Anyone know what size this is?

[travis]

IMG_20240313_185003_557.jpg

'99 vortec heads, trying to install an aftermarket water temp gauge and can't find anything that fits this square drive plug. Bigger than 1/4", smaller than 3/8". I tried grinding down a cheap ratchet but apparently ground through enough of the hardened outer layer that it twisted off with very little pressure. I tried to find some square drives locally and came up empty.

[modok]

jeez
you cant measure a square...
try 5/16
I like to use square thread extractors

snap on sells all sizes of square drive, down to 32nds

[Geoff2]

Most likely 5/16". If it is in really tight, good chance you will snap off the socket end.....even with a preliminary prayer to Allah.....
If it is an iron head, heat up the plug with oxy to cherry red & feed candle wax into the joint. When it cools down, it will come out easily....

[travis]

jeez
you cant measure a square...
try 5/16
I like to use square thread extractors

snap on sells all sizes of square drive, down to 32nds

I stole the pic off the Internet trying to find a size. I can't measure it without removing the header and lifting the engine a bit which is an absolute PITA on this truck. I was just trying to avoid a bunch of extra work and thought someone might know off the top of their head.

[BCjohnny]

Likely 5/16", if so I'd use a common 8mm 'sump plug' bit

As said, I doubt it's going anywhere, with any bit, without prudent use of heat prior .....

[strokersix]

I've used a square section high speed steel tool bit for this sort of thing

[modok]

Yeah, best to use hardened keys or something like that.
But DO buy the full set of female square sockets.
MANY uses
Put a KEY or square thread extractor in them and it's stronger than a solid tool, and can also drive taps

[BillK]

Just want to add that it is not going to come out easily. BTDT Almost always involves use of the fire wrench.

[dannobee]

I just whipped out a vortec head to see. It takes a 5/16" external pipe plug socket. I used a snap-on PPM410 and it fit fine. And yes, by all means use the hot wrench if it's stuck. And for anyone who gets stuck working with pipe plugs, the right sockets pretty much eliminates the twisting or breaking of your extensions and ratchets by using the wrong tool. BTDT, even with snap-on stuff.

[stealth]

Don't put the gauge sensor there....

[travis]

Don't put the gauge sensor there....

Huh? I don't have any other place to put it. Nowhere on the intake we have to put it there.

Although I am wondering...the factory temp sensor in the driver's side head...does it run both the factory in-dash gauge and provide the coolant temps to the computer? It would almost have to. 1994 GMC K1500... originally a TBI 350. The factory gauge doesn't read correctly, but then again neither does any of the other gauges.

[Schurkey]

the factory temp sensor in the driver's side head...does it run both the factory in-dash gauge and provide the coolant temps to the computer? It would almost have to. 1994 GMC K1500... originally a TBI 350. The factory gauge doesn't read correctly, but then again neither does any of the other gauges.

OEM was to have a coolant temp sensor in the intake manifold next to the thermostat housing, supplying the computer with coolant temp info. The dash gauge was supported with a temp sending unit in the side of the cylinder head, left front. Common for the dash gauge to read somewhat hotter than the coolant temp sensor.

[Bill Chase]

5/16" key stock, find a socket that fits it. Hear the plug with a map gas torch until a dull red glow, drip water on it to quench it. Usually come right out. If the head has a lot of internal corrosion may want to run a tap through the head before you shove anything back in.