Random High Engine Temp

[Forty61]

So yesterday coming home from work I got stuck in traffic, I sat for probably 20-25 minutes and happened to notice the coolant temp needle about 3/4 of the way up the gauge. Luckily traffic started moving but as I started moving away the gauge started to spike towards the red so I took the first exit and pulled over. I left it running and popped the hood to check the fan was running, it was and by the time I walked back around to peek at the temp it was falling back to normal.

After that I drove home at 80mph, AC on, temp needle never moved above just below vertical. It's the first time I've seen a random temperature spike so what's my likely culprit? Fan relay? I know I've seen that mentioned multiple times before.

 

[JC SSP]

Maybe Fan relay getting hot… but that’s usually the stock wire is ready to short/burn out.

Might be sticking thermostat or fan motor itself is starting to go…

Do you have stock fan or GT500 upgrade?

 

[StockishS197]

Check both the low and high speed fan relays, because either could melt. If the low speed melted, the fan won’t come on until the high speed is commanded so could explain the issue. When mine failed, it was on the high speed so once the coolant temp got hot enough or AC was on, it would overheat.

If all that looks good and confirm the high and low speed fans are working, next would be checking coolant level, and considering thermostat replacement.

 

[Forty61]

Maybe Fan relay getting hot… but that’s usually the stock wire is ready to short/burn out.

Might be sticking thermostat or fan motor itself is starting to go…

Do you have stock fan or GT500 upgrade?

All stock GT stuff, nothing related to the fan has ever been touched.

Check both the low and high speed fan relays, because either could melt. If the low speed melted, the fan won’t come on until the high speed is commanded so could explain the issue. When mine failed, it was on the high speed so once the coolant temp got hot enough or AC was on, it would overheat.

If all that looks good and confirm the high and low speed fans are working, next would be checking coolant level, and considering thermostat replacement.

Coolant looks to be at a good level, I'll inspect the relays.

Surely if it was a stuck thermostat the issue would show up quicker right? The car had been running for 30-45 minutes prior to getting stuck in traffic.

 

[Pentalab]

I had the relay burn up on my 2010 GT a few years ago. Neither low / high speed fan would engage....and I was stuck in down town traffic. Once moving, it started coming down.
In normal operation, temp gauge is always just below 1/2 scale. The only time the high speed fan kicks in is if in stop and go traffic on a hot day. The 7 bar upper grille helps a lot, and gets more air in there..... when moving.

 

[JC SSP]

Old racers trick… when temps start to climb turn on your heater full blast… works like a mini radiator (heat exchanger).

 

[MrBhp]

When you check the relays, you need to actually check the connections below the relay. I would separate the two halves of the box and inspect terminals. Sometimes it's hard to see the problem until you are right on top of it.

 

[thirwin]

If you look under the fuses in the fuse box you might find the burned out terminals that power the two fan motor settings. Both of mine were fried and the high temp completely failed.

 

[thirwin]

I got a lot of advice from the guys on this forum. They’re awesome.

 

[Forty61]

Yesterday I opened up the fuse box under the hood, I didn't find any terminals visibly burned from the top so I need to take it all apart and look from the bottom. I did however fire the car up and it kicked the fan on and off with the AC, then I turned the AC off and it ran for a while and then kicked the fan on also, never climbed above vertical on the gauge.

Either I'm going to find a burned connection on the bottom or I had a weird relay issue... Between this and the random misfire code that comes and goes I feel I may be chasing some electrical gremlins down soon..

 

[Juice]

Any work done recently on the cooling system? Sounds like it burped a small air pocket.

 

[Forty61]

Any work done recently on the cooling system? Sounds like it burped a small air pocket.

I'm a little ashamed to admit the only work the car has had in months is an oil change in the driveway, it's been sitting mostly idle for quite some time and is just now getting back into regular use.

Definitely weird that it kept climbing in temp after I got moving again but then dropped once I pulled over, whatever the issue was must have self-righted itself before I could get eyes on it.

 

[Forty61]

Random questions to save me making a new thread...

The fan on these cars, there's a ground and two power wires, one for high and one for low. Are both lines 12V with the resistor at the fan or is the low speed kicked down higher up in the circuit? I briefly looked over the schematic but didn't see where the low speed gets regulated.

And for actual operation and how it's supposed to function because I've never actually paid attention to it.. it cycles when the AC kicks in and out, is that the high or low setting kicking in with it? And the fan should cycle on and off at warm idle correct? It is not a constant low speed when the engine runs?

I popped open the bottom covers of the fuse box yesterday and didn't see any damage but the relay prongs themselves show a little bit of heat so I'm planning to probably move the fan power to external relays. I'm figuring if both power wires headed to the fan are 12V I can convert those to the coil wires for the external relays and run a new hot line for the fan itself. This is a little redundant with two relays in each circuit but it would be the least intrusive as I can make all my splices and wiring changes in one spot along the fender edge.

 

[Forty61]

I've driven the car to work the past two days.. traffic both days but it is a little cooler.. gauge has not gone above vertical at all, I've been watching it like a hawk and I swear I see a wiggle in it every so often but I'm just paranoid now it's going to happen again.

 

[Robert Larimer]

Random questions to save me making a new thread...

The fan on these cars, there's a ground and two power wires, one for high and one for low. Are both lines 12V with the resistor at the fan or is the low speed kicked down higher up in the circuit? I briefly looked over the schematic but didn't see where the low speed gets regulated.

And for actual operation and how it's supposed to function because I've never actually paid attention to it.. it cycles when the AC kicks in and out, is that the high or low setting kicking in with it? And the fan should cycle on and off at warm idle correct? It is not a constant low speed when the engine runs?

I popped open the bottom covers of the fuse box yesterday and didn't see any damage but the relay prongs themselves show a little bit of heat so I'm planning to probably move the fan power to external relays. I'm figuring if both power wires headed to the fan are 12V I can convert those to the coil wires for the external relays and run a new hot line for the fan itself. This is a little redundant with two relays in each circuit but it would be the least intrusive as I can make all my splices and wiring changes in one spot along the fender edge.

I know this is a late response but anyway..... The resistor mounted on the fan shroud drops the current for the low speed fan both feeds are identical. Your fan should come on low speed as soon as you turn on AC and stay on. If it is cycling that is the high speed fan kicking on because compressor pressure is too high. It goes off when the pressure drops. So you have no low speed fan and it is either the resistor or melted wiring. It seems to me that melted wiring may be caused by the fan motor drawing more current with age and you should replace the fan and fix the wiring if that is your problem. I really don't know how the fan acts without AC because here in S. Florida it is rare to run without it

 

[Forty61]

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..

 

[Juice]

If your temp climbed while driving 60+ mph, its not a fan issue. At 60 you have way more airflow than what the fan can pull.

 

[Forty61]

If your temp climbed while driving 60+ mph, its not a fan issue. At 60 you have way more airflow than what the fan can pull.

Well that's what I figured too but it didn't overheat at speed, just ran hotter than normal. And why would it be so intermittent other than an electrical issue? Not trying to sound rude, genuinely curious..

 

[Laga]

Before you do anything drastic. Check actual temperature of the coolant with external thermometer. This could be the stepper motor on the dash.
My temperature gauge always reads 3/4, yet I have a separate temperature gauge and water is at 190ish.
I’ve replaced the stepper motors once. Not a bad job.

 

[Juice]

Well that's what I figured too but it didn't overheat at speed, just ran hotter than normal. And why would it be so intermittent other than an electrical issue? Not trying to sound rude, genuinely curious..

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.