Mangusta Freeze Plug Leaking / Blown Out

Think you have bad luck, and the freezeplug was not mounted the right way.

When there is overpressure from a leaking headgasket or something like that ,the pressure cap from the coolant pressure tank will open .

just my 3 c.

Simon

There are six and few can be done with the engine in place. There's only about 10-20 psi ever developed inside the cooling system, and that high point is only momentary. If the blown plug is not rusty, someone installed one incorrectly. There have been millions of SBFs made and very, very few actual plug failures.

Hammering a plug in will distort the shape and relax the wall tension that actually holds the plug in place. Some use epoxy, RTV or other glues when installing but that's unnecessary and makes a real mess to clean out when replacing plugs. THere's a rather complete article in a recent POCA Newsletter on this very subject.

I've never heard of anyone ever having had this problem before.

When I rebuilt my 302 I used thread in pipe plugs like used on the Boss 302 blocks.

I wasn't taking any chances.

It is a lot of work to do this and even my engine builder thought that it was unnecessary.

Once I decide on a course of action it seems next to impossible to deter me from it?

it will be a few weeks before I have time to tear into it, but like the rest of you, I'd never even heard, much less seen something like this.

all I know at this point is that it blew a freeze plug on the right side.  I was able to find the blown plug on the road and it looked surprisingly good.  Once I get time to see what happened I'll let y'all know.

MH

M!ke, I'm curious, has your engine ever been out of the car?

ONE MORE THING TO CHECK.

What kind of pressure are you running on your radiator cap?  

A lot ofnpeople think that because the cars in NASCAR run over twenty pounds that it is the thing to do.

The more pressure you run the harder it is to for the water to move in the system. In a mid engine car with water traveling so far that is not good.

Every pound of pressure lowers the boiling point in the cooling system by two degrees.  With any adequate cooling system you should run no more than seven pounds. That still gives you a boiling point of 212 plus 14 degrees, or 226 degrees.

I suppose that very high pressure in the cooling system could blow out a freeze plug that was not real tight.

DICK RUZZIN

Technically, they aren't "freeze plugs". They are core plugs. The holes in the block are there in order to remove the sand from the casting process.

In my experiences, the coolant pressure doesn't pop the plug, the plugs corrode on the inside where you can't see it, then eventually fail.

The only way to be assured that they can't come out like that is to convert the block to screw in pipe plugs.

I did that on my 68 302 block. It has the added safety features plus it helps stiffen the block for high performance use.

The 69 and 70 Boss 302 blocks came with threaded pipe plugs installed. A few other Ford blocks intended for high performance use did also, but not many.

Some late 427 blocks. The C7FE GT40 block. The Boss 429 blocks all came equipped with them.

They are not difficult to install. You need a 1-1/2"NPT tap and the pipe plugs. Those taps are not expensive since they are commonly used by everyday plumbers.

Here are some pictures of the Boss 302 block v. the 68 302 4v block.

I installed a 347 kit in my original block. From the exterior it looks stock. You can't tell it's a 347. In addition to the plugs I also am using a main stud girdle.

I think that the threaded plugs are worth the effort and time to install.

Ford installed them for a reason for maximum durability under extreme conditions. Ignor that as you wish. It's your block.

It is more important to have threaded plugs in the oil passages as you can see here in the back of the block.

On some engine like the Q code 428's, they used press in plugs. Considering that you are running at least 50 psi cruising and maybe as much as 100 psi with a high volume pump, pressed in plugs NEED to be replaced with threaded inserts.

@leea posted:

M!ke, I'm curious, has your engine ever been out of the car?

I'm pretty sure it's never been out of the car, I've spoken with the previous owner ('77-'97) and he said it had not been out before or during his ownership...  that only leaves a gap from '97-'05 (when Gary B. bought it).  Gary did replace the oil pan though...  but to my knowledge he didn't pull the engine.

@panteradoug posted:

Technically, they aren't "freeze plugs". They are core plugs. The holes in the block are there in order to remove the sand from the casting process.

In my experiences, the coolant pressure doesn't pop the plug, the plugs corrode on the inside where you can't see it, then eventually fail.

The only way to be assured that they can't come out like that is to convert the block to screw in pipe plugs.

I did that on my 68 302 block. It has the added safety features plus it helps stiffen the block for high performance use.

The 69 and 70 Boss 302 blocks came with threaded pipe plugs installed. A few other Ford blocks intended for high performance use did also, but not many.

Some late 427 blocks. The C7FE GT40 block. The Boss 429 blocks all came equipped with them.

They are not difficult to install. You need a 1-1/2"NPT tap and the pipe plugs. Those taps are not expensive since they are commonly used by everyday plumbers.

Here are some pictures of the Boss 302 block v. the 68 302 4v block.

I installed a 347 kit in my original block. From the exterior it looks stock. You can't tell it's a 347. In addition to the plugs I also am using a main stud girdle.

I think that the threaded plugs are worth the effort and time to install.

Ford installed them for a reason for maximum durability under extreme conditions. Ignor that as you wish. It's your block.

It is more important to have threaded plugs in the oil passages as you can see here in the back of the block.

On some engine like the Q code 428's, they used press in plugs. Considering that you are running at least 50 psi cruising and maybe as much as 100 psi with a high volume pump, pressed in plugs NEED to be replaced with threaded inserts.

I've learned about that over the past few weeks.  Makes sense that they'd need them to make the castings and just called them "Freeze Plugs" to make it sound like they were added for safety or some other such "benefit".

I'll take a picture of the plug, I don't see ANY significant corrosion, hopefully there isn't on the block either...  but, I've gotta get the car up on jackstands to even see which one came out.  I also plan to run a compression check on all cylinders while I'm at it.

Once I have more info I'll post it and as always, advice and input are appreciated.

MH

To err on the side of caution, I'm going to pull the engine for a full rebuild.  Too many unknowns to chance it.

I'll start a new thread on it

MH

M!ke, that is the most dangerous thing you can do...because how can you Not go back with a 347ci stroker kit... Lee

@leea posted:

M!ke, that is the most dangerous thing you can do...because how can you Not go back with a 347ci stroker kit... Lee

Yeah, that thought HAS crossed my mind...  we'll see...  I might do the mod to the transaxle support Dick Ruzzin has talked about while I'm in there as well.

MH

If you think that threaded core plugs are best, you're right. But unless you have lots of engine building skills and lots of tools, have a professional shop thread the block for you. First, DIY'ers will need TWO 1-1/2" pipe taps (last I checked, they were over $125 ea)  because the first one will only cut about 1 thread, then run into the cylinder walls inside the casting. So you take your second tap and with some sort of cutter or grinder, remove the tapered end up to the first full thread. That tap will then give about 4 full threads.  Which is enough with pipe tape.

And its remarkably difficult to hand-align the giant tap so it cuts straight. But once you've marked the core-plug hole with a single thread or more, you're committed- stock press-in plugs will not seal in that hole. So you may as well continue, or call the shop. And you have five more to go....Most shops will cut threads in a block using a milling machine with a boring head, not a pair of taps. They may be able to salvage a badly done thread and shorten the pipe plug enough to work.

Not sure about 302 Ford blocks but when threading 351-C blocks and tightening  the plugs, the pipe-plug tension distorts the cylinder walls enough that a honing deck plate is necessary to return to straight cylinder walls for good ring seal. Once done, threaded core plugs actually strengthen the block a little but its kind of overkill for street engines.

@bosswrench posted:

If you think that threaded core plugs are best, you're right. But unless you have lots of engine building skills and lots of tools, have a professional shop thread the block for you. First, DIY'ers will need TWO 1-1/2" pipe taps (last I checked, they were over $125 ea)  because the first one will only cut about 1 thread, then run into the cylinder walls inside the casting. So you take your second tap and with some sort of cutter or grinder, remove the tapered end up to the first full thread. That tap will then give about 4 full threads.  Which is enough with pipe tape.

And its remarkably difficult to hand-align the giant tap so it cuts straight. But once you've marked the core-plug hole with a single thread or more, you're committed- stock press-in plugs will not seal in that hole. So you may as well continue, or call the shop. And you have five more to go....Most shops will cut threads in a block using a milling machine with a boring head, not a pair of taps. They may be able to salvage a badly done thread and shorten the pipe plug enough to work.

Not sure about 302 Ford blocks but when threading 351-C blocks and tightening  the plugs, the pipe-plug tension distorts the cylinder walls enough that a honing deck plate is necessary to return to straight cylinder walls for good ring seal. Once done, threaded core plugs actually strengthen the block a little but its kind of overkill for street engines.

I've decided to pull and rebuild the engine (started a new thread).  There is a VERY good machine shop that I will send the engine to for the rebuild.  I'll talk to them about the threaded freeze caps, if I go that route I'll have them add that to the list.

I don't know ALL my limits, but I know SOME of them!

MH

On threaded freeze plugs, how much is piece of mind worth? Once bitten, twice shy.

A 1-1/2 NPT is currently $33.54 at Home Depot. You really want the non-tapered tap though and that you'll have to order and wait for.

The existing bore is perfect for it to start and it threads easily with a 15" Cresent wrench. Use plenty of oil on it.

I have the threaded plug just on my C8AE 302 block. I can't recall any issues installing them and just checked my tap and it was not modified but yes, it does come close to the bore sleeves.

My shop did my 351 at the time and installed brass press ins, but I'm tellin' ya', those things rust out from inside no matter what you do. 30 years on them is a long time.

It's just a thought to install them and if the block is in the shop anyway, why not ask how much to do them?

I do as much of my own work as I can and in addition my own brain surgery, although it does look like I need to redo my own pre-frontal lobotomy. I'm getting feisty again?

It is of interest to note, that even on the Ford installations, not all the plugs are seated 100% on the threads so it is normal for them to bottom against the bore liners.

I did notice that on this recent XE block, it did have threaded plugs in it.

Preparing an engine saying that you don't "need" certain items because you're never going to rev it past maybe 5,000 rpms and that they are overkill is silly.

IF you ever do a high speed track event in your STREET car, it's difficult to limit the engine to ONLY 7,000 rpm.

On the track that isn't much. You need to prepare it for maybe 8,000rpm, at least I do. That adrenaline is a killer.

I'm using main studs and a girdle. In addition, shaft mounted Jessel type roller rocker arms