Coolant leak in engine valley (fixed)

I have a leak in the valley between the valve covers, near the front injector on each side. It appears to be only around the front, but I can't see back under the intake plenum on the driver side.

The oil I drained a few months ago was dark but normal looking. The level in the coolant overflow reservoir is slowly dropping, but that's kind of been true for years. I cleaned the valleys of this stuff a year ago when doing the injectors. Gradually it has returned a little. Judging by how much of it was piled up before, it's been at this for years.

No valve cover leaks.
Coolant at the radiator cap looks fine. Coolant temp is normal. I don't see coolant leaking down the back of the engine.
Compression is different all around, from 172 PSI (cyl 4) to 198 PSI (cyl 6), the others in between.
The engine does a slightly weird stumbling start for the first instant when warm sometimes. Runs smooth, good power.

What would produce this? Keep in mind these are zoomed in shots of a small amount to show the texture. But I can imagine there might be a big mess under the manifold.

 

Lower intake manifold gasket

 

I think there is a heater bypass tube under there that could be the problem.

 

Definitely lower intake gasket

 

That's good news to me. Sounds like it's not a head problem which is what I was worried about. I can dig down and replace that gasket. If the bypass pipe also has any signs of a leak I can reseal it as well.

 

X2 on bypass tube.

Edit: Reconsidering my response being that the residue is atop the intake manifold.

 

So to pull the lower manifold, I need to disconnect the fuel line somewhere. Is it best to disconnect the rear union pipe from the fuel rails, along with the FPR? The alternative is to disconnect the flare nut further up that line, which is way simpler and avoids replacing gaskets, but I've heard that that can damage the flare nut and cause a leak?

Also, in case I have to replace the FPR O ring, anyone tried the Felpro ES70600 O rings for injectors/FPR? If those O rings were recently installed with Super Lube (I used OEM and the ones that came on the new injectors), is it generally fine to reuse them?

 

Would not break at the flare nut unless there is no other choice....

there are many things that can go wrong......the threads.....double flare crimp is pinched....ect..

and they want a fortune for that replacement hose.....

somehow people cannot reseat that correctly......three hand job
receiver end is real soft metal.......


when people out of past cant get it to seal they over way over tighten....making a one way trip.........touch it...and you die


IF you do have to break one of those......I'd have a set of these handy...especially back at the tank



just incase

 

I disconnected mine at the flare nut by the fuse box. Should be 23801P on the diagram. It did not go well. The nut was completely seized, and I mangled the hell out of it before it came out.
Had to find a replacement flare nut and cut and reflare the fuel line to fix it. Was a complete pita, but it did work. Alternative would’ve been replacing the fuel line, but it is stupid expensive.
Here’s what I learned from that experience if you run into problems with the flare nut.

 

https://www.tacomaworld.com/threads/smoke-coming-from-back-of-engine.716853/#post-25513256

 

I'm sold, the flare nut is lava and I'll pull the line off the fuel rail instead!

 

Everyone should keep on hand spares on the banjo crush washers

differential and oil pan washers....

 

Fixed the leak! It was indeed mostly the intake manifold gaskets.

• Re-sealed bypass pipe going to heater valve
• New heater valve and hoses
• More new air hoses, fuel hose
• New foam tape around bypass pipe rear flange
• Wiped out gunk everywhere, sprayed cleaned, vacuumed, air blasted
• Prepped mating surfaces with sandpaper and alcohol
• New gaskets on intake, EGR, fuel rails
• New knock sensor harness
• New coolant temp sensor, gasket, harness
• Tesa tape wrapped over rest of plastic wire loom
• Coolant change
• Oil change after firing it up to flush anything out

All are aftermarket parts except the sensor, which I think was working fine but what the heck. The harness connectors were a terrible fit against OEM, had to sand them to fit. The old connectors and wire sheathing were very brittle.

Valve clearances were all in range despite never having been checked before!

 

Good job now go grab yourself a beer you earned it.