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I have a 99' F350 CC DRW 4x4 long bed gas V10 Lariat. I am experiencing my issue only when pulling the heavier of my two horse trailers. I have established the towing capacity through help from folks on the Towing Forum to be 13,200#. My issue is this...my thermostat gauge wants to fluctuate while pulling this 3 horse GN trailer, between normal to as high as into the "red zone". The first time it did this, I was pulling approx. 9000# on a 90+ degree day. It didn't overheat or malfunction and I made it home and took it to the mechanic who replaced the thermostat. Two weeks later, I am towing approx. 11,000# on an equally hot day and look down to see the gauges doing what can be seen in the attached image. It did not smell "hot" or like it was burning. Took it to my mechanic again but he could not get it to act up or even rise slightly. He suggested possibly a bad cluster but the only way to determine was to remove the dash cluster and "send it off" to have it tested. Hugely inconvenient for me. I towed the same trailer again last night with two horses and towing weight was approx. 8500# and the temp gauge fluctuated again...not into the red zone and the oil light didn't come on so I am lost.
When I tow, I always tow with the overdrive turned OFF if I'm going to be city driving or climbing hills. Can someone also provide insight about towing and RPMs...with the OD off, my RPMs stay around 3000 at 60mph...could this be causing excessive heat buildup? The truck only has 160k miles on it.
Any and all advice/input/help would be greatly appreciated.
I'd get a scanner that can read live data first and see the actual temperature's you're getting so you can troubleshoot. The stock temperature gauge is a "dummy" gauge. Once the engine reaches operating temp it doesn't move until the temp exceeds a fixed number. Not sure what it would be on a V10, but on my 6.0 diesel it read "middle" at 185 and doesn't start moving again until ~225 ECT.
Simplest method for a scanner is get an OBD-Wifi adapter (~$30), connect to your phone and download one of the apps ($5) and you're off to the races. There are other more expensive options like a Scangauge or Edge CTS but the cost is much higher.
Is your radiator fan screaming at when the temp gauge spikes? If not, it should be and it may indicate a bad fan clutch. My 6.0 fan sounds like a jet engine when it engages full speed.
I have a 99' F350 CC DRW 4x4 long bed gas V10 Lariat. I am experiencing my issue only when pulling the heavier of my two horse trailers. I have established the towing capacity through help from folks on the Towing Forum to be 13,200#. My issue is this...my thermostat gauge wants to fluctuate .... The truck only has 160k miles on it. ....
An OBD port monitor (i.e. ScanGauge or equivalent) can display what the computer sees for the coolant temp.
I have a ScanGauge mounted on the dash to display numbers, not a needle pointing somewhere.
I think the dash engine coolant temp gauge is still a "real" gauge that varies with temp, my 2002 trans temp gauge is definitely a 3 position display (not a real gauge).
Maybe the engine coolant temp sensor or the signal from the computer to the gauge panel is not working properly.
Also, you could try using an infrared thermometer to take readings of a spot next to the sensor on the crossover tube.
I have a laser pointer temperature gauge, like people point at you to check if you have a temperature at the doctors or dentists office since the covid. You could check your radiator to see if it is cooling right, you could test by turning on your heater and see if the temperature goes down. I had a v8 ford car years ago that had a slightly plugged radiator, did not overheat bad, and during hot days in summer the temperature gauge would go up. I turned on the heater, and the heat went down. Had a new core put in the radiator, solved that problem.
fan clutch, stopped up radiator, thermostat......all good points to start. my 99 v10 would spike the temp gauge, and ping when towing heavy at highway speeds. it was a clogged up cat. i went thru all the above also, finally gutted my cat, and ive been golden for 3 years now. you could always just separate the pipe at the cat, and load up and run it to see what happens. just gonna be loud and obnoxious
oh, and running the OD off did make it worse for me
Yeah I like the infrared thermometers. You can get them cheap online or at Home Depot/Lowes. Drive the truck around normally for a bit and measure the top of the radiator and the bottom of the radiator. Also point under the intake to the cylinder head areas and take note the temperatures. Top of radiator hose vs bottom radiator hose should be at least 10F hotter (maybe more, see if you can find the acceptable temp difference online). Cylinder head temperature should be 180-200. If there is a very small difference at the upper/lower radiator, you could probably blame the overheating on the radiator.
Does the overheat happen during speed, or stop and go driving? If stop and go driving, I'd verify that the fan clutch is working properly. Ensure when you start the engine in the morning that it roars up.
Overheating Issue
