My 99 ls400 is having a overheating issue that I can't resolve. I have change the coolant temperature sensor that send data to the ecm ,but no luck on the overheating. I notice I have been losing small amount of coolant everytime I check the reservoir . The temperature doesn't actually go all the way to the H , but it does move up to the middle mark. I also notice the gauge moving back and fourth slightly. When the temperature goes up the car loses alot of power and kind of missfire. My LS has 170k miles and I have recently did a tune up. It was overheating before the service.

 

Check your thermostat and cooling fan.

 

The thermostat was change recently , but it was having this problem before the change. Also I notice the main fan supposed to be hard to turn while the engine is hot but it's actually very easy to turn by hand . I'm thinking the fan clutch is slipping .

 

Make sure that between the AC condenser and radiator is clear, I had one with it packed with dirt and sand in there and was surprised it cooled at all. Also a bad water pump and or a radiator that won't flow good can do it too. Any flow restrictions such as bad hoses etc. Also check and make sure the gauge reads correctly. A scan tool that can read real time data will show what the sensor is reporting as the temperature though I think that is from the ecu temp sensor. Make sure no brakes are dragging.

 

Water pump and thermostat was change no more than 20k miles ago . Everything seems normal I'm thinking it's fan clutch but I don't know if that would make a issue with over heating in stop and go traffic . I don't know it's weird that it always comes short I n coolant everytime I check it . It's not smoking or leaking so I don't know what's causing all this .

 

Without informing us all what you have done so far, you can't be advised well.

The stop and go traffic is hard for a car which has a limited capability of the heat dissipation. A slipping fan clutch is one of causes of it too. A clogged radiator may be another reason.

You mentioned that you are losing small amount of coolant and that means a leakage. A leakage causes an insufficient pressure and this is also one of the cause of the overheat.

I suggest you to do the radiator pressure test in addition to the fan clutch slipping test.

 

The radiator drain **** gasket has been one of the problems I have noticed with ours. It lasts about 65K-70K miles. Because this drains directly out the lower drain tube you'll seldom see any leakage in the garage unless the car is left running. That was how I found the leak in ours. I forget the O-ring size, the local home improvement store should have the size too. Lexus will get ~$4.50 for one. The drain **** is nylon and becomes brittle over time. When the thermostat is replaced this part is also changed out.