Large Coolant Leak under the Vehicle - No wet carpet

[kawrtknee]

Hi guys, I have a 2009 XC90 with 120,000 miles. I have a significant coolant leak that I believe is related to the heater core. Problem is that the leak is only showing under the vehicle directly under the rear passenger seats on both left and right side, but the left side is much more significant that the right. It looks to me like the leak is running as far back as possible and the exit just so happens to be under the rear passenger seats. My carpet is not wet anywhere!! Although, my heater is not as warm and the smell is very strong when turned on. The inside of my windshield has a thin layer of fog as well. I have had to fill my coolant up a few times, I only use 50/50 solution and watch it carefully as well as avoid turning on the heater. Everything seems to be pointing to my heater core but my carpet isn't wet. Any other ideas? I don't want to go through replacing the heater core until I know without a doubt that's the problem. Anything helps, thanks!!

[SuperHerman]

Your symptoms are heater core in nature. I pulled up the parts diagram but couldn't tell if your XC90 has a rear heater core - mine doesn't but maybe a dual zone does. Hopefully some one will chime in.

That aside, the best approach is to get some coolant dye and put it in the system. Drive around a bit and then take a look at the heater core (or cores if you have two). There are write ups and videos on changing out the heater core, but for diagnosis purposes all you need is which few screws and panels need to be removed. With the UV light you will know right away if you have a leak. Your other option is to skip the dye and just look (taking off the needed parts) and feel for wetness and/or signs of coolant. If inconclusive then try the dye. You can also check the engine compartment and heater hoses with the dye and light.

As to why your carpet isn't wet, maybe the coolant drains before the coolant can fully saturate the carpet, but it sounds like you are also missing a grommet as if coolant leaks out - water can leak in. The dye and light will tell you this also - if you need a grommet you will know.

[kawrtknee]

Thank you for the advise! My model does not have a dual zones. Originally I thought the same thing but there isn’t a separate set of controls for the rear heating/cooling. I will definitely attempt putting the dye in and start from there. Hopefully I will have a more concert answer and solution to this problem with the help of the dye.

[oragex]

I'm not saying the leak goes under the carpet, but be aware that no matter what is leaking, if it goes under the carpet, the top of the carpet will be dry on these cars because these have a rubber layer that can keep the top dry while there's full of water/coolant underneath. The only way to see if there's liquid under the carpet is to lift a corner and slide a head underneath.

[kawrtknee]

I am aware that their is a protective layer under the carpet in this car but I lifted the carpet up and couldn't see or feel any liquid.

[ggleavitt]

Rear is AC, refrigerant only. Coolant path does not extend past the heater core in the console, at least that I can see.

Not sure what engine this car has, can see a diagram of the coolant paths with the 3.2 I6 and the V8 (heater core is #4 in the diagram)

Cooling System XC90_B6324S.JPG (41.64 KiB) Viewed 2926 times

Cooling System XC90_B8444S.JPG (59.44 KiB) Viewed 2925 times

edit 121218- add V8 diagram

[ggleavitt]

Legend for the V8:
1-Cylinder block
2-Right cylinder head
3-Electric coolant pump
4-Heat exchanger (passenger compartment)
5-Preheating crankcase ventilation
6-Throttle body
7-Upper cooling hose
8-Bypass pipe
9-To cylinder head
10-Radiator
11-Oil cooler
12-Lower cooling hose
13-Thermostat housing
14-Coolant pump
15-Left cylinder head
16-Expansion tank with level sensor
17-Air bleed circuit

[SuperHerman]

Good info on coolant routing. Based on this info the coolant is traveling internally or externally before landing on the floor in middle of the car. If internal I still think you have a grommet missing as it shouldn't be draining. It sounds internal b/c of the other symptoms you point out.

Hose it all down well if you can and then put the dye in. The leak source is most likely near the fire wall. ggleavitt's post of sources brings up many other causes, but based on your internal observations I would stick with the heater core related items to start. Either way the dye and said check list makes finding the leak fairly straight forward (only a few tricky ones).