Sudden Drop in Coolant Temperature - Diesel Forum - TheDieselStop.com
6.0L Power Stroke Engine and Drivetrain Discussion of the 6.0L Power Stroke diesel engine and drivetrain in the 2003-Up Super Duties and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 6.0L Power Stroke engine.

 
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post #1 of 11 (permalink) Old 06-15-2016, 10:59 AM Thread Starter
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Sudden Drop in Coolant Temperature

Hi Folks,
On a recent trip I was driving west up Tioga Pass when I noticed my coolant temperature reading on my ScanGauge suddenly went from about 210 to 170, where it remained for the rest of the drive around Yosemite that day.. The oil temp readings stayed in the normal range. The next morning I started the truck and the temperature was normal-it warmed up from about ambient air temperature to 190ish. I went up the same pass again (we were camping on the east side of the Sierra) and the exact same thing happened and the gauge read low all the way home to the SF bay area. I have no codes or pending codes. I changed the thermostat back in the fall with the factory part so I don;t think this is the issue. If the coolant temp sender was bad, would this throw a code? Is it a problem with the Scangauge? Also, if the pcm thinks the temp is low, would this affect the way the truck runs (mpg, etc)? Thanks

05' Dark Metalic Stone FX4 Crew Cab
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Four Wheel Camper (Hawk)
MBRP CAT back exhaust with slash cut tip.
Raceline 17 x 9 Wheels and 33" Toyo MT's
Flashpqaq: Currently on tow performance tune
Dieselsite Coolant Filter, CAT1 ELC Coolant,BPD Radiator
Autometer Phantom Series EGT, Boost, Fuel Pressure Gauges
Diehard Platinum Batteries, ScanGauge2
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ARP Studs / Ford Head Gaskets
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post #2 of 11 (permalink) Old 06-17-2016, 04:36 PM Thread Starter
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It's still doing the same thing driving around town. It gets up to 190 then drops to between 170-180, Does the PCM or the FICM get data from this sensor? If so, I will replace it, if not I will ignore it. The oil temp reading is still normal, and I believe that is what controls the cooling fan.

05' Dark Metalic Stone FX4 Crew Cab
6.0PSD, Automatic
JVC DVDHead Unit, JVC AMP,KickerSpeakers, Sub
Four Wheel Camper (Hawk)
MBRP CAT back exhaust with slash cut tip.
Raceline 17 x 9 Wheels and 33" Toyo MT's
Flashpqaq: Currently on tow performance tune
Dieselsite Coolant Filter, CAT1 ELC Coolant,BPD Radiator
Autometer Phantom Series EGT, Boost, Fuel Pressure Gauges
Diehard Platinum Batteries, ScanGauge2
Upgraded HPOP, BPD EGR Cooler, Blue Spring Mod
ARP Studs / Ford Head Gaskets
WARN Winch/Trans4mer Mounting System/HID Off Road Lights
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post #3 of 11 (permalink) Old 06-17-2016, 06:08 PM
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The PCM gets and uses data from the sensor. If the sensor gets too far out of spec on the cold side you may end up with a P0118 code. Also the PCM controls the fan engagement and speed using several different parameters including coolant temperature, oil temp, AC condenser temp, trans temp, and so on. It will normally start fan engagement around 228F, which means your truck could possibly overheat. The best way to check if it is the sensor is to check the coolant temperature and compare it with the ambient temperature after the truck cools overnight. They should be the same.

White 06 F350 Lariet CC 2WD DRW Tow Boss, Timbren SES, Bilsteins, Smiths Ultimate Bedliner, RK Tool Box, CondensorGuard, IntakeMod, S&B Intake, SEIC, Banks 4"TB, Accufab elbow, Edge Attitude CS, Blue Spring Mod, DCPower 185a alternator, Rebuilt FICM, STC and Standpipe update, Harpoon Mod, Coolant Filter, Glove Box Light, Hood Insulator, Rewired Mirror Heat, Seat Heater Indicator.
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post #4 of 11 (permalink) Old 06-17-2016, 06:15 PM Thread Starter
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Thanks for the reply-the temperature reading is right on the oil temp (and the ambient air temp) when it's started cold. It only drops once the truck gets to normal operating temperature, and then it won't go back up to normal. This is what is so weird! I'm going to check the wiring and the connection to the sensor right now. Is there an ohm test on the sensor that can be done when it's unplugged?

05' Dark Metalic Stone FX4 Crew Cab
6.0PSD, Automatic
JVC DVDHead Unit, JVC AMP,KickerSpeakers, Sub
Four Wheel Camper (Hawk)
MBRP CAT back exhaust with slash cut tip.
Raceline 17 x 9 Wheels and 33" Toyo MT's
Flashpqaq: Currently on tow performance tune
Dieselsite Coolant Filter, CAT1 ELC Coolant,BPD Radiator
Autometer Phantom Series EGT, Boost, Fuel Pressure Gauges
Diehard Platinum Batteries, ScanGauge2
Upgraded HPOP, BPD EGR Cooler, Blue Spring Mod
ARP Studs / Ford Head Gaskets
WARN Winch/Trans4mer Mounting System/HID Off Road Lights
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post #5 of 11 (permalink) Old 06-17-2016, 08:07 PM
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Yes there is I just don't have the specs handy. Even though it is a fairly new thermostat it may still may have gone bad.

White 06 F350 Lariet CC 2WD DRW Tow Boss, Timbren SES, Bilsteins, Smiths Ultimate Bedliner, RK Tool Box, CondensorGuard, IntakeMod, S&B Intake, SEIC, Banks 4"TB, Accufab elbow, Edge Attitude CS, Blue Spring Mod, DCPower 185a alternator, Rebuilt FICM, STC and Standpipe update, Harpoon Mod, Coolant Filter, Glove Box Light, Hood Insulator, Rewired Mirror Heat, Seat Heater Indicator.
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post #6 of 11 (permalink) Old 06-19-2016, 02:37 PM
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Originally Posted by ritschner View Post
Yes there is I just don't have the specs handy. Even though it is a fairly new thermostat it may still may have gone bad.
Agreed. Check your thermostat. Sounds like more water then normal is being pushed into the engine: it just means your new thermostat cant handle the heat and is opening more then it should. Your thermostat is located right next to your coolent temp sensor. You'll just have to move your turbo inlet pipe, from your intercooler, out of the way to gain access.
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post #7 of 11 (permalink) Old 06-21-2016, 06:09 PM Thread Starter
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I appreciate the ideas, but I doubt the thermostat would cause the temperature to suddenly drop 20+ degrees. It's got to be electrical or sensor related. The good news is it stopped doing it, so hopefully that will be the end of that-I did check the wiring and maybe the connector was a little loose or needed a "jiggle"??? If it happens again I'm just going to change the sensor.

05' Dark Metalic Stone FX4 Crew Cab
6.0PSD, Automatic
JVC DVDHead Unit, JVC AMP,KickerSpeakers, Sub
Four Wheel Camper (Hawk)
MBRP CAT back exhaust with slash cut tip.
Raceline 17 x 9 Wheels and 33" Toyo MT's
Flashpqaq: Currently on tow performance tune
Dieselsite Coolant Filter, CAT1 ELC Coolant,BPD Radiator
Autometer Phantom Series EGT, Boost, Fuel Pressure Gauges
Diehard Platinum Batteries, ScanGauge2
Upgraded HPOP, BPD EGR Cooler, Blue Spring Mod
ARP Studs / Ford Head Gaskets
WARN Winch/Trans4mer Mounting System/HID Off Road Lights
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post #8 of 11 (permalink) Old 06-22-2016, 11:07 AM
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Get an IR thermometer from Harbor Freight and check the temp of the thermostat housing when the temperature has dropped. It could well be a sensor.

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Ford Remote Start; High idle mod; Timbren load levelers, Scangauge II, Blue Spring upgrade, Quick Start 200 amp large frame alternator, 2 batteries January 2010; GPCM replace October 2011; 2 EGR valves; EGR Cooler replaced 12/30/11; Performance Machine & Mfg. coolant filter added 1/2/12; Rotella T6 5W40 oil; turned rotors, replaced brake pads for 1st time 1/7/12 101K miles; GPCM, both subharnesses and all 8 glowplugs replaced 1/5/13 at 118,000 miles; 2 Ford batteries replaced under battery warranty twice, the latest 9/18/2015; FICM power supply board replaced with Dorman board 11/20/13. Coolant flushed and replaced with Prestone ELC 9/27/14. STC fitting 10/19/14; Dummy Plugs 11/8/14; Turbo rebuilt 11/29/14; cold side CAC tube and boots replaced with metal tube 1/24/15; replaced hot side boots 1/30/16.
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post #9 of 11 (permalink) Old 12-03-2018, 08:35 PM
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Thumbs down trans temp going down not up

hey there i was just wondering if anyone figured out for sure whats happening with my truck. it runs like a champ and we pull our skidster with it every day when i first bought the truck i had 3 s10 blazers to get rid of and towing was great and the trans temp went down not up and i figured it was the new inter-cooler and cooling system that was put in before i bought it. this was the dead of summer and pretty hot and dry, my 2004 ford f250 turbo diesel with the 6.0l in it, most the time it sets the temp where it should be. with that said its snowing here in colorado and everything moves slower so it was alot of coasting and slow speed damn near in idle and the trans temp was way down and my heater wasnt pumping alot of hot heat out into the cab nor was it blowing as much as it should. is this the thermostat? or the trans temp sensor ? any help would be greatly appreciated
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post #10 of 11 (permalink) Old 12-04-2018, 03:46 PM
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These thermostats fail open so It could be that. They are fairly easy to change and pretty cheap.

2006 F250 Lariat Supercrew, ESOF 4x4, 18" tires, FX 4, HD Alt., block heater, Integrated Trailer Brake Controller, Upfitters, power rear window, cab lights - delivered 10/25/05

Ford Remote Start; High idle mod; Timbren load levelers, Scangauge II, Blue Spring upgrade, Quick Start 200 amp large frame alternator, 2 batteries January 2010; GPCM replace October 2011; 2 EGR valves; EGR Cooler replaced 12/30/11; Performance Machine & Mfg. coolant filter added 1/2/12; Rotella T6 5W40 oil; turned rotors, replaced brake pads for 1st time 1/7/12 101K miles; GPCM, both subharnesses and all 8 glowplugs replaced 1/5/13 at 118,000 miles; 2 Ford batteries replaced under battery warranty twice, the latest 9/18/2015; FICM power supply board replaced with Dorman board 11/20/13. Coolant flushed and replaced with Prestone ELC 9/27/14. STC fitting 10/19/14; Dummy Plugs 11/8/14; Turbo rebuilt 11/29/14; cold side CAC tube and boots replaced with metal tube 1/24/15; replaced hot side boots 1/30/16.
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post #11 of 11 (permalink) Old 12-06-2018, 02:24 AM
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Diesels run cold as it is a stuck open thermostat could definitely be the culprit. I ran my 2006 35miles home with a violent coolant leak after a freeze plug popped off, temp never went over 178ish. Got a new freeze plug in and it ran the same as always.
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