Robert Perkins

I am trying to remove the pipe plug in the drivers side head between 1 and 3 cylinder. It is square recess 3/8 extension to large 1/4 inch to small. I am trying to remove the plug to install a fan temp sensor. 1990 L98 engine

chris1

Robert: I took an old 3/8" extension and ground down each side a little bit until I was able to get the perfect fit. Yes, it does ruin the extension for future normal use, however I had a couple laying around so it was no big deal, plus now I have the "tool" in case anyone needs to borrow it. Let me know if you can't come up with another solution....

Regards, Chris.

mako41

That plug is a nightmare to remove! I think the 3/8" NPT steel pipe plug has a 5/16" square female recess.

Snapon makes an external pipe plug socket that fits into the square recess of that plug and even with the right tool I couldn't get it out..... all I did was round out the square recess.

https://store.snapon.com/Pipe-Plug-i...--P641829.aspx

The only members here with success removing that plug have mig welded a bolt or nut to that plug and then turned it out while still hot from the weld. Check out this thread; and good luck!

https://www.corvetteforum.com/forums...lant-plug.html

ex-x-fire

Harbor freight has a plug socket set that has all square sizes, I use them daily at work (esp. the 3/8 square & 10mm hex) & haven't broken one yet.
Sometimes adding some heat to a plug then cooling it quick will cause the grip to loosen. It works on rear end plugs great.

Robert Perkins

Thanks, I will go to Harbor freight tomorrow and get a set.

ex-x-fire

Call ahead, the set #is 94961. Looks like they no longer have it on their website. Maybe it's a glitch.

WVZR-1

If you have access to air an impact will work well and you could likely avoid the heating thing, if you don't a hand impact driver could also work well providing you've got access and a BFH.

I believe that an unmolested square on a 3/8-18 recess plug is .324 so if there weren't that particular size in the package I'd avoid a complete kit buy. I'd work with maybe the suggested "file to fit" 3/8 square drive, an air impact or hand hammer impact. It's a tough job no doubt.

HF would have a 67011 square drive to hex wrench kit. You could use the 3/8 - 9/16 knock out the ball and file/grind to fit, grind the end to flat to allow deeper penetration. That's only $4 and the rest that you don't need to file/grind could be used occasionally. If you thought that it were going to be a waste then the 3/8 square drive would be very useful when servicing the rear.

If you've already attempted and have maybe destroyed the square then maybe the file to fit is required anyway.

mako41

I tried the correct snap-on tool with an air impact gun..... No dice!
After 20+ years of galvanic corrosion between the steel pipe plug and the aluminum head along with thousands of heat cycles from engine operation that plug was literally welded in place. No way to remove it without adding some carefully placed heat before mechanical manipulation.

8a8mfh

I used the square end of a thread tap. With vicegrips on the threaded end.

WVZR-1

That's pretty damned creative but likely to fail in this case I'd think.




If it were here I wouldn't maybe use the impact either but an air chisel with a blunt tip to aggravate the bond. I didn't suggest that because most likely don't have access to the chisel or the correct blunt tool. We use the blunt tips regularly for rivet installations. Low air and patience and maybe some heat but certainly a last resort. Yes it does need to be well placed.

If the OP has air it could be an excuse to buy something that's actually quite useful.

mako41

And that worked??

8a8mfh

Well I would have said anything if it didn't

I was relocating the factory temp sender to the driver side head, just a coincidence I had a 14mm tap forever that I never used and it fit right in. I thought it would be too brittle and break, but it didn't even ruin the tap.

Robert Perkins

I went to Harbor Freight and they no longer sell the square pipe plug sockets. I ground down a 3/8 extention and got it fit fine however the plug was so tight I snapped off the end of the extention were I ground to fit.

WVZR-1

If the car still runs/drives take it to a shop and have them loosen it using the air chisel with a "blunt tip" or if you've got air borrow/buy chisel tool.

There's multiple size blunt tips.

Joe C

...that's assuming the shop has sufficient clearance to get an air chisel in there to access the plug. there might be considerable piece, parts, and hardware removal first, and even then, access would be questionable. another issue is the electrolytic reaction between dissimilar metals. a few years ago, I removed a steel pipe plug from the bottom of an aluminum intake manifold. a 1/2" drive, long ratchet, and the "proper tool (pipe plug socket, 5/16-4 point,) and that wouldn't cut it. I had to revert to a 1/2" drive impact, and I still had a hell of a time getting the damn thing out. the galling action between the aluminum threads of the intake and the steel threads of the pipe plug played hell with the manifold threads, which ended up needing some minor repair and clean-up. I would say, caution needs to exercised here, and the use of the proper tools for the job. this just might be one of those things that calls for the head removal - ???



proper tool - proper tool - proper tool --

again, CAUTION NEEDS TO BE EXERCISED HERE!

ex-x-fire

You could avoid the whole stuck plug ordeal, put a sensor tee in the heater hose that comes off the intake.

WVZR-1

Certainly an alternative that maybe could/should be considered. A quality Tee could be an issue and then there's the determining the sizes of the male aspects of the Tee and the placement.

TA

When I removed mine many years ago I went through the same issues. I ended up buying a section of 5/16" steel rod from Home Depot. I cut a section to make a "bit" and then found a 12 point socket to fit. IIRC it was still a bit of pain due to the unhardened rod twisting, but the plug eventually gave way.

Joe C

that could be a solution, but unless you have continuous flow through the heater, I'm thinking the temp reading might be erroneous. besides, the attached pic looks to be in a lower radiator hose - sure looks like an electric radiator fan. ???

mako41

Could you elaborate more on what exactly you mean by doing this. Maybe a pic of the tip. I have an air hammer but I'm not really sure what procedure one would use to loosen this plug. Are you just impacting the plug w/the air hammer tip to break the bond w/ the aluminum head without using heat, or are you referring to something else?