Coolant Leak at the Back of the Engine

[RiverCityDave]

OK folks, I pride myself on using search, and looking for the already answered questions that seem to cover almost everything on here, however I've hit a bit of a brick wall. As the title says, I've got a coolant leak up at the back of the engine. I've already bypassed the rear heater core to rule that out, as the water runs across the transmission and drops on the passenger side of the truck. Just a few minutes ago I used a length of heater hose to run from the heater control valve to the hardline next to the head, bypassing the whole heater core (except the PHH) and the water still pours out. I don't think its the PHH as I said the coolant drains across the transmission and down the passenger side. It's high enough that I cant see where its coming from, so I was positive it was the rear heat lines, but they've been ruled out.

Any thoughts? There is no visible water up behind the head, but it is POURING out. Fast enough that with both hoses removed from the radiator, and filling from the top drivers side (US), virtually nothing comes from the lower hose, so its a big leak.

I'm pretty frustrated today, so I figured I'd take a tactical pause and see what the oracle had to say.

 

[Rusty Marlin]

Point out where you by-passed. I think I know, but I like pictures.

 

[ALX4X4]

Welch plug rusted out ?

 

[RiverCityDave]

Welch plug rusted out ?

I was thinking this too. I didn’t realize there was one on the back of the cylinder head. In fact, I still can’t find a picture of it. I’ll have to dig deeper into some archive pics. I may end up pulling the bed before all is said and done…

edit: found one. There are actually TWO plugs back there. Should be pretty easy to confirm when the sun is up tomorrow.

 

[BILT4ME]

I was thinking this too. I didn’t realize there was one on the back of the cylinder head. In fact, I still can’t find a picture of it. I’ll have to dig deeper into some archive pics. I may end up pulling the bed before all is said and done…

Read this thread.

'94 FZJ Another Mysterious Coolant Leak (above trans)

Hi all, first Toyota, first time posting, have been reading MUD, mostly 80 series tech threads instead of books since I bought Chrundle in Oct. '18. I'll do my very best to stick to the pertinent facts (EDIT: In review I failed that last sentence so skip to end to avoid verbose back story)...

forum.ih8mud.com

 

[flintknapper]

Check the outlet/hose just in front of the PHH (goes from the head to the throttle body). IF it is leaking....the fan or wind could be blowing it back on the firewall and trans.

There are also a couple of freeze plugs in the very back of the head:

 

[RiverCityDave]

Read this thread.

'94 FZJ Another Mysterious Coolant Leak (above trans)

Hi all, first Toyota, first time posting, have been reading MUD, mostly 80 series tech threads instead of books since I bought Chrundle in Oct. '18. I'll do my very best to stick to the pertinent facts (EDIT: In review I failed that last sentence so skip to end to avoid verbose back story)...

forum.ih8mud.com

Damnit man! I searched those same terms and did NOT find that thread. That looks to be the issue I’m thinking. Fingers crossed the head didn’t crack at the same time.

 

[Rusty Marlin]

Too funny. My very first thought was, sounds like a freeze plug.". But I looked at the OP's location and went, "Oh Texas, can't be a freeze plug!". Didn't think one could have rusted out. What a pain in the d!ck.

 

[flintknapper]

Too funny. My very first thought was, sounds like a freeze plug.". But I looked at the OP's location and went, "Oh Texas, can't be a freeze plug!". Didn't think one could have rusted out. What a pain in the d!ck.

It would be unusual for a freeze plug to rust out here in Texas, unless the vehicle spent a lot of time on the Coast or came from a different location.

But it does 'freeze' here during the winter. Last February we had several single digit days (3 damn degrees at my house) and IF a cooling system were not properly filled with antifreeze, you could pop a freeze plug or crack a head.

But yes, freeze plugs are way down on the list of things we look for in the Great State.

 

[RiverCityDave]

Hey all, in the interest of not leaving things incomplete here for future searches, it is indeed a freeze plug on the head.
I was able to get my fingers in between the head and the firewall and found the open plug port. I then found the plug itself laying on the frame, just like it belonged there.

So the head is coming off. I’ll treat it as a chance to do a pre-emptive head gasket, as I might have been smelling a little coolant in the exhaust last summer.

It was, as several posters have noted, assuredly our deep freeze in February that did it, I had the cooling system drained at that time since the truck was immobile, but with the slope and what I couldn’t get out of the block and head, there was enough left in it at that level to pop the plug. Here at my place, we stayed down in single digits for four days. Fingers crossed, that‘s all it did. I’ll find out this weekend when I pull it all apart.

I plan to update this thread with the process, I’ll be machining and doing any rebuilding the the head needs etc. so pics to follow, for posterity.

Thanks for the feedback, as always, you folks got me going in the right direction.

 

[jht3]

damn. you sure are in good spirits considering

do you run pure water or coolant/antifreeze? i'm shocked that w/ a nearly empty system there would be enough pressure to blow that out.

 

[zapatius]

Hey all, in the interest of not leaving things incomplete here for future searches, it is indeed a freeze plug on the head.
I was able to get my fingers in between the head and the firewall and found the open plug port. I then found the plug itself laying on the frame, just like it belonged there.

So the head is coming off. I’ll treat it as a chance to do a pre-emptive head gasket, as I might have been smelling a little coolant in the exhaust last summer.

It was, as several posters have noted, assuredly our deep freeze in February that did it, I had the cooling system drained at that time since the truck was immobile, but with the slope and what I couldn’t get out of the block and head, there was enough left in it at that level to pop the plug. Here at my place, we stayed down in single digits for four days. Fingers crossed, that‘s all it did. I’ll find out this weekend when I pull it all apart.

I plan to update this thread with the process, I’ll be machining and doing any rebuilding the the head needs etc. so pics to follow, for posterity.

Thanks for the feedback, as always, you folks got me going in the right direction.

Had the same issue. I was flushing with distilled water and didn't realize how cold it was going to get. Popped out a rear freeze plug....and cracked the head in 6 places. Hope yours turns out better.

Head freeze plug turns into head gasket replacement

Iceman here. Some of you may remember when I accidentally left distilled water in my truck at our first freeze. Well, fast forward and I put the new oil cooler on, new thermostat and housing, etc.... I went to fill it up with 50/50 Toyota red and distilled water. Got about two gallons in and...

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