flflatsaddict

Have a 2004 F150 with the 5.4, and it's got 205k miles on it. It's been the best truck I've ever owned and problem free since I bought it. I understand that at this high mileage, some issues are expected... No problem, just looking for where to start looking at the root of my problem.

The problem: the truck runs great in town, i.e.: below 70 mph. If I go over 70mph, the temp gage will climb drone it's normal mid way between cold and hot position. It will hover at about 3/4 and then suddenly peg out to hot. The check gages alert will go off. Once pulled over, I'll park it, turn off the ignition and immediately crank it back up. Once running again, the gage returns to the normal half way point. I'm thinking it's either the sending unit or a gage issue being as there is no way it could cool down that quickly! Additionally, it never runs even slightly hot when driving in traffic in the city. Also, the oil pressure never changes as would be expected if it were actually overheating.

Does anyone have any idea what I should start looking at to fix this?
Thanks to all who may help!

flflatsaddict

Nobody has any idea?

F150Torqued

Two important considerations. Your 'oil pressure gauge' on the instrument cluster is NEVER going to budge. It is nothing but an idiot light designed in the form of an analogue gauge. (Fraudulent misrepresentation by Ford). Your PCM has NO analogue transducer reading oil pressure. Only an 'oil pressure switch' that switches at 5 - 7 lbs. The dash gauge will either read ZERO or midway depending on the oil pressure switch being open or closed!


Your truck has NO engine coolant temperature sensor in the coolant system. The computer (PCM) reads Cylinder Head Temperature, and from that calculates engine coolant temperature. The results of that calculation is transmitted on a two wire "bus" to the instrument cluster computer, who outputs an analogue signal to the dash temp gauge.


There's a SX#*t load of places between one end and the other for things to go ary.


I don't think it is overheating. The CHT sensor is a highly developed gizzmo. The PCM goes through a calibration procedure on it each run cycle. The PCM places a lot of reliance upon it. AND, if the PCM thinks your engine is overheating based on the CHT, it will go into the "limp" mode and start shutting off one half of the fuel injectors alternately trying to 'air' cool the engine the best it can. If that happens, you'll definitely notice it.


Fortunately, the PCM outputs the Engine Coolant Temperature that it has calculated on an OBDII PID. By far the best way to sort the issue out is use an OBDII scanner capable of giving live data, and see what coolant temperature is being calculated as indicated on PID # 0105 (TCM). This should give you an idea whether to be looking toward the CHT sensor, or the instrument cluster. It's near impossible to troubleshoot the darned computer controlled systems without more sophisticated test tools.


Good luck

flflatsaddict

Quick update for anyone interested:
The source of the overheating issue was a clogged radiator. There was steam pockets building near the temp sensor and the radiator finally gave out. Gave the cooling system a good flushing and put a new radiator in the truck now it runs like the day it was new..... Ps: it's got 208,000 miles on it.

F150Torqued

Thanks for posting back @flflatsaddict. You have done a valuable service to fellow members and your thread Title is perfect. And yes, I am interested, if only to better my understanding my truck. (These new vehicles are quiet complicated).


I have actually monitored the output from the CHT quiet extensively with the Torque Pro app, logging and graphing the data trying to figure out what it is doing (ACTUALLY stupidly - because for a while I thought the OBDII port (PID) I was watching was from the Charge Motion Control Valve !!!). But I figured out it does a very bizarre "Bell Curve" thing playing games with the upper half and lower half of a binary word, ..... way too technical for here.


But what is important here, and I fault myself a little for not clicking to a symptom you mentioned in your original post:



From the above mentioned research, I observed that within the FIRST minute or so of each OBDII "Run Cycle", the ECU does some sort of "calibration routine" on the CHT to verify it is working properly, since it performs such a critical function in protecting the engine (ie limp mode) - and transmission, whose oil is cooled by the coolant system. PROBLEMS WITH THE CHT CAN EVEN PRODUCE Torque Converter Clutch (TCC) symptoms. I think during this "calibration" time - it must assume, having just started up, water temp is likely going to be fine.

I happened upon A very good article on this whole subject here:
http://www.searchautoparts.com/motor...ure-cht-sensor


Your personal experience along with this might help someone else along the way some day. Thanks for reporting your solution to symptoms.