View Full Version : Manifold Drain Plug Broken

09-06-2010, 09:31 PM
Took some time off from working on the trailer to go out on the water tonight with my boys.

When we got back I was looking over the engine getting my plan together for winterizing it since this is my first year with this boat.

I noticed one of the pipe plugs in the rear of the manifold was broken and the other ones torx was pretty mangled. Not leaking. Oh crap.

So do I need to get these out to properly winterize the engine or can I get antifreeze in there so it's not a problem? Or can I tip the boat forward enough to drain from the front?


09-07-2010, 11:53 PM
What engine?
You need to get those plugs out.

09-08-2010, 11:32 AM
351 in a 83' S&S

Here are a pic of the suspect plugs.

Port side is the problem, starboard should be OK.

I think there may be hope. The plug is not completely broken off. Hopefully I can get enough grip on it to get it out. Going to start dousing it with PB Blaster for the next few days.

09-08-2010, 11:40 AM
Once you have it saturated with penetrating oil (don't forget to tap it lightly with a ball peen hammer to assist getting the oil into the threads), I would try to remove with an impact turned waaaaaaaaaaay down and let it lightly work it loose.

09-08-2010, 12:47 PM
Oxy-Acetylene torch and a squirt bottle full of water.

Heat up the plug with the OA torch until it glows orange.
Squirt with water until it stops steaming.
Repeat two more times and you will be able to remove that plug with hand tools, I promise!

09-08-2010, 09:17 PM

I wish you guys were around here to help look over my shoulder for this one...or at least crack some jokes after I burn my eyebrows off.


09-08-2010, 10:16 PM

09-08-2010, 10:20 PM
Great advice Cloaked.

09-16-2010, 10:54 AM
Went with all good intentions that I could get the plugs out. No chance. The part of the plug that was left to grab hold of just broke off. The other one the hex was rounded out.

Called a couple of the local marinas and told them that I couldn't get the rear plugs out of the manifolds. They both said:

"Yea...why do you want to take them out? When we winterize we just circulate antifreeze through the engine. 99% of the time those plugs get frozen in there unless the boat is only a couple years old. We don't even try to remove them...no need to."

So my plan is for $99 to have the local marina do the winterization. Before I take it in I am probably going drain the block and pull the front manifold hoses and tip the boat forward to drain the manifolds from the front. Thinking I can flush them a couple times and suck the any remaining water out from the front with a tube hooked to my shop vac. Should be good enough for who it for.

09-16-2010, 12:13 PM

09-16-2010, 12:39 PM
Well the boat guy is partially right and a lot wrong, but it's not my biz.....

Sorry the plug broke off. You still need to get it out at some point in time, but for now.......

Save yourself the $99.00 (damnn that is high to add fluid). Leave all plugs in. Add a 50/50 solution through the raw water intake until you get a pink (RV antifreeze) color coming out the exhaust. Done deal. I have done it many times and no problems with climate in TN. Your drain process will still allow the possibility of water remaining in a low spot in the manifold. Water will freeze and expand.....bla bla... just sayin'.

It's really easy to add antifreeze. Add into the top opening of the tramsmission cooler. A funnel and about 2 - 2.5 gallons of mixed solution will do the trick. Crank the engine and while it is at idle just add the antifreeze and keep a look for the pink to comes through the exhaust. There may be a better way but so far, so good for the last many winters for me. An exception to this is that I will (and have several times) drain the engine and leave it without antifreeze if I know I am going to work on it during the winter sometime. Thus no need to keep adding fluid after a cold start in the driveway. But if it's going to remain dormant through the winter, no reason to be hesitant of adding antifreeze and checking on it in the next season.

$99.00 is highway robbery....

In the spring (or now, before you winterize) you can find a machine shop (or do it yourself) to drill the plug and extract it. Just be careful with the manifold. It is sensitive to impact and stress sources.

What I have shown here is the water hose in the top of the cooler.


I wouldn't recommend a 50/50 solution for someone in the Northwest. A gallon of RV anti-freeze is less than $3...not worth the risk of a diluted solution not having proper freeze protection, especially when you are adding it to an engine you already know will have some water in it.

09-16-2010, 07:15 PM

09-16-2010, 08:13 PM
fyi for some that may not have an older boat like this but you can not get an impact wrench on it and I expect it would be hard for a machine shop to drill it out because it is under the exhaust tube. the proper way to turn it is with a 1/2 inch square drive wratchet, no socket, just the wratchet. this may still work on the one that is broke off but probably not for the one that is rounded out. put the pb blaster or other penetrating oil on it for a couple days and see if it helps.

I have been putting teflon plumbers tape on my threads when I put the plugs back in, for the last few years and that works well. If you saw what sludge, ie. rusted chunks of metal come out of here when you winterize you would want to remove them each year, contrary to what the boat dealer says. good luck.

added thought, you can get to this with impact or drill if you seperate the riser from the manifold. I forgot about this when I first started.

09-16-2010, 08:52 PM

09-16-2010, 09:21 PM
I just pulled my manifold off to get a suck plug out. Put it in the vise and used some heat. But there was lots of the plug sticking out I could get a pipe wrench on it. The plug was only in maybe three threads.

09-16-2010, 09:36 PM

09-16-2010, 09:45 PM
Never heard of using candle wax, I'll have to try that some time. Makes sense to only tighten till it stops leaking.

09-16-2010, 09:49 PM
At work I use pressure gauges all the time, I put thread tape on the threads and only go hand tight with them and they hold pressures of 1200 psi!

09-16-2010, 10:59 PM
The optimum coolant combination is a 50/50 mixture of antifreeze and water. The 50/50 mixture will produce freeze protection down to minus 34F (-36C), and boilover protection up 265F (129C). However, in colder climates, where lower temperature freeze protection is needed, a mixture of up to 70% antifreeze can be used.

While this is true for automotive antifreeze it isn't the case with the RV antifreeze that is a lot more environmentally friendly and is usually used to winterize boat engines. Every jug of the RV antifreeze I've used specifically warns against mixing with water.

To be sure I get the full strength solution into the engine, I always drain the block before sucking the antifreeze through......using a bucket to draw the antifreeze out of and then pump back into through one of the hoses leading to the exhaust manifolds. This creates a loop while the engine runs for a minute or so and works well.

This method however, will not run the antifreeze into the manifolds (the second hose is pulled and plugged)......when I bought my 91 a few years back, I had to work on the drain plugs but felt they needed to come out. Once you start pulling them every year they are not a problem. Some good penetrating oil, time to soak (several days) and a bit of heat should break them loose eventually.

09-17-2010, 02:56 PM
The optimum coolant combination is a 50/50 mixture of antifreeze and water. The 50/50 mixture will produce freeze protection down to minus 34F (-36C), and boilover protection up 265F (129C). However, in colder climates, where lower temperature freeze protection is needed, a mixture of up to 70% antifreeze can be used.

Your point is moot.
DO NOT use automotive anti-freeze to winterize in an open cooling system.... ever.
It is very very toxic to your lake, or your sewer system if you fresh water flush before you put your boat in the lake in the spring.

09-17-2010, 03:30 PM
I had a lot of trouble with the plugs on my 84 until I started using anti-seize. No more issues. Also, like was stated before, no need to tighten very tight.

09-17-2010, 03:52 PM
I striped the threads a bit this year, I was able to retap then I installed 1/4 ball valves from Home Depot (18 bucks for 2). Now I just turn the valves to drain.

09-24-2010, 10:34 AM
Thanks for all the replies.

Unfortunately one of the previous owners over tightened the plugs and then stripped the hex on them both trying to get them out.

I really don't want to or pay pull both manifolds off.


09-24-2010, 12:39 PM
Not to worry, you can still do this yerself!

Here is just one example of probably dozens of extractors out in the market right now. I have used several different types and this particular version has worked well for me over the years consistently.


The basic idea is you will drill a hole all the way through the plug. This will relieve just a little bit of the pressure on the threads. It will also allow you to apply some penetrating oil on the backside of the plug! Let it sit overnight, then tap in the extractor and use a wrench to remove the plug. You can't go Medieval on the wrench, if the plug doesn't yield right away just try using some heat then more penetrating oil and try again after another day of soaking.

You can do this! I am pulling for ya!