Does anyone really do this to their cooling system?

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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?

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That's talking about the pipe plugs, not the freeze plugs.
 
cruiser? Where did you find that nos radiator cap?
I first found the correct part number in my 1974 parts catalog (see photos), then bought a NOS one on e-Bay about a year and a half ago. I don't remember the name of the vendor. As an aside, I visited my favorite junkyard in western MN to find a spare radiator for my Duster at that same time. The slant six radiators are getting really hard to find, but I found one still with its factory original cap. The cap looked pretty worn, but I popped it on my Duster and it worked perfectly! Sorry, too much information - I know.

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In your case as the system has been opened and fluid changed that recently ago, you probably don't have to go nutz on a flush. but it should be done, and that pipe plug pulled. As long as you get a good, (not worn out, decent quality brand) 6 POINT!!!! socket on that pipe, plug it shouldn't come out too hard. the worst thing, is to try with a wore out, or cheap, (or any 12 point) socket on it, when breaking it loose. The one on my 74 block came out easily, and this was a Rust belt block since it was new.
Any sediment will settle to the bottom of the water jackets, which is where that pipe plug is.... the point of a flush is to get rid of that sediment that can break free under normal use and plug up heater cores, take out water pump seals or such. by doing what you say, you won't flush that sediment upwards and outwards.
Let gravity help you, by having it flow out that pipe plug opening.
 
Would vinegar hurt the system ?
If not you could run a few gallons of vinegar theu the system and drive (or let it sit after running the engine) for a few days then drain it . That should disolve rust in the jackets.
 
So will the iron out I suggested.it was originally marketed for cleaning the same type of deposits out of boiler radiators, and I have some old Prestone flush cans that are exactly the same thing (sp?) Oxalic acid. Flush with water til as clean as it can be, add a cup of iron out, finish the fill with water, drive a bit to circulate it, if real bad let sit with this in it over nite, pull block drain and radiator drain and flush with water again til clean, fill er up and let er rip
 
So will the iron out I suggested.it was originally marketed for cleaning the same type of deposits out of boiler radiators, and I have some old Prestone flush cans that are exactly the same thing (sp?) Oxalic acid. Flush with water til as clean as it can be, add a cup of iron out, finish the fill with water, drive a bit to circulate it, if real bad let sit with this in it over nite, pull block drain and radiator drain and flush with water again til clean, fill er up and let er rip

Right ... missed that post .
 
Confuscious say: "Man who goes through airport turn style side ways is going to Bangkok".... :D
 
I’ve been turning cars upside down to drain coolant since my father taught me years ago.

Well, your daddy do e taught you wrong. Everybody knows that you need to disconnect the radiator hose, get a friend d with a truck and a winch and drive it down to a quarry. You hook your bumper to the winch hook and lower it into the quarry. As you lower it, the old water drains s out. You then let the front end dip into the half filled quarry water a few times to wash the block out, and call it good. As an added bonus, the front end of the car gets washed too.
 
I just got the drain plug out of the engine in my 85 pickemup yesterday, probably the 1st time it's been out since the truck was going down the assembly line. I had to put a "cheater" on the ratchet handle to get it loose but it came without stripping the head of the drain plug.
And yeah I had to probe the drain plug hole with a screwdriver for it to flow.
Before I pulled that plug I was trying to drain it just thru the radiator drain, and I had the upper hose off/ I could hear it sucking a vacuum thru the thermostat housing and would barely trickle.
Once I probed the block drain and gave it some air it glugged out both the block drain and radiator drain. I then pulled the thermostat out and it drained pretty quickly from both points.
That engine is getting ready to come out hopefully later today or tomorrow.
 
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!
Yeah, the cornfusion came from the generic service text, using the identical service text as the V-8's w/o distinguishing the Slanty. Plural plugs had You eyeing the core hole plugs, & as above, fooling with more than needed can cause other problems to pop up. Happy cooling!
 
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 would not knock out the plugs unless they are rotted or leaking there should be a drain plug on the right side if the block
 
I agree thats true but your still allowing air to be in the system
Only in the top of the rad tank for expansion. It does not travel through the system, as the inlet to the pump is from the bottom of the rad, no air down there.
 
Without pulling the block drain plugs (or plug on /6), you'll never get most of the sediment out of the block. As someone else mentioned, use a high-quality 6-point socket (9/16"), or your chances of rounding it off increase substantially.
I've owned my car (original 318) for 4 years. Never overheated but temp would rise uncomfortably high when climbing a long hill & always had a little bit of coolant "purge" or boil over after shutting it down hot. 2 years ago I pulled the block drain plugs (who knows if they were ever out prior) and did a thorough flush. I did have to dig through crusted sediment behind the plugs. Removed heater hoses & T-stat. Using a short piece of 5/16" steel fuel line tightly inserted into a length of fuel hose, I back-flushed the block through the drain plug holes. Alternating between them, the heater hose outlets, radiator & T-stat opening, I was a bit shocked at the amount of sediment I got out of it. Haven't had an issue since - also changed to a 180* stat, added a reservoir for a closed system, and "Dex-cool" long-life coolant.
 
Only in the top of the rad tank for expansion. It does not travel through the system, as the inlet to the pump is from the bottom of the rad, no air down there.

That exactly why old system had the coolant passages and water turn rusty. Air in the system.
 
The slant has a single drain plug, 3/8" NPT on R side. I put knock sensor from a Chevy 1985-95 V-8 there (w/ 1/4" NPT bushing) for later use w/ an engine controller. No fan of the old Prestone flush kits which install a tee in a heater hose. I flush a few times w/ tap water, then add 1 lb citric acid and drive for a few days, drain flush fully, rid all water (w/ heater core change), and use Evans Waterless coolant for no future corrosion worries. I change all 5/8" hoses to silicone. Did this in all my vehicles, even 2002 Chrysler T&C w/ rear heat. No more coolant issues or worries.
 
Ok guys I have said this before I will repeat proper flush and fill procedures.
Don't use chemicals. find a good rad shop and they will do a reverse system power flush with compressed air and water. this goes thru your heater hose in reverse flow and flushes out your complete system.

(your top hose is removed and a down spout is added to rad to point the water coming out down to the floor.)

after the water runs thru system for a while the compressed air is hit and it "flushes" out your system and boy is it dirty!
then when your whole system has been flushed numerously add in 6 litres of anti freeze and 1 in your overflow. then top up with water and your good to go.

Most people say you just need 50/50 but it depends where you live. Extreme hot or cold weather will dictate how much antifreeze. so if you live in arizona or Canada and the northern states, 6 liters plus one in the overflow will help you as low as -51degrees C and +51degrees C.

also change your thermostat and cap every 2-3 years when you do the reverse power flush.
 
Cruiser, did you do a video on your car? brown Gold Duster/snake skin top and fold down rear seat? very nice car indeed!
 
Cruiser, did you do a video on your car? brown Gold Duster/snake skin top and fold down rear seat? very nice car indeed!
Yes I did. It's entitled "1974 Plymouth Gold Duster Restoration and Walkaround".
 
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The slant has a single drain plug, 3/8" NPT on R side. I put knock sensor from a Chevy 1985-95 V-8 there (w/ 1/4" NPT bushing) for later use w/ an engine controller. No fan of the old Prestone flush kits which install a tee in a heater hose. I flush a few times w/ tap water, then add 1 lb citric acid and drive for a few days, drain flush fully, rid all water (w/ heater core change), and use Evans Waterless coolant for no future corrosion worries. I change all 5/8" hoses to silicone. Did this in all my vehicles, even 2002 Chrysler T&C w/ rear heat. No more coolant issues or worries.
Bill, I'm not sure that the drain plug is 3/8". I just put a tape measure on it and it looks like 5/8".
 
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