97 Disco, 173K, overheats at idle. So far (from previous post) I have changed to 180 degree high flow stat (from Summitt Racing), flushed radiator, had radiator shop soak it and rod it out (which opened up a few tiny leaks that they also fixed), replaced fan clutch multiple times. Borrowed a scanner to read actual temp. First fan clutch was used one, roared on cold start, but with engine warmed up the fan blades would stop when AC turned on. Saw it with my own eyes, felt no air flow, and AC is running, AC fans are running, and radiator fan coasted to a stop. Could hold it stopped with a magazine (don't use fingers). Tried the light duty "Chevy" fan clutch detailed on another post. Installed OK, but still went beyond 227 degrees with AC on at idle. Changed to the "heavy duty" version of the Chevy fan clutch, which is 7 inch diameter. Have to use spacers to mount Rover fan to the clutch.
Ran tests this afternoon and wrote down readings. 84 degrees outside. Coolant would warm up to 174 and stay close to that at idle with no AC on. A 5 mile trip at 50 mph saw the temp go to 178. Return from trip and at idle with no AC temp stayed 183 - 185 - idling for ten minutes.
Turn on AC and temp reaches 219 in 8 minutes of idling. Repeat 5 mile drive and temp dropped to 178-180. Park truck and it goes to 216 in five minutes. Might go higher, certainly on hotter days. Around here we can be at 105 - 108 in the summer with 99% humidity. Before radiator repair it would hit 227 or more, before I chicken out and stop idling.
Idle RPM is 680 - 715. Revved up to 1000 and it cooled back to 207. With AC off, dropped to 207-210 (idling another 15 minutes).
During all this time, the temp guage stayed right on the wavy line of the icon on the guage. From 135 to 227 - same reading! When temp above 212 and engine turned off the AC fans keep running (as it should). At cold start radiator fan pulls enough air (roars) to rotate AC fans. When engine is off and hot, radiator fan feels stiff, does not free wheel.
No coolant loss, no smoke from exhaust.
Would AC refrigerant level greatly change heat in condenser that is blown back to water radiator? What about if air is in the A/C system (high head pressure)? What is the normal temp range for a Disco in good condition? Is RPM supposed to bump up when AC is on (some cars do that to increase cooling)? Should I go back to the 190 stat? Should I go back to the standard duty fan clutch? Ac stops being "cold" at idle after about 3 minutes - is this related?

 

Could be that your ac condenser isn't flowing air very well. Then when it heats up with the ac running, the reduced air flow, plus extra heat cause it to over heat at idle. How do the condenser fins look? Perhaps try washing it if it looks ok.

 

I think he hit the nail on the head.
I have a 195*F t-stat and my truck runs right at 196* while driving a/c on or not.
At idle it runs around 200-210*F depending on traffic or off roading.

 

Hooked up the gauges - when compressor cycles, high side pressure hits 400 - 425. Low side fairly normal. Temperature of lines in/out of drier within 5 degrees, so blockage is not suspect. Previous owner may have installed mutiple cans of "freon fix" without gauges. Could have air in system. While driving AC provides cold air. At idle it quits being cold in 3 or 4 minutes. O rings must be OK to stand that many PSI.... Both AC radiator and big radiator fins washed out from both directions previously.

Will recover refrigerant and vac down tomorrow, and refill.

All the other things needed to be done anyway (radiator had crud you could see on tubes when you peek through the bung hole), fan clutch had lost some (or most) silicone, thermostat was OEM 14 years old. I will check gas milage after AC repairs to see if the heavy duty fan clutch (Hayden-Imperial #2744 - Advance Auto Parts 215107) reduces mpg, if so, will go back to the "standard duty" model.

In comparison, I have a KIA minivan with 175K, V-6 3.8 liter, and it will sit at 178 degrees idle with AC on for hours. Electric fans, and a radiator much smaller than the 4 row unit in the Disco.

 

Darn those KIA's. A technological wonder, makes you mad huh.

 

Remove the entire AC system from the ZRover and throw it away and you won't have to worry with it again. Roll down the windows and open the sunroofs all the way. Mount large air circulators inside the rear. Place a block of ice in front of the blowers.

Replace ice block as neeed. Insulate the interior of the Rover. Problem solved.

 

400 is pretty high on the high side. How hot and humid is it where you are? That could be restricted or reduced air flow. It could also be overcharged, but you'd expect slightly higher low side pressures too. It could be overcharged AND have a SLIGHT restriction in the refrigerant flow, that would cause high high side and not so high low side. Too much oil can cause the pressures to get all funny too.

 

Per the RAVE, I'm going to replace the drier as well. When I made the readings last night it was in the 70's here. With this problem going on and on, I have removed and replaced radiator several times, which gave me space to back flush the fins of the condenser. Also made a special tool for doing that without removal - a long thin plastic pipe with holes in the side, just pull out the rubber top gasket strip and wash both sets of fins. I guess that it is not water pump, as no problems with vehicle under speed, or without AC. Each item replaced has made incremental improvement, but we will see what the AC vac & fill does for us. It is an education to see the difference between the digital temp reading and the POS factory guage. I suppose it may have been designed to give a normal reading under a wide variety of conditions, so as to not overwork service managers.

 

Replaced drier. Vac down to -30, it held for 10 minutes, then ran vac pump another hour. Installed most of three 12 oz cans of R134a. No rear air. Purged supply hose from gauges at each can swap. Did a coil wash with foaming commercial HVAC cleaner and garden hose. Looks clean when checked with bright light from between radiator and condenser.

Cools to 40-42 F at center vent, at 1500 rpm 35 PSI low, 275 PSI high. Engine coolant 185, ambient 75. Take a 5 mile test run, coolant drops to 178.

Back at the shade tree, idle for 5 minutes and AC blows warm. High side 400 - 425, some cycling. Coolant temp rises, after 10 minutes idle it is 221. Turn off AC and it returns to 175-178 slowly.

Removed blower and cleaned out a handful of leaves. No change, other than a little more air flow.

So would this be O rings (cheap fix, but should there be a significant freon loss)?

Or compressor (too weak for ide cooling, OK at speed) - but where is that 400 PSI coming from?

Or expansion valve? But why does it work at 1500 RPM? Compressor is easier to get to....

Or air in system because I goofed?

 

That's hard to say. It still sounds like an air flow problem.... too high of temps at the condenser will cause high head pressure. Any chance the electric fans are weak? Or maybe the engine getting hot is what is causing the high head pressure, and not the other way around... Also, too much oil in the system will cause high pressures. Maybe the previous owner recharged with leak stop or cans with oil. An expansion valve sticking closed or plugged up will cause high head pressure, but usually has low suction side pressure too.