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Mystery slow coolant loss

5K views 10 replies 6 participants last post by  cinergi 
#1 ·
Hello All,

I have a slow coolant loss on my 3.2 that I can't pinpoint. The coolant level goes from the MAX to MIN fill lines on the expansion tank in approximately 6-7 weeks and triggers the low-coolant warning, so it is a very slow loss. I've performed the following steps:

1) Replaced the radiator, which was leaking (confirmed visually). I thought this was the cause of the coolant loss, but it's still losing some.

2) Visual inspection of all cooling hoses, radiator and expansion tank with engine running after a long drive. No leaks seen. System is holding pressure, as removing the coolant tank cap results in a release of pressure (as would be expected).

3) Performed a test to determine whether combustion gases are present in the coolant, which would point to a blown head gasket. This is a chemical test involving a tool that sucks air from the expansion tank through a blue solution that turns yellow if combustion gases are present. The test was negative.

4) Oil looks clean with no milky residue on the oil cap nor dipstick (which would indicate coolant in the oil).

5) No smoke through exhaust.

6) Interior carpets are dry (wet carpets would indicate a leaking heater core).

7) Engine runs perfectly.

At this point I don't know what to do next! Any suggestions? I can certainly live with it and add coolant every 6-7 weeks, but it's bugging me :confused:.

Thanks
cinergi
 
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#2 ·
I haven’t experienced that level of loss but I also have a very slow coolant loss on my 3.2. Never had the low warning, but I probably lost about half of my coolant from min to max.


2010 xc90 3.2 | 2017 Prius V Five
 
#3 ·
Have you done a UV or blacklight inspection? Sometimes that's the only way to track the coolant loss.

Have you also checked the thermostat area, the rear left side where the water pump is at, and the lower hoses that run under the intake manifold? Any coolant sweet smell outside or inside the vehicle?

What's the maintenance history? The water pump, hoses, thermostat, all done? What's your mileage or kilometers?
 
#7 ·
I've checked everything I can from the top of the engine without disassembling anything. This does not give a 100% full view of everything, but it's the best I can do without digging into it further. No coolant smell. The next step could indeed be a dye test. When I bring it in for the next oil change, I'll ask my indy to remove all the shields from the bottom, have a look from underneath, and add some dye if he can't see anything.

Thanks
cinergi
 
#6 ·
With a leak that small it could be a hose connection that evaporates before you get a chance to see it. A UV dye test may be the only way to find it, or just top it up every month...
 
#8 ·
Sounds like a good plan. Good luck and keep us updated!
 
#10 ·
I had a Rover 2000TC many years ago that had a coolant leak that I did not tend to. Turns out the head gasket had a slow leak and the antifreeze entering the combustion chamber ate out the head rendering it useless. Luckily I bought a scrap car for $100 that had a good head.

If you can't find the source I would try some Bars leak. I have had good luck with that stuff in a few vehicles. If you don't rectify the problem it may get expensive.
 
#11 ·
Indeed, I was worried about this which is why I conducted the chemical combustion test that I described in my original post. My understanding is that this test conclusively proves whether or not there is any fluid or gas exchange between the coolant circuit and the cylinders. That test was negative.

-cinergi
 
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