For the past year 9 months I have been trying to decide if I have a possible tranny problem coming on or bad readings from my scan gauge. towing my 6,500lb TT, I will get readings in the 190-200 degree range while towing fairly flat terrain in MN. Even unloaded I am getting reading in the 170's with my scan gauge. These temps appear to be higher than most others.

This winter while towing a 2 place snowmobile trailer on a 225 mile trip, I was hitting 185-190 on my scan gauge.

What makes me think I may be getting a bad reading or have a bad temp sesnor are the temps I get at start up. My coolant temp and tranny temp never align at start up. Even when the vehicle has sat for a two week period of time, my scan gauge always shows my tranny temp to be a minimum of 4 degrees cooler than the coolant temp and sometimes it can be off 8-10 degrees.

I have also noticed my console gauge will read different than scan gauge. At times, the dash gauge will get into the "normal" range at 84 degrees scan guage, other times not until my scan gauge hit 115-123.

On a trip this winter pulling a 8,000-10,000 lb load with outside temps in the 40's, my scan gauge was reading 228 degrees. My dash gauge never moved. From my understanding, the dash gauge should start to move when the trany temps hit 220.

Do the scan gauge and dash gauge use the same temp sensor?

How many of you get the same coolant and tranny temps at start up?

With TT season just around the corner, I want to get this diagnosed.

Any ideas on where to start?

I did replace tranny fluid 5,000 miles ago with mobil 1 synthetic. This does ont appear to have lowered my temps.

 

I have a scangauge and a ISOPRO gauge with a sender in the test port - the standard thing most people add when they add gauges.

They both read almost exactly (1 - 2 deg) the same. I added an aux tranny cooler a couple of years ago, so my normal driving temps are around 140-150, and towing around 170-190 (flat - hill). Before the aux cooler, they were about 20+ higher than that.

Sound like your scangauge is reading correctly to me, and sound like you should consider an aux cooler.

 

That's not unusual.

Yes, they use the same sensor.

 

I was just going to start a new thread but it's on this same subject. I, too, just got my scangauge. I'm getting the same type numbers as the OP.

My question is:

At what temperature to things start to explode? At what temp should I actually pull over and let it cool down?

Just curious but I will be buying the six-oh cooler here very soon.

 

Never really compared the startup temps so you caught my interest. I just went out to the driveway and started the EX to check. I haven't been able to get the water temp to work after installing the SC in my new 2003 7.3PSD so I compared engine oil temp with trans temp. Here's what I just got:

Exterior air temp: 60.6
Engine oil temp: 45.6
Trans temp: 56.0

Just driving around I usually average somewhere around 170 TFT; when towing my rockcrawling jeep with my 16' trailer I am usually in the 190's to as high as 202 or so when I push it. I don't think it has ever been higher than 202 maybe 204. I have been told that you should be concerned if it goes over 220?

 

Somewhere above 400°F. That's not a typo, I said somewhere above four hundred Fahrenheit.

You can go up to 220°F all day long. You can go up to 250°F for no more than a half hour. If you get over 220°F, that would be a good time to put it in park or neutral and idle or fast idle until it cools down.

 

Our GPS sent us on a 'shortcut' yesterday. We wound up towing the 6,500 lb truck & trailer up and over Mt. Greylock (3500') on the narrow, winding, roller coaster access road.

I thought to check the trans temp and just when I saw 225 it started smoking. I eased off, pulled over ASAP (1/4 mi ?) and let it idle to cool off. There was no fluid trail or drip, so I chalked it up to fluid expansion vented out due to the sharp up/down hills.

Once cooled off, trans temps stayed mostly below 200. We stopped and let it cool at 205 a couple of times.

What a relief to see hard, factual info here "You can go up to 220°F all day long."

I bought some Mercon last night, will check to see if it's needed after breakfast.

 

I have been told that Scan Gauge people said water temp is unreadable on the 7.3L, It sure does not work on my 7.3L, shows -40F all the time.

 

I contacted the ScanGauge folks and was told the same thing; they say they do not have a code for the water temp?? Seems hard to believe that the OBD system would not monitor the coolant temp??

Also would be nice to have a read on the oil pressure.