Core Plugs - Alfafan {P}
When I bought my Celica, I spotted an invoice in the service history saying the core plugs had been changed. In the dim and distant I used to do the routine services on my Alfasuds, but never came across this expression. Excuse my ignorance but what are they?
Core Plugs - Primera_p
I'm sure someone else can provide the correct description but I think they are basically metal plugs used to seal up the cooling system (I think their presence is a by-product of the engine manufacturing process)

I hope that makes sense - can anyone else provide the correct definition?
Core Plugs - RichardW
About right. When you cast an engine block you have 2 parts to the mould - outside and inside (which makes the waterways, bores etc). You have to hold the inside mould inplace whilst you pour the metal in. When the mould is taken apart this leaves holes in the outer block. These needs to be sealed up, and this is done with core plugs - basically thin metal lids that are driven into the holes in the block. They can sometimes start to leak which is why they sometimes get replaced. Not a service item, just something that needs doing occasionally.

Core Plugs - Peter D
THe use of core plugs in the block of an engine was to protect the block from cracking if it froze up. However modern coolants protect you from this put it remains a safety feature as well facilitating the casting process. Core plugs ocassionally corode and require to be replaced. However they have stopped putting the hole in the bumper so you can crank start it. Regards Peter
Core Plugs - Dizzy {P}
The use of core plugs in the block of an engine was to protect the block from cracking if it froze up.

Peter, I'm sorry to disagree but that was a very common misconception from many years ago. Core plugs are needed purely to fill the holes left from the casting process, as Richard said. Core plugs don't really do anything to stop the block cracking if it freezes.

Engine designers would love to get rid of core plugs. The cast holes that they fill cost money to machine, the plugs cost money to buy and fit, and they are a potential leak-point that we could do without.
Core Plugs - Altea Ego
Hate to diagree with you, but thats exactly what they did on my fathers 1932 austin 7 tourer. He didnt put anti freeze in, the core plugs came out, and block stayed in one piece. He used araldite to fix them.
Core Plugs - martint123
Beg to differ again. The plugs are a requirement of the manufacturing process. It's only because they are the weakest link that they pop out if the block freezes - other damage is common (possibly not on an ancient sidevalve '7 though)

You can also find plugs in crankshafts, camshafts any places where there are voids in a casting for things like oilways.
Core Plugs - M.M
Dizzy is right. Core plugs are a result of the casting process with perhaps an added benefit that they *may* push out and save a block if you are lucky. I wouldn't rely on it though.

Aren't they used to get the casting sand out or are engine blocks done a different way?

Core Plugs - Tony Bee
Many many years ago I drove Atkeys Mini Clinic in Nottinham ( ah nostalgia --a thing of the past ) mad trying,Under guarantee, to cure water in sump syndrome on my new Minivan.
They tried everything including changing the head gasket of course all to no avail.
One day I had the lid up and was just tinkering about when my wife said " Why did that drip of water run down that hole with that stick thing in it ?"
Sure enough a regular drip of water came out of the core plug above the dip stick hole and scurried like a jackrabbit straight into the sump.
New core plug cured it of course.
No wonder BMC made nothing on every one they sold.
This was the car that had 6 replacement heater matrixes before they got one that did not leak.
Unbelievable but unfortunately true.
Core Plugs - Peter D
Hi Dizzy, You did not read all the message as I detailed that the holes are for facilitating the casting process. In the days when you only put antifreeze in during the winter, Yes the Austin 7 for instance, the core plugs were designed to be the weekest link and were simple a dished disc that was placed in the hole then flattened with a drift to lock them in. With the advent of continuos coolant antifreeze the modern core plug is much more sturdy with a lipped insert and much more secure. although I have come across people who have even blown them out in a freeze. Regards Peter
Core Plugs - glowplug
I'm not sure what's the real reason for them, but about 18 years ago my brothers Transit (fitted with a 3.0ltr V6) was borrowed by a friend who holed the rad, repaired it and refilled without antifreeze. So the water in the block froze and popped out the core plug on the back of the lump above the bellhousing. The plug was replaced and all was well.

Core Plugs - Dizzy {P}
I know Peter said that this was secondary to aiding the casting process but I still feel reasonably sure that core plugs were never actually *designed* to pressure-relieve the block when it froze.

If there was very localised freezing right next to a core plug, then I agree that it might pop out and save the block cracking. But what happens when the freezing is taking place away from a core plug? If the freezing is adjacent to where a water hose connects to the block, the hose might expand and relieve the pressure -- so do we then say that water hoses are designed to stop the block cracking?

I well recall the almost-flat core plugs and these were universally replaced by the cup-shaped plugs because the latter were far more secure. However, our engine production people still found the need to use a sealing compound on the plugs to assure a 100% leak-free engine, this being Loctite 575 when I was involved 10 or 15 years ago. (In fact, the Loctite was applied to the hole, not the plug, because it would wipe off the plug as it was fitted.)

Loctite 575 has very good sealing abilities combined with low strength, the idea being that the plug can be easily removed if necessary in the future. ThreeBond 1110B is an equivalent that we found equally suitable. Industry buys these sealants in 2-litre cans but they may be available in small amounts from local factors. If not, there are other grades that would do the job if you ever need to replace a core plug, though a *hydraulic* sealant is preferable to Studlock or any other high-strength, low-viscosity, grades that might be found in the local accessory shop.

Sorry to ramble on again. Some day one of my ramblings just might help someone! Yes, I know, confusion is more likely!

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