I have a 2009 LS460. I can sometimes hear a water flowing sound from the passenger side. Sounds like under or behind the dash. When I accelerate it sounds like the water flow increases. I'm guessing that it is coming from the heater core? Maybe air trapped in there? No water in car or outside. Once the car warms up, the sound gets fainter and disappears. In the morning it is very pronounced. Any ideas on what it is and how to get rid of it? Thanks!

 

Sounds like your condensate drain is clogged. Get under the car and look for a hose that hangs down on the passenger side and push a small piece of wire (36" long) into hose or blow some compressed air into the hose to clear out the gunk that is clogging the hose preventing the condensate to drain. I also suggest changing your cabin filter after you do this.

 

Normal water flowing through heater core noise. Our cars are so quiet that we hear stuff like this that is inaudible on other vehicles. One thing to check - make sure coolant level is up to the mark.

 

This is not a normal sound. We've had several reports of this condition in other threads of our forum. It is caused by air in the engine cooling system. It is very likely your engine coolant is low. It may be due to a leak or a failure to refill after maintenance or failure to properly tighten the coolant reservoir cap. It takes some special attention sometimes to get the air out.

 

My LS made the same noise (like fluid rushing around the dash). Turned out my coolant was just a bit low. Further investigation revealed the cause - a leaky water pump. Anyway, as mentioned, you likely have low coolant. Topping it up should cure your ills, but will likely reveal a bigger problem (like the water pump).

 

If you notice the temperature gauge going up and down, that's dead give-away you have air in the cooling system. Just needs to be bled and topped up. I suspect the blocked AC drain, though.

 

Air is possible. There's a vent plug on top of the radiator where the upper hose connects. When the engine is cool, open it and the add fluid to the rad until the bubbles are no longer coming out of the plug. When fluid come out uninterrupted from the vent, close and tighten it.

 

Thanks for the insight! I'm having this symptom lately on my 2011 (110k mi; coolant changed at 100k) and noticed my heater not working properly at idle this morning. I'll take it in this week and report back, but I'm expecting the same results as RoadFrog...

 

I've noticed this my 13' ls. it sounds like water is being pumped to the engine and sometimes when I accel or idle I hear it moving around. It doesn't seem like the drains or anything, maybe air in the lines, but the temp is pegged in the middle, and doesn't budge. should I take it to someone who knows these cars well? does it even warrant concern?

 

See post 5.

 

I heard a running water noise behind the dashboard of my LS600hL yesterday. Thanks to this thread I just checked the coolant level and it's really low.

 

Now check valley for coolant signs around it and back.

 

Yep, that coolant went somewhere. Radiator leaking is another place to look.

 

Thanks, I’ve only had the car 3 weeks, let me have a few more days thinking it’s a leaking coolant hose or something like that.

 

Topping off the overflow reservoir solved the problem on my end...will monitor closely here on out. We got a snap of really cold weather here in TX the last week+ and I've been running the heat pretty hard. Water sloshing noise is gone and everything in the engine bay/underneath is generally clean/dry, but will keep periodically checking. Thanks CL!