overheating when AC on

[yosi]

I have a 95 Discovery.
When I drive it when it is over 90 F outside my engin temp does not go over the middle gage, but when I turn the AC on it goes all the way up to the red line and I have to stop the car and let it cool down.
I was told by a friend that it was probably the thermostat.
I have enough water in my tank and I don't see any leaks.
If it is the thermostat, can I replace it my self or I need to take it somewhere?
Thanks for your reaply,
Yosi

[Hank]

I would take a temp reading of the coolent just to make sure the gauge is not messed up. Search Dweb. Someone over there had the same issue about a week ago.

Are your A/C fan coming on when the A/C is on? That may make a little difference, but not that much....

I'm betting a bad sensor, or something is grounding the sensor when the switch is cut on....

[Black Magic]

I am having the same issue, except my gauge reads WAY low - I have a new sensor and thermostat that is going in this weekend. With the A/C on the gauge goes to slightly below 1/2 way - and some engine coolant leaks out so I am sure its boiling.

Its possible that the radiator is partially clogged needing a flush.

My fan viscous coupling/fan clutch is about shot as well, it is easy to stop the fan when the engine is running. About to change to 2 x 14" electric fans.

[Black Magic]

Replaced gauge temperature sensor - gauge now sits in the normal range!

Replaced the thermostat - the temperature does not fluctuate like before.
The old thermostat was partially open (closer to being closed than open) and the moving parts were off centre. Seems this was restricting flow and leading to an overheating condition at low speeds with the AC on - I have not yet driven enough to say the problem is fixed for sure but its looking good.

The electric fans are still going on there as the viscous coupling is $200 (Not inc shipping or tax), and the two 14" electric fans with a variable thermostat cost $214. Will have to fabricate a nice shroud for them but its still a better solution.

Changing the thermostat is easy - remember to get a new gasket as well.

• Take top radiator hose off (Coolant will leak onto the ground if the system was not drained)
• Lift the distributor cap (Makes it easier to get to the bolts and thermostat housing)
• Unplug the sensor in the thermostat housing
• Remove the two bolts in the housing
• Lift the housing out
• Take note of the thermostat orientation, and remove it
• Clean up the gasket faces etc
• Place the thermostat in - with the little plastic bead valve at the 12:00 position
• Place the new gasket on the housing and bolts
• Reinstall in the reverse order