Is this coolant leak from the O-ring behind the thermostat?

Trying to track down at least one and possibly a couple of different coolant leaks. A couple of months ago I replaced the upper radiator hose as I clearly had some coolant seeping out at the hose to radiator interface. I continue to smell burning coolant and my reservoir runs low so I'm back hunting for more leaks. On first glance I saw obvious evidence of coolant at the bottom of the fins on the radiator.


I thought that was for sure the culprit but also thought why not do a pressure test to confirm, and upon pressurizing to 13 psi I actually see no evidence of leaking at the radiator, but I did find some puddling in this spot, which I can describe as behind the thermostat but I cannot assuredly see where it exits the block/housing, I can only see this slight puddle from above.




I have read several threads (https://www.tundras.com/threads/what-is-this.146390/ and https://www.tundras.com/threads/leaking-coolant.54959/) about the leak from the O-ring behind the thermostat but mine looks a lot better than those did, from the top at least.


In any case I am planning to proceed with replacing the radiator (original, 18 years 189k miles), cap, lower hose, thermostat, thermostat seal and this o-ring as well in the next week or so. Just want to make sure there might not be something else back there that I haven’t read about yet and I need to have more parts on hand.

I suspect I can get a better look at things by removing the air intake tube from the throttle body, so I'll plan to do that tomorrow.

I’m actually only about 10k miles from needing the timing belt and water pump done also, but that’s over a year away by my usage so as long as this leak isn’t from the water pump itself I’ll probably hold off on that a bit longer. There are some seeping oil leaks I might like to address when it comes time for that job and right now I just need to focus on the coolant leak at hand.

 

Replacing those things, especially the radiator, is a great step in the right direction regardless of if it's leaking or not. The radiators in ours trucks are known for going bad and leaking coolant into the built-in transmission cooler. This is a nightmare to deal with when it happens. The radiator and hoses are all super simple to remove and replace, it took me less than an hour to replace my cooling fan a couple months ago.

The thermostat and that O-ring should also be pretty straightforward. You might need to remove the fan to get good access to it, but that's not a huge challenge. Make sure to be careful when unbolting the thermostat pipe/housing from the water pump, I had one of those bolts snap on me when I changed my timing belt. Your bolts are likely in better shape then mine were, I've got a rust belt truck. There isn't a gasket between the water pump and housing from the factory. Make sure that you buy the Toyota-specific sealant when putting it back together. (Part #

$21 00295-00103 Formed-in-Place Oil Pan Gasket - 3 oz. Tube

00295-00103) It's really great stuff. Thermostat seal is also essential. I've done two timing belt jobs, and that seal has torn on both of them when removed.

I'm also noticing some evidence of a leak in the last photo you added. Right in that joint that uses FIPG (Form-In-Place-Gasket, AKA gasket maker). You can see the red/pink crusty stuff from dried up coolant. At 189k miles, the timing belt has very likely been changed before. I wonder if a previous mechanic used incorrect gasket maker when reinstalling that thermostat housing.

 

In addition to what you mentioned there are front and rear water crossover pipes that each have 2 metal/neoprene gaskets prone to leaking.

 

A good exploded of the parts associated: https://www.tundras.com/threads/05-4-7-2uzfe-overheat.135301/#post-3429269

Pics from the FSM related to thie t-stat housing etc. and instructions on re-seal: https://www.tundras.com/threads/coolant-leak-on-radiator-return.147204/#post-3689993

If you have no history on the radiator, proactive replacement at same schedule as timing belt (roughly every 100k miles) is advised to avoid bricking your transmission ("pink milkshake" is real).

 

I did see that as well, I'm curious if the fresh coolant I'm seeing might be coming directly from the bottom side of the FIPG junction. I've had the truck since about 45k miles and was admittedly late in having the timing belt done, which happened at 109k miles. Hence I'm about a year away from it needing to be done again, so I will likely do all of these things now only to shore up a few obvious spots only to have to redo a bit of it in a year with the timing belt. But that's not the end of the world to have to replace a couple of seals and the coolant again a year down the line.

I've read about those as well but haven't gotten into the details, can either/both of those gaskets be accessed without pulling the intake manifold?

 

Rears really can’t be accessed without pulling intake. Fronts probably just need to remove throttle body and thermostat housing.

 

Gotcha, I'll get a better look when I get into this and if the fronts show leakage when I get in there hopefully I can source the gaskets from a local dealer. Thanks.

About to fire the RockAuto parts cannon and have a side list going for OEM parts that I'll attempt to source at the dealer, am I forgetting anything?

RockAuto:
Denso radiator
Lower radiator hose (I replaced the upper a couple months back)
Aisin thermostat
Aisin thermostat seal
3 gallons of Aisin coolant

Local parts counter:
OEM Radiator cap 16401-20353
OEM water pipe O-ring 96761-35035
FIPG for thermostat housing
(additional gaskets if need arises to dive in a little further for front crossover pipe)

 

Looks great to me! I can't think of anything else.

 

Is there a part number for that o-ring? Can't seem to find it

 

Why yes there is.

This post will teach you how to fish, it's important to be self-reliant on your truck. You really only need to read the first 2-4 bullet points.

Once you hit that site in the 1st bullet point, and plug your VIN# into search, then click Search button,

• Click on Engine, fuel system and tools b/c we're looking for stuff related to the engine
• Click on 16-03 - Radiator & water outlet b/c we're looking for stuff related to radiator/cooling
• Click on "Open full size scheme" under the 1st exploded diagram because the pic is so damn tiny
• Hover your mouse over the number that's pointing to the part you want to see its name, and if the name looks right, click that number, and your part number will appear at the top of the next page.

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I don't know how you do it, but I appreciate you!

 

The O-ring part # was also listed in my last reply outlining my parts list.

Regardless, that resource shifty shared is infinitely more valuable overall.

 

Completed this service yesterday, although I am second guessing myself that I used a bit too much FIPG after seeing how much squeezed out externally, and assuming a similar amount squeezed into the passage internally. Shouldn’t go anywhere though I don’t think.

 

Don’t kick yourself. It looks good. Did you replace any of the small coolant hoses? If so post the part numbers.

 

I wouldn't worry about it too much. A similar amount squeezed out when I did mine for the first time, no issues so far. Probably better to have too much than too little.

 

I did not, only hose replaced was the lower radiator hose since the upper got done a couple months back. When the timing belt comes due in a year or two I’ll likely replace the crossover gaskets all the way around as well.

 

I wish I had replaced those gaskets when I did mine as few years back. I’ve been procrastinating taking the intake off lately. It seems every job I do recently has been fighting me.

 

I broke the temp gage sensor off in the housing.. Tried using an extractor but the drill wouldn't turn it out. I then used a reverse drill bit to try and catch on the threads with no luck, so I tried a tap to clear them out, no luck, so I went with a 5/16 drill bit and tried to lightly bump through the threads of the broken sensor, well it took all the threads out, so I then tried to retap but the hole is now too big for the sensor, will a helicoil work on this, if not I suppose that whole housing will need replaced, is there a part number for this?

2004 Tundra double cab sr5 4.7l

 

You can look up the housing part number here: https://www.tundras.com/threads/howto-use-the-toyota-parts-system-to-find-order-parts.113808/

First couple bullet points explain it. IIRC, it should be in the Engine section, under 'cooling' or 'radiator'.

 

Thank you, I'm hoping just a helicoil will take care of it, but planning for the worst case scenario

 

I don't think that specific area is under an intense amount of pressure, but if you're running the correct coolant for your truck (pink, or sometimes red, never yellow or green or other), you should know pretty quickly if you've got anything leaking by or not. If you see pink crusty crystals forming around the base, you don't have a good seal.

I just looked, and it does appear the water bypass joint is still manufactured. It's in the EPC (see thread I linked) under the "Engine, fuel system and tools" section, then click through to the "Radiator & water outlet" sub-section.

When I looked up a 2004 truck, which may or may not match yours, the part number it kicked back (NOTE: Always check using your own VIN!!!) was 16355-0F020, which, if you click that link, you'll see Toyota's MSRP (if you go directly to buy at a dealer parts counter) for a replacement is $185 but if I start my order at the Toyota Parts website for local pickup, I get an extra discount and can pickup for as little as $132, depending which dealer I choose for pickup location (one is $143, another is $136, and the last one is $132).

If you do end up picking up a new housing, you should pick up the three related gaskets. They are shown with index# (those aren't the actual part number, just a reference number) in this diagram of 16323C and 16355A (exploded diagram makes it look like you need two of the latter).

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Just got it back together first hell coil went too far down for the sensor to hit threads so I stuck another on top of it. Sensor wouldn’t go down far enough. Red rolled and retapped second try the cheap ass tool that came with it to install broke the tip off. So I used a valve stem screwdriver thing. Got it in with two threads sticking up. Sensor screwed in slowly but surely. With one thread of helicoil sticking up. Tightened it down now bleeding the air out. Once that’s done gonna put the cap on and pressurize it. Sad part is I reused the old sensor incase I do have to replace the housing. We shall see. Thank you for the parts help if it leaks will replace. Had sensor on order from O’RILEY’s but didn’t come in on time so waiting on it. I’m assuming that is why the temp gage has been stuck on cold. Already did thermostat cap plugs

 

These trucks often don't like aftermarket sensors. Just a heads-up.

Others have had issues, so we usually recommend going with OEM where possible. If not OEM, go with the best possible major-name brand as you possibly can. The sad reality is, parts-store brand names have declined drastically in quality since all those fuckers started offshoring parts manufacturing to mainland China. You almost cannot get reputable, quality parts from the parts stores anymore. These days they just slap a "lifetime warranty if defective" on everything, because it's purchased from places that don't do QC (quality control) checks on any parts, they just assume if there's a problem, it'll be DOA straight out of the box, and you'll waste your time bringing it back, and still feel good about saving 10%-40% on an inferior, untested part.

OEM parts, if you purchase from a legitimate source (i.e. not scAmazon/fleaBay/WallyMart or other places littered with knockoffs), should provide the exact life you've already seen, i.e. another 15-20 years of service, and are tested thoroughly for defects before they go into the box or bag for sale. This is and has been the case for Toyota Parts, their entire brand and reputation is on the line with every part they sell directly. Your average cheapo local parts store brands could give a shit less about what you think of their brand, and their counter-jockeys looking up and grabbing the part for you don't get paid enough to give a shit if you have a problem with something they supply.

 

So the heli coil is seeping just a bit, I took the new sensor plugged it in without installing and held a lighter to it for a minute or two and got it really hot, the temp gauge never moved off a notch above cold, where it has been stuck. Is there anything else that controls the temp gauge. Also I will be ordering the whol housing unit and gaskets and new sensors from the toyota site.

 

unfortunately there are no dealers that support this within an hour of me, is there another site to order and have shipped that is discounted as well?

 

https://autoparts.serratoyota.com

If you’re not in Alabama, they’ll ship for free and no tax if the order is over $75. BUT you better confirm the part numbers using the website, if you get the wrong part, you can’t return it.