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Shawn E
Shawn E, Ford Senior Master
Category: Ford
Satisfied Customers: 1707
Experience:  23 Years with Ford, 12 Year Ford Senior Master, ASE Master.
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operating temperature the gauge pegs..runs rough..cylinder overheat

Customer Question

ihavea1998 ford150with a 4.6 the problem is that when the truch gets to operating temperature the gauge pegs out. and the motor runs rough. I replaced the temperature sensor and the temperature cylinder overheat sensor but it still does the exact same thing. any ideas what it might be
Submitted: 7 years ago.
Category: Ford
Expert:  Shawn E replied 7 years ago.

Hi, welcome to my name is XXXXX XXXXX I will be answering your question.



Start by checking the coolant level make sure it is not low and repair any leaks. Check the fan clutch and make sure it is not wet with oil on the front of it indicating it is bad. I would replace the thermostat it sounds like it is sticking. If its not the thermostat clean the radiator fins sometimes they clog with dirt and debris. The water pump could also be defective make sure you are getting good coolant flow through the system.


I hope my assistance helped you and resolved your concern, if you need further assistance please ask.

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Thank you, Shawn.


Customer: replied 7 years ago.
I have a new thermostat .no leaks anywhere coolant is good fan is good (dry) radiator clean. and I have good coolant flow.oil temp. light comes on at the same time as temp. guage spikes al lthe way up. but oil presure shows good. change both coolant temp. sensors . and still no change. .
Expert:  Shawn E replied 7 years ago.
Is it overeheating or is it a guage problem?
Customer: replied 7 years ago.
it is does not appear to be overheatting ,but after about 8 to 10 min. of the truck being started thats when the temp. spikes.and then the motor starts to run rough.also just had the trans rebuild.and instaled.trans seems to be working good.
Expert:  Shawn E replied 7 years ago.
Check the water pump maybe the impeller is broken I have seen that on a diesel if you drive for about 5 minutes the temp will peg.
Customer: replied 7 years ago.
Lets review what we know... When the truck is started for approximately eight to ten minutes the oil light comes on but the oil gauge is normal and the temperature gauge spikes and a check engine light also comes on. This afternoon it was started for approximately thirty minutes with no problem (lights on or temp spikes). When shut off and restarted my original problem presisted. But the water appears to be flowing good. Vehicles heats up well. Hoses are warming up. So, I'm 90% sure it's not the water pump.
Expert:  Shawn E replied 7 years ago.
Is there any codes for the check engine light. This could make a big difference to determine if its a bad sensor or a problem with the cluster itself.
Customer: replied 7 years ago.
Thank you for your quick response, it's really appreciated. And sorry for the headache...we have one too. :-) Yes, there is. We had it put on a diagonistic machine today. This is what it says....P1299 Cylinder Head Overtemperature Protection Active.
Expert:  Shawn E replied 7 years ago.

Here is the code definition:



    • Engine cooling system concerns.
    • Base engine concerns.
    • Low engine coolant level or loss of coolant.
  • Diagnostic Trouble Code (DTC) P1299 indicates an engine overheat condition was detected by the cylinder head temperature (CHT) sensor. An FMEM Strategy called Failsafe Cooling was activated to cool the engine. (Refer to Section 1A, Electronic Engine Control (EC) System , for more information on Failsafe Cooling Strategy and the cylinder head temperature sensor.)

    Possible causes:

  • Check engine coolant level.

Is the engine coolant level fill correct?

Yes No
GO to the Powertrain/Engine Group, Engine Cooling System Section in the Workshop Manual for symptom, Engine Overheats. GO to the Powertrain/Engine Group, Engine Cooling System Section in the Workshop Manual for symptom, Loss of Engine Coolant.


The vehicle runs rough because it is cutting off injectors in order to cool the engine. I would double check and make sure the vehicle is not overheating.


If you are absolutely sure the truck is operating at a normal temperature and the cylinder head temp sensor is new then there are only 2 more things it could be. A concern with the wiring harness or connector or a processor concern. Check the harness for any chaffed wires grounding out against a metal bracket. The pcm is the absolutely last step because there is no way to test it other than replacing it.

Shawn E and 4 other Ford Specialists are ready to help you
Customer: replied 7 years ago.

Where is the pcm located? Is that the one under the kick panel?

Expert:  Shawn E replied 7 years ago.
The processor is located on the right side of the engine against the firewall. Check the harness around those AC lines they sometimes rub through and short out against them.
Customer: replied 7 years ago.
Thank you sooo much for your help. It has been greatly appreciated. But one more quick much do the pcm's approximately run?
Expert:  Shawn E replied 7 years ago.
About $300-$400
Customer: replied 7 years ago.
Thank you again. I'll work on this tomorrow. I appreciate you time.
Expert:  Shawn E replied 7 years ago.
Your Welcome