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Discussion Starter #1
Got a '11 Crown Vic base model w/ 270k miles I'm using for a delivery vehicle and I'm trying to drill down it's overheating problem. It started overheating this summer when sitting idling when outside temps were over 90. Parking it in the shade or opening the hood (while still running) would get the engine temp back down to normal. But last night something new happened. It started overheating at night with outside air temp at 70, so I guess whatever it is has gotten to the point where a part needs to be replaced. Coolant is full btw.

This car is new to me as of 4 months ago, and I don't have a lot of experience working with this engine so I'm not sure where or how to start diagnosing it. What do I look at to start diagnosing? And if no hard evidence shows up pointing to one thing or the other, what part should I change out first? I would guess thermostat and water pump.
 

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first is thermostat. after removing, temporarily reconnect thermostat housing, take top radiator hose off from radiator, start engine. water should shoot out of the hose. if not-- change water pump. if good flow, try new thermostat. after that ---radiator
 

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The thermostat is designed to heat up engine coolant as fast as possible by shutting off coolant flow from leaving the engine. If coolant stays in the engine it gets hotter. If a thermostat fails usually it sticks in a position. Open closed or partially open. The thermostat should open and close. Coolant will exit the engine at the top of the engine to the top of the radiator. The temp of that coolant coming out of the top radiator hose should be at the rated temp of the thermostat or higher.

What cools the coolant is the radiator. (Heat exchanger) Typically the radiator is designed to over cool the coolant no matter the condition. Aiding in that cooling at slow vehicle speeds only is the radiator fan. Either electrical or mechanical fans.

The water pump drives the coolant round and round.

Possible issues for your situation:
If the thermostat is sticking and letting go that could cause the concern. Usually the thermostat just fails in an open or closed position. If closed the engine will over heat very quickly. In this case the upper radiator hose will be cool as the engine over heats.

If the coolant has not been changed frequently it is possible the water pump impeller will erode diminishing coolant flow and causing over heating. This is a very slow processes. The proceedure above would determine if there isn't enough flow. The issue is the thermostat may need to be removed first. Since a working thermostat's job is to restrict coolant flow.

Again if the coolant has not been changed frequently solids that would be removed with a coolant change will accumulate in the bottom of the radiator restricting coolant flow. If this is the case the core of the radiator will not have uniform temps from hot at the top to cooler at the bottom. A infra red temp probe would be best for this.

>>>>>>>>>>>>>>>Action
 

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Discussion Starter #4
Thanks for the replies.

After watching it overheat a couple times now a pattern has emerged of coolant leaking from under the reservoir cap while the dash temp gauge still reads normal. After that the gauge goes up to full overheat. What would leaking around the reservoir cap indicate in this situation?
 

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If the cap is leaking coolant when the system is not hot the cap is bad. For clarity over heating is when the coolant boils out of the cooling system through the radiator cap opening. If the gauge is reading high or hot the system is not overheating. It is running hot. Gauges are not that accurate.

>>>Action
 

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Discussion Starter #6
Ok I've done more testing now and I'm almost sure it's the rad fan not turning causing all this. Here's what I'm seeing...

1 - The overheat condition doesn't happen while moving, it only happens while in park after idling for a while

2 - Top radiator hose DOES get hot

3 - If the a/c is off, the rad fan DOES NOT turn at all during overheating as the temp gauge moves all the way up

4 - At normal engine temp the rad fan DOES turn as soon as the a/c is turned on, but I've only observed this so far at normal temperatures.

5 - During the times it overheats and the a/c is on, the cabin vent air gets hot and humid right when the overheating occurs. I haven't yet made it a point to check the rad fan at this point to see if it's still turning.

6 - During testing, after getting the engine temp up to idle hot and the temp gauge read normal in the middle, to trigger it to overheat I had to run the engine at 2k rpm for over 5 mins before the dash temp gauge began to rise. After the gauge begins to creep up I've let off the gas but the temp continues to go all the way up. Although to trigger the overheat condition I ran it at 2k for a while, it DOES overheat by simply sitting in park and idling.

7 - The coolant reservoir cap has a small leak but I don't think this is a major factor. I've continued to top off the reservoir throughout my testing and overall there doesn't seem to be much coolant leaking from the reservoir. Although, you CAN hear air seep from the reservoir cap when you squeeze the top rad hose.

The main problem seems to be the rad fan not turning. Any ideas? I'm all ears.
 

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Repair Tips:
  • Relays that operate motors typically have diodes which provide circuit protection. Light, radio and auxiliary relays may or may not have resistors and diodes. For proper performance, select the correct relay for the application.
  • When replacing a relay, locate the OE number and specifications on the non-functioning relay. Many OEs label relays as "miscellaneous" making it difficult to identify the correct replacement
  • Before replacing any relay, visually inspect the entire electrical circuit including the component, relays, connectors, and wiring in the circuit. Look for heat damage and damaged wires
 

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Work from the known to the unknown.

Replace the cap.
Get the fan to operate.

>>>>Action
 

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coolant resivoir cap has a small hole so the coolant can return to the radiator. the cap on the radiator itself is the one to replace. cheap insurance.
 

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Discussion Starter #11
Tested water pump and it's working good. Now, I've replaced both the reservoir cap and thermostat with new.


Then did some more testing by way of observing the fan speed when turning the a/c on and off. Fan speed seemed sluggish as if it wasn't being properly commanded. At different points it seemed like it wanted to turn but would stop. Maybe a dumb idea but after turning the a/c off and the blades came to a stop I took a small twig and gave the blade a quick push and it slowly started going again.


So what is this a bad fan motor maybe? And if so, where do you get just the motor? Can't find it at any of the major car store sites.


I've also read the connectors on either end of the fan control module (connected to the fan body) can get corroded.
 
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