Where is my coolant going? (1 Viewer)

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2004 GX470 2UZFE 120,000 miles, purchased about 3 months ago. Timing belt and water pump replaced 4 years ago. Original rad and hoses as far as I can tell.
The coolant level in the overflow tank is dropping gradually. I noticed it was low after I bought the truck, I topped it up a few times and then it seemed to stabilize. After a highway run the other day the level was down again and needed to be topped up.
I've looked everywhere for a sign of a leak and can't find any (around water pump, hoses, sides of heads, rad, etc.).
Maybe there's a pin hole leak somewhere that is allowing coolant to vent while vehicle is at speed, and leaves no traces?
I replaced the radiator cap and no effect.
No sign of head gasket failure (spark plugs are clean, blue fluid tester for fumes at rad reveals no exhaust gases present, no noticeable fumes in the exhaust). I know these 2UZFE engines are not known for head gasket issues.
A bit of loss is probably natural, but I've probably added half a gallon of coolant since buying the truck, to top up the level in the overflow tank.
Any ideas on where else to look for where the coolant is going?
Should I replace the upper and lower rad hoses in case there's a pinhole leak I can't see?

Forgot to say: my mechanic did a cooling system pressure test today and all was good. He's also the one who looked at the spark plug condition and checked all around the engine for signs of leaks.
 
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Perhaps the truck was low on coolant (air in the system) when you bought it, and over time the air has worked its way out?


No smell of coolant from the engine compartment when the truck is hot? Any pink coolant boogers visible anywhere?
 
The overflow bottle was empty when I bought it (silly me for not looking at it!). My mechanic suggested the same thing, air working its way out. So maybe you've got a point there. I haven't driven it much since buying it, just a couple of freeway runs and driving around town, until I can get it a little baselined. The level in the overflow seemed to have stabilized until I did a highway run the other day (about 3 hours) and then it was low again upon cooling. No smell, no boogers.

I remember my Toyota Cressida had the same issue (overflow bottle going down) which made me fear HG (notorious on those inline 6 engines). Then one cool late fall morning, I had the hood up and noticed a wispy bit of fume coming up from around the rad. There was a pinhole leak in the rad. Replaced the rad and the coolant level stabilized. So maybe this GX is due for a rad change (120k).
 
Check the HVAC drain to see if the heater core is leaking. The drain is on the passenger-side of the fire wall in the engine compartment. It pokes through the firewall just a couple of inches, right above the frame, near the exhaust manifold. If you see coolant residue there, your heater core is leaking. Fingers crossed that is not your problem.

If so, then see my thread I put up last week about changing the evaporator and heater core.
 
Check the HVAC drain to see if the heater core is leaking.
If so, then see my thread I put up last week about changing the evaporator and heater core.
Thanks, I'll check that when I get the truck back from the mechanic (he has to replace a sticking caliper in the front).
 
It's much more probable the radiator is leaking than anything else. Not saying it absolutely can't be anything else, but these trucks are terribly notorious for radiator leaks. Mine started at 130k
 
So maybe this GX is due for a rad change (120k).

You might be on the right track. Radiator leaks are relatively common in these trucks (that, and alternators). A good way to tell would be to pull the radiator and look for crusties from dried coolant. You might just watch it for a bit more to see if the coolant continues to drop.

EDIT - BlackCat beat me to it. :)
 
The mechanic pressure-tested the cooling system when the engine was warm and no leak was revealed.
He then left the system pressure-tested overnight and again no leak.
He says he's pretty confident there isn't a head gasket issue.
So where the coolant is going remains a bit of a mystery for now. I will stop fretting about it, and just keep topping up the overflow tank when it needs it and keep monitoring for possible leaks.
Yes, hopefully it's not the heater core or something like that, but I will look at the areas indicated by kwkshift above.
Weird...
Anyway thanks everyone.
 
I would take the time to top off and bleed the coolant system so you have a known baseline. Check the water pump area and the underside of the radiator for coolant residue while you're at it.
 
It holds 4 gallons of coolant. My reserve tank was empty as well, I refilled it a few times and thought I had a leak. It turned out I was just really low, and it was slowly burping the air pockets. Parking it nose-up on a steep driveway helped.
 
My 05 GX seems to have a leak also, 130K, like you my overflow was empty but I did find the sponge under the radiator on the drivers side lower corner was wet. I took a clean paper towel and blotted it on the sponge and it was red coolant. Look There.

Now I need a recommendation for a new radiator as Lexus replaced this one at 90K so I don't want one going out ever 30k.
 
My 05 GX seems to have a leak also, 130K, like you my overflow was empty but I did find the sponge under the radiator on the drivers side lower corner was wet. I took a clean paper towel and blotted it on the sponge and it was red coolant. Look There.

Now I need a recommendation for a new radiator as Lexus replaced this one at 90K so I don't want one going out ever 30k.

I went with Koyo.
 
I had my rad and two main hoses replaced, will monitor and see if coolant level stabilizes. At least I know the radiator and upper/lower hoses are not the source of the leak now (if there is still one) and that critical part of the engine has been baselined.
I went with a DENSO radiator.
 
Check the HVAC drain to see if the heater core is leaking. The drain is on the passenger-side of the fire wall in the engine compartment. It pokes through the firewall just a couple of inches, right above the frame, near the exhaust manifold. If you see coolant residue there, your heater core is leaking. Fingers crossed that is not your problem.

If so, then see my thread I put up last week about changing the evaporator and heater core.

I finally looked at that hose and can't tell if anything is leaking out onto the frame. There is some surface rust on the frame but not only at that spot. I attached a 6" length of clear plastic hose to the drain hose, capped it at the end, and will observe from time to time to see if anything is collecting into that hose.

I'm hoping the rad replacement addressed my coolant loss, but it lost a bit again after a 3 hour highway drive, maybe it's settling in (air bubbles etc.) or maybe the leak still exists, somewhere...

I also thought of putting a dye in the coolant and checking the truck in the garage with uv light, but I read on the dye that it's not recommended for long-life coolant (does it compromise the life of the coolant?).
 
I finally looked at that hose and can't tell if anything is leaking out onto the frame. There is some surface rust on the frame but not only at that spot. I attached a 6" length of clear plastic hose to the drain hose, capped it at the end, and will observe from time to time to see if anything is collecting into that hose.

I'm hoping the rad replacement addressed my coolant loss, but it lost a bit again after a 3 hour highway drive, maybe it's settling in (air bubbles etc.) or maybe the leak still exists, somewhere...

I also thought of putting a dye in the coolant and checking the truck in the garage with uv light, but I read on the dye that it's not recommended for long-life coolant (does it compromise the life of the coolant?).


This is my first post.Thought I'd share this.
Both my coolant losses on my 3.0 KZn 185 Manual 1996 ( now 21 years old) have been down to pin holes in the connecting Metal elbows that connect two coolant pipes together at the back of the engine, slightly to the left hand side (RHD). Look at the back of the engine, under a fluid reservoir you'll find this elbow that corrodes. A pin hole under pressure ejects quite a bit of coolant, will overheat the engine and boil in the reservoir tank. Also, with mine I had no heat coming from the heater.
I replaced the original metal elbow connected with a piece of copper piping, got my Plummer mate to bend it and hey presto.. no coolant loss, no overheating, heat from my heater.
You could try brazing the original one, but It will go again eventually.
 
Now that the weather is getting cold up here, I'll drive the GX out of the garage one evening and let it idle in the driveway. In cold weather, small coolant leaks at hoses and elbows etc usually show up better. I remember a coolant loss on a Toyota Cressida (inline 6) that I bought a few years ago (these were notorious for head gasket issues), one evening I popped the hood up and saw a wispy stream of steam escaping from the top of the rad (pinhole leak) which would not have shown otherwise. I replaced the rad and all has been well with the car for the last 5 years. I'm hoping something similar will be revealed on the Lexus (on which I've already replaced the rad and two main hoses). The TB and WP were replaced some years ago by PO, and I wouldn't doubt that his indie garage may have used non-Lexus(Toyota) parts, which may mean a small leak around a water pump gasket. Those are my thoughts.
 
My 05 GX seems to have a leak also, 130K, like you my overflow was empty but I did find the sponge under the radiator on the drivers side lower corner was wet. I took a clean paper towel and blotted it on the sponge and it was red coolant. Look There.

Now I need a recommendation for a new radiator as Lexus replaced this one at 90K so I don't want one going out ever 30k.


I'm having the exact same problem right now...o4GX 143K, radiator replaced in 2015 by previous owner from Lexus. When you pulled the radiator where exactly was the leak? I have pink bookers in the lower left corner of drivers side on radiator. I pulled the fan shroud today, but couldn't see anything behind it...I was very surprised.
 
My GX radiator it has been leaking very slowly for couple months but nothing to really be concern about I finally bought a new one it has the pink coolant in there does it make difference what brand of coolant and what color I put in there . Any suggestions what kind of coolant I should put in there ?
 

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