When I removed my transmission I noticed that the rear of the driver side engine block looked wet (above the rear main seal). There wasn't enough fluid there for me to easily tell if it was coolant or oil but it was enough to make that area look damp. The passenger side was mostly dry.

The reason I think it could be coolant is that the fluid looked thin. I've also noticed that coolant levels in my reservoir would slowly decrease to where it would drop about an inch below the full mark every few months. This has been going on since 2014. I haven't concerned myself about it too much because I haven't been able to find a leak & haven't experienced head gasket symptoms (yet).

There reason I don't think it's coolant is I didn't see any dry crusted red coolant residue in this area. I don't know what else it could be but I'm assuming the back off the engine block looking wet is not normal?

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Likely valve cover gaskets. If you've been leaking antifreeze back there for the last 6 years, you would see crust somewhere. I'm sure you are leaking antifreeze, don't get me wrong, that's just not the source of your leak. If it is a head gasket, a leak that slow into the exhaust passage would not create enough steam to alert you of a problem. How many miles are on the 4Runner? If high, why not pull the engine since you're half way there? Would be the perfect opportunity to replace the timing set, water pump, head gaskets, fresh valve job, valve cover gaskets, drop the oil pan and inspect everything, clean the pan if needed and replace the gasket. Just freshen it up and know it's done.

My GUESS, since I am not there, is either a hose for the heater control valve is leaking (or maybe the valve is cracked) or the coolant pipe that resides under the lower intake manifold is cracked (don’t know if it has a gasket that mates to the block, never been that deep in the 5vz). I don’t think there is a freeze plug that high.

Any pics of the transmission removal process? Hopefully the Metabo has earned its keep.

i'm going with LittleCaesar's diag here. that position makes me think heater hose or control valve. i have a very slow leak there in my '95 pickup (same basic config) but it's so slow i just don't really care. it creates a pink crust and nothing worse that we could detect when we had the engine and clutch out.

is there any chance your clutch is still off, and you could wipe up some of the wetness to do a sniff test or other sort of diagnosis? what does your firewall look like (engine side, and back if you can access it)?

If I was having engine issues I would consider pulling it since I already have the transmission out but it's been functioning normally so far & don't want to have my DD down any longer than I have to.

If it was a leaking coolant pipe under the lower intake manifold I'm guessing signs of dried coolant residue would be more difficult to see which could explain why I haven't been able to find where the coolant has been going correct? Since I haven't seen dried coolant in the firewall area near the heater control valve or behind the engine, would this indicate that the coolant leak would more likely be coming from underneath the intake manifold?

I actually used the milwaukee 3/8 impact for a lot of the work this past weekend to see what all it could do. It won't be replacing my metabo but very happy with it.


The transmission is still out. I tried smelling it when I was cleaning up the undercarriage but there wasn't enough fluid there for it to have a distinct smell. Firewall is clean and no signs of leaks from what I could see. The back of the engine has the damp spot but nothing dried or crusted.

The leak you have in the heater control valve area, I'm assuming you can see coolant residue there?

yeah just a little dried residue. it has looked more or less the same for several years, so either it self-sealed, or is so slight that i just don't see a change. i know i should just fix it, but given the lack of severity and that it's my back-up vehicle, it constantly gets de-prioritized.

If it's a 3.4 you're due for a timing set every 80K miles or so. Keep that in mind.

If I were in your shoes I would try and rent a coolant pressure tester and go past the allotted 15psi, maybe up to 17 or 18 and see if you could see any current leaks. If no go, then put dye in the coolant and have a UV light at night and try and find the leak that way.

I wish I had the insight to tell ya more about the coolant pipe but since I have never had my hands on it, I don’t want to engage in “maybes”. See if you can find a member who has changed their knock sensors and PM them for some insight. I doubt it is the heater control valve but as someone who has a real handle on plumbing, water can leak from all sorts of places.

Glad to hear about the 3/8 Milwaukee impact. I have used mine so much that the white lettering is all but worn off. I actually broke the battery housing on a 6.0 battery using it to remove a 22 year old Canadian seasoned oxygen sensor. Well worth every penny.