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O/T GMC Jimmy question freeze plug blowing them out

O

old

Well-known Member
Location
Camdenton Missouri
Ok so this GMC S-15 jimmy went to Gulfport MS and back again with no problems now all at once it is blowing freeze plugs out of the engine. Blew one out the drivers side of the engine then 4 miles later the one out of the other side. So what the heck is going one. In all my years never seen this happen to any engine. The right side of the engine was a soft plug type that you tighten a bolt and it looked good other then it was blown out and laying on the starter. If it makes a difference the boy ran the tranny low on fluid so it now need work big time
 
Pressure cap is the wrong pressure or is stuck closed and not holding the coolant pressure to the proper value is all I could think of.
 
Metal expansion plugs do get corroded. But it is abnormal to have two come out. Use the all metal double washer expansion style and a bit of #1 permatex on the outside to make a hold in edge.
 
Ya that is what I am thinking is the cap has a problem and not letting off the pressure as it should when it should. This has happened twice in less then 20 miles of driving so maybe the cap has gone bad. I hope lol since these plugs are not easy to install in this rig
 
Where theses plugs it is very hard to get to them. The first one that blew I have no idea of what it was but the 2nd one was a rubber nut type plug that blew out. Thinking maybe the radiator cap has gone bad and it not letting off at the pressure it should and will replace it when we do the next plug
 
When something like this happens the first thing I suspect is a bad head gasket or a cracked head. Usually you have a radiator problem instead of a frost plug problem. Have you checked the cooling system for compression gases?
 
Old check the vent tube in the radiator neck too, I have seen them plugged from GMs anti freeze problems.
 
I'd think a even a new radiator hose would blow before a freeze plug would blow out of the block. that is unless they are about rusted out.
 

Given the choice, I prefer to use the Deeper replacement freeze-Plugs..

That last one that blew out could not have been an Original..

If you had enough pressure to blow out GOOD freeze Plugs, the radiator and hoses would have failed first..
If they are in place GOOD, I am sure you could Stand on a Socket and never move a good freeze plug, no matter what you tried..that would only equal about 70+ PSI..

Ron..
 
I wont use the soft plugs,had one fall out.I cleaned the hole and made sure it was dry.Put the plug in and tightened it up.Next morning it was laying on the floor.
 
If it blew out one freeze plug, how did the car make it another four miles? I have to assume you replaced the plug, and it blew the second plug after driving another four miles.

The most likely suspect would be a blown head gasket.
 
Your problem is in using that rubber thing in the first place. If you MUST use one, be extra careful to have a clean, dry surface when you install it, and get a low pressure radiator cap (7psi).
Good Luck and God Bless
 
We had a 4.3 in a Jimmy that would get hot enough to spring thermostats stuck half open.Never did find the cause even after pulling the engine down. New coolant pump, all hoses etc.
 
X 2 on the 7 lb pressure cap. Had a problem with my 2.8 Chevy blowing the radiator drain plug. Radiator shop said 16 was way to high even though it was a new GM cap & suggested the 7 lb cap. Never had a problem after changing it.
 
Driving a cup type freeze plug with a socket or anything that hits the plug in the middle is wrong. What you are doing is distorting the plug & it takes away the press fit. You need a driver that contacts the plug on the top edge of the plug. measure hole & measure your plug if I recall there should be around .003-.005 press. Sand your holes in the block & use a loctite sealer on them.
 
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