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Discussion Starter #1
Here's a little background:

https://forums.vintage-mustang.com/mod-custom-forum/1155818-guess-my-dyno-results.html

My new engine has about 20 miles on it and about 1-2 hours of run time and keeps popping freeze plugs on the dyno at high RPM.

It doesn't overheat. There's no indication of oil-coolant mixing or any indication of excessive blow-by. We've kind of ruled out that the head gaskets are on backwards because I think things would have gone south quickly that way.

The water pump is a regular old water pump, not high volume or pressure or anything like that:

https://www.ebay.com/itm/Engine-Water-Pump-GMB-125-1420AL/332227911024?hash=item4d5a539d70:g:1HQAAOSw7VJcpDEp

All the freeze plugs were installed by the shortblock builder:

https://treperformance.com

Can you screw up the free plug installation that bad, that many times?

We're going to try a new radiator cap. Other than that, brainstorming as to the cause is kind of at a dead end. If the block or heads were cracked I would think it would not seem like an otherwise good, healthy running engine.

I don't want to keep popping freeze plugs every time I rev to 6000 RPM in a cascade of weakest links.

What am I missing?
 

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Discussion Starter #3
Different one this time. So now I'm worried they put them all in wrong and eventually one of the hard to get to plugs will pop out. I don't know if I should cross that bridge when I get to it or pull the engine and redo every @#$&ing plug myself so I'm not left stranded somewhere. It's not like it's hard to pull one of these engines. Kind of bittersweet that I exceeded my power goal, and at only 6200 RPM.
 

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If it’s coolant pressure popping out the plugs, switch to a low pressure radiator cap. That way pressure will release out the cap instead.
You can also try running without a thermostat.

Still, coolant pressure shouldn’t be getting that high. If it’s not overheating then it’s gotta be compression/combustion leaking past the head gasket.

Try the lower pressure cap first.
 

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Boy, the freeze plug thing stinks, but not the power! Impressive! I thought for sure you were running a high volume water pump or something weird. You'll figure it out.
 

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Is this why the Boss had screw-in plugs, was it actually just water pump and normal heat pressure?
History of your block? Maybe it just has very excessive corrosion around the holes. I used some type III on mine but I really don't think it has much strength to it. I do know that some core plugs have noticeably deeper lips than others that ensure they are more square. One more and I'd be reaching for the JB Weld for every one.
 

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Discussion Starter #11
No history, the block, crank and rods were supplied by the builder. I'd give them a call but I bought this thing six years ago, I doubt they care.
 

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You shouldn't need to pull the engine but you do need to remove each engine mount to get them all.
Yea, it's not bad. A least it's not a SBC with freeze plugs between the engine and trans! I think mine may be epoxied in.
 

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Discussion Starter #13
Yea, it's not bad. A least it's not a SBC with freeze plugs between the engine and trans! I think mine may be epoxied in.
Yeah, I dunno, with the TCP mounts it might not be bad, I put those in with the engine in the car so I can easily get them back out. It's the headers that will suck. I really don't want to R&R them with the engine in the car. I'm kinda weird, sometimes I'd rather take something more apart to have easier access than to work in tight places. I have big hands and they get beat up even just changing plugs.
 

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Yeah, I dunno, with the TCP mounts it might not be bad, I put those in with the engine in the car so I can easily get them back out. It's the headers that will suck. I really don't want to R&R them with the engine in the car. I'm kinda weird, sometimes I'd rather take something more apart to have easier access than to work in tight places. I have big hands and they get beat up even just changing plugs.
With all my issues I've had my motor(s) in and out a half dozen times. I think I'm down to less than 2 hours each way. It's the mental thing about having to pull the motor yet again that get's to me. Good excuse to put in the top loader though!
 

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I'm trying to wrap my mind around this problem and can't imagine a freeze plug popping from internal coolant pressure. Water freezing, sure, a LOT of pressure develops when that happens. But if a coolant system pressurizes to the point that would push out a correctly installed freeze plug it seems to me that something else in the cooling system would blow first. Like maybe a radiator hose or even a seem on the top tank. I have seen top tanks blow like that.
I would suspect that freeze plugs that are a couple thou small were used or the block has some sort of problem in that area.
I've installed my share of freeze plugs and none of them were easy to get in their sockets. They all took a properly sized socket and a few good whacks with a hammer. Wouldn't it take that much force to pop one out?
 

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Discussion Starter #16
I agree that it's a physical problem between the freeze plug and block. Do you guys think my solid motor mounts are making my block flex instead of rotating normally like it would with rubber mounts, and the flex allows the plugs to pop out? I also made the error of using a rubber transmission mount with the solid engine mounts, could the give back there be exacerbating the flex in the block? I have a poly trans mount but I didn't figure it would be big enough of a problem that I had to get to it immediately.
 

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Buy the tester that indicated presence of hydrocarbons in coolant. If there is a positive test, then head gasket problem or crack in block between cylinder and water jacket. I don't think water pump should matter unless the plugs are put in wrong. Don't think that under 350hp really is going to stress the block enough to cause problems. I have seen some turbo/superchargers put a lot HP without problems. Do make sure your rad cap is good but if engine is showing no signs of overheating the pressure would have to be from another source (crack block/head gasket). I hope the plugs were just put in bad.
 

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No history, the block, crank and rods were supplied by the builder. I'd give them a call but I bought this thing six years ago, I doubt they care.
This is why I baulk at buying a pre-assembled shortblock or crate motor.

So lets say they screwed up... so what are they going to do now? You’ve already done the work of pulling it apart, and finding the problem they caused. It’s not like you can bill them, and they’ll pay you for the time.

Stories like this just make me lean towards Dad, and I getting the parts, and spending the day putting an engine together like we did back when we were drag racing.

Those were great times.
 

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I agree that it's a physical problem between the freeze plug and block. Do you guys think my solid motor mounts are making my block flex instead of rotating normally like it would with rubber mounts, and the flex allows the plugs to pop out? I also made the error of using a rubber transmission mount with the solid engine mounts, could the give back there be exacerbating the flex in the block? I have a poly trans mount but I didn't figure it would be big enough of a problem that I had to get to it immediately.
I don't think that has anything to do with it.
 

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May have been a batch of bad offshore freeze plugs. As long as everything else checks out replace them and enjoy the power!
 
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