Thanks for answerin.
Thermostat? Head Gasket? HELP!
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New User
Joined: Jul 2009
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From: Lewis County, KY
Thermostat? Head Gasket? HELP!
I know there are similar threads on here but they have some variations so I thought I'd just start a new thread...sorry!
I have a 2000 Ford F150. The heater just recently started blowing cold air...not all the time though. Just once in awhile. Tonight, it started blowing cold air and the temperature gauge pegged in the hot zone. I immediately pulled over but the engine sounded like it was running normally. I shut the heater off and the temperature gauge then went back to normal. I didn't run the heater until I got closer to home for fear it would tear up the engine. When I got closer to home I turned the heater back on, it blew hot air and the temperature gauge stayed normal. What could this be?!?!
I have a 2000 Ford F150. The heater just recently started blowing cold air...not all the time though. Just once in awhile. Tonight, it started blowing cold air and the temperature gauge pegged in the hot zone. I immediately pulled over but the engine sounded like it was running normally. I shut the heater off and the temperature gauge then went back to normal. I didn't run the heater until I got closer to home for fear it would tear up the engine. When I got closer to home I turned the heater back on, it blew hot air and the temperature gauge stayed normal. What could this be?!?!
Thread Starter
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New User
Joined: Jul 2009
Posts: 16
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From: Lewis County, KY
Had the radiator and hoses checked, no leak. Now my truck overheats, periodically, because it's not pumping water to the motor for some reason. Talked to my mechanic this morning. Going to try a new thermostat, probably an excercise in futility since it's not stuck all the time. Likely a head gasket.
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Hotshot
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is the coolant tank in the full range?? it sounds like it is a quart low or so. that lets an air pocket form at the top of the head by the temp probe and gives a "hot" reading since it is measuring air not water. Does the tank ever belch coolant ?
Hotshot
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no, the air gets trapped at the high point of the motor, near the sensor. when you start the motor the thermostat is closed. As the water gets up to 180 degrees, the thermostat will start to open, but the top if the head has had no coolant and the air will get "real hot". About the time the gauge gets to 195. degrees and the thermostat is open and water starts to flow, the temp gauge will spike up to 250 degrees for 20-30 seconds, the water will start flowing and touch the probe and the temp will then drop to the water temp of 195. When the air hits thee coolant tank it is likely it will belch and loose several ounces out of the pressurized cap. The air in the system will also collect in the heater and it is a poor heat transfer medium and the heater output drops to cold.... one good way to get the air into the system is to have a pin hole in the head or head gasket. If that cylinder is on compression when parked, the combusion gas will leak into the water jacket overnight. Overheating normmally will occure about 5 minutes after startup in the morning.
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Posting Guru
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actually the reason the temp spikes is because the coolant is really that hot, the air pocket is around the t-stat it doesn't allow the transfer of heat as well as the coolant so it takes a hotter engine to get the t-stat to open but you do have a nice well thought out theory