Pop out 2 freeze plugs

Had a eariler post about motor pushing out water. Got that fixed now its popped out 2 freeze plugs. One on each side of motor. by motor mount. 545 is really being a pain lol

What kind of water pump?? Are you using a thermostat??
The reason I ask is because years ago, I was using a regular belt driven water pump and a thermostat, but I was spinning the water pump much faster than normal, and the T stat would not allow the water to "escape" the engine as fast as the pump was pushing it through.
It created a hydraulic situation, and blew out a freeze plug.
I just happened to be making a low 10 second pass when it blew out, and like an idiot, I had anti-freeze in the system!!
Next thing I knew, the car was skating all over the track, I spun around backwards, then back around again....and by the grace of God, I was able to keep it off the walls on both sides of the track!!
After that, I removed the T stat and replaced it with a restrictor washer that had a 13/16" hole in it. Fixed the freeze plug and buttoned it all back up. Made more passes (with only water in the system this time!!) and rechecked everything.
Although it did not blow out any more freeze plugs, there was still enough hydraulic pressure to bend the restrictor inside the water outlet neck!!
I could have swapped different pulleys to slow down the water pump speed, but instead, I put a Meziere electric pump on it!!

We just ordered smaller pulleys and took out the thermostat. We had a gutted out thermostat in it to start with. But i think the 13/16 hole like you did may help to. Thanks for the info ill let you know how it goes

Years ago I had a 79 F150 with a 460 in it. My dad had an 86 Supercab that chucked a rod so I swapped my 79 460 in there using the L&L swap kit (ie mounts, headers, accessory brackets and pulleys). That thing blew core plugs out all the time in the 86 and never once did it all the years in my 79. It has to do with the pulley ratio and how fast the water pump is turning is my guess..

Hope pulleys come in today. The block is a 71.

Usually it is because the block is absorbing quick stressing forces to deform it enough to cause this ...
simply another reason to use a front motor plate and NOT use solid motor mounts on the side of the block when having a heavily stressed chassis.

Using a deeper plug with more press or a screw-in plug normally keeps this from happening.

Watch your water chemistry too, it can cause pressure to be created.

I put a pressure gauge on mine once with a mechanical pump and big crank pulley. It would make 25+ psi when revving the engine and the pump was turning ridiculous rpm.

I switched to an electric pump and it was a consistent 10psi.

DETONATION. have seen a few guys wreck their car because of this, they heard the engine detonate, next thing they knew they were sideways


We run 20 to 25lbs

were they installed with no1 permatex? If not they should be. nothing else. be sure to use the deep plugs

no1 drys rock hard

Does it make a difference which freeze plugs you use ? I know you said to use the deep freeze plugs but is brass better than the steel ones its got the steel ones in it now.thanks again guys for your help

My 460 powered comet did this same thing it was the plug at the starter .I went to a 13 pound cap from a 16 that stopped it .It started doing this without my changing anything .When I changed radiator caps it stopped .I have used a 10 pound cap as well . Doug

capncruncher1965 wrote:Does it make a difference which freeze plugs you use ? I know you said to use the deep freeze plugs but is brass better than the steel ones its got the steel ones in it now.thanks again guys for your help

leave the steel ones in it, we run 21 pound caps ,18 min

BOSS 429 wrote:DETONATION. have seen  a few guys wreck their car because of this, they heard the engine detonate, next thing they knew they were sideways  


We run 20 to 25lbs

were they installed with no1 permatex? If not they should be. nothing else. be sure to use the deep plugs

no1 drys rock hard

Rich, is that Permatex the old "Form-a-Gasket"?

Colt Macara wrote:

BOSS 429 wrote:DETONATION. have seen  a few guys wreck their car because of this, they heard the engine detonate, next thing they knew they were sideways  


We run 20 to 25lbs

were they installed with no1 permatex? If not they should be. nothing else. be sure to use the deep plugs

no1 drys rock hard

Rich, is that Permatex the old "Form-a-Gasket"?

yes, stuff dries like rocks, brown stuff.

I once took a 351c apart in the 70s that a guy had put that stuff on both sides of the head gasket ,yuck

LOL....did you have to grind the gaskets off with a Makita??

When i built both 460's several years back Lem said to use red loctite on the freeze plugs , so far so good.

I blew out a freeze plug on a burnout,I am running a Edelbrock high flow water pump and 180 t-stat, so when I built a new short block I tapped the block for screw in plugs, never had an issue since.