Hello,

I have a well-maintained 2003 with 180,000 miles. Purchased from member Extinct a few years ago, and he has been invaluable in providing advice and consultation. The truck has his in-line thermostat mod.

About three months ago, the truck overheated on me, out of the blue. It seemed to be over-pressurization of the expansion tank, and/or the small return line on the expansion tank leaking at the hose clamp. I had it towed home and investigated the next day. I did discover a small crack in the plastic y-fitting in the lower radiator hose. I replaced the hose, expansion tank, and cap. Truck still overheated (I use an Ultra Gauge set to alarm at 220 and to monitor max temp.). Tried running without a thermostat, and truck would still overheat. Installed a new 180 thermostat. Still overheated.

Did some testing with Extinct and radiator/hose temps seemed to suggest a clogged radiator. Replaced radiator. Still overheated.

Checked coolant for exhaust gas. Negative. No loss of coolant, no milky oil, no white exhaust…

Next up was fan clutch. I replaced with a new heavy duty clutch and new fan blade that I saw others have used. Truck sounds like a semi now, but I’m getting used to it. Truck overheated again.

I took thermostat out and tried running for a bit. All seemed well for 2-3 weeks, until the other day when I was driving home (highway speed). Once again it overheated. Granted, it was 93 degrees here in Virginia, but I got to 245 on Ultra Gauge. I had the AC on, so maybe that was a factor…

Now the odd part, which has been more-or-less a recurring theme with these overheating issues. Generally, after sitting and letting the truck cool down, it behaves with temps between 140-180 degrees (again, without thermostat). I drove it again this morning with no issues.

About the only thing I haven’t replaced is the water pump, but I’ve been told this is extremely unlikely to be the root cause. Haven’t replaced head gaskets either. About all I can think of is head gaskets, cylinder liner slipping, or cracked block, but unless I’m missing something, there are no classic symptoms of any of these. And the intermittent nature of the overheating is really strange.

Any ideas?

DRW

 

Due to the intermittent nature I am going to propose a failing temp sensor.

It is almost impossible for a D2 without a thermostat and a good radiator to overheat. I pulled a D2 home today with my 2000 from the DC area where I saw 99 degrees on the exterior temp sensor. Up and down blue ridge foothills through Charlottesville, AC runnning the entire time. 226 uphills, 212 down the hills, pulling the Disco.

The other possibility is that the new radiator is bad.

The day it hit 245, did you shoot it with an IR gun. I remember the day we were looking at it the IR gun was reading different than the temp sensor. I would recommend carrying an IR gun in the truck to troubleshoot.

Also, you might want to consider the Innovate motorsports MTX-D 3913 dual function temp/oil pressure gauge. The install is very straightforward and does not depend on the ECU sensor.

 

Tim,

It is truly overheating - overflow tank spitting coolant and cap whistling. I didn’t hit it with the IR gun; probably should have but it was obvious the temp was high. I’m almost certain it will overheat again, so I will try to determine if there’s a radiator problem. Not sure how a new radiator could be bad and manifest these symptoms, though.

I’ll look into that gauge!

Thanks,

DRW

 

Well the intermittent nature of it does not suggest radiator. So some days it runs hot and others it doesn't? Does length of drive affect it?

 

Gotta make sure the Efan for the AC works. If not it will certainly overheat when using the HVAC. It should also come on if the D2 is truly overheating in the 210-212F range. If you never have heard the Efan come on with the AC or when overheating check the fuse & relay for it, or put 12v at the actual Efan to see if it works.

 

Some days yes, others no. Mostly no. The other day it was legit 93 degrees and I had AC on. I’m trying to correlate outside temp with other times it’s overheated. I <think> these were high temp days earlier in the spring. I tend to leave climate control in Auto so essentially AC is always on (I think). I’ve had climate control completely off these past few days, and no issues (though it’s cooler outside right now).

Is the electric fan associated with the 40a fuse in the engine compartment?

DRW

 

I am skeptical the AC fan would cause overheating with the clutch and engine fan you have on there now, it is not that much extra airflow and at highway speeds should not have any impact. I run electric fans on my 00 and the fans turn off completely below 195 degres and stay there most of the time on the highway (of course the AC fan is on). The main reason the AC fan turns on with the AC is to make sure there is airflow across the condenser when idling, with a clutch fan it is conceivable the clutch dis-engages and leaves little airflow across the condenser without the AC fan. You can jumper the AC fan at the fuse box to do a test, I forget which one it is but it is labeled clearly.

 

That Efan is also a critical part of the cooling system. If you go past 210-212 it will automatically come on and stay on to help cool the system. If it's not working you are adding extra heat to the radiator from the condenser (on a D2 every degree cooler = helps even if it's just 5 degree's).

Drive around without using the AC at all (ECON Mode disables the AC compressor) and get yourself an OBD2 Bluetooth or Ultra gauge to monitor the temps.

You also need to remove the top plastic cover and verify no debris is between the condenser, AT cooler, and radiator which would also cause you to overheat.

 

I have had the AC off for several days now, with temps fluctuating between 150-170 degrees or so (measured using Ultra Guage). So, there does seem to be a correlation with the AC fan - but haven't checked operation yet.

What is the plastic cover you're referring to? The one over the top of radiator with indentations for the radiator hose?

Thanks!

DRW

 

Haven't checked fan yet but will do so.