Random High Engine Temp

[Forty61]

The factory ECU settings for a 2005 Ford Mustang's cooling fan trigger on the following coolant temperatures:

• Low Speed On: 216°F
• Low Speed Off: 208°F
• High Speed On: 228°F
• High Speed Off: 224°F
• Thermostat opening: 192°F

Therefore 208-216°F (98-102°C) is the desired engine operating range.
In extreme conditions up to 228°F (109°C) is acceptable for short periods.



Sounds like your fan is working as it should in low speed mode.


I suggest you merely drain the coolant, thoroughly flush the entire cooling system including the cooling passages in the engine itself, and replace with fresh coolant (Motorcraft Gold & deionized water). You could also add a "water wetter" agent that reduces the surface tension of the coolant and improves heat exchange.

Thank you for the actual numbers, that helps a lot as a reference point. Sure seems like it's in range so I need to catch it when the gauge spikes (if it does again) and see what it's reading at that point.

For what its worth:
All my vehicles run @tstat temps on the highway, reading 192*.
Idling gets a little warmer, 210-215.
Open track pushed high near 230*.

Got it. Thanks!

 

[Kev555]

I'm dragging this thread back from the dead instead of making a new one as this problem showed itself again yesterday..

I was in traffic, not standstill, crawling at like 20mph for a bit. Car was fine for most of it but right before getting free it started getting warm, like just past vertical on the gauge. I grabbed my reader and plugged it in to look at the live data it offers. I'm watching the "ETC" variable which I think is actually supposed to read ECT but whatever.. the gauge started falling by the time I got it plugged in but I saw 105 degrees Celsius before it fell to 95 and it stayed there the rest of the drive. It maintains 93-96 degrees idling in the driveway.. hell, it's holding that while I'm idling in traffic right now!

My misfire code has not returned, car seems to run strong. So I need thoughts and ideas.. glitchy fan relay? Fan going bad? Temp sensor issue? It sucks not being able to have confidence to drive the car for fear of getting stuck in traffic.

Interesting. I was under the impression it would be closed to aid with initial warmup and then just be wide open after that and just regulated by air flow/fans.

Here's what I had driving home, it looks like it's not fan related.. it's probably in the upper 70s, light rain so added benefit of the radiator being hit with spray when moving..

- Sat in traffic for 45 minutes, 205-207F
- Running at 55mph, crept up to and held 212-214F
- Through town at 35-40mph, 208-210F
- Running at 60-65mph, peaked at 219, hovered around 214-216F
- My road at 40-45mph, lowest of 199, highest of 214F

So if running in damp, cool conditions, at speed, leads to those temps is PROBABLY not the fan. I'm leaning to faulty thermostat or failing water pump. System I'm sure could also use a flush..

Its the bit where your running at speed and its still got a high temp that made me suspect the Thermostat. Change it as its only a few quid and see if that cures it, if not start looking at the Radiator that its not partially blocked and the fins are all clear, then the water pump although i cant see it unless the propellers in it has disintegrated or rusted away. What colour is your coolant in the reservoir ATM? I defo would not want my engine hitting 212F or over it

 

[Forty61]

Its the bit where your running at speed and its still got a high temp that made me suspect the Thermostat. Change it as its only a few quid and see if that cures it, if not start looking at the Radiator that its not partially blocked and the fins are all clear, then the water pump although i cant see it unless the propellers in it has disintegrated or rusted away. What colour is your coolant in the reservoir ATM? I defo would not want my engine hitting 212F or over it

I had similar thoughts. I'll plan on grabbing a 180F thermostat, drain/refill the coolant and go from there.

 

[Kev555]

I had similar thoughts. I'll plan on grabbing a 180F thermostat, drain/refill the coolant and go from there.

If your coolant looks dirty bung a can of coolant system cleaner in there a day or so before you drain it to break up any sludge and sediment.

 

[whitmanink]

So two things come to mind ..
First it sat for awhile...
Id suspect coolant is no good or greatly reduced it's cooling properties and or the thermostat is starting to stick from gunk or old age or defective now.
And right now only shows or fails when it gets hot..

 

[Forty61]

So two things come to mind ..
First it sat for awhile...
Id suspect coolant is no good or greatly reduced it's cooling properties and or the thermostat is starting to stick from gunk or old age or defective now.
And right now only shows or fails when it gets hot..

You mean leaving it sitting for months and then returning it to daily, 150 mile round trip commuting isn't a good idea!?

180F thermostat and coolant in the passenger seat right now, it's just gotta get me home!

 

[MrBhp]

You mean leaving it sitting for months and then returning it to daily, 150 mile round trip commuting isn't a good idea!?

180F thermostat and coolant in the passenger seat right now, it's just gotta get me home!

Changing to a 180 thermostat is generally not a good idea.

 

[StockishS197]

Changing to a 180 thermostat is generally not a good idea.

+1 to this. A lower tstat won’t fix an overheating condition unless the old tstat was stuck closed.

Though the 05/06s ran a 180 degree tstat, the 07+ with the updated coolant crossover ran a 195.

 

[Pentalab]

This is why the radiator is vacuum filled, so no air pockets or air bubbles. At 60 mph, the eng fan should never be on...even with AC on.
The high / low fan speed thresholds are set in software....(low and high eng coolant temps). These can be independently adjusted using a hand held tuner.
On my 2010 GT automatic, temp gauge only ever gets to just under 1/2 scale.

Even at 30 mph, the low speed fan never comes on. That's with 75 deg F outside temps.

 

[Pentalab]

This is why the radiator is vacuum filled, so no air pockets or air bubbles. At 60 mph, the eng fan should never be on...even with AC on.
The high / low fan speed thresholds are set in software....(low and high eng coolant temps). These can be independently adjusted using a hand held tuner.
On my 2010 GT automatic, temp gauge only ever gets to just under 1/2 scale.

Even at 30 mph, the low speed fan never comes on. That's with 75 deg F outside temps.

Here's what I found did reduce under hood temps a bunch.... like by 40 F. Ceramic coated LT's and hi-flow cats. The new hi-flow cats are bigger diam (4") but shorter than oem, but are located below the seats. Oem cats are at base of eng bay and run stupid hot. The ceramic coated LT's just don't get hot. Made by JBA, and coated both inside and outside. After a romp, I can put my fingers on any of the 8 x primary tubes, and hold em down firmly.

Upper grille on any 2010 is 80% blocked off. Replaced with a 7 bar grille (which also deleted oem upper foglamps). The 05-09 cars get the aftermarket 9 bar upper grille. That very top radiator cover was also replaced, with an offset on the new one, which forces more air through all the rads.

The OP might want to just swap the T stat on spec.....and probably flush the rad and engine, and replace....and use distilled water, and anti freeze. I had mine vac fi;led, to eliminate air bubbles.

The T stat does not snap open, it gradually opens.

 

[Dino Dino Bambino]

+1 to this. A lower tstat won’t fix an overheating condition unless the old tstat was stuck closed.

Though the 05/06s ran a 180 degree tstat, the 07+ with the updated coolant crossover ran a 195.

They all ran a 192* thermostat.

Changing to a 180 thermostat is generally not a good idea.

Not the best idea but won't do any harm either. It won't fix an engine that's running hotter than normal though unless the old one is stuck partially closed.

If the engine runs hotter as the vehicle speed and engine rpm) increases on the highway, the most likely problem is a clogged radiator and a full cooling system flush might just remedy it. The factory grille has 50% of its opening closed off for a good reason (to allow the engine to warm up quickly after a cold start).

 

[Robert Larimer]

The factory ECU settings for a 2005 Ford Mustang's cooling fan trigger on the following coolant temperatures:

• Low Speed On: 216°F
• Low Speed Off: 208°F
• High Speed On: 228°F
• High Speed Off: 224°F
• Thermostat opening: 192°F

Therefore 208-216°F (98-102°C) is the desired engine operating range.
In extreme conditions up to 228°F (109°C) is acceptable for short periods.



Sounds like your fan is working as it should in low speed mode.


I suggest you merely drain the coolant, thoroughly flush the entire cooling system including the cooling passages in the engine itself, and replace with fresh coolant (Motorcraft Gold & deionized water). You could also add a "water wetter" agent that reduces the surface tension of the coolant and improves heat exchange.

You should also mention that the low speed fan is always on if the AC is on. That means where I live the low speed fan is on 90% of the time the car is running.

 

[whitmanink]

You mean leaving it sitting for months and then returning it to daily, 150 mile round trip commuting isn't a good idea!?

180F thermostat and coolant in the passenger seat right now, it's just gotta get me home!

when you said it sat for months , i took that as it sat for years and you now got it back out,?

if you have a descent scanner like i have, you can turn the fan on and off to check if its working and even change what temp it will come on

so if it works on the obd2 test but wouldn't turn on when the car is just running than a sensor issue ?
and if it wouldnt run on the obd2 test then either the fan itself went or the fuse or the control box has a short

 

[Forty61]

Thanks for the input all.

Car has been sitting for a few months but even prior to that it was only getting driven once every couple of months. It's been a very low use car for years now.

The coolant in the reservoir looks clean, I don't see a bunch of contamination to it but we will see properly when I crack the drain plug.

The fact it showed higher temps at highway speed leads me to believe either the coolant is shot, there's a clog somewhere or the thermostat is not behaving correctly. Initially I had thought fan related issues but knowing it can hold 199-205F at idle in traffic shows me the fan works like it should or my symptoms would be reversed.

Why would a 180 thermostat be bad? I understand it has no control over actual engine temp. I figure an extra 15 degrees of range it's open would make almost no difference except perhaps a little more buffer to the hot range.

 

[Brooke]

I just got a 2005. the low fan wasn't running. wires good, relay good. take the power distribution box... bad. I was at the junkyard for other parts but found 6 mustangs with the same issue. people say it's the wires but I disagree. it's the relay/distribution box that's sized for the current. and the fuse is oversized to prevent it.

 

[Brooke]

I just got a 2005. the low fan wasn't running. wires good, relay good. take the power distribution box... bad. I was at the junkyard for other parts but found 6 mustangs with the same issue. people say it's the wires but I disagree. it's the relay/distribution box that's sized for the current. and the fuse is oversized to prevent it.

and 2 of them were on the high fan wires. I also changed the resistor on the fan for $20

 

[StockishS197]

They all ran a 192* thermostat.

Odd. My 06s OEM was 180F per the factory stamping when I swapped it

But yeah, my 07 had a *192* not a 195.

 

[MrBhp]

I just got a 2005. the low fan wasn't running. wires good, relay good. take the power distribution box... bad. I was at the junkyard for other parts but found 6 mustangs with the same issue. people say it's the wires but I disagree. it's the relay/distribution box that's sized for the current. and the fuse is oversized to prevent it.

Lots of info on here about removing that load from the power distribution box. An awful lot of fans have been replaced when the problem was the box.

 

[Kev555]

Thanks for the input all.

Car has been sitting for a few months but even prior to that it was only getting driven once every couple of months. It's been a very low use car for years now.

The coolant in the reservoir looks clean, I don't see a bunch of contamination to it but we will see properly when I crack the drain plug.

The fact it showed higher temps at highway speed leads me to believe either the coolant is shot, there's a clog somewhere or the thermostat is not behaving correctly. Initially I had thought fan related issues but knowing it can hold 199-205F at idle in traffic shows me the fan works like it should or my symptoms would be reversed.

Why would a 180 thermostat be bad? I understand it has no control over actual engine temp. I figure an extra 15 degrees of range it's open would make almost no difference except perhaps a little more buffer to the hot range.

I would change like for like thermostats and other parts if needed until you get to the bottom of the problem. I'm curious if the ECU would adjust the fuel trims (if that's the right term?) if the running temp got too low? The more technically minded guys here could tell me if that could be an issue or bullshit?

 

[Kev555]

You mean leaving it sitting for months and then returning it to daily, 150 mile round trip commuting isn't a good idea!?

180F thermostat and coolant in the passenger seat right now, it's just gotta get me home!

Leaving a car standing for a few months shouldn't be an issue. If the cooling system was diluted with water over time that could be an issue but you would see it starting to show a brown colour if rust was present in the system. Thankfully most of the engine cooling system is alloy from memory on the GT. thermostat, water pump propellers, and heater pipes are the only steel i know of in the GT