Freeze plugs or casting plugs will fall out if they corrode. Some
manufacturers use steel plugs, other brass and neither will blow out under
water pressure if hooked up to pressurized dock water even if the water pump
seals hold. Although the plugs are a force fit, the different expansion rates
between the cast iron head and the brass or steel plug and the electrolsis
between the different metals can and do loosen the plugs. Sealing the plugs is
a good idea but DO NOT use any brand of RTV or silicon sealant. RTV is made to
be crushed after it has set. Driving the plug in will remove a RTV or silicon
based sealer. The best product to use for this is a product called Copper
Coat. It comes in both liquid form with an applicator brush and a spray. Coat
both the edges of the plug and the machined opening. Allow it to dry for about
a hlf hour then tap the new plug into place with a wooden dowel or the proper
tool. A dowel should be only slightly smaller than the plug or you will
distort it and it too will fail. Make sure the plug is square to the opening
and drive it only far enough so that a small amount of its out edge can be
seen. Copper Coat can be found at any automotive parts store. It's some of
the best sealer on the market. Hope this helps.

Dennis
Former ASE Master Auto Tech and now marine tech.


I've had several Volvo MD series engines and never experienced this.

Is there a possibility that someone put dockside hose pressure on the
coolant system?? Maybe when flushing?? If the discharge were closed or
restricted, the pressure could not only do this, but damage the waterpump
seals.

However I have replaced core plugs in other engines I have rebuilt.

A core plug is simply pressed into a machined open in the casting. In fact
there is seldom any shoulder behind, to keep it from being pressed all the
way into the coolant passage.

I recommend that you examine the machined surface where the new core plug
would seat. Make sure you don't have excessive rust and pitting. There
should be at least 3/16" clean, machined surface to seat and seal. If there
is pitting from coolant leakage in the past and there is still sufficient
good metal to retain the new plug, they you could use some High Temp RTV on
the plug. Other wise this should be a metal to metal seal, dry press fit.
You can purchase brass replacement plugs from Volvo and just tap them into
place with a wooden dowel until the plug lip is flush with the casting
surface.


--
My opinion and experience. FWIW

Steve
s/v Good Intentions