1997 Disco 173K - problem with overheating at idle solved! Found that previous owner had made a splice near radiator and reversed polarity to the condenser fans.

Truck would do normal temp at highway speed, and at idle if AC was not on. With AC on temp would head toward 230 in ten minutes or so of idling. Had strange pressure readings on AC, at idle the high side would hit 450.

Low cost test - hold a thin strip of paper betwen radiator fan and water pump WITH ENGINE OFF, but key on and AC on, so that electric fans are running. Paper should blow toward engine block. Mine was sucked toward the radiator.

More sophisticated test - used an HVAC anemometer (a propeller attached to a volt meter) and meaured cubic feet per minute readings of air flow behind engine fan. While not calibated to the diameter of the fan cowl opening, I did get basic readings. 1250 at idle on cold start (when viscous fan clutch is fully engaged for a few minutes), dropping to 600 when warmed up. Turned on AC, expecting reading to increase with extra fans, but mine went to 160 cfm. The air flow from the reversed fans was reducing the flow across the water radiator, and to the compressor it looked like the condenser was covered with gunk and had poor air flow. Put polarity right and cfm reading went to about 925.

Made 10 mile test run, then let it idle under the shade tree "garage" with AC on. Center duct temp stayed 44 degrees, and after 15 minutes coolant temp had moved up from 180 to 196 (checked with scanner, not the fudge factor factory gauge). Temp has to rise to somewhere around that to activate the thermal valve on the fan clutch and bring on more air flow.

I noticed that electric fans were a lot noiser when blowing the correct direction, this may be why PO reversed the wiring.

Thanks to all who responded to previous posts on my cooling problems. And it was an air flow problem, just hot air going in the wrong direction (kind of like our elected officials).

 

Glad you got it figured out.
And a great big THANK YOU for reporting the fix.
We get way to many threads of problems with no answers.

 

Thanks, Spike.

In review, I did the following over a period of weeks, and did not drive the truck daily:

Replaced fan clutch with salvaged one
Flushed radiator
Replaced thermostat with 180 from Auto Zone
Replaced salvage fan clutch with new "chevy conversion"
Removed radiator and home soaked with muratic acid (lot of junk came out - could have been PO head gasket goop - which will build up in old partially restricted radiators)
Swapped standard duty 6" "Chevy" fan clutch for "HD" seven inch version
Installed high flow Robert Shaw 180 stat
Installed salvage radiator, only to "discover" that salvage unit oil cooler was blocked
Had radiator shop boil, rod out (and solder up some small leaks) my original radiator
Evac and refill AC with 30 oz of R134a - suspected air in system for high head pressure
Discovered reversed electric fans.

Since I noticed that the truck stays at 180 without Ac or on road, until it warms up to 196 at idle with AC, I guess that the 196 is a function of when the viscous clutch starts to come back to full power. So would I be better off to go back to factory stat, which would keep heat range in a smaller range - say 192 - 198, vs 174 - 198? Seems like a little cooler on highway would be better, most of my travel is 45 - 60 mph secondary roads. I should note that this forum's distinguished senior service manager warned not to tamper with themostats...

 

I have a 195*F t-stat and my truck runs right at 196 on the road once the truck isw fully warmed up.
A/C on or not makes no difference.
Off roading in August 95+ temps driving in deep sand with the a/c on for 5 hours and the temp never gets past 210.
The DI cooling system is a well designed and very efficient system when working properly.
A hotter running engine will get you better mpg.
Personally I would not use the 180 t-stat on a DI because of the larger 3 core radiator.

 

The root cause was pretty goofy. Hopefully there will not be a trend of this sort of problem.

Previous operator DUMBASS.

Glad you figured it out. I would call him up and congratulate him appropriately.

 

That's what's called a SPOT (Stupid Previous Owner Trick). lol

You should be able to tell visually by watching which way the fans are turning as they slow. When the fan is turning the leading edge of each blade should be further from the radiator than the trailing edge.

 

It actually could be a pretty easy mistake to make if you're not careful (at least for a DII, like in my case). A lot of people probably install a fan motor from a Toyota Carolla when the original fan siezes up on a DII. I just did this myself, it's an exact fit, the only problem is you need to splice the LR plug on there. The thing is the Toyota motor has a blue and a black wire. The LR wiring is also blue and black so it seems pretty obvious that the blues connect and the blacks connect when installing, they are the exact same color. The problem is the Toyota fan must have the fan blades on opposite to LR, so it spins the wrong direction. This mod saves you a lot of money, but I wonder how people wire it wrong.