Temperture climbing then falling
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Joined: Aug 2007
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From: Fort Wayne, IN
Temperture climbing then falling
Having an issue, about every mile or so, the Bronco (95EB with the 5.8) temp guage goes up slowly to HOT, then falls again to where it should always be. My dad isn't super mechanically inclined, I'm thinking the sending unit, or a sticking thermostat. But as quickly as it falls I think it's electronic rather than mechanical, plus the engine just doesn't seem to be getting that hot. No CE light. It's going to Ford for diagnosis tomorrow, the guage was replaced about 8 months ago because it just sat on the peg at C (basically it was dead), I'm thinking it's more of the same. If so it'll be a warranty repair.
Lead Driver
Joined: Sep 2002
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From: Gateway to the West
Let it cool down and check the coolant level in the radiator itself. Sounds like the system is low and is circulating an air bubble. Fill the radiator with the engine running. As it circulates the air should bubble out of the system. Be sure to turn on the heater and make sure both hoses to the heater core are getting warm as well. The heater core is typically the highest point in the cooling system and if the air bubble is big enough you may need to open one of these hoses at the core and let the air out. Once the thermostat opens, the level should drop again. Top off the radiator and let the truck run til it holds its normal operating temp. If the rise-and-fall situation still exists, then worry about bad sending units.
Elder User
Joined: Jan 2005
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From: Houston
I had a leak in my water pump. it wasn't bad enough to change it so I just kept adding water. During this time I would notice my temperature would do as you describ. It seems like what greystreak is saying. I am sure I had air in it cuz It would run low then I would fill it. After I replaced my water pump and put new coolent in it, my temperature stays as steady as a new truck. If I was you, I would disconect the top and bottom hoses to the radiator. Flush that baby out with a hose until clean water flowed. Hook it all back up with new coolent and I bet it would be fixed.
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From: Mattawa Washington.
never heard of a plugged radiator cooling back down like you describe. Plugged rads. stay HOT.while operating only cool when you take the load off like idleing if even then.
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From: Fort Wayne, IN
The t-stat is good. We checked it with the boiling water technique. Pops on que.
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Joined: Mar 2009
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Chiltons has a measurement to test the sensor, but I am guessing it is something else. Do you have the in line oil cooler?
