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wojf72
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Vehicle: 1998 Ford Expedition XLT
Joined: Sep 2008
Member # 4680
From: MA
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97F1504RAD
Supercharged Member
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Vehicle: 1997 F-150/ 2006 Mustang
Joined: May 2005
Member # 55
From: Nor Cal CA.
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 Posted
- September 6 : 6:58p
| | Very hard to diagnose a overheat condition online. Could be the mechanical fan is not operating properly and is worn out. Could be air trapped in the cooling system. Could be a flow issue with a broken impeller on the water pump. could be a flow issue within the radiator. Usually if it only happen in city driving it is a clutch fan failure where it is not drawing enough air across the radiator. | |
MrSVTGal
Supercharged Member
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Vehicle: 2000 Ford Expedition
Joined: May 2005
Member # 5
From: South OC CA
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Posted
- September 6 : 8:00p
| ^^^ I'd say that the system needs to be burped (air in the system). That can cause odd variations as sometimes the sensor reads the actual coolant temperature, and other times it reads superheated steam. And in some systems it might even read just air (and likely read really low). So the needle can be very unpredictable.
How FAST is it going from normal to spiked to normal? Over several minutes? 10 minutes? seconds? Only in traffic (stopped, basically)? or even when you're moving?
There are lots of other things that could cause this, but I think the most likely one, and the one that costs basically zero to try/fix, is making sure the coolant is topped off and burped properly.
MrSVTGal | |
Tom in Tacoma
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Vehicle: Truck? What truck?
Joined: May 2005
Member # 9
From: Over yonder WA
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Posted
- September 7 : 11:20a
| | I'd suspect the temperature sending unit. | |
Thermo
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Vehicle: 97 Ford Expedition lifted
Joined: Sep 2006
Member # 1199
From: Norfolk VA
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Posted
- September 8 : 10:52a
| I am placing money on the temp sending unit myself. Assuming that it rises very rapidly (over the course of a few seconds or less), then that would indicate an electrical issue. If the temp rises over say a minute, then I would be looking at either air in the system or the water pump is starting to go and with the higher engine RPM, it can move enough water to keep things cool, but slow down and it can't move the water like it needs to.
Chris "Thermo" Coleman and Nukie, the radioactive 97 X | |
JMC
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Vehicle: 2000 F-150 SC XLT 4x4
Joined: Apr 2006
Member # 599
From: Windsor Ontario
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Posted
- September 16 : 10:07a
| Your 98 uses three sensors to monitor the engine temperature. One Coolant Temperature Sender is for the instrument cluster. A second Engine Coolant Temperature sensor is for the PCM (computer) to help control fuel delivery, timing and EGR. A third Cylinder Head Temperature sensor is used by the PCM to monitor and control the fail safe cooling available for the V8 engines of that model year. If the engine was actually overheating to the point of pegging the needle the PCM would initiate Fail-safe cooling. The truck would run on alternating 4 cylinders. The PCM would illuminate the oil pressure light and the over heating light at the same time to alert you to the Fail-safe Cooling mode. I also suspect the Engine Coolant Temperature Sender because you posted that the truck still ran fine. On the intake manifold coolant crossover it should be the one on the right (passenger side). There are two sensors on the crossover.
JMC | |
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98 Exped Temp Spike Then Back To Normal
