392 1st Gen Hemi. Have water leak and i believe it to be the freeze plug. The engine is in the car (48 DeSoto). The water seems to be running from down thru the motor mount, p***enger side. 1. Is that the location of a freeze plug, behind the motor mount? 2. Do i have to remove engine to get to the plug? 3. Above my ability to remove the engine. Can I remove the plug without removing engine? If yes, tell me how? Thanks, moparjack
I’ve drilled a hole in the plug and pry them out with a screwdriver or heel bar. I would make absolutely sure that’s where the leak is first and if possible take a couple pics and post them up.
^This. Get up in there with a cell phone camera or similar and take multiple pics to make sure that's where it's leaking from first. You can remove a freeze plug while the engine is in place, provided you can access the plug-- that might not be possible in your case if the attached image is the same as your 392, and the suspected leaking plug is the forward-most one, behind the engine mount.
If it's behind an engine mount, you should be able to unbolt the mount, jack up the engine, remove the mount completely and any surrounding wingdings to give yourself room. Make sure to use a block of wood to double up the jack so nothing falls. You can set some boards across the fenders to put a safety chain on the engine, if the paint/body hasn't been done yet. I've used moving blankets to protect paint. -rick
Thanks for your responses. I can't see it with my naked eyes, did not think about using cell phone to see if I can get a picture. Will try the cell phone and getting back to ya'll.
Could not get a picture. Not much room, when you stuff a 392 into an engine block that originally held a straight 8 flathead.
I picked up a Depstech boroscope online that works well enough for the girls I go with for about 40-50 bucks. I decided on one that blue tooths to my phone instead of having it's own screen because the reviews on the under $100 units showed most failures in the screen itself. -rick
Here is the HAMB tech thread for hemi cooling systems. I'll mention that it's discussed in there (I didn't read it all, YOU should) and from my experience that the early hemis used the flat style plugs, which are less service friendly. https://www.jalopyjournal.com/forum/threads/hemi-tech-cooling-systems.659020/ Provided it hasn't been modified too much, the front clip on a 48 isn't that bad to remove. If you have no joy in doing this plug in place, I'd pull the clip and see if it helps. It will probably be necessary to pull the clip to R&R the engine anyway. EDIT: since you mention pulling the engine is beyond your current abilities, I'd say replacing a plug behind the mount on the forward end of the engine (probably above the big crossmember and the more difficult style plug) is going to be also beyond your abilities. It can be done, but it's going to take a very skilled, determined effort.
When deciding if you can do it in the car, remember that the removal can be accomplished with more of a crude approach and with less room than the installation of the new plug. You need straight on access to install the new plug and get it properly seated so you don't wind up with just a better looking leaky plug.
Many years ago I had a 1974 AMC with the 304 V8 that I had purchased new. After a (in my opinion) short 4 years I noticed an antifreeze leak from a nearly identical freeze plug location right behind the motor mount on the side of the block. At first, I thought I would just take it to the AMC dealer and let them fix it. They called me with the quote to repair just the one plug…. I think it was around $300 and they clearly stated that it could be more depending on the difficulty of the job. I brought my car home and decided to do it myself. I set aside a weekend and rented an engine hoist. I pulled the engine completely out and removed the p***enger side motor mount to easily access the leaking plug. As it turned out, the decision to do this myself was the correct choice. Almost every freeze plug was just about rotted through, including the hidden one behind the flywheel. While I had the engine out I replaced them all, plus I replaced the water pump, the motor mounts, and while I was at it…the entire exhaust system. Including the cost of the rental hoist, I had under $300 for everything. Of course my labor was free. I would have started banging my head against the wall if I had just paid the shop to fix the one leaker, and discovered the next one leaking a month later.
I found the plug is behind the motor week. Why would they do something so stupid?? I had a mechanic check it out. He said he could remove the motor mount and jack up the engine and get to the plug. This guy is old time mechanic. His dad was a mechanic, his grand dad was a mechanic, and his uncle is a mechanic. Will see, suppose to take to his shop next week. Thanks for everyone's response. To install the engine had to remove entire front sheet metal, including the grill. Would like to replace all 6. Time and money, not my friend. I'm 81 very healthy, just don't get around as I did when I was 30. LOL Jack
Hot Heads makes a stainless steel machine plug set that seals nicely and lasts. I’ve used them on a couple engines. Definitely replace all. The OEM style plug is not as reliable as the Hot Heads design, in my opinion.
This is a huge defect in hemi design. Not only are they sketchy disk plugs, they put them in inaccessible places. Once the factory plugs fail, it is a challenge to replace them effectively. Just the act of pulling the old plugs causes problems. They are wedged on the pockets and when you remove them you likely scratch the walls of the pocket making sealing new plugs problematic. I have heard of some guys who machine out the pockets so they can use deep-cup welch plugs. You definitely need to pull the engine to fix the problem. Not good news, I know. You need direct access to have any hope of getting the old ones out with minimal damage. Then if you are going back with original disk style, whether original steel or br***, you need direct access to be able to hammer them to expand and seal. I have tried to do it in-place only to have a plug blow out while driving due to inadequate hammering. I have been replacing leaking plugs with Hot Heads bolt-expanded copper plugs which seem to work well. It goes without saying, whatever you use, goop it up with silicone sealer.
I replaced a core plug behind a motor mount once, it seemed impossible at first but actually was not too bad. It was a cup plug though. As said, the old one can be popped out with a pry bar or big screwdriver jammed through the rust hole, the surrounding metal is probably very thin so easily poked through. I held the new plug, and a medium sized socket on it, in place with one hand, and levered on the socket by prying against the motor mount. Once it went in just a little I moved the socket around and pried in little steps to get it in straight.
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