Random High Engine Temp

[Forty61]

It could be: air bubble, intermittent lean condition, intermittent sticking thermostat.
I'd be curious what the radiator temp is when the gauge is 'warm'. If the radiator is just as hot as the gauge, that would eliminate a tstat or air bubble issue. I'd check it with a temp gun.

You know, lean condition is one I hadn't thought of but alongside the occasional misfire code it throws that may very well be something I need to dig into..

 

[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.

 

[Forty61]

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.

Ok so excuse my naivety on it but can I park it slightly uphill, open the coolant cap and run it up to temp to purge air like I would on my old truck?

In the mean time, this weekend I will run it up to temp and see what my handheld code reader gives on the live data for the temp. Hopefully the gauge acts up and I can verify it's not an actual cooling problem. Then I guess it'll be throwing some relays at it to future proof the wiring and fuse box.

 

[Pentalab]

Ok so excuse my naivety on it but can I park it slightly uphill, open the coolant cap and run it up to temp to purge air like I would on my old truck?

In the mean time, this weekend I will run it up to temp and see what my handheld code reader gives on the live data for the temp. Hopefully the gauge acts up and I can verify it's not an actual cooling problem. Then I guess it'll be throwing some relays at it to future proof the wiring and fuse box.

I was going to suggest plugging the scanner into the OBD port. AFAIK, the temp it spits out is an inferred temp reading, based on an algorithm.
It sounds to me like ur low speed fan is not coming on at all, only the high speed. When my relays crapped out + burnt / melted wiring, on my 2010 GT auto, I had no low or high speed fan. I was in down town heavy traffic, and heat gauge pegged. I forget what the oem temp thresholds were for low + hi speed fan operation. I think it was like 205F for low speed fan...and 215 F for high speed fan.

In normal operation, idling in the driveway, fan is off, then temp climbs from 190 F up to aprx 205F, then low speed fan kicks in...and temp drops back to 190 F, and low speed fan shuts off..... then it just repeats that format over and over.

 

[Juice]

You know, lean condition is one I hadn't thought of but alongside the occasional misfire code it throws that may very well be something I need to dig into..

Random misfire code....the plot thickens. Same root cause I'm betting.

 

[Forty61]

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.

 

[StockishS197]

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.

105C translates to 221F, which is when the high speed should kick on, with the stock fan temp settings in the tune. That said, my car never goes above 210 even in bumper to bumper traffic with all my mods but my low and high speed fans kick on sooner than stock.

Is the fan on? Can you tell if it’s low or high speed is running?

 

[Forty61]

105C translates to 221F, which is when the high speed should kick on, with the stock fan temp settings in the tune. That said, my car never goes above 210 even in bumper to bumper traffic with all my mods but my low and high speed fans kick on sooner than stock.

Is the fan on? Can you tell if it’s low or high speed is running?

Every time it has happened, by the time I get the hood open, the fan is running. It also cycles the fan with the AC on (not sure if that's low or high setting). I sat in traffic today for 25-30 minutes and the live data never went above 92C or 197F but when I pulled up at work it was 99C or 210F with no change on the dummy gauge.

I'm thinking my low speed is intermittent. It's just so intermittent right now I can't properly diagnose it. I may pull the relays and look for any new discoloration.

 

[bambam 06]

https://wireeverything.com/products/ols/products/2005-14-mustang-dual-speed-fan-relay-harness. This is what you need.

 

[Forty61]

https://wireeverything.com/products/ols/products/2005-14-mustang-dual-speed-fan-relay-harness. This is what you need.

I've seen that but for $200 I'll wire my own, just haven't got to it yet.

At lunch I swapped the relays around, the rear defrost had the same relay in it so I swapped that with the low fan. Idling at temp the fan was running which I can't say I saw yesterday in the driveway unless it wasn't quite to the threshold yet..

I'll monitor it and start collecting the parts I need to move the relays out.

 

[Kev555]

So this stupid issue reared it's head again yesterday..

Tooling home at 60-70mph, all good for about 30 minutes then the gauge climbed to about 3/4 of the way up and stuck there.. drove 10-15 minutes to see if it came back down which it did, then it did it again so I pulled over and like last time, before I could even pop the hood the temp dropped. I turned the AC off and drove over an hour home without issue after that.

Looks like I'll be doing some external fan relays this weekend. Then I need to research the blend actuators because I can't get air from the main dash vents.. all these little things came up right before I start leaning on the car more often for commuting which is a hassle..

my guess is a sticking thermostat.

 

[Juice]

220*F is not abnormal when in stop&go traffic.

 

[Forty61]

my guess is a sticking thermostat.

This has been mentioned before but why would it be closed after the car has been run up to temp? Should it not stay wide open after the initial warm up?

220*F is not abnormal when in stop&go traffic.

What is deemed safe on these for the upper limit? All my older stuff if I see 220+ I'm looking for a place to shut it down and cool it off.

 

[Juice]

If you have the right amount of coolant/water mix, and the system holds pressure, 270*F is the boiling point.
Personally, Id pull off and shut down @230-240.

 

[Kev555]

This has been mentioned before but why would it be closed after the car has been run up to temp? Should it not stay wide open after the initial warm up?


What is deemed safe on these for the upper limit? All my older stuff if I see 220+ I'm looking for a place to shut it down and cool it off.

Thermostat opens and closes usually between 80-90 degrees Celsius. They don't stay open at running temp unless they are faulty Forty61. I have removed faulty thermostats over the years to cure overheating problems until I got a replacement. Its not often you see faulty stats compared to years ago prob due to superior coolants in engines now but it still happens. 105 Celsius is dangerous territory to be running an engine temp with alloy heads.

 

[Forty61]

Thermostat opens and closes usually between 80-90 degrees Celsius. They don't stay open at running temp unless they are faulty Forty61. I have removed faulty thermostats over the years to cure overheating problems until I got a replacement. Its not often you see faulty stats compared to years ago prob due to superior coolants in engines now but it still happens. 105 Celsius is dangerous territory to be running an engine temp with alloy heads.

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..

 

[StockishS197]

220F is nothing for these…the stock high speed fan doesn’t kick on until then. Heck the stock low speed fan doesn’t come on until something like 214F.

when my 06 GT high speed fan relay melted, my car got up to 240F before I saw the temp gauge pegged and it was fine…wouldn’t have known otherwise.

Are you using an OEM water pump? I ask because on my 06, I used a “high flow” pump from the parts store that had a different pump design that didn’t work worth a crap and didn’t cool properly.

My 07 doesn’t get above 210F in Houston with the stock cooling system + cams and headers, with the AC on in the peak of summer.

 

[Forty61]

220F is nothing for these…the stock high speed fan doesn’t kick on until then. Heck the stock low speed fan doesn’t come on until something like 214F.

when my 06 GT high speed fan relay melted, my car got up to 240F before I saw the temp gauge pegged and it was fine…wouldn’t have known otherwise.

Are you using an OEM water pump? I ask because on my 06, I used a “high flow” pump from the parts store that had a different pump design that didn’t work worth a crap and didn’t cool properly.

My 07 doesn’t get above 210F in Houston with the stock cooling system + cams and headers, with the AC on in the peak of summer.

Factory cooling system, hell it's probably the damn factory coolant.

I drove it to work again today, at a sustained 65-75mph I saw a range of 212-219F. Any lower than about 55mph it would hover from 208-212. Dummy gauge on the dash never moved at all. No pending or stored codes in the system either.

Consensus on temps seems to vary, some people say they never see over 210, some say up to 230 is acceptable.. soooo run it until it quits? Replace coolant and see if it changes? Throw a temp sensor and thermostat since they're cheap enough parts?

 

[Dino Dino Bambino]

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.

- 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

Factory cooling system, hell it's probably the damn factory coolant.


I drove it to work again today, at a sustained 65-75mph I saw a range of 212-219F. Any lower than about 55mph it would hover from 208-212. Dummy gauge on the dash never moved at all. No pending or stored codes in the system either.

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

Consensus on temps seems to vary, some people say they never see over 210, some say up to 230 is acceptable.. soooo run it until it quits? Replace coolant and see if it changes? Throw a temp sensor and thermostat since they're cheap enough parts?

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.

 

[Juice]

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*.