Popped a freeze plug

[Bitch'nBronco]

This is a weird one, I idled the bronco for maybe 10 mins, not long enough for the fans to kick on and then all of a sudden coolant everywhere. A freeze plug on the passenger side behind the motor mount popped out. I'm not sure what the cause would be, the radiator was barely warm, I cant imagine I have a blown headgasket that would make enough pressure to pop out a freeze plug before causing the radiator cap to gush. For additional info, it was nowhere near freezing outside, and I am running coolant, not straight water.

Should I add some sort of adhesive to the freeze plug when I install it again? Looks like there was some grey rtv around the edges. Needless to say, I don't want this thing popping out again.

 

[DirtDonk]

Never heard of one popping out if it was properly sized and installed.
Do you have any history of working over there that you can remember if it was all the way in or not?

First thing I would do would be to clean it up and then clean the hole and size it manually. Push it in and see if it slides all the way in by hand. If it does, it’s too small.
If it barely goes in, then it should be correct.
Is it in good condition? Or is it rusty?

No matter what, I would use sealant. But check the condition of the mating surfaces first. You might or might not be able to see well in that corner, but you should be able to feel if it’s really rough.
When I had a leaky one that had rusted through, that was the same one you’re dealing with.

 

[DirtDonk]

Oh, and yes, your thinking is correct. If there was ever enough pressure to push out even a single freeze plug, a lot of other things would’ve given up first.
Almost no amount of internal pressure from water temperature or pump pressure can do that. Normally only freezing can apply that much pressure.
Or something not right…

 

[Bitch'nBronco]

Never heard of one popping out if it was properly sized and installed.
Do you have any history of working over there that you can remember if it was all the way in or not?

First thing I would do would be to clean it up and then clean the hole and size it manually. Push it in and see if it slides all the way in by hand. If it does, it’s too small.
If it barely goes in, then it should be correct.
Is it in good condition? Or is it rusty?

No matter what, I would use sealant. But check the condition of the mating surfaces first. You might or might not be able to see well in that corner, but you should be able to feel if it’s really rough.
When I had a leaky one that had rusted through, that was the same one you’re dealing with.

Its a brass freeze plug, my guess is it wasn't seated completely. I'll be honest, I don't generally inspect freeze plugs unless I have a coolant leak, which I haven't had. Are the plugs supp0sed to be bottomed out against the block or is the lip of the freeze plug just flush with the freeze plug bore? Thanks

 

[DirtDonk]

Completely bottomed out.
I don’t remember ever seeing one flush, and certainly not proud of the engine block casting.
Seem to remember them always being inset slightly. From a sixteenth to almost a quarter of an inch depending on the engine.

Yeah, the only reason I ever had a reason to mess with that particular one was because it started leaking from rust-through.

 

[ba123]

I'd love to know if you have any success reinstalling with the engine in. The one on my pass side behind the motor mount seems to drip the slightest amount and it's infuriating but only when cool and it's intermittent.

 

[pcf_mark]

I coat them with RTV then tap into place until they are flush with the surface. Go too far and they drop into the cooling jacket and you need to fish them out with channel locks. Clean the bore really good in case there is something that caused it to come loose. Machine shops let the new guy install these so maybe it was just a bit cocked? Getting to that look terrible.

 

[Bitch'nBronco]

I'd love to know if you have any success reinstalling with the engine in. The one on my pass side behind the motor mount seems to drip the slightest amount and it's infuriating but only when cool and it's intermittent.

I'll be sure to share. I'm def not pulling the motor for this and I don't really want to try to put one of those rubber ones in

 

[ba123]

I'll be sure to share. I'm def not pulling the motor for this and I don't really want to try to put one of those rubber ones in

My feelings exactly...although yours a little more urgent than mine.

You could connect the motor to a hoist, undo the motor mounts and only remove the affected side and see if there is room.

Make sure to clean, maybe with a copper wire brush on a drill if you can fit it and then use a little rtv (like Mark says above as well)

 

[DirtDonk]

Interesting comment by Mark. I thought there was a lip inside that kept you from going too far.
If not, then definitely do as suggested with flush.
If there’s no stop, you definitely don’t wanna have to try to fish one of those out from that angle!

 

[ba123]

I don't remember any stop or lip either but been a VERY long time. I just remember going flush edge.

 

[Bruners4]

I have always used Permatex Aviation Form-A Gasket non-hardening #2 to seal expansion plugs into cast iron blocks. And also use brass plugs when available. I use a driver that sets the depth to just below the block surface.

 

[jamesroney]

I don't remember any stop or lip either but been a VERY long time. I just remember going flush edge.

no lip, no stop. I drive them in in order to remove them. Never once had one that wouldn't fall in the block.

A good deep cup can go flush, but they look funny. So I always drive them to the bottom of the chamfer. Most of the new kits are shallow cups. So you have to be super careful to drive them square.

 

[Steve83]

They're not freeze plugs because 1) you should never let the coolant freeze, and 2) the plugs aren't designed or intended to do anything differently if you make that mistake. They're just bore plugs (or core plugs) because they're only there to plug holes in the casting that were necessary to hold the sand during the pour, which were later bored smooth so the plug could fit & seal. Ford never leaves a stop lip because that would make it nearly impossible to remove one without damage to the block. I usually add some Hylomar Blue to the bore before driving the plug in, but in a block that had rusted due to rubber plugs leaking for years, I added JBWeld to a couple.

I suspect yours came out because it was undersized, or the bore was damaged, and it was only the silicone holding it in until now. If you clean the silicone off (a cup brush in a die grinder works well), does the plug fall into the bore?

 

[DirtDonk]

The lack of a step makes sense and now I'm second-thinking my memory.
So a follow-up question is, are the bores tapered in any way? Or are they straight through in every instance?

And good luck trying to change the decades of calling them freeze plugs too. But glad you're trying at least.
I've known them as "well plugs" or "core plugs" or one or two others for most of my life. But I still revert to "freeze plug" when discussing them even today.
Oh well, keep up the good fight. Just like "proportioning valve" (even though that has more truth than false in the name) too.

Paul

 

[ba123]

The lack of a step makes sense and now I'm second-thinking my memory.
So a follow-up question is, are the bores tapered in any way? Or are they straight through in every instance?

And good luck trying to change the decades of calling them freeze plugs too. But glad you're trying at least.
I've known them as "well plugs" or "core plugs" or one or two others for most of my life. But I still revert to "freeze plug" when discussing them even today.
Oh well, keep up the good fight. Just like "proportioning valve" (even though that has more truth than false in the name) too.

Paul

I'm pretty sire they are straight bores. It's the plugs that are tapered.

 

[DirtDonk]

Thanks. Guess this is showing me that it's time to work on my own junk again. Time to start putting some of my engines back together!
Got three of them just sitting and waiting for me to do something about it. A '72 302, a '97 5.0 and a '79 400. And whatever else I find buried there.
So it's not like I don't have the resources. Just don't have the memory capacity!

Paul

 

[ba123]

Thanks. Guess this is showing me that it's time to work on my own junk again. Time to start putting some of my engines back together!
Got three of them just sitting and waiting for me to do something about it. A '72 302, a '97 5.0 and a '79 400. And whatever else I find buried there.
So it's not like I don't have the resources. Just don't have the memory capacity!

Paul

Get to it! You've helped enough people for you to ask for all the help you need!!! Just pick one to start with and get a move on!

 

[Johnnyb]

I had my 5.0 apart a few years ago and I can confirm two things. First, they will drop into the jacket and second, my plugs slid in way too easily for comfort.
I remember putting some kind of sealant/glue (maybe RTV) around the edge and tapping them in to flush. So far, so good and I run a 190 thermostat, so there's pressure sometimes.

-JB

 

[Steve83]

...are the bores tapered in any way? Or are they straight through in every instance?

Ford's are always straight.

And good luck trying to change the decades of calling them freeze plugs too. But glad you're trying at least.

I feel like I've made some progress on "starter relay".

Just like "proportioning valve"...

Well, a proportioning valve IS a proportioning valve. It's just that Ford didn't put them on Broncos, ever. My '98 Taurus has one, but none of my trucks.

...I run a 190 thermostat, so there's pressure sometimes.

The thermostat has nothing to do with system pressure. Its only function is to reduce warm-up time so the PCV system works sooner; nothing else.