After getting my new alternator upgrade in place today, I started up the truck to monitor its response to the new system, and dsicovered something quite disconcerting.

According to AE, my coolant temp started ramping up and hit 480 degF before I noticed. The dash gauge didn't reflect that, and this was within just a couple of minutes after starting the truck which had not been run in two days. It just doesn't seem right to see that kind of temp that fast.

The only thing I can think of is that the stat may be stuck even though it is only about 16 months old. What do you guys think?

Coolant level is completely normal and I haven't lost a drop since tightening my clammps on the Ranger valve back in the early spring.

 

Electrical gremlins. Check the voltage of the coolant sensor circuit and compare it to what the manual calls out.

I suspect that the new alternator is putting out a radio frequency from those three long wires to the rectifier assembly. You have AC current flowing through them. Long wires with AC are broadcast antennas. If you drive the truck, be prepared for other issues, like shifting, if the radio frequency interference affects other systems controlling the PCM.

PMS sometimes has unanticipated problems!

 

My first thought, when I read the title, was a thermo stuck closed too, but there's no way you can reach that high of a temp in just a couple minutes on a completely cold engine.

Absent anything else I can think of, Jock has a good idea about electrical interference.

Hey, just to be sure, you can always remove the stat and run the engine under duplicate conditions and see what AE reads.

Stewart

 

Pete, AE will only show the ECT on handshakers. The PCM on the auto's doesn't read actual coolant temps and for some reason AE picks up some random signal. Mine does the same thing.

 

there is no way a motor would live to see 480 degrees period. LOL Definitely circuit / sensor malfunction.

 

But not on e99 handshakers.

 

It doesn't matter. The ECT PID for the 7.3L is useless anyway no matter whether or not it's an OBS, SD, E99, automatic, or manual.

Disregard the ECT. Your only concern should be the Engine Oil Temperature (EOT).

 

there would be no water...it would have turned in to steam and messed up a lot of stuff

 

Great input, guys. Thanks.

Jock... I had not thought about the "antenna" issue. Is there a way I can wrap the 3 AC wires between the alternator and rectifier to provide enough sheilding to prevent/minimize the interference potential?

Regarding the oil temperature, I pointed that out to my son while we were watching the show on AE, and it had not even gotten above 141 degF while all the ECT values were ramping up. That's why I didn't hit a complete panic, but I also wanted to post the ?? for you guys with more experience.

Also, I know that the only way to get 480 degF in a water-based system is to have steam. I also felt the engine hoses and components after that 5 minutes, and there were no 480 degF hotspots anywhere.

 

Yep, disregard coolant temps. It's just the nature of the PSD that you can't accurately monitor coolant temps through the OBDII port.

 

Should I be concerned about installing some shielding material around those three wires or not? The EMI shielding tapes and sleeves are not cheap.

 

I'd drive it and see if everything works, including the AM band of the radio. If it works normally, don't worry about it.

For a test, wrap tin foil around the wires (being careful not to short to the terminals/posts) and tie the foil to ground.

 

I wouldn't bother. My truck has a stock alternator and does the exact same thing.

 

So far everything seems to be working fine, but I haven;t even thought to try the AM radio band... can't even remember the last time I listened to an AM station! I'll try that on the way home tonight.

Before this upgrade, I had the ECT as part of my DD scan file and it normally ran in the 210-220 degF range, so it was the dramatic increase which had really caught my attention. I knew that the 480 couldn't be right, but didn;t know how to interpret the situation.

Thanks for all the excellent input.

 

Youse haven't been out in Far West Texas at 3AM in a while, has ya'?

AM is about the only thing you'll get for radio.

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