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HDGENE, ASE Certified Technician
Category: Mercury
Satisfied Customers: 5708
Experience:  25 years experience Ford Senior Master Technician/Diesel certified ASE Master Technician
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I have a 2006 mountaineer with a 4.6. I have a problem with

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I have a 2006 mountaineer with a 4.6. I have a problem with the vehicle trying to overheat and going in to limp mode only with a/c on and driving. At idle it does fine. With a/c off never tries to overheat. Any suggestions
JA: Have you checked the coolant? Have you checked for a leak in the cooling system?
Customer: yes replaced thermostat earlier this summer, just replaced radiator a cpl weeks ago as the top tank was leaking. no leaks currently
JA: Are you fixing your Mountaineer yourself? What have you tried so far?
Customer: yes, drove it yesterday with the scanner and it shows its trying to overheat, turn off a/c goes back down, sprayed out the bugs on condenser, no changes
JA: Anything else you want the mechanic to know before I connect you?
Customer: can't think of anything

Hello, and thank you for using Just Answer! My name is***** me a few moments to review your question and Ill do my best to assist you.

Hello, when it goes to overheat is it actually running hot if you check the engine temperature or does the gauge just peg. Do you hear the fan clutch lock and roar loudly as it runs hot? Do you have good heater operation?

Customer: replied 2 months ago.
I don't think it's actually running hot the computer seems to think so.. I shot the hoses and thermostat housing with laser and getting 160ish.. and yes clutch locks and good heat operation .. gauge pegs after about 4 or 5 minutes of driving
Customer: replied 2 months ago.
Once I turn off the a/c it goes back to normal

Ok it could be caused by an air pocket near the coolant temperature sensor but i f you have good heat all the time then the system should not have air in it. There should be about 10 degrees difference with the upper hose hotter and the lower hose cooler. Since the radiator is new and the thermostat is new. For it to overheat with a load on of the ac but its not running hot could point to a defective temp sensor or issue with the instrument cluster itself. you would need to look at the actual temperature sensor input using a scan tool when it runs hot to see if the sensor is showing its overheating or pointing to a problem with the gauge itself which is part of the cluster.

Customer: replied 2 months ago.
I drove yesterday with the scanner hooked up and it did match the gauge overheating. . What I'm confused on is it a cylinder head temp sensor or is their an actual coolant sensor? and when the thermostat stuck earlier this year it shut off the a/c as I've read it should

On the 4.6 its a cylinder head temperature sensor, so I would shoot the area where it sits and see if the temp matches whatthe sensor is reading, if not replace the sensor and retest. The wiring to the sensor is a common spot of animals to nest and chew up the harness as well. So inspect the wiring for damage and repair as needed.

Customer: replied 2 months ago.
Sounds good.. that's located convinantly under the intake twards passenger rear correct? and can it be done by just removing alternator or intake have to come off?

On the rear of the right head and yes the intake must be removed

Customer: replied 2 months ago.
Ok thanks. . Sounds like the culprit I'll let you know how it goes

Good luck if you need more help please let me know. If I was helpful, pleasel eave a positive rating so I get credit for helping you.

Customer: replied 2 months ago.
Will do

Very good, thank you.

HDGENE and other Mercury Specialists are ready to help you
Customer: replied 2 months ago.
Well I think we figured it out. . On a last thought I ran at idle with a/c off and just vent ..compressor off, tried to over heat so I thought well maybe a hidden air pocket like you mentioned. . Cranked front and rear heat and drove for 4-5 miles various speeds and rpms.. turned a/c back on in town and at highway speeds.. working fine now!.. thanks for all your help!

Very good and thank you for the update, it sounded more like an air pocket and when it has a lack of heat it is a good indication of that being the case.