Random High Engine Temp

[Forty61]

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?

I am sure the ECU is constantly adapting to engine temp, ambient temp, the knock sensors, all kinds of stuff..

I guess I'm struggling to see the issue with a slightly lower thermostat. If it's going to naturally settle and be managed by the factory fan settings of roughly 200-220F, then the thermostat opening at 180 instead of 195 is a non-issue. It may take a little longer to reach full temp but it should be negligible if it's still not fully circulating until 180F anyway.. oh and OReilly listed all the way down to like 165F as "alternatives" so I'm sure there's somebody running further from spec than I will be.

 

[Forty61]

Just an update for reference if anybody ever refers to this thread..

So I pulled the, what I assume is, factory thermostat out (looked immaculate) and replaced it with the new one. Refilled the coolant with 50/50 concentrate and distilled water. Fired it up with the tank cap loose and let it run up to about 195 before I got pulled off to do other things so I let it cool off.

This afternoon I fired it back up, topped the coolant off a hair since it had cycled and let it warm up again.

Then I found my actual problem...

I turned the AC on to put a little more load on the motor and I noticed the fan wasn't coming on with the system.. uh oh. I switched relays around and it came on with a groan, flipped the relays back and it came back on, same noise. So my relays are good, my wiring is good, my fan is not. I hadn't heard that noise before but it explains the temp problem being so intermittent if that fan has been hit or miss about actually kicking over when it needs to.

It's now making that noise any time the fan runs so I need to source a replacement. Sure wish it had made that problem known before I took the time to change coolant but at least now I know it's got fresh stuff in it and a fresh thermostat.

 

[JC SSP]

Go with an upgrade GT500 fan.

 

[08TorchRedShelbyGT500]

Go with an upgrade GT500 fan.

I wouldn't recommend doing that with the age and wiring of a stock Mustang. He's lucky he hasn't melted any wires yet. Fix this before you end up with a mess. AT the very least, a New stock fan replacement would be a must. The current fan is laboring and drawing excessive current just to run and is no doubt stressing the Fan relays and slowly degrading the 12 gauge undersized wiring.

That 7 Blade FP SVT Cooling fan draws alot more current, even if its brand new and the stock 12 gauge wiring really can't handle it unless you install the wireeverything Dual Relay 8 gauge harness assembly.

Yes. I have installed both and it works great (IF) you install both at the same time. If you don't take care of the stock wiring, you will no doubt be on borrowed time until a wire melts or a receptacle melts.

Placement of the Dual external Relays. The rest of the harness is tucked under the fuse box. This makes the fan assembly bullet proof.



40 amp external Fuse and 8 gauge ground wire.


8 Gauge power wire from the harness to the strut tower side of the fuse box.

 

[Forty61]

I wouldn't recommend doing that with the age and wiring of a stock Mustang. He's lucky he hasn't melted any wires yet. Fix this before you end up with a mess. AT the very least, a New stock fan replacement would be a must. The current fan is laboring and drawing excessive current just to run and is no doubt stressing the Fan relays and slowly degrading the 12 gauge undersized wiring.

That 7 Blade FP SVT Cooling fan draws alot more current, even if its brand new and the stock 12 gauge wiring really can't handle it unless you install the wireeverything Dual Relay 8 gauge harness assembly.

Yes. I have installed both and it works great (IF) you install both at the same time. If you don't take care of the stock wiring, you will no doubt be on borrowed time until a wire melts or a receptacle melts.

View attachment 116314

View attachment 116315

View attachment 116316

View attachment 116320


Placement of the Dual external Relays. The rest of the harness is tucked under the fuse box. This makes the fan assembly bullet proof.
View attachment 116317


40 amp external Fuse and 8 gauge ground wire.
View attachment 116318

8 Gauge power wire from the harness to the strut tower side of the fuse box.
View attachment 116319

Surprised it hasn't burned the wires up myself. I've seen that premade kit but for the cost I will happily make my own, I'll just order some relays when I order the fan and I have plenty of wiring stuff lying around to tie it all in.

 

[08TorchRedShelbyGT500]

Surprised it hasn't burned the wires up myself. I've seen that premade kit but for the cost I will happily make my own, I'll just order some relays when I order the fan and I have plenty of wiring stuff lying around to tie it all in.

I am guessing you haven't disconnected the fuse box receptacle to the fan housing assembly connection. You better check that connection while you replace the fan. Its possible that connection has taken the brunt of the heat stress from the failing fan. It should show (NO) signs of heat stress or melting.

My receptacle when I pulled my fan assembly. It was fine. My car only has 12,000 original miles.



A generic file photo receptacle that has melted due to a fan assembly that was a way overdue for replacement. It melted the receptacle.

 

[JC SSP]

GT500 is a common upgrade. Many have done it including me. I did do a homemade wire upgrade too. I live in S. FL and car runs cool in the hottest summers.

 

[08TorchRedShelbyGT500]

GT500 is a common upgrade. Many have done it including me. I did do a homemade wire upgrade too. I live in S. FL and car runs cool in the hottest summers.

Maybe you could do a nice picture tutorial on how to make a "Homemade" wire upgrade! That would be beneficial for those who don't want to spend $199.00 on a WireEverything Pro wire harness.

 

[JC SSP]

I was out of the country several years ago and had a Local perf shop do the install and upgrade wires. Unfortunately the guy retired after 30 years, so now back to looking for a reputable auto shop. So hard to find in S. FL.

 

[MrBhp]

Maybe you could do a nice picture tutorial on how to make a "Homemade" wire upgrade! That would be beneficial for those who don't want to spend $199.00 on a WireEverything Pro wire harness.

There is already a thread or two here on that exact thing. It's a very simple mod.

 

[Kev555]

Just an update for reference if anybody ever refers to this thread..

So I pulled the, what I assume is, factory thermostat out (looked immaculate) and replaced it with the new one. Refilled the coolant with 50/50 concentrate and distilled water. Fired it up with the tank cap loose and let it run up to about 195 before I got pulled off to do other things so I let it cool off.

This afternoon I fired it back up, topped the coolant off a hair since it had cycled and let it warm up again.

Then I found my actual problem...

I turned the AC on to put a little more load on the motor and I noticed the fan wasn't coming on with the system.. uh oh. I switched relays around and it came on with a groan, flipped the relays back and it came back on, same noise. So my relays are good, my wiring is good, my fan is not. I hadn't heard that noise before but it explains the temp problem being so intermittent if that fan has been hit or miss about actually kicking over when it needs to.

It's now making that noise any time the fan runs so I need to source a replacement. Sure wish it had made that problem known before I took the time to change coolant but at least now I know it's got fresh stuff in it and a fresh thermostat.

That's great that you have found the source of the issue.