kday

I noticed on my old engine that when I drained the coolant with the plug at the back of the block, lots of crud came out as the coolant drained. Same deal with the new engine, check this out:


<img src="http://www.boost-instruments.com/v6/DSCN1729.jpg">
<img src="http://www.boost-instruments.com/v6/DSCN1736.jpg">
<img src="http://www.boost-instruments.com/v6/DSCN1742.jpg">
<img src="http://www.boost-instruments.com/v6/DSCN1743.jpg">
<img src="http://www.boost-instruments.com/v6/DSCN1746.jpg">

I don't know exactly what that stuff is, it's green and sandy and may be some sort of precipitate from coolant mixing or just a product of corrosion. In any event it doesn't look like the coolant was drained through this plug any time recently. Note that it looks like this little pocket where the crud accumulated is in a "dead end" in the system, and appears to be designed to catch this kind of stuff.


It's really easy to remove the rear main seal with the flange removed. Looks like it would be a challenge with the flange in place, it's a tough seal.


Here's the new flange gasket. Out of all of the gaskets I've replcaed (pretty much all of them) this one was in the worst shape by far:

<img src="http://www.boost-instruments.com/v6/DSCN1749.jpg">

Removing the plug. That's an 8mm key (the hole is too small for a socket):
<img src="http://www.boost-instruments.com/v6/DSCN1755.jpg">

kday

<img src="http://www.boost-instruments.com/v6/DSCN1731.jpg">
<img src="http://www.boost-instruments.com/v6/DSCN1738.jpg">
<img src="http://www.boost-instruments.com/v6/DSCN1756.jpg">
<img src="http://www.boost-instruments.com/v6/DSCN1757.jpg">

A6Gary

Are you going to tank the block and other components to get them clean?

kday

Nah, I need to get this project done soon...

scoop713

The crud in the coolant is likely core sand from the original casting process. When cast, the coolant passages are filled with a core. This core is shaken out after the casting cools/soldifies. The core sand is often not 100% removed. It collects in low/dead flow spots, in this case above the drain plug. For this reason, you will always see oil/critical passages drilled, rather than cored like the cooling passages. For gray iron, this material is typically a chromite core sand.

Depending upon how well the casting was shaken, there could be more or less of this core material. In any case, the stagnant coolant flow around this collected material is undesirable. It will corrode there preferentially. It should be cleaned out if possible to prevent crevice corrosion.

egp320i

I would assume if you ever had your 5/60 service done at a dealer or competent shop they pulled the block plug and if any casting sand existed it was flushed out long ago.
As a used engine possible that plug was never touched.

haraldpost

Interesting read. A few weeks ago I did a coolant flush on my 12V. I was surprised that absolutely no coolant came out when I undid the block drain screw.. I poked in there with a screw driver and sprayed some WD40. I had done several cycles of filling with clean water and running the engine hot before it finally came gushing out from the block. Lots a nasty. It was filthy even though I'd done 2-3 flushes and the radiator drain came out clean.

egp320i

Yeah, as the low point of the engine which is a dead zone all the gunk settles there on purpose.
I can't believe how tiny the plug is though and how recessed up there it is.
Without being able to start the thread by hand one has to be careful.
Not a place you want to x-thread a bolt.

ktleop1959

I bought a set of long allen keys cut them at the bend and just use either 1/4 in or 3/8th sockets with a ratchet with the corresponding key inserted in them

egp320i

I happen to have a set of SK long allen sockets so all good. Just sucks you can't hand thread it first so getting it started you have to go by feel.