Engine Block Coolant Plug

[someotherguy]

It'll be same threads as a knock sensor, which is 1/4-18, and according to a couple different sites that GM plug's part number is 1/4 NPT and 1/4 NPT is 18 threads per inch. So there ya go.

Richard

 

[Schurkey]

It'll be same threads as a knock sensor, which is 1/4-18, and according to a couple different sites that GM plug's part number is 1/4 NPT and 1/4 NPT is 18 threads per inch.

WHICH knock sensor?

The SBC knock sensors go into the block-drain holes, which are both tapped the same--1/4 pipe thread.

V6 knock sensor goes somewhere else. 7.4L Vortec knock sensors go into blind holes that I think are straight-thread, not pipe thread. (I've never had my 7.4L knock sensors out.) The big blocks keep the block drain plugs in place on both sides. They have separate bosses for the knock sensors.

Photos of my '97 K2500 7.4L draincocks instead of plugs, right next to the knock sensors.

Right side, camera angle is goofy. The block draincock is horizontal, not angled "up".

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Left side. No 45 degree street elbow needed.

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[tayto]

use a brass plug, its what they do in marine engines. as far as galvanic corrosion I would not be worried about brass and cast iron. the brass wont seize in the block and if you strip it its easily drilled and chiseled away. now aluminum and steel or aluminum and stainless steel is where you'll see the most problems...

 

[someotherguy]

WHICH knock sensor?

The SBC knock sensors go into the block-drain holes, which are both tapped the same--1/4 pipe thread.

V6 knock sensor goes somewhere else. 7.4L Vortec knock sensors go into blind holes that I think are straight-thread, not pipe thread. (I've never had my 7.4L knock sensors out.) The big blocks keep the block drain plugs in place on both sides. They have separate bosses for the knock sensors.

Photos of my '97 K2500 7.4L draincocks instead of plugs, right next to the knock sensors.

Right side, camera angle is goofy. The block draincock is horizontal, not angled "up".

You must be registered for see images attach

Left side. No 45 degree street elbow needed.

You must be registered for see images attach

OP specified 5.7 Vortec, so I was responding re: SBC's

Pretty sure the Vortec 7.4 knock sensors are pipe thread, also. It's been a few years.

I have no idea what V6's use.

Richard

 

[Caman96]

OP specified 5.7 Vortec, so I was responding re: SBC's

Pretty sure the Vortec 7.4 knock sensors are pipe thread, also. It's been a few years.

I have no idea what V6's use.

Richard

Yes, 5.7 Vortec.

use a brass plug

I’m sure brass is fine, but I ordered the GM part. Coolant will be maintained on truck, so plug being rust welded in won’t be a problem.

 

[Vanishing Point]

Hopefully this might be helpful as to what everyone is looking for 1/4NPTF X 18TPI with 9/16 Hex head

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• Solid Brass Pipe Plugs (MPT)

Fittings & Couplers​

Solid Brass Pipe Plugs (MPT)​

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$1.19

Pipe Thread Size: 1/4" NPTF X 18TPI x 9/16 hex head
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SOLID HEX HEAD PIPE PLUGS​

Brass Pipe Fittings​

Industrial quality solid brass pipe thread plugs. Durable brass construction makes these plugs excellent for use with both solvent-based and water-based products.
Four pipe thread sizes available: 1/8", 1/4", 3/8" and 1/2"
* NOT FOR USE WITH ACIDS!

Essentials​

• 1200 psi Working Pressure
• Premium Brass Construction
• Hex Heads
• Male NPTF Threads

1/8" NPTF plugs have a 7/16" hex head.
1/4" NPTF plugs have a 9/16" hex head.
3/8" NPTF plugs have a 11/16 hex head
1/2" NPTF plugs have a 7/8" hex head.

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[L31MaxExpress]

I'd wager that actual metal to metal contact is minimal with proper application of thread sealant and that any reasonable plug will do the job. The cheapest 'low pressure' pipe plugs at McMaster Carr are rated to 150psi, way more than the coolant system will ever see.

The block sees around ~100 psi under the head gaskets at WOT. That came directly from a former GM powertrain engineer. The high pressure needed to prevent hot spots and localized boiling and thus possible cracking are good reasons to avoid electric pumps on street driven vehicles.

 

[Caman96]

I really was just trying to confirm the correct GM part, and it is. Good information for those who want a brass plug though.
…shut the light off when your done.

 

[Schurkey]

The block sees around ~100 psi under the head gaskets at WOT. That came directly from a former GM powertrain engineer. The high pressure needed to prevent hot spots and localized boiling and thus possible cracking are good reasons to avoid electric pumps on street driven vehicles.

God bless you. I've been trying to pin down a number on the PSI, and have had problems getting accurate info. Was considering chucking a pressure gauge into one of the pipe-thread bosses on the intake manifold to take a reading myself. You're probably right about the head gasket being something of a restriction, so that the block sees more pressure than the head. Hard to say how much the gasket restricts flow--and therefore pressure.

Not so much a matter of throttle position, but of pump RPM. The water pump is a centrifugal unit, so up to the point where it stalls/cavitates, more RPM means more pressure.

This is also why the heater core has a restriction somewhere in the inlet plumbing--the core doesn't like ~100 psi.

 

[Erik the Awful]

The cooling system should be running about 10-20 psi when hot. The factory radiator cap relieves at 16 psi. Even considering fluid dynamics, 100 psi under the heads sounds like a tall tale to me.