Weird to me coolant leak - Fixed Bypass hose

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Oct 31, 2014
Charlotte, NC
This morning added about a cup of distilled water to radiator before driving to Brown Mountain, was a little low. Drive was perfect, got to parking lot, engine off, started to air down. AC water dripping in same spot as always, then I noticed on the driver side of the engine, towards the back, coolant dripping down!

I couldn't get under to find the source, and t stops. Not a great photo below, it seemed to be from somewhere to the right of the intake manifold. Anyway, I figured screw it, let's go, truck temp gauge was cool as always. Drove through trails, stopped to check motor, and all was perfectly dry. Drove home, parked truck, perfectly dry, no leaks.
Checked coolant level a little while ago and is good, installed the new Toyota radiator cap. Everything is dry and I can't see where it came from. Any ideas?

Are your rear heater hoses bypassed? They were on my other 80, I assume because they rotted.
I'd have to go with rear heater hoses as well.
Haven't you already posted one mystery coolant level thread? :)

then I noticed on the driver side of the engine, towards the back, coolant dripping down!

Anyway, I figured screw it, let's go,

..... maybe it just reads funny but I'm gonna go out on a limb and guess Scott Brady would not approve of that Expedition decision there. I know it's not likely to cause part of your truck to fly off and nearly kill someone and if it did overheat you probably had your expo full brim hat and expo approved snack pack and probably some expo rated footwear too but the expo classes taught on walking out of the woods are pretty much all the same. While brown mountain isn't remote wilderness a blown line would make for a long stroll.

Rotten rear heater lines would typically leak on the passenger side.

The driver rear of engine block has a few well known culprits as well. PHH, the other 2-3" heater hose #2, throttle body coolant line. It could be any of those. You may just be leaking when it heats and pressurizes like mentioned in your last thread.

Throttle body hose may be split at the clamp. You could get lucky and pull it off at block, trim an inch or so and reinstall

Good luck
Brady would frown but Darby egged me on, Darby always wins by seeking my inner teenager. Long story, but i did stop frequently to try to recreate it to no success, even ran the heater full on to see if that would do it, drove up a rock to look under. Nothing, all was very dry, all afternoon. Charlie and Mike showed up and whispered "let's go" in my ear, "the expo approved hat will keep you cool"...

Oh and worse, and at one point I heard a loud click form the front, I thought "here we go, another birf post just to piss some people off". Stopped to analyze the situation, and realized I am driving on this giant single rock "parking lot", looks like a giant slab of concrete and I am in 4 L trying to turn! Duuuhh....

The PO told me he did the PHH. the hose on top is red and the pre purchase inspection I took it too told me that was a good heater hose. It's rubber. Not knowing what PHH was back then, I took their word for it. Now I see the red hose goes all the way to the bottom, the metal section is not there. Will get under it later before the it gets too hot.
Got to love knowledge. Found them leak guys, thanks!

The box of parts from the PO had the original PHH and a piece of the "coveted" gates green line. Now it has a direct piece of hose. Is it worth replacing the original? Not a show truck, so I don't mind leaving as is.


Looking at post, found where the hoses are. Substantial coolant leak somewhere under upper air intake manifold

I wiggled and squeeze the PHH, nothing. Same for the heater hose and a stream came out. Looks like a newer hose judging by the letters on it, 5/16 hose. It's the black one next to the red one, and looks like it has a lot of extra length. Going to take your advise jfz80 and see is cutting it and resetting will do.
I am guessing access is via the front driver wheel like the PHH? I can't barely see it otherwise. I don't find it in the hose schematic.

Found it! Thanks to you guys. The bypass, what's wrong with this picture?
This is the hose going into block. Yeah.. No clamp, at all.

I carry a few in my trail tool bag, tried a couple and found one to fit nicely.


It was hard to get a socket back there, even the tiny ones, then I remembered I had 24" long screw drivers from fixing stupid European cars, slid that in from the bottom and tighened the clamp. Leak no moh. I hope.
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Now this!
Went on test drive down the road, heater valve. Lost all coolant pretty much, good thing I was less than a mile from home, coasted pretty much to driveway, opened hood, and the valve looks rotten. I guess the pressure change to the bypass found the next weak point.

There was a heater valve in the box of parts I got from the PO too, now I know why! The new valve doesn't have them link underneath, looks like that part screws in.
Replaced old nasty with newbie. Added the gates hose downstream, might as well... Now wondering where's the next weak point... Hope that was it!


Plastic fantastic. I think in order to be up to snuff, these plastic cooling bits need to be swapped out every 100K miles whether you need them or not. I know I changed out the plastic T's on the wife's LX at 115K. They were brittle but not broken...yet. Good insurance IMO.

At least Mr. T uses regular hose barbs and clamps. BMW uses those plastic snap-fit pieces with O rings. When one of those things break (oh, and they will) you get to buy a metric sh@t ton of factory piping that you don't need for an astronomical price just to replace what should be a $2 hose clamp. Genius.
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If you ever need to change the thermostat on a BMW I-6, I got the weird wrenches.... Done it in a couple of E-46's

The new valve is not Denso, and the PHH hose only went in 2/3 of the way. Well enough so the clamp grabs it, but I may take it apart in near future and seat it all the way into the valve. No time today, work and travel...... and heat... Just glad I had the valve and enough Toyota red at home!

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