Does anyone really do this to their cooling system?

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pipe goes by INSIDE DIAMETER. outside diameter is bigger. 3/8" "pipe" is actually larger than 3/8 outside diameter.
 
IIRC it's the same size as the radiator drain. My dad put 2 on the 273 decades ago
 
volaredon said:
pipe goes by INSIDE DIAMETER. outside diameter is bigger. 3/8" "pipe" is actually larger than 3/8 outside diameter.
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So will this brass pipe plug work in the side of my slant six?

IMG_3147.jpg
 
. I usually put petcocks in like on the bottom of the radiator. I thought that hole was threaded 1/4 npt not 3/8.
 
cruiser said:
On the previous page of replies, member Bill Grissom says its 3/8" NPT.
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In the radiator? All I've ever seen were 1/4" NPT. That doesn't mean a lot, though. lol
 
RustyRatRod said:
In the radiator? All I've ever seen were 1/4" NPT. That doesn't mean a lot, though. lol
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Rusty, perhaps I wasn't clear in my previous comment. What I'm talking about is the coolant drain plug threaded into the right rear of the engine block of my 1974 slant six motor. Currently, I have a plug with a hex (Allen wrench) fitting on it. I'll shortly be removing and painting the engine and I'd like to replace this coolant drain plug with a plug that has a square head. A square head would be very easy to remove when doing coolant changes, as all I'd need is a crescent wrench or an open end box wrench. So I bought this plug and am wondering if this is the correct one for my engine. The one currently installed in the engine looks to be 3/8", but until I get it out of the motor I won't be able to tell what size it is. Do you think I bought the correct plug?
 
cruiser said:
Rusty, perhaps I wasn't clear in my previous comment. What I'm talking about is the coolant drain plug threaded into the right rear of the engine block of my 1974 slant six motor. Currently, I have a plug with a hex (Allen wrench) fitting on it. I'll shortly be removing and painting the engine and I'd like to replace this coolant drain plug with a plug that has a square head. A square head would be very easy to remove when doing coolant changes, as all I'd need is a crescent wrench or an open end box wrench. So I bought this plug and am wondering if this is the correct one for my engine. The one currently installed in the engine looks to be 3/8", but until I get it out of the motor I won't be able to tell what size it is. Do you think I bought the correct plug?
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Give me a minute and I'll go look at the 225 block I have on the stand.
 
cruiser said:
Rusty, perhaps I wasn't clear in my previous comment. What I'm talking about is the coolant drain plug threaded into the right rear of the engine block of my 1974 slant six motor. Currently, I have a plug with a hex (Allen wrench) fitting on it. I'll shortly be removing and painting the engine and I'd like to replace this coolant drain plug with a plug that has a square head. A square head would be very easy to remove when doing coolant changes, as all I'd need is a crescent wrench or an open end box wrench. So I bought this plug and am wondering if this is the correct one for my engine. The one currently installed in the engine looks to be 3/8", but until I get it out of the motor I won't be able to tell what size it is. Do you think I bought the correct plug?
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Both the 225 on the stand and the one in the car have 1/4 NPT plugs in that spot on the block.
 
RustyRatRod said:
In the radiator? All I've ever seen were 1/4" NPT. That doesn't mean a lot, though. lol
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If true you can bush the hole or find a petcock that directly threads in.
I'm thinking that the block drain is 1/4 not 3/8 NPT because the petcock I used also fits the radiator in my truck. Maybe it's a "different year" thing?
My current build is also a 74 block
 
volaredon said:
If true you can bush the hole or find a petcock that directly threads in.
I'm thinking that the block drain is 1/4 not 3/8 NPT because the petcock I used also fits the radiator in my truck. Maybe it's a "different year" thing?
My current build is also a 74 block
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Yep, for the record its a 1/4" NPT plug. I just checked on my 1974 slant six block. Rusty and volaredon were right. Thanks to all who weighed in. I still think I'll just replace it with a square head brass pipe plug, as I don't like the look of a petcock coming out the side of my engine. But that's just me!
 
Sometimes convenience outweighs looks. How often will you be looking at that part of the block?
Original plugs for that hole had a 9/16" hex (wrench head) on them. With a SIX POINT socket usually not too bad to get out.
 
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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If you dont mind the mess
..take the top hose loose from the radiator and run it into a shop vac hose down over the grill or near the strut rod..then put a running hose into the radiator and fire it up.


Wait for the stat to open and spew out the shop vac hose till clean. Have someone keep an eye on the gauge while you watch the color coming out.
 
Does anyone know the Thread size for the Coolant Block drain plugs on a '68 318 ? Or a source for a pair of them ? Thanks
 
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