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86-95 Trucks & 4Runners 2nd/3rd gen pickups, and 1st/2nd gen 4Runners with IFS

Coolant leak drip behind engine, freeze plug?

Old 05-22-2019, 06:10 PM
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Coolant leak drip behind engine, freeze plug?

1994 3vze 3.0 4runner RWD
Dumbass me, replaced my radiator and left the lower radiator plug on, inside the lower hose it blocking the flow, the blockage pressure caused a coolant leak from behind the engine. I have taken off my lower plenum now four times trying to figure it out. I have replaced the gaskets all four times and even replaced the heater bypass pipe under my lower plenum. Im down to all else i can think of is my freeze plugs. (100% not the coolant block or heater core hoses) When I put coolant in with engine running or not, it leaks from the same place but unable to see it with my eye from any which direction. O was barely able to fit my phone behind to see the plugs, all 4 large plugs look AOK, but on the driver side, there is a tiny plug under the two large plugs, what appears to be the plug to be missing, but i am un able to get a good enough quality photo of it to know for sure. Lets say it got pushed out, does any one have the dimensions and or know how to get a replacement, or even another means of fixing this with out pulling the motor. I can touch it with my fingers, was thinking a Jb weld type fix but i want a more permanent fix.
SEE PICS! However, now to thinking more, the leek drips on my passenger side of trans, which it either drips onto the exhaust from driver side and works its way to passenger side, or its the main block plugs? In the image with the two plugs circled in yellow. How could i make them leek with lower plenum off to where i can lean over and watch it leek, i dont want coolant to flow into my open heads while i fill the radiator. Where else can the coolant be coming from???

Driver side plugs, is the little one missing?

Little plug pic off google

Maybe one of these? 😫 do these have oil or coolant behind them, not much of a mechanic, but learning as i go and i had just recently successfully replaced my timing belt. 🙃 if these leek coolant, do i need to remove the exhaust back there to get to them

Passenger side, These look okay

Wasn’t my pipe, gaskets, or hoses
Kinda looks like i can see the little plug in this photo.

Also, i have no coolant in my oil, idk for certain if that crosses off the head gasket or not. Aside from the leek, runs beautifully..

Last edited by DH4runner; 05-22-2019 at 06:42 PM. Reason: Typo
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Old 05-22-2019, 07:19 PM
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I believe that the hole your two arrows are pointing toward is a threaded mounting hole, and ordinarily has nothing to do with coolant.

It helps to remember that the heads are (almost) reversible, so the hole you see on the back of the left head, also appears on the front of the right head. Unfortunately, I don't have good enough memory, photographs, or drawings that show what, if any, bolt goes into that hole on the front of the right head.

But none of that matters to you, because that hole on the back of the left head should be empty. So why is coolant coming from it? The only explanation I can think of is a small crack in the head.

I would be tempted to get a 8mm-1.25 bolt just to see if it would thread into that hole. If it does, I'd dope it liberally with thread locker (or maybe just RTV), and screw it in snug but NOT tight (if there is a crack, you want to plug it, not make it worse).
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Old 05-22-2019, 09:39 PM
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Originally Posted by scope103 View Post
I believe that the hole your two arrows are pointing toward is a threaded mounting hole, and ordinarily has nothing to do with coolant.

It helps to remember that the heads are (almost) reversible, so the hole you see on the back of the left head, also appears on the front of the right head. Unfortunately, I don't have good enough memory, photographs, or drawings that show what, if any, bolt goes into that hole on the front of the right head.

But none of that matters to you, because that hole on the back of the left head should be empty. So why is coolant coming from it? The only explanation I can think of is a small crack in the head.

I would be tempted to get a 8mm-1.25 bolt just to see if it would thread into that hole. If it does, I'd dope it liberally with thread locker (or maybe just RTV), and screw it in snug but NOT tight (if there is a crack, you want to plug it, not make it worse).
Im not sure if the leek is coming from there or not, felt/looked like an empty cavity that may or may not leak. Based on what you told me, is it possible the leak could be coming from one of the two plugs circled on the bottom? Im going to see also of it is threaded.
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Old 05-23-2019, 08:57 AM
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A good way to find a leak is to rent a pressure tester from Autozone. Pump up the cooling system to 15 psi or a bit more, and then start looking for drips. That way you can do it while the engine is not running and is cool enough that you don't risk burns or injury sticking your head and hands in these tight places.
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Old 05-23-2019, 08:47 PM
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Originally Posted by RJR View Post
A good way to find a leak is to rent a pressure tester from Autozone. Pump up the cooling system to 15 psi or a bit more, and then start looking for drips. That way you can do it while the engine is not running and is cool enough that you don't risk burns or injury sticking your head and hands in these tight places.
^^ what he said, pressure test. And get a mirror, like the dentist uses. It is far more likely to be a head gasket or intake gasket than it is to be a freeze plug.
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Old 06-05-2019, 07:23 AM
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UPDATE!
Rebuilt my upper half of the motor once again. Got down to my water bypass heater pipe, and replaced it, thinking maybe it rusted through, it hadn't >.<... Still not 100% what the leak was but I'm now suspecting the surface of my of the aluminum where my intake manifold gasket sits allowed coolant to flow, but still could have been an external leak on the head gasket. I originally went with felpro, twice, 3rd time went oem. This time around the leak had reduced drastically, added the k seal and plugged it up! 2 weeks going strong no leaks.

Last edited by Aaron Borhegyi; 06-05-2019 at 07:32 AM.
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