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Hello, I have a 2006 Sienna in almost immaculate condition that I'm selling after about 10 years. Amazing vehicle. The week I listed it, literally, it threw its first code which turned out to be a knock sensor failure. No knocking, just the damn sensor. With no time too spare I had to take it in to be fixed ($800 later!!!). It has been sitting in my driveway now for about a month without moving, and it is leaking coolant pretty bad. I've wiped it down from the bottom several times, but it's still coming out. Vicinity of the transmission. I need to arm myself with some knowledge before going back to the service station and giving them another $800. Anyone know where that leak might be coming from, following knock sensor 1 replacement? Thank you!
 

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Coolant leaking the valley on the 3.3liter is a common issue and will get into the knock sensor. Did they fix the leak(?) if there was one?
Second thing that comes to mind is that they pinched the oring on the thermostat gasket. Hard to say.
Kind of sounds like whoever did the repair messed up something.
 

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Very interesting. Thanks for the quick reply!
The common leak in that valley -- where does it generally come from? What does it take to stop it?
They had noted on the receipt that there were 'crusties present' at lower plate in intake Valley.
Are you saying that perhaps a small coolant weep in that location may have damaged the knock sensor? I had assumed that they caused this significant leak, but maybe just exacerbated it? Either way I need to get it stopped so that I can sell this otherwise flawless van.
 

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Hey Enduro, having just gone through this myself, I can give you a few ideas from my experience on our 2004. First off, if they saw "crusties present" they should have known WAY better than to put everything back together before consulting with you about the possibility of a coolant leak here. Complete negligence in my opinion. I would think that they should have some responsibility in reporting something like this to you, just as a matter of good business practice.

"Crusties" as they noted, are not something you can just ignore. This is indicative of an ongoing, albeit possibly slow coolant leak, and also possibly only when the system is hot and pressurized. I had been experiencing drips under ours and found the broken (plastic) water intake pipe to the thermostat. Thinking this was the only problem, I fixed the pipe, but still experienced leaking. Digging deeper, I learned about the problematic coolant valley leak issue. Here are a few pics from mine.

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Note that to reveal this "horror show" of pink crusties, it takes several hours of labor to remove an awful lot of parts. Most annoyingly, the intake plenum. Also note that after removing the plenum and intake manifold, there are gaskets under each that must be replaced (not reused). You can see the black intake manifold gasket poking out from underneath the masking tape (being used to prevent things from falling into the engine). There's a gasket like this on both banks of the engine and each seals off a coolant passage. I can say for sure that if I had tried to re-use this gasket, I very likely would have introduced a new coolant leak due to the poor condition of the gasket after pulling off the manifold. So there's at least one possibility for a new leak. I would try to confirm if they charged you for the manifold gaskets. If not, this is a good sign that they re-used them, which they should have known better not to do.

Despite the level of crusties you see in my picture, both of my knock sensors were still fine, so if your knock sensors died due to excessive exposure to coolant, I'd say your leak may have been even worse. You can see that the sensors are sort of "above the flood zone" so-to-speak, and these parts are completely potted in some sort of thermal epoxy, so it would take a LOT of exposure to coolant over time to kill them. If this was the case, then it's just another argument that they should have stopped right then and there to call you and let you know. I should also point out that the connectors to the knock sensors in this area will get extremely brittle over time with the heat. Not saying that your sensor fault was necessarily due to a failed connector, but I guess you can't totally rule it out either.

Here's what it looks like with the cooling valley plate removed and all the old Fixed-In-Place-Gasket (FIPG) material cleaned up. This took a lot of time to get this point. It's the FIPG material that gives up over time and causes this problem in the first place.

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Here's what it should look like after all cleaned up and re-sealed. Note that where you see the open pipes is where you would normally see the "cross-over" pipe. This is just a short rubber hose. Again, a part that they should have suggested to replace while doing the job.

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Picture with the cross-over pipe still connected.
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Not sure it's at all helpful to you, but when I called one of my local reputable Toyota dealers to quote the cost of re-sealing the cooling valley plate, they quoted me $800. Is it possible that maybe they did actually re-seal the plate after noting the crusties? Definitely warrants a few followup questions on your part to find out.

I would also inspect the black plastic water intake pipe to make sure you don't see any wetness anywhere around that pipe. If you follow the rubber hose from the BOTTOM of the radiator, you'll see where it connects to this pipe, which also doubles as the thermostat cover. And like 3Wheeler stated, there is a rubber gasket between this plastic pipe and the aluminum thermostat housing, but I don't believe they would have had to separate it if they were only replacing the knock sensors.

Having just re-read your post that says you're getting a good amount of leaking off the bottom of the transmission, while it's sitting still and not being driven, I'm now even more suspicious of that intake pipe. Mine broke when I put my hand on it to check out the connection, so maybe yours got cracked in the process? It could definitely leak into that area. If it's just the pipe, then this is not an expensive job. Of course, if you were keeping the van, you'd probably also want to replace the thermostat while replacing the pipe, especially if it's the original.

Good luck! Hope you can get a non-expensive resolve to the problem.
 

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I did this job couple months ago. My leak was not as bad as pictured here , with just a trace of wetness and crud. My fixing this was primarily preventative and I took the opportunity to renew the knock sensors and bypass hose. I agree with pethelmans view . Kindly report back your findings as to the new leak. Good luck
 

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Wow, thank you for that informative reply. That's the most comprehensive and conclusive response I've ever received on a forum. Perfectly relevant pictures too! Thank you so much! Almost makes me want to keep this van so I can have you as a resource! :)
I ended up taking the van back to the shop, and they told me they added some sealant to stop the leak and it should be good to go. Didn't charge me. If I was keeping this thing, I'd tear it apart and shine it up nice like yours with all new seals and gaskets.
Fingers crossed that their fix worked, and some other family can get years more reliable driving from it. Thanks again for the advice here!
 

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To Pethelman, I will be changing this metal plate for cooling reservoir, I cant seem to find torque specs. Any ideas?
 

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I used Genuine Toyota FIPG ( form in place gasket) on the water inlet housing. Others have used different brands with good results. I use a torque wrench that is in inch lbf. to tighten those nuts and bolts.
 

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Thanks for gasket info I have several colors of rtv , has anybody had any luck with or bad luck with red , black, or grey rtv?
 
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