ill explain whats going on and what i have done to try and resolve issue..

2000 ls2

heater blows hot only when engine is revved up..when at idle cool air comes out when heater is on full.

i have bypassed the electrical heater water motor..
flushed heater core
checked and rechecked coolant levels
bled the system
checked vent doors inside cabin

heater core inlet hose got really hot while the outlet was warm.after a while the outlet did warm up a bit

i squeezed all hoses as well as moved them to release any air bubbles and checked to make sure no damage..

there are no leaks but do recall a leak at 1 point in time.possibly over the summer..this year or last.i dont remember exactly.this was at the heater core on the floorboard..no leaks since then.

heater worked great last winter.

i have not replaced or looked at tstat or the water pump..

car is not over heating at all.

ill mention my ac only work when rpm is up as well and learned the pressure is low (just want to throw this in there as its acting the same as the heater)

i noticed when bleeding system water would not stay and the low coolant light would come on until i filled the coolant reservoir up.

im at a loss and dont want to mess with the tstat or water pump unless i absolutely have to.

any ideas?thank you in advance.

 

I would flush the heater core again. The water pump pushes the water through the system. It is not a pressure pump it works more like a trash pump, any restriction and the water will not flow. The front heater in my daughter's Chrysler T&C acted the same way last winter. I flushed the heater core and the system works great now. It was not very restricted. Flush both ways until there is no restriction.

 

Pressure test your radiator cap. If it's weak or worn out, you won't have enough pressure in the system. No disrespect, Andy. I just think this could be a possibility, since he says he's already flushed the heater core. Did you flush the core in both directions, like Andy suggested? Sometimes a back flush will cure the problem.

 

unfortunately mine doesnt have a radiator cap.its closed and only way to access coolant is through the reservoir..i did flush it both ways..while not the best way of doing it.i poured water into it until it came out then blew into it putting a rag over the hoses in both directions( i live in an apartment and dont have access to a water outlet) i also poured coolant down the hose after connecting the outlet and pouring down inlet to fill it up before connecting and adding coolant to reservoir..

i have a few friends telling me to check tstat but yet the engine does not over heat and hot coolant is getting to the heater core.im wondering if the electric pump really is that necessary..i will say when flushing the core it was hard blowing into it then all of a sudden something felt like it blasted out..but yet its like there is no circulation to it fully..i plan on flushing again just to make sure and check a few things.but may also reconnect pump if it works.i was told there was a bulletin on it and was bypassed a long time ago.

 

The cap on the expansion tank is a pressure cap. I flush heater cores by disconnecting the hoses at the core and using a garden hose flush back and forth until clear water comes out both ways. You may have to disconnect the hoses at the engine, I don't have my LW300 any longer. All I have now are L 200s.

 

thats how i flushed mine except i live in an apartment complex with no water hose hookups so i just poured water down the inlet and outlet hose until i seen it run clean and then blew into it putting a rag over the hoses and then just blowing a couple times each way..its definitely a water flow issue..im going to flush the core again possibly tomorrow after work.any other ideas what could be the problem?or something i can look at while im at it?

 

I think you need more pressure on your flush, just pouring and blowing is not enough volume. The water will take the easiest route and not remove any debris. Did the car overheat last summer? This might indicate a water pump issue causing low flow.

 

thats the only downside..i may speak with a family member about using their water hose but the may not let me due to where they live..the car has never overheated in the couple years i have had it..the heater worked great last year as well.i will say i thought i remember a leak sometimes during the summer.floor was wet by core and smelled like coolant..in fact i never inspected the lines on the inside.that might be something i can do when i flush it again.

 

The heater hoses are in the engine compartment. The core is in the heater box under the dash, only hard pipe there. My cars have quick connects with o-ring seals at the core. I live where they do NOT salt the roads. That may be causing you an issue with corrosion. Good luck.

 

luckily theres isnt any salt on the roads here.i live in Phoenix so we rarely see below freezing temps..i thought of pulling out the heater core and finding a place to connect my hose to. there might be a connection in the back of complex but i would have to remove it..i thought of draining some coolant from radiator just to see how dirty it is..removing the core also lets me look at the vents for any debris or anything.i dont have a cabin filter in the car and i know the owners before me have used one either.during the summer i always took air from outside as some days reached 120 and it was a lot hotter in the car.