D1 overheat around town
Rock Crawling
Joined: Jul 2012
Posts: 464
Likes: 5
From: Warren PA
I'm having the same problem. Runs low notmal for about 20 minutes and then the temp shoots right up to the normal high on the temp guage. Turning the AC off helps right away. I did notice the electric fans turn on with the AC, but they shut off after about 20 minutes too resulting in what I believe to be the issue. If I turn the AC off & drive it for a bit, the fans turn back on & stay on after I shut the Disco off for about 3 minutes. Can that relay be getting hot & turning the fans off?
Super Moderator
Joined: Jan 2011
Posts: 16,322
Likes: 88
From: Savannah Georgia
Electric fans should run as long as the AC is on. Fan motors could be starting to sieze up, or you could have fried wiring or relay. The fans turn on with AC off when coolant hits 212 F (like they are supposed to) and continue after truck turned off to cool under hood temp.
Looking at the wiring diagram, you can see that the ECM is "between" the relay coil and the second page. The ECU can apply a groud at that point "internally" and turn on the fan relay. That much works.
Following the Purple Black wire (PB) to the second page and you will see that it makes its way down thru the Off-1-2-3-4 switch for the AC fan. That fan switch is prone to gunk, you may be able to wiggle it and get fans to come on. You can take off some of the plastic dash parts and actually see the brass contacts mounted vertically behind the selector, squirt good with contact cleaner. Not MAF cleaner, which will discolor plastic on dash (trust me, I'm a Shade Tree Mechanic Second Class).
So from you description, the ECU can put a ground in place and make the relay turn on the fan, but the AC fan switch contact is dirty and has a mind of its own. The ECU grounds lots of things, like injectors, etc.
Now back to your temp readings. Above 1/2 scale is very suspect. If you can get a plug in scanner or Ultra Gauge you can see the temp in digital fashion. Driving along a level road at 55 mph should not be making 220F, or even 212F. There are lots of things you can check, look at that cooling problems link in my signature. Driving slow with AC on and no electric fans will make temp too hot. But there are others. Once you get cooling system back in shape you might consider a 180F thermostat.
Looking at the wiring diagram, you can see that the ECM is "between" the relay coil and the second page. The ECU can apply a groud at that point "internally" and turn on the fan relay. That much works.
Following the Purple Black wire (PB) to the second page and you will see that it makes its way down thru the Off-1-2-3-4 switch for the AC fan. That fan switch is prone to gunk, you may be able to wiggle it and get fans to come on. You can take off some of the plastic dash parts and actually see the brass contacts mounted vertically behind the selector, squirt good with contact cleaner. Not MAF cleaner, which will discolor plastic on dash (trust me, I'm a Shade Tree Mechanic Second Class).
So from you description, the ECU can put a ground in place and make the relay turn on the fan, but the AC fan switch contact is dirty and has a mind of its own. The ECU grounds lots of things, like injectors, etc.
Now back to your temp readings. Above 1/2 scale is very suspect. If you can get a plug in scanner or Ultra Gauge you can see the temp in digital fashion. Driving along a level road at 55 mph should not be making 220F, or even 212F. There are lots of things you can check, look at that cooling problems link in my signature. Driving slow with AC on and no electric fans will make temp too hot. But there are others. Once you get cooling system back in shape you might consider a 180F thermostat.
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