Searched topic before posting, sry if this is a duplicate. Son and I, purchased '08 4.6 L Shelby conv (w/K Bell SC) last summer. 102K on odo. Have tried to resolve this by scouring the internet, but I'm out of ideas.

ISSUE:
Since purchased, when driven from cold and brought up to operating temp, it usually will do fine. You can drive it for an hour, OBD reader engine temp stays in 190-194 degrees.
- However, rarely the temp gauge will instantly spike to into the red, and then just as quickly go back to normal.
- Most often the issue sporadically shows itself after your park the car for 10 - 20 minutes. When you start it up again, after 20 seconds - 2 minutes(ish), sometimes the cluster temp gauge and an OBD reader will very quickly jump to the red, sometimes putting car into limp mode.
If you shut car off and promptly restart, the temp usually is at "normal" again (190ish).
- On very rare occasions car will not heal itself and has to be left to cool down
- Temp can also peg into the red for a few seconds and return to normal with the car running the whole time.
- Sometimes the car will run without issue for weeks (approx. 50-100 miles/week)
- The other day the cluster temp gauge dipped to 0 for just a second, back to normal, into the red, and back to normal. Only observed this a couple times.
- The cluster gauge and OBD temp don't always agree, with cluster gauge lagging by a few second.
- Rarely the cluster gauge and OBD temp won't agree, one will show a spike 200-240, the other shows "normal"
- This is the only symptom we can most often (not always) reproduce. With a warm engine, after about 10 seconds under mild aggressive highway acceleration, OBD temp often will instantly spike. Cluster gauge usually isn't fast enough to react. Temp instantly returns to 190ish a few seconds after taking foot off accelerator.

OBSERVATIONS:
- It doesn't do this all the time. Just often enough for me to trust it again. It can go weeks without any issues, but then back to unreliable. I want my son or wife to be able to take it out, have fun and confidence, and not get stranded in traffic.
- We not loosing coolant
- Thermal camera confirms coolant leaving radiator is definitely cool, barely warm to touch. Coolant entering radiator is hot.
- Coolant appears clear, bright (orange in this case)
- Coolant passed our own combustion leak test, didn't detect combustion gasses in coolant (could try it again?)
- Oil filler cap is clean, clear. Oil on dipstick isn't milky
- Do not observe white smoke


ATTEMPTED SOLUTIONS: in order
- New thermostat, 170 degrees
- New GT 500 fan (fan wasn't running at high temp)
- During fan replacement we discovered the melted fuse block connection under fan relay. (Repaired connection, we thought YES! But no)
- Replaced water pump
- New coolant, with some water wetter
- Replaced upper, lower radiator hoses (Mishimoto)
- 2X,did our best to burp air from system as much as possible (hot engine, steep incline, alternating low to 3000 rpm cycles, aggressively squeezing hoses during process), Did liberate some air
- Brought in an old priest and a young priest

PISSING IN THE WIND
- Head gasket leak? Ugh
- Air bubble left in coolant system?
- Bad engine block temperature sensor?
- Bad ground? (all other gauges appear to work as intended)

Any feedback, wisdom appreciated. Thank you in advance!

 

Sounds Electrical Not Mechanical if Temp Can Change So Dramatically Either Way. Certainly Replace Sensors With Oem Parts To Eliminate That Posability.

https://www.fordpartsgiant.com/parts...&filter=(39430)

Punch in Vin To Be Sure on Part Number.

Shows Different Number By Engine Tag Number.

Cooling System Shop Manual PDF Below!

https://www.fordpartsgiant.com/parts...tml?pnc=12A648


KC

 

Thank you!

 

You Are Welcome!

Just Posted Sensor Locations Pdf as Well!

KC

 

Hate those threads where you never hear the outcome? What was the actual issue? Me too. So, an update on my phantom overheat issue. It's been a slow process getting motivated to continue. However, I did finally discover the issue and wanted to share my misery with the rest of you! I'm mechanical, but not a mechanic. Be kind?

Pulled Kenne Bell supercharger and replaced the cylinder head temp sensor with Motorcraft. Old sensor looked surprisingly clean. Since the insulation on the old sensor wires was brittle/cracked, I also replaced the pigtail assembly at the sensor. Out of curiosity, I checked the resistance of both sensors prior to installing new. They read approx. 26k Ohms and 24.5k Ohms at room temp. Also ordered new KB bolts, gaskets, etc. ...and replaced spark plugs and fuel injectors while everything was apart. Got it all put back together. Started, ran fine except...the temp gauge wasn't responding. OBD reader confirmed no signal from CHT sensor. Poop!!

Scratching head, I picked up a new pigtail assembly to plug into CHT main harness with ohm meter without pulling anything apart. Meter read ZERO ohms, complete short. Doubt crept in that I failed to properly terminate the new pigtail harness assembly (which I failed to confirm continuity before reassembling everything). Ugh, something so simple?

Removed everything a second time to get back to the sensor. Now with supercharger off the engine, and sensor still in block, I tested CHT sensor resistance again. This time it reads 24.5k Ohms again. Audible grunt! Now, the belly pan of this KB supercharger comes ridiculously close to the top of the CHT sensor. Upon closer inspection of the new pigtail assembly, I see two very small, bright copper spots showing through the insulation. The aluminum belly pan was shorting the harness. Called Kenne Bell and they recommended torqueing and driving sensor deeper into the block. I went about 1/16" of a turn deeper and stopped, It was already bottomed out.

So, I carefully ground a very thin. small area off the belly pan (at sensor). I also put heat shrink wrap on each conductor, a second layer over both conductors together, and a final, third layer over the entire end of the pigtail. Since then (last weekend), it's been flawless! (Sort of, see sidebar below.)

I suspect the old harness was also the issue. As the supercharger and block heated/expanded, the cracked insulation likely leaked just enough current to decrease sensor resistance and intermittently peg/zero the temp gauge. This is a KB/sensor combo fluke, but I am SO relieved that there wasn't/isn't some type of head gasket issue.

**SIDEBAR**
Unfortunately just a little more drama. While proofing the car last Sunday, there was a sudden screeching noise coming from the engine. Immediately killed the power to inspect. Fluid leaking on the ground! Turns out, while I was reinstalling everything the first time, I dropped a plastic shim into the engine compartment and assumed it fell through to the ground. No. It apparently landed somewhere near the radiator fan. While driving it went through (and ruining) the new GT500 fan and punctured the radiator. Ordered Cold Case radiator and another GT500 fan from American Muscle. "Drop in" radiator is thicker than stock and wasn't a fast process but it's back up and running.

Went through this process with my 17 year-old son, who's the reason I bought this Mustang. That indescribable feeling you have when you're young and fall in love with a car. So, it's been frustrating that it took almost a year to resolve the temperature issue. Watching the car sit in the garage as my time with my high school senior is slipping away. He's so happy right now to be able to drive it again. However, I wouldn't change anything because we got to work together figuring things out together. Borderline emotional about it. Thank you all in this geneious network for giving me the confidence.

 

You Have No Idea How Much I Miss Those Times With My Son! He Was Lost to Leukemia in 2010 at 21. Thank You So Much For Sharing Your Story & Outcome. It's Many Times a Trial & Error Process. Had a Similar Issue With a Member Who Had a Car With The IMRC Charge Plates Removed and The Disconnected Wire Got Crimped Between Manifold & Head. It Would Keep Blowing a Fuse and Throwing a Code.

Also Had Similar Issue on My Harley Truck Where Tech Had Installed Supercharger on Top of One of The Knock Sensor Wires So Doubtful it Was Doing it's Job. I Won't Go Into Other Things I Had To Fix After The So Called Master Tech Had Swapped A Head out After Blowing a Spark Plug Out on The Truck. It Was Years of Little Issues Here & There I Had To Fix From a Half Assed Repair! The Spark Plug Blowing Out was A Common Issue On The Model. What is it With Fords & Plugs!

Thanks Again For The Update!

Stories Like These Help Us All Think Outside The Box on These Issues!

Thanks For Adding The Pics It Gives a Good Mental Picture For The Symptom!

Enjoy The Times With Your Son For They Grow Up So Fast! Try & Make it a Habit To Wrench on The Car or Go To a Car Show When you Can!

KC

 

Glad you were finally able to figure out and resolve the intermittent overheating issue, Ritch... Needless to say, you have far more patience than I do...LOL

-Rocky

 

Thanks for posting and glad you got it figured out. My guess was that it had to be an electrical/sensor issue, but I had no clue how to narrow that down.