Engine overheated, but didn't ?

[medic]

This mornign it was about -20f. I started my truck as normal, let it idle for a minute and then started down the road - nice and easy.

About 5 miles into the trip I got in the highway. At this point the transmission was warm enough that the TC had locked up.

About 2 miles down the highway, I realized my temp guage had topped out at H and the idiot light came on followed by the CEL. I immediatly pulled off the road and shut the engine off. I poped the hood and everything looked okay. I got back in the truck and turned the key to find the temp guage had dropped back to where it should be. So, I started it back up and continued on my way.

When I got to my destination I pulld the code and got two codes of P1299 - which is a safe guard to prevent the engine for becoming damaged - I think.

Anyway, all seems fine and I don't think my engine ever overheated, but instead I experienced some sort of electrical malfunction.

Any ideas?

BTW, '97 Ford F150 4.6L (w) engine.

 

[kenw]

perhaps the thermostat just got stuck.

Or the cold caused a bad connection at the temp sensor connector. Slamming the hood or something like that "jiggled" the connector enough to get the juice flowing. Pull the connector and clean it and make sure it stays secure.

just slightly educated guesses here.

 

[medic]

I don't really think it was the thermostat. The guage went from overheating (maxed out at the H end) to normal operating temp in less than 2 minutes without running. Even with the ambient temp being -20f, I doubt any engine could cool that quickly without coolant running through it.

edit:

I looked up the code, P1299

quote:

---

P1299 Cylinder Head Overtemperature Protection Active

---

If there was an electrical problem, the computer still thought the engine was overheating, therefore throwing this code.

[ January 28, 2005, 01:24 PM: Message edited by: medic ]

 

[427Z06]

Is your coolant up to snuff? Could it be freezing in the radiator core at highway speeds? On second thought, weak coolant is probably a bad assumption for the typical BITOGer.

 

[brianl703]

An electrical short circuit in the engine coolant temperature sensor circuit or the sensor itself will cause it to read a very high engine temperature. I suspect that contamination of the sensor connector with coolant or road salt/water would do the same.

Suggest inspecting the connector for damage.

 

[The_Jeff]

The thermostat can get sticky and open with the heat soak once coolant stops flowing. Once the thermostat is open the water pump will pull in cold coolant from the radiator REALLY fast.

But, here's hoping it's something electrical.

 

[kenw]

not sure, but changing a t-stat is usually a VERY inexpensive operation. It fixed a strange one on my son's accord this past weekend. FINDING the t-stat was the hardest part, instead of being on the top radiator hose at the "front" of the engine, it's on the lower and buried under the intake.

$15 and 20 minutes and it's not a problem anymore.

 

[Kestas]

Like brian said, try checking the temperature sending unit. Maybe some deposits from the coolant have accumulated around the sending unit or the wires are corroded.

Next time you experience this problem try to see if it gradually goes to the red zone or if it shoots up there. If it shoots up there, it suggests an electrical problem.

 

[punisher]

On most of the 4.6s in 97 there are actually 3 sensors, a gauge sensor, an ECT for the PCM and a CHT (Cylinder head temp sensor. In that year for some reason the CHT sensor also took over some functions of an ECT on some engines/calibrations.

If your dash guage read high, as well as the CHT sensor setting a code as well, you likely overheated, it wasn't just an electrical problem.

On the Coolant crossover (behind alt) there should be two sensors, gauge and ECT (C105 and C104 if you have a book) and on the drivers side head below that crossover there should be the CHT sensor (C179) if you want to check them.

EDIT: Echo what kenw said. T-stats are quick and easy on a 4.6. That would be my first guess in this situation.

 

[The_Jeff]

I have had sticky thermostats that were worse in the cold. Better change yours out, and soon. This will get worse.

Do check the coolant level first in case you got an air bubble in there.

 

[ZR2RANDO]

Were you running the heater at the time? Seems like if the gauge was pegged at hot, and the coolant was really that hot, the hot air coming out of the vents would have been correspondingly hot as well. I think you would have noticed the extreme hot vent air. Did you here any engine pinging/knocking? I'm going with the electrical connection needing cleaning/checking for grounding..looking forward to hearing the answer.

 

[SWS]

I have heard of this before many years ago --> super cold ambient temp combined with driving on the highway can lead the engine to overheat on an otherwise well-maintained car. Pulling over to the side of the road, engine running or not, causes the problem to almost magically go away!

This happened to an old-time mechanic one winter day in his '60s-vintage truck. He said to me that the radiator was being so super-cooled by the low ambient and rush of air at highway speeds that the coolant in the radiator got slushy and would not flow through the rather small radiator tubes. He said it was rather common on certain vehicles in his experience.

Of course check the coolant, thermostat, and water pump belt and let us know if you find anything.

 

[Gary Allan]

quote:

---

Is your coolant up to snuff? Could it be freezing in the radiator core at highway speeds?

---

That was my first thought. I've had this happen when the coolant wasn't quite good enough for the ambient temp. The stuff in the rad was slush. Passed quickly with no apparent ill effect after a brief stop.

 

[medic]

I haven't tested the coolant yet this year, but the entire system was flushed and refilled about 1 year (
The engine wasn't pinging, knocking, etc... The heat from the vents wasn't overly hot or cold, it was normal temp.

I will be checking the coolant for temp within the next couple of days. I will alse check the sensor conections that I can find. I am also hoping we don't see temperatures that low again this year.

I posted this question on a F150 board and got similar responses - either coolant was near freezing or thermostat is bad. One guy asked "You got oil in that thing right?"