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Discussion Starter #1
I have a 2004 ford mustang base model with 106k on it. I've replaced the thermostat and it is still over heating after driving less then a mile. The fan is working. Any ideas of what is causing it to over heat?
 

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Low on coolant
Air in system
Radiator has debris in the bottom that may or may not be flushed out.

Thermostats rarely cause over heating. The design is to restrict flow at cold temps and be open during hot temps. Most are bullet proof in doing this mission

Check coolant level when engine is stone cold. Top up as needed.
You may have introduced air into the system when you changed the thermostat. IF the thermostat was bad you swapped one issue for another
If you have a infrared thermometer, with engine running and warmed up, check the temps at the top and bottom of the radiator and post back. If you don't have one, for under $15 at Walmart you can have one. It is a good diagnostic tool to have in the tool box.


What engine is in your Mustang?

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My engine is a 3.9. I checked the jug where I add the antifreeze and it is still full. I know 6 months ago we drove about 15-20 miles on the highway and it started over heating then. We stayed at the store for 20 minutes and left. It was over heating when we first left but when we got on the highway it went to the normal range. Since those 6 months we've drove it around our town and no issues until just a few days ago, when it over heats after 5 minutes of driving
 

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Thanks for the reply
For definition - overheating means the coolant boiled out of the cooling system
Is that what happened?

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Discussion Starter #5
Thanks for the reply
For definition - overheating means the coolant boiled out of the cooling system
Is that what happened?

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No the coolant has not boiled over. In fact the radiator coolant is full. It's the temperature gauge that goes up to the red line and the ac starts blowing warm instead of cold air after only running the car for 2 minutes
 

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When was cooling system last flushed (Not just drained and refilled) out?

Possible issues to cause higher temps on the gauge -
Debris in cooling system
Water pump impeller wear
Electrical system issue .. bad sender or ?

The AC blowing hot is a separate issue. (Unless the processor is disconnecting the AC clutch. If that happens the idle speed is higher as well)
Likely the AC system is low on refrigerant. And to confirm that a set of gauges would nee to be connected.
Do you have gauges? If so post pressure readings?

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Discussion Starter #7
When was cooling system last flushed (Not just drained and refilled) out?

Possible issues to cause higher temps on the gauge -
Debris in cooling system
Water pump impeller wear
Electrical system issue .. bad sender or ?

The AC blowing hot is a separate issue. (Unless the processor is disconnecting the AC clutch. If that happens the idle speed is higher as well)
Likely the AC system is low on refrigerant. And to confirm that a set of gauges would nee to be connected.
Do you have gauges? If so post pressure readings?

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Not sure when it was last flushed, as I bought it a year ago. I don't have any gauges. I do know the ac blows nice and cold air until the temp gauge raises more then 50% then it starts going blowing warm. even with the ac off the gauge still runs in the hot area
 

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I would highly recommend flushing out the cooling system. (Likely with the thermostat removed so the thermostat do not restrict flow for the cold water)
A drain and refill won't do it.
If this is something you want to attempt on your own, remove the radiator. Likely there is debris on the bottom of the radiator.
If you want to confirm buy a $15 point and shoot thermometer. Point to the top and bottom of the radiator after the engine is heated up.

Diagnose the AC after the cooling system has been resolved. YOU will have to find some one with AC gauges to get pressure readings to understand what is happening inside.

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Discussion Starter #9
for the infrared thermometer to check the radiator temp, do I need to get a forehead thermometer like the doctors use or do I need to get one that is only for vehicles or does it not matter?
 

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The cheapest one you can find.
The thermometer doesn't know what it is measuring
There is a link in post #2 for one at Walmart

I got one about a decade ago. I forget where I got it. Not sure there are thermometers that are industry specific.


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Discussion Starter #11
I just ordered one off amazon and it should be here tomorrow. I might not be able to check it til later this week as I have a busy week.
 

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I think busy or hurry up and wait has dominated 2020.

When you have the chance post the results.

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Discussion Starter #13
I think busy or hurry up and wait has dominated 2020.

When you have the chance post the results.

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Ok here goes it was 60 degrees outside and the gauge did not go past half way after 25 minutes of running it. The ac stayed cold the whole time as well. the read outs I got was 155 degrees at the middle top of the radiator and 165 at the middle bottom. I did notice the fan was on the when I first started the car til I shut it off. When the temp gauge would go the whole way up it was at least 80 degrees or a bit warmer outside and we only had to run the car 5 blocks to get the gauge up to almost the red. I'm totally lost at what could be wrong now.
 

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The coolant exits the engine past a thermostat and goes into the top of the radiator.
Coolant is supposed to shed heat as it travels down through the radiator and exits the bottom of the radiator.
Then the water pump sucks up the cooler coolant from the bottom of the radiator (via the lower radiator hose) and pumps coolant into the engine to pick up more heat.

You are posting the temp was 155 at the top of the radiator
In the middle of the radiator it got hotter at 165

If correct, you have issues in the radiator!
The radiator needs to be removed and flushed out or replaced

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BTW this costs you about $15 to diagnose.
Way to go!!!! Good job. Saved one hour of labor at a shop.

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Discussion Starter #16
The coolant exits the engine past a thermostat and goes into the top of the radiator.
Coolant is supposed to shed heat as it travels down through the radiator and exits the bottom of the radiator.
Then the water pump sucks up the cooler coolant from the bottom of the radiator (via the lower radiator hose) and pumps coolant into the engine to pick up more heat.

You are posting the temp was 155 at the top of the radiator
In the middle of the radiator it got hotter at 165

If correct, you have issues in the radiator!
The radiator needs to be removed and flushed out or replaced

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I meant the temp was 165 at the bottom of the radiator. I checked the radiator temps as soon as i turned of the car if that makes a difference cause when I took the temp with the fan runnung it was showing 20 degrees cooler. After driving it 5 blocks and the car sat for 2 days why would the gauge move to red when it's 80 degrees or above out, but when it was 60 out today it ran for 25 minutes and the gauge would not go past half way. Wouldn't the gauge run on the hotter side at any temperature outside as long as the cars warmed up. I just didn't think outside temps made a difference in the radiator. Hope you can understand that all
 

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Discussion Starter #17
Can I just remove the top and bottom radiator hoses and flush it like that with a garden house or does the radiator have to come out? If the radiator has to come out what's the best way to clean it and do I need a flush kit? I'm asking cause I wanna try to do this on my own, but I have major back issues that will cause me to have a procedure Monday and then again 2 weeks later. if you have any tips, I'd appreciate it. Thank you for your help
 

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If you can remove the radiator hoses you can do the job.
Removing both hoses and flushing in the car may work.
If you do that I would refill with water and do the same test. (Fill it with water, run the engine to get up to temp and remove the air. Then take temperatures. If it is hotter on top than the bottom, you have gotten when you want.
If you can not achieve cooler temps on the bottom, radiator removal would be needed. This may allow the sludge in the bottom of the radiator to work it's way out.
Or if that does not work, replace the radiator.

Most flush kits that I have seen allow a garden hose to be connected inline to a heater hose. You do not need that.
The flush chemical, that may help. However I believe the chemical should be in the radiator (or cooling system) for some time. With the hoses disconnected the chemical won't stay in there long.

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