Does anyone really do this to their cooling system?

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cruiser

cruiser

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Hi Mopar guys and gals: Cruiser here with a cooling system question. I'm pretty particular about keeping up the cooling system in my bone stock 1974 slant six Duster. The owners manual says the proper way to change the coolant is to knock out the freeze plugs in the side of the motor to drain all the dirty coolant out. I've never done this in any slant six car that I've ever owned. First of all, I wouldn't know how to get them out or back in. And second, they're nearly impossible to access as they're under the exhaust manifold. Looks like there are four of them back there. In any case, I've been backflushing my cooling system with a backflushing tee in the 1/2" heater inlet hose for a number of years. Seems to do the job very well. But now I'm thinking that I might be trapping some dirty coolant in my engine because (I'm assuming) the thermostat is closed during the backflushing process, and I haven't knocked out the freeze plugs. There's also another plug in the right side of the block under the #5 spark plug (see photo). What does this do? Does it drain the block? So the question is: How thorough of a job does backflushing my cooling system do? Thanks.
 
I don’t know the slant, but on the LA there is drain plugs on both sides of the block to drain it.

I would not remove the soft plugs unless the motor is out and your doing a rebuild…

And if you have a stock system that’s not having problems, best is to just drain it, DO NOT USE FLUSH, and put some new coolant in it. When you use flush, it is like solvent and can actually cause problems… so now you have problems where you did not have one…
 
There's no way in HELL I'd ever do that. First off, what a pain in the ***. Secondly, the freeze plugs are on the WRONG SIDE to drain by removing them. If they were down low on the passenger's side, you'd get more out, but then you couldn't get to them. lol No. I think I'd just flush it good after removing the thermostat and bottom hose until I got clear water and call it good.
 
cruiser said:
Hi Mopar guys and gals: Cruiser here with a cooling system question. I'm pretty particular about keeping up the cooling system in my bone stock 1974 slant six Duster. The owners manual says the proper way to change the coolant is to knock out the freeze plugs in the side of the motor to drain all the dirty coolant out. I've never done this in any slant six car that I've ever owned. First of all, I wouldn't know how to get them out or back in. And second, they're nearly impossible to access as they're under the exhaust manifold. Looks like there are four of them back there. In any case, I've been backflushing my cooling system with a backflushing tee in the 1/2" heater inlet hose for a number of years. Seems to do the job very well. But now I'm thinking that I might be trapping some dirty coolant in my engine because (I'm assuming) the thermostat is closed during the backflushing process, and I haven't knocked out the freeze plugs. There's also another plug in the right side of the block under the #5 spark plug (see photo). What does this do? Does it drain the block? So the question is: How thorough of a job does backflushing my cooling system do? Thanks.
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I have doubts that the “owners manual” instructs one to remove the freeze plugs to drain the antifreeze. It’s not that I don’t believe you, it’s just that is insane.
The hex head plug low on the block under # 5 sparkplug is the drain for the water jacket. Get that threaded plug out and you will still probably need to probe the hole with a stiff wire or screwdriver to punch through the rust and crud to get it to drain. Thread the plug in hand tight re fill the block with clear water and remove the plug several times to get it flushed good.
 
I just looked ay my service manual and it says nothing about the freeze plugs. Of course it's a 1964 version, but still.
 
my68barracuda said:
I have doubts that the “owners manual” instructs one to remove the freeze plugs to drain the antifreeze. It’s not that I don’t believe you, it’s just that is insane.
The hex head plug low on the block under # 5 sparkplug is the drain for the water jacket. Get that threaded plug out and you will still probably need to probe the hole with a stiff wire or screwdriver to punch through the rust and crud to get it to drain. Thread the plug in hand tight re fill the block with clear water and remove the plug several times to get it flushed good.
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Here's the excerpt from page 43 of the 1974 Plymouth Duster Owner's Manual. Perhaps I've misunderstood it. It says to "remove the drain plugs in the sides of the cylinder block". I took this to mean the freeze plugs because I can't find any "drain plugs" in the side of the block. So now I'm assuming that they are referring to the single plug that I posted a photo of. I guess what I'm wondering is if you do a better flushing job by using the backflushing tee instead of draining the block like the owner's manual says. To me, it seems like using pressurized water to blow everything out of the cooling jacket is better than simply using gravity to drain coolant out of a hole. Your thoughts?

IMG_3016.jpg
 
cruiser said:
Here's the excerpt from page 43 of the 1974 Plymouth Duster Owner's Manual. Perhaps I've misunderstood it. It says to "remove the drain plugs in the sides of the cylinder block". I took this to mean the freeze plugs because I can't find any "drain plugs" in the side of the block. So now I'm assuming that they are referring to the single plug that I posted a photo of. I guess what I'm wondering is if you do a better flushing job by using the backflushing tee instead of draining the block like the owner's manual says. To me, it seems like using pressurized water to blow everything out of the cooling jacket is better than simply using gravity to drain coolant out of a hole. Your thoughts?

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You have found the block drain. It is the pipe plug below #5 spark plug.
I think that removing the block drain plug is an effective way to flush the block. The rear of the block can be a dead space where cooling passage debris can collect. It is worth the time to drain the block from there periodically.
 
but they are refering to the drian plug. big allen headed or square head gub screw, not the core plugs

one presumes this is an early version of cut and paste
the same text appears in my manual published in Austrlia and mine has 1 drian plug, plugs is inaccurate in my case.

the core plugs were there to fill holes that were used to remove casting sand after the block was cast... i have some in my clinder head as well
early heads had screw in plugs my later head has minature core plugs between the rocker posts and valves

mine isn't a slant.. mind
 
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I usually put petcocks in those after all the rust is out for maintenance every year. I just crack them and see if any crap comes out if it does time for a good flushing out with the petcocks removed.
 
I know this is a 360 block, I don't have a slant 6 to get an example from.
<the mentioned items are circled in green>
But the basic concept should be the same. As said previously they're either allen set screws or a pipe bolt of some sort at bottom portion of the engine block.
22J4-5.jpg
 
Agree with Post 11. Good to put drain peacocks in . Also great for draining when replacing a timing chain.
 
cruiser said:
Here's the excerpt from page 43 of the 1974 Plymouth Duster Owner's Manual. Perhaps I've misunderstood it. It says to "remove the drain plugs in the sides of the cylinder block". I took this to mean the freeze plugs because I can't find any "drain plugs" in the side of the block. So now I'm assuming that they are referring to the single plug that I posted a photo of. I guess what I'm wondering is if you do a better flushing job by using the backflushing tee instead of draining the block like the owner's manual says. To me, it seems like using pressurized water to blow everything out of the cooling jacket is better than simply using gravity to drain coolant out of a hole. Your thoughts?

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That's pretty crazy. Pull out all the core plugs and do your flush and fill and report back to us how that works. :poke::lol:
If A plug isn't leaking I don't disturb them. Just sayin' I am trying to figure out why you feel the need to remove every last drop of coolant out of the system?
 
I unhook the heater hoses and pull the pipe plug(s) (1 on a /6. /2 on v8s).then I put a garden hose with one of those twist nozzles in the heater hose I disconnected and let er rip til I get clean, clear water out of the other heater hose and removed pipe plug. If it's bad I'll run some iron out in there and run the engine a while then flush til clear. Then I drain the radiator and block drain. And finally with straight antifreeze (not 50/50) i fill it 1/2 way whatever the capacity is, then finish filling it with water. At this point is when I have to run it and belch the air out and top off til it's full. Last, I fill the side bottle with mixed antifreeze
 
My 97 Dakota with 330K and my 98 Dakota with 270K on the clocks both still have their original super clean radiators.
 
Seems like overkill to me, and I like to do things the right way. Removing the plugs might open another can of worms.
 
I learned something new! Never heard of doing it this way
 
When its all said it done whether you do nothing or turn the car upside down, a closed cooling system is next step. It keeps the rad full (keeps air out) and the nasty off the street. IMHO
 
Frank Mopar said:
When its all said it done whether you do nothing or turn the car upside down, a closed cooling system is next step. It keeps the rad full (keeps air out) and the nasty off the street. IMHO
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Thanks, everyone for the great suggestions. After reading through the replies, I think I may end up taking TF360's advice, to just leave the side drain plug in place and keep backflushing it as I have in the past. I have a bad feeling about trying to get that plug out after it has been in there for the past 34 years. Usually, I just foul it up somehow and end up opening that can of worms that he mentions. Toolmanmike asked why I feel the need to remove every drop of dirty coolant from the system, which is a good question. There's no logical reason, other than I'm a bit obsessive about purging old coolant. Since 2019, I've replaced the incorrect radiator that the car came with and installed a correct part number recored and rebuilt radiator. I've also replaced the water pump, thermostat and housing, heater core, all heater and radiator hoses, and installed a NOS correct part number (one year only for 1974) radiator cap. There's nothing left to replace in the system, and it cools beautifully. Thanks again to all who took the time to weigh in with their opinions. You guys have been extraordinarily helpful in keeping my 49 year old car running like a brand new Plymouth. Muchos gracias!
 
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