i have an 03 disco. when i run either the AC or heat it leaks coolant and over heats. I haven't run either the last two weeks and its fine. someone told me i need a new temp thermostat. Any help or advice would be greatly appreciated.

 

Where is it leaking from?

 

I would think that you are just about ready to overheat anyway from low coolant, and the slight extra load from AC pushes you over. Coolant is always running thru the heater core, no on/off valve. You need to resolve the leak, even if you rent/borrow a coolant pressure tester from a parts store. Be sure coolant is normal level at every cold start until you resolve. The motor does not like to be overheated and it can blow head gasket or worse.

 

i haven't lost any coolant in two weeks of not running AC or heat. it's hard to see where the leak is coming from but i can hear coolant sizzle on the manifold after i shut the car off

 

I can't get a grip on coolant loss only when running heat or AC, as there are no diversion valves. The coolant runs in the heater core all the time, dampers block or allow air to pass over the core. Here is a plumbing map, perhaps looking at all the possible connections, like the throttle body heater plate (has a gasket also that leaks). Could be external head gasket leak. Could also be valley pan gasket, the four corners are coolant channels. # 16 in exploded view attached. There have been reports of bolts found finger tight at the rear. And the front engine cover gasket and water pump gasket.

 

I have a 01 range rover & recently I have been hearing like a hissing noise coming from the rear driver's side. When I get out&cut the truck off can somebody please help I have no clue what's going on & this is the first time I have heard this. My truck has been sitting for a couple weeks don't know if that has anything to do wit it or not?????

 

If you don't do a coolant pressure test you will not find your leak, if you don't do it, chances are you will have a coolant failure and toast your engine , so do it.

 

Pepelapoo2 - I'll bet your problem is not cooling system related, but could have to do with the air suspension components, like a leaking fitting or bag. Air leaks can be hard to find, sometmes you have to squirt soapy water from a spray bottle on suspect areas and watch for bubbles to form (just like old school tire repair).