Car runs fine with the a/c off, but when it's on the engine starts to overheat slowly, especially when i come to a stop and am not moving for more than a minute.I replaced the thermostat, don't have anything leaking, so i feel confident that it's not the water pump (right?) I've been out there trying to bleed the radiator in between the thunderstorms all day with no avail. I bleed it, and once the coolant starts to run over the radiator, cap and drive it, only to start overheating again. When i go to bleed it again, there's more air pockets. I happened to look through the grill and noticed that the "heat exchangers" finned tubing ( i call them this because that what they're called on the helicopter i fly on) were caked in mud. I just hosed them off. Do you think that the mud could have caused it to not work properly, or do i need to keep trying to bleed the radiator? do i need to have the reservoir cap on or off when i bleed the radiator? and i've been doing this with the two front wheels on ramps.

98 land rover discovery le
147700
about to drive cross country

 

Its one of 4 things:
1 water pump
2 thermostat
3 fans
4 radiator

I would guess either fans or rad. first take the top fan support off and clean down between the radiator and the other cooler (its the tans cooler i think) mud and crap gets sandwiched between them, then check that your two electric fans kick on when you turn the a/c on, then with the engine off see if the main fan spins freely or if it is stiff turning, it should be stiff. you prbably have a combo of things that the a/c just puts it over the edge. My electrics don't work and when I bought the truck neither did the clutch fan, I didn't know it was bad cause it never overheated til it got drove for 40 min or so then slow or stopped traffic or long slow offroading, anytime it got drove that long was highway and the air flow kept it cool. If you have a good rad and nothing stopping it up and your cluch fan works it should never overheat.

 

I had a similar occurrence twice in heavy traffic, so I cut A/C off to avoid overheating. Spike said it was most likely clutch fan. I have not replaced it yet.

If you had mud caked in the front, most likely it saw some heavy duty muddy off-roading in the past. Mine certainly had before I got it. I took my air compressor turned way up and blew out all the nooks and crannies around the radiator and the other coolers found around there. IU had to replace the serp belt, so while I had it off and shroud removed, I hit hard with about 90-100 psi air. It looked like a Sahara Wind Storm. I have never seen so much dust blow from so many areas. My horns had severe corrosion and mud stains, the blanket under the hood was nasty so I ripped it out. Just spraying it with a water hose did very little compared to the air compressor blow-down.

 

My bet is on the fan clutch, electric fans, or both.

 

I bled it again, and it seems to have gotten better,doesn't overheat at all while driving with the a/c on, and very, very slowly starts to over heat at a stand still with a/c on. I'm gonna bleed it again tomorrow to see if it resolves it completely. but i did notice that the driver side fan never came on while i had it on and a/c running. So are both supposed to come on when the a/c?

 

Yes,both are supposed to run. Mine did exactly that. Only one fan was working. It would overheat, but only with the a/c on and not moving.

 

how fast are these fans supposed to go? the one that is blowing, isn't going too fast, a ceiling fan would be spinning faster than what the passenger side was going.

 

Both electric fans should be spinning very fast, so fast and loud you cant hear yourself think with them running if you stand infront of the truck.
Leave the radiator cap off while bleeding it.
The clutch fan cools the engine.
The electric fans cool the a/c.
If it overheats while driving over 30 or so the radiator is bad.
Under that then its a fan problem.

 

the electric fans should spin fast.

However the fact that the fans aren't spinning shouldn't cause you to overheat.

And the temperature that the gauge shows that your overheating is WAY above a little on the hot side.

 

Same exact thing was happening to me. Would overheat only with the AC on. Replaced the clutch fan and fixed everything. 98 Disco as well.