I've got 2001 excursion 5.4 4x4 with a ton of miles but still runs perfect until the temp gauge just pegs randomly. First happened to me the other day on my way to work, which is only a 10 minute drive. Got to work early and shut it off without any trouble. I should also mention that before the gauge pegging I'd been fighting a hard warm start issue. Vehicle would start cold no problem but once warm like this day, I would have to let it crank alot longer before it would start but then ran smooth and acted fine. Until this day, after I got to work no prob then decided to run to Subway and grab lunch since I was early. So I restart which cranked longer than a cold start as usual but then ran fine until i got to Subway. The temp gauge pegged and dinged but still ran fine for about 10 seconds and then seemed like it was only running on like 2 cylinders! So I limped it into a parking spot and figured I'd deal with it after I got my food. I pretty much thought it was all related to the hard warm start issue but when I came back out 10 minutes later it started easy just like it does when it's cold first thing in the morning and to my surprise the gauge was back to normal and it ran perfect again until a couple days later. I hop in start it up, real easy cause it's cold after sitting all day at work. I only get about 30 seconds down the road and the gauge pegs again and kills most of the cylinders again. So I let it sit probably 10 minutes but keep turning the key on and off the whole the time until all of sudden the gauge goes back to normal and then I drive it home. I even unhooked both temp gauge electrical plugs but the temp gauge remained pegged until it just went back to normal. I figured the gauge would drop to zero if I unhooked it but still worked as normal as it could in this weird scenario. So anyway, I make it home with the gauge in the middle like normal most of the way. Right before I get home it pegs again but I'm able to limp it the last block. So of course I search all through the forums for a similar problem and fix. I find a few similar threads and try what I find but most don't have definitive answers. So far I've replaced both the coolant temp sensor in the crossover tube and the cht sensor in the head but no change. Still pegs the gauge after a while now but runs perfect again after waiting a couple mins. I'm pretty sure I'm losing coolant at this point but the gauge pegs now before I can run it long enough to tell if the coolant level is going down. My next step is to do a compression check but I'm also really thrown on how unhooking both sensors has no affect the temp gauge in the dash. How can this be?

 

replace the thermostat.

Not sure why your gauges were working with the sensors unplugged, but I'm a little puzzled how you would have unhooked the head temp sensor with the alternator in place.

 

There is an extension. Is it possible there is another cht on the other passenger side head, I thought I read that in another thread?

 

 

I agree with 96firephoenix, there is some issue with your cooling system. In addition to the t-stat, replacement of the pressure cap is likely a good idea as well. Of course, checking for any external coolant leaks is a good start.

The taurus I have as a DD had blown head gaskets when i bought it. After replacing the head gaskets and water pump and flushing out all the stop leak the prior owner added (grrr), I noticed the electric cooling fans werent kicking on. No check light, but I eventually traced the issue to a failed engine coolant sensor. It was stuck cold and wasnt giving the proper signal to the ECU. The taurus has 2, one for the gauges and one for the actual ECU/cooling fans. You could have a similar issue given the hot restart issues. I admit, Im unsure how Ford has these Excursions/ Super Duties wired up, so it could be different.

 

Motorcraft Thermostat and draining the coolant from the radiator would be where I start.

 

The temp gauge attitude sounds like an electrical problem. On my diesel I would often get the loping idle at cold start up after I bought it. I replaced a couple sensors, which helped, but it was not fixed. In short what I found after digging around, were several pigtail connectors needed to be replaced. Many of them had exposed wiring at the plastic plug, or just within the split loom. One sensor plug had already been replaced, but was only butt connected, which was not a stable connection. I redid all my engine connectors throughout making sure to solder and shrink tube all connections. Since then, my cold starts are perfect.

 

Ok, so I found another plug at the rear of the passenger head and unplugged and boom with the other two sensors unplugged it finally killed the temp gauge in the dash. I cant be positive its another cht for the passenger but it makes sense to me. It also keeps the gauge from pegging and was running great until it actually warmed up. As I stated earlier the gauge would peg instantly, so there was no way it could be hot or over heating. So now im back to where I started before I had this temp gauge pegging issue. I traded this vehicle a while back and drove it home without issue about 70 miles. First 10 miles was stop and go through the city and then the rest was highway home. When I got back almost home it almost killed on me at a stop but I was able to 2 foot the gas and brake to get it the rest of the way. So the next day I went to the junkyard and grabbed a maf sensor and tps sensor but couldnt find a iac. So I bought a new one. When I went to replace the maf sensor I realized the rubber grommet around the wiring to the maf sensor was just dangling, so I put it back in place and seemed to fix the almost killing and stalling issue until all of a sudden I had this new temp gauge pegging issue. So now I since this new temp gauge issue, I have replaced the coolant sensor and the driver side cht sensor as well as thermostat and coolant and threw on the maf sensor I got from the junkyard and tps. I even bought a new iac valve. So currently with all that, the temp gauge is not pegging anymore and runs great for probably 20 minutes until its all warmed up then wants to kill or stall at a stop and eventually does shut off. I can get it started after cranking for a while and holding the throttle open but have to keep the rpms way up but eventually dies and smells totally flooded. If I wait till its all completely cooled down again, it will start right away but idle a little erratic at first and then calm down and drive fine again until it warm. So I should probably start a new thread on what I believe to be the fuel pump is going out? I am going to replace the fuel pump this weekend and go from there. Thanks for all the replies thus far!

 

I did replace the fuel pump and it's been running great ever since! So apparently there is another cht sensor on the passenger side and it has failed. It seems I was battling 2 different problems at once but all is working great now, with just the passenger side cht disconnected and new fuel pump.