Steel or brass core plugs?

[Spinneyhill]

I was wondering why some seem to prefer brass core plugs. I observe my parts book says they should be steel 0.083" thick. I know galvanic corrosion will be less with steel.

 

Any thoughts, anyone, on the benefits of one or the other?

[Guest]

I read here about people using brass core plugs but have never used anything but steel ones myself.  In fact I have never seen brass ones in any of our local suppliers.  Any that I removed were steel and any that I have replaced have lasted from 20 to 60 years.  I also never have used sealant of any kind.  Always installed the plugs dry and seated them with one sharp blow.

Edited May 26, 2018 by Guest (see edit history)

[Bush Mechanic]

I have just had 3 steel plugs leak in a rebuild. Same sealant and method as usual. The edges did seem rougher than usual. These are saucer plugs, not cups.

Talking to the local engine machinists, and they are now turning oversize plugs down on the lathe, due to leakage problems from roughly punched plugs. They recommend pinning the plug against a 3 jaw chuck with pressure from the tailstock.

My local tractor parts stockist no longer carries steel plugs, only brass, so I am giving them a try. Not sure how the dissimilar metals will get along, but in an antifreeze environment they should be OK.

[Spinneyhill]

2 hours ago, Bush Mechanic said:

they are now turning oversize plugs down on the lathe

Yes, that is what an engine rebuilder said they would do. Mine are saucer or disk or lens (depending on who told you) and they would turn down what they had, which were pretty much all cup plugs.

 

They said they would pin it against a piece of pipe in the chuck - faced off first, of course.

[Curti]

I have always used steel core plugs available at the local auto parts store. In addition to all of the ordinary precautions, I put a small amount of gasket sealer around the circumference.  I always run a reasonable amount of stop-leak in the cooling system.  Never had a problem.   

[joe_padavano]

After replacing more than my share of rusted, leaking steel freeze plugs, I only use brass whenever I build a motor.

[JACK M]

Manufacturers wouldn't spend the extra for better parts would they?

Being from the Marine industry I have seen a lot of brass core plugs and I use them in my cars when I can.

[RansomEli]

LIke Joe_Padavano, I have replaced quite a few leaking and just-about-to-leak steel freeze plugs with brass ones. Every time I touch rebuild an engine I make the switch

[Spinneyhill]

Thank you for your responses. The steel plugs I removed have been in for at least 20 years and probably more like 40 or 50 years. There is some corrosion but still plenty left.

 

The corrosion on the back of them looks like erosion corrosion. From www.corrosion-doctors.org,  "Erosion corrosion is an acceleration in the rate of corrosion attack in metal due to the relative motion of a corrosive fluid and a metal surface. The increased turbulence caused by pitting on the internal surfaces of a tube can result in rapidly increasing erosion rates and eventually a leak. " So between me and the P.Os of my car, we haven't quite changed the coolant often enough - the anti-freeze anti-corrosion chemicals have been used up and the coolant has become slightly acidic. They have lasted pretty well though.

 

There may be an element of galvanic corrosion too. Steel is just above cast iron in the galvanic series. Brass is way below, so any galvanic corrosion will be in the block around the plug.

[DavidMc]

Brass is way below, so any galvanic corrosion will be in the block around the plug

 

Isn't that a reason to avoid brass plugs?

[c49er]

Chrysler Flathead eight and six engines used brass core plugs at the rear of the block between the rear of the blockand  bell housing and also behind the front engine support plate when the engines were new.

This... as to replace  leaking steel plugs  as factory installed on the side of a flathead is easy... not the front or rear of the block. So I always use brass as I have seen way too many steel plugs start to corrode and leak... especially modern day Chinese core plugs.