cap --> very bad idea, I swear it was water in there.
Can this be a bad radiator cap?
the water was not boiling until i open the cap.
that can the boiling problem be? bad cap?
08-28-2014, 10:10 AM
#2
Race Director
It's not a "radiator" cap. The cap on the overflow tank holds the system pressure. If you remove the cap while the engine is hot it will release the pressure as steam or heated water.
Your engine overheating probably wasn't caused by the cap, time to check that the radiator isn't blocked and that the fan is functioning as designed.
Your engine overheating probably wasn't caused by the cap, time to check that the radiator isn't blocked and that the fan is functioning as designed.
08-28-2014, 11:34 AM
#4
Race Director
http://autohowstuffworks.com/cooling-system2.htm
Last edited by haljensen; 08-28-2014 at 11:40 AM. Reason: add link
08-28-2014, 12:55 PM
#5
Race Director
It's not supposed to release the pressure unless the engine is cold. It's designed to hold the pressure since the cooling system is designed for pressurized coolant. There's no pressure when the system is cold.
http://autohowstuffworks.com/cooling-system2.htm
http://autohowstuffworks.com/cooling-system2.htm
Operating under pressure (15 psig or more) raises the boiling point of the coolant assuming water to about 250degF. Without pressure, water boils at 212degF at mean sea level pressure. Big Difference!!!Webpage that shows a 50/50 mix at 15 psig has a boiling point of 265 degF:
http://www.answers.com/Q/What_temper...a_car_radiator
Last edited by GOLD72; 08-28-2014 at 01:09 PM.
08-28-2014, 12:59 PM
#6
Racer
Thread Starter
ok then thats not the probelm 
and the fans are working the t-stat have like 1300miles can that get stuck?
or is the paddle in the water pump not pumping the water around?
and the fans are working the t-stat have like 1300miles can that get stuck?
or is the paddle in the water pump not pumping the water around?
08-28-2014, 01:28 PM
#7
Race Director
The thermostat can certainly fail to open wide enough to circulate enough coolant to cool the engine. If nothing appears to be obviously wrong and you did mention that the reservoir was basically empty of liquid when you opened it, I would suggest replacing the reservoir cap as easy and cheap next step in case it is failing to allow the system to pressurize up to spec. Refill the reservoir and get the air purged out of the circulating system. Once the reservoir is empty, air can be drawn into the system and a partially filled system with air will lose cooling capacity. I am assuming you haven't found any obvious coolant leaks like a leaking water pump or radiator or hoses. Hopefully you are not losing coolant into the engine at a head gasket. Once you have the system properly recharged by running the engine and stopping and letting it go through several heating and cooling cycles and refilling the reservoir as needed as the level goes down, normal temperatures should return. If not, suspect a thermostat going bad. If normal temperatures return, I would monitor the reservoir over a period of weeks and months to see if there is a gradual loss of coolant. Good luck.
08-29-2014, 09:22 AM
#8
Racer
Thread Starter
i filled the reservoar up and started the car turned on full heat and filled it with water a few times more but on when it stod on idle the temp rised to 215f very quick. but i can put my hands on the radiator, its warm but not super hot.
08-29-2014, 06:13 PM
#10
Race Director
215° isn't overheating. Sitting at idle in the summer I frquently see 215°. Most C6's will run between 190° and 215° and vary slightly with outside temperature, traffic and load.
08-30-2014, 09:37 AM
#11
Tech Contributor
Member Since: Oct 1999
Location: Charlotte, NC (formerly Endicott, NY)
Posts: 40,081
Received 8,924 Likes
on
5,330 Posts
You need to get a little more methodical in your diagnostic process. Let me summarize a couple of things you have mentioned.
1. The coolant temp went to 259 degrees while you were driving the car.
2. The coolant reservoir looked empty
3. When you removed the cap the coolant in the system boiled
4. When you added water and idled the engine the coolant ran at 215 degrees.
5. You recently had a new thermostat installed.
259 degree coolant temp while driving is excessive and out of the normal range while a 215 degree coolant temp with a full cooling system with the engine idling is a normal temperature.
What could make the temperature swing the way it did? A partially stuck open thermostat which will allow sufficient coolant flow while the engine is idling but not when it is producing power while the car is being driven. However, a thermostat doesn't usually cause the system to lose coolant unless the system boils over from excessive heat. This can be spectacular when it happens and you haven't mentioned seeing it happen. I sort of doubt the thermostat is the problem.
From the things you describe it sounds to me that you have one of two things that could cause your symptoms. First, when the thermostat was installed an air bubble was introduced into the cooling system and not purged properly so you didn't have sufficient coolant. If so you resolved your problem by adding coolant. Second, a cooling system leak that is small enough to maintain some pressure (why coolant boiled when you removed the cap) but allows coolant to leak out (why the reservoir seemed empty). If the reservoir was empty when you were driving there may not have been enough coolant in the system to cool the car properly. This type of problem is usually caused by a slow leak in the water pump or at a hose fitting that isn't tightened properly. Get the car up in the air and look for leaks on every hose and hose end and then look for a leak at the water pump. Feel behind the pump to see if there is some dampness or a sticky feeling. Water pump leaks will drip on the lower pulley and the serpentine belt and the stabilizer bar. You may see a few drips on the floor under the front of the engine after you let the car sit over night.
Bill
1. The coolant temp went to 259 degrees while you were driving the car.
2. The coolant reservoir looked empty
3. When you removed the cap the coolant in the system boiled
4. When you added water and idled the engine the coolant ran at 215 degrees.
5. You recently had a new thermostat installed.
259 degree coolant temp while driving is excessive and out of the normal range while a 215 degree coolant temp with a full cooling system with the engine idling is a normal temperature.
What could make the temperature swing the way it did? A partially stuck open thermostat which will allow sufficient coolant flow while the engine is idling but not when it is producing power while the car is being driven. However, a thermostat doesn't usually cause the system to lose coolant unless the system boils over from excessive heat. This can be spectacular when it happens and you haven't mentioned seeing it happen. I sort of doubt the thermostat is the problem.
From the things you describe it sounds to me that you have one of two things that could cause your symptoms. First, when the thermostat was installed an air bubble was introduced into the cooling system and not purged properly so you didn't have sufficient coolant. If so you resolved your problem by adding coolant. Second, a cooling system leak that is small enough to maintain some pressure (why coolant boiled when you removed the cap) but allows coolant to leak out (why the reservoir seemed empty). If the reservoir was empty when you were driving there may not have been enough coolant in the system to cool the car properly. This type of problem is usually caused by a slow leak in the water pump or at a hose fitting that isn't tightened properly. Get the car up in the air and look for leaks on every hose and hose end and then look for a leak at the water pump. Feel behind the pump to see if there is some dampness or a sticky feeling. Water pump leaks will drip on the lower pulley and the serpentine belt and the stabilizer bar. You may see a few drips on the floor under the front of the engine after you let the car sit over night.
Bill
08-30-2014, 02:18 PM
#12
Team Owner
Member Since: Oct 2004
Location: San Clemente CA
Posts: 27,420
Likes: 0
Received 59 Likes
on
48 Posts
You need to get a little more methodical in your diagnostic process. Let me summarize a couple of things you have mentioned.
1. The coolant temp went to 259 degrees while you were driving the car.
2. The coolant reservoir looked empty
3. When you removed the cap the coolant in the system boiled
4. When you added water and idled the engine the coolant ran at 215 degrees.
5. You recently had a new thermostat installed.
259 degree coolant temp while driving is excessive and out of the normal range while a 215 degree coolant temp with a full cooling system with the engine idling is a normal temperature.
What could make the temperature swing the way it did? A partially stuck open thermostat which will allow sufficient coolant flow while the engine is idling but not when it is producing power while the car is being driven. However, a thermostat doesn't usually cause the system to lose coolant unless the system boils over from excessive heat. This can be spectacular when it happens and you haven't mentioned seeing it happen. I sort of doubt the thermostat is the problem.
From the things you describe it sounds to me that you have one of two things that could cause your symptoms. First, when the thermostat was installed an air bubble was introduced into the cooling system and not purged properly so you didn't have sufficient coolant. If so you resolved your problem by adding coolant. Second, a cooling system leak that is small enough to maintain some pressure (why coolant boiled when you removed the cap) but allows coolant to leak out (why the reservoir seemed empty). If the reservoir was empty when you were driving there may not have been enough coolant in the system to cool the car properly. This type of problem is usually caused by a slow leak in the water pump or at a hose fitting that isn't tightened properly. Get the car up in the air and look for leaks on every hose and hose end and then look for a leak at the water pump. Feel behind the pump to see if there is some dampness or a sticky feeling. Water pump leaks will drip on the lower pulley and the serpentine belt and the stabilizer bar. You may see a few drips on the floor under the front of the engine after you let the car sit over night.
Bill
1. The coolant temp went to 259 degrees while you were driving the car.
2. The coolant reservoir looked empty
3. When you removed the cap the coolant in the system boiled
4. When you added water and idled the engine the coolant ran at 215 degrees.
5. You recently had a new thermostat installed.
259 degree coolant temp while driving is excessive and out of the normal range while a 215 degree coolant temp with a full cooling system with the engine idling is a normal temperature.
What could make the temperature swing the way it did? A partially stuck open thermostat which will allow sufficient coolant flow while the engine is idling but not when it is producing power while the car is being driven. However, a thermostat doesn't usually cause the system to lose coolant unless the system boils over from excessive heat. This can be spectacular when it happens and you haven't mentioned seeing it happen. I sort of doubt the thermostat is the problem.
From the things you describe it sounds to me that you have one of two things that could cause your symptoms. First, when the thermostat was installed an air bubble was introduced into the cooling system and not purged properly so you didn't have sufficient coolant. If so you resolved your problem by adding coolant. Second, a cooling system leak that is small enough to maintain some pressure (why coolant boiled when you removed the cap) but allows coolant to leak out (why the reservoir seemed empty). If the reservoir was empty when you were driving there may not have been enough coolant in the system to cool the car properly. This type of problem is usually caused by a slow leak in the water pump or at a hose fitting that isn't tightened properly. Get the car up in the air and look for leaks on every hose and hose end and then look for a leak at the water pump. Feel behind the pump to see if there is some dampness or a sticky feeling. Water pump leaks will drip on the lower pulley and the serpentine belt and the stabilizer bar. You may see a few drips on the floor under the front of the engine after you let the car sit over night.
Bill
