Calliope

I have a 1997 LS400 with a strange problem I can't seem to find a solution to. When accelerating the car heater works just fine. When at a stoplight, it quickly cools down and the fan speeds up.

The temperature gauge stays at the second marker up from cold perfectly.

I've checked the coolant level (which is consistently at normal levels), the thermostat (which tested fine out of the car), replaced the coolant temperature sensor (the old one must have been from the factory because the green plastic connector pretty much crumbled in my hand and the sensor tip was black as coal), and hooked a OBD2 scan tool up to it ( not one code and live data didn't show a change In coolant temperature when idling). Everything appears normal.

Any ideas what what I should try next?

dicer

Run the heater diagnostics.

Losiracer2

Did you start the car and open the fill valve directly behind the thermostat to see if it's not low? I had the same issue with my 97 and I had to add about a quart of coolant in to top off the system.

Also what is the condition of your radiator cap? Is it correctly pressurizing the system?

AandSC

My heat wasn't fully functional until I flushed my coolant system. Makes me think I had some sort of blockage in the system. Has worked perfect since then.