Mystery coolant leak

i have a coolant leak somewhere that I can't see. I have to top off every few weeks, and no, there is no evidence of a head gasket problem. I do smell coolant when I turn on the AC, it goes away. But no sign of a coolant leak in the cabin. Ideas?

 

Water pumps are pretty common on these, check the lower side for any dried coolant. If you're not blowing white smoke/the exhaust doesn't smell "sweet" I'd head into a mechanic for a pressure test or go to Harbor Freight and grab one of their kits and see if you can pin point where it's coming from. Smelling coolant upon energizing the A/C says heater core to me. Might just be a slow leak right now so you're not getting a ton of coolant leaking out.

 

I second the recommendation for the HF pressure test kit, I've used mine on other vehicles.

 

First question, do you see it while the truck is running or no? If not, could be a coolant bypass pipe. Feel at the back of the engine where the hoses come out that go to the heater core at the firewall. There's a foam gasket that lets leaking coolant out that collects between the valley between the heads. The coolant bypass pipe runs between the heads below the intake manifold, it's rtv'd to the engine block in the front of the valley.

Another symptom that can help diagnose it is after the engine has ran for a while, like driving around for a half hour or more, turn the truck off, let it sit and as the engine cools look for coolant dripping from the back of the engine. The reason it leaks so slow is as the engine gets hot, the metal expands (thermal expansion) and makes a seal, so no leak while the engine is running at normal operating temp. As the metal cools it shrinks but the coolant is still hot and under pressure. Once the coolant cools, the leak stops again, so you have to look in that specific window.

The link I posted has a good list you'll need for parts with factory part numbers including the Toyota hi temp coolant rtv.

Another possibility is freeze plugs, but they leak when the truck is running

 

I second this possibility. As I currently have this exact issue. Used one of those long mirrors and found the source at that plate you mentiined, as well as drippage down the tranny underneath. My question is, since I've been putting off the repair and haven't fully researched it yet since I discovered it, what could happen if I let it go too long? Or will it just keep leaking and thats that?

 

It's pressing imo only in the fact the leak will get worse and eventually not reseal.

Overheating these trucks equals death.

Aluminum heads warp or crack when overheated, and you can blow a head gasket easily. My recommendation is pay a shop the grand to fix it or do it yourself for $300.

Also, in that same cavity are your knock sensors. They aren't a complicated part, only a hunk of metal that measures resonance, but if they fail your truck will throw a code.

A must while you're in there is to replace the wire harness for the knock sensors. Relatively cheap.

$45 Genuine Knock Sensor Harness 82219-34010 is Compatible with Toyota 4Runner, T100,Tacoma,Tundra

https://www.amazon.com/gp/aw/d/B00KQ3HT2S/ref=ox_sc_saved_image_34?ie=UTF8&psc=1&smid=A2QEJ1BGOVPAGN

I still have yet to see this problem arise, but at near 290,000 miles I anticipate it happening so I've been collecting/bookmarking parts.

 

Concur with @Laxtoy fix it before you're fixing something exponentially more expensive. Not to mention it's better for the environment if you're not leaking coolant everywhere you go.

 

Yeah ivebeen aware of my leak for some time now. Just been putting it off. Kinda anxious about doing it myself but should be able to. Kinda limited in time and funds. But I also was trying to look up what else I could do while I was in there. Like replace any other gaskets, cam seals (as I already have those from the timing and water pump kit that I didn't install with it at the time), and maybe the injectors. I did review that ttora post back when it had pictures so I got a fairly good idea what to expect.