Coolant leak in the BACK of the engine?

Hey friends!


This is for a buddy's tundra.

He has a 2006 Tundra with 325k on it.

Runs really smooth actually.

BUT it now has a coolant leak on the back on the engine. What could that be?



Oil looks clear.
He had to put about a gallon in over the last 2 weeks.
It doesn't seem to be burning.

 

 Coolant leaks: Three common causes: One is the is the gasket behind the thermostat housing, another is the coolant crossover at the rear of the block, and last but not least, old radiators is another source. Here's a list of things to check if you're losing coolant. For repairing the leak behind the t-stat housing, check this out. For the coolant crossover tube issue, you'll likely find coolant at back of the block, near where the trans and engine meet, check this reply for video/fix. This post is for leaks at t-stat housing/inlet neck. This reply contains links to three other off-brand/odbball leak cases. For radiator leaks, this is one example of a tiny one - always replace with Denso brand radiator, and know different cab types use different sizes, careful where you order, scAmazon especially tends to deliver damaged products often (RockAuto has a spotless record with forum members). Proactive radiator replacement is wise. The transmission line routes through the bottom of the radiator ... go look up "pink milkshake", it happens in these trucks.

Info copied from HERE

 

Re-pasting so the links show up:

• Coolant leaks: Three common causes: One is the is the gasket behind the thermostat housing, another is the coolant crossover at the rear of the block, and last but not least, old radiators is another source. Here's a list of things to check if you're losing coolant. For repairing the leak behind the t-stat housing, check this out. For the coolant crossover tube issue, you'll likely find coolant at back of the block, near where the trans and engine meet, check this reply for video/fix. This post is for leaks at t-stat housing/inlet neck. This reply contains links to three other off-brand/odbball leak cases. For radiator leaks, this is one example of a tiny one - always replace with Denso brand radiator, and know different cab types use different sizes, careful where you order, scAmazon especially tends to deliver damaged products often (RockAuto has a spotless record with forum members). Proactive radiator replacement is wise. The transmission line routes through the bottom of the radiator ... go look up "pink milkshake", it happens in these trucks.

 

Can you get a picture below the throttle body to see if you can see coolant pooling up.

 

Looks at the O-rings on the water pipes and the gaskets for the front and rear coolant crossover pipes. Coolant leaks into the valley drain out the back of the engine.

 

Most likely coolant cross over at the back of the engine, under the intake.
With 325k on it, would lean towards not having changed the rad fluid and its getting acidic and has eaten the o-ring. I found this out the hard way, i too have been bitten by the "ah its a toyota it will run forever" and left things box stock until something happens. Not long ago i developed a coolant leak on my daily driver around the thermostat housing. I took it to the trusted import mechanic who does the very minimal amount of work i ever need done and he said "ah coolant leak, yep shes got 245k on the clock, bet'cha never changed the fluid have you" to which i responded "no i havent, i dont normally crack them open at all cost." He then went on to tell me the coolant gets acidic over time, maybe the repeated runs thru the water pump, maybe an age thing, may be the heat / cool / heat / cool generates an electric charge to it. He didnt tell me how or why, he just said the coolant becomes acidic over time and starts eating everything up, which is why you're supposed to change your coolant. It was quite funny only a few days later i saw a video of a mechanic talking about the 2nd gen tundras and he too said the same thing. The coolant gets acidic and is eating the rubber layer off the head gasket allowing coolant into the cylinders. He had stacks of gaskets to show it and said he has a long list of them to do after the one he was working on.

Here is the video just looked it up, he talks a LOT, might wanna skip on down a bit towards the middle. Coolant getting acidic eating up the head gasket seal and allowing water to pour direct into the cylinders. He said lots of stuff, but in my mind its basically saying change your coolant often.
https://www.youtube.com/watch?v=dfGTI0sWozc

Hopefully this will embed at the right time and you can see him pointing at the blown out gasket where he claims the acidity of the coolant ate the gasket up, fingers crossed.
https://youtu.be/dfGTI0sWozc?t=360

 

I think it’s not acidic coolant but heat and time that causes the o-rings to fail.

 

I mean anything rubber has a limited lifespan. So it makes sense.