Cruz 86

I need to remove the water plug from the side of the cylinder head on my 86 vette. I'm installing a water temp sending unit to turn cooling fan on sooner. PROBLEM IS, the plug has a square female hole in the center of it. I can't find anything that will fit it. Usually these type of plugs are 3/8 so you can use your ratchet or extension on them. This thing is smaller, a hair less than 5/16 square, maybe 7 or 8 mm. I went to Sears and they didnt have anything to fit it. I tried to grind down some 5/16 square stock but it wasnt hard enough (rounded off). Does GM make a special socket or something for these odd size plugs? All replies welcome. Thanks. CRUZ 86

04Z16

Don't know if this will work for sure but I have had some luck with finding the right size allen wrench and tapping it into place. The allen wrench is made from semi hard steel so it shouldn't round off. Just a thought.
:seeya

Cruz 86

Thanks 96 Gransport. This plug is really in there (tight) and I'm afraid that if I dont catch all four corners I'll end up buggering up the square hole. If all else fails, as a last resort I guess I could drill it and use a large easy out. That will require a right angle drill because there isn't enough room to get a regular drill in there. Anyone else?

nobodyunknown

That might be an unremoveable plug.Why dont you use the current temp sending hole?

tempest

here's one long shot.
take your ground-down 5/16 square and put a torch to it until it gets cherry red. then dunk it in a bucket of water until cool.

if the material is mild steel, this type of heat should make the steel more harder, but more brittle, so be careful. (martensizing, i think the process is called in engineering circles.) i used to do this to crappy center punches that used to mush at the tip when you use them. works great for that. might work for you. again, be careful. when brittle steel shatters it may send small shards shooting out so wear gloves and goggles when you try to get the plug out.

good luck. let us know how it goes.

john25

I have had to remove this same plug on 4 different cars. The only way I found was to make the correct size square to fit the plug. The plug is not a 5/16 nor 3/8 square. I took a 1/2" hardened bolt, grade 8 or better and ground the end square. First I cut the bolt so that the overall length was about 1.5" to 2.0" long. Then I ground the end of the non threaded shank down little by little until it snugly fit into the square of the plug. By snugly I mean that you still need to tap it all the way in with a ballpeen hammer. Make sure that you soak the plug several times with liquid wrench. Then you take a breaker bar and carefully try to loosen the plug all the while applying inward pressure on your new square plug remover. It may take a few tries until you get it, you may even have to make a few removal tools to get the right size, I did. The good thing is that it will work. It does however require patience.

h rocks

Just get a short 3/8" drive extension and methodically grind it down on all four sides till it just fits. You need to have something that strong because of the torque that it's going to take to remove it.

Someone suggested quenching the piece of square stock that you tried, but rounded off . It probably doesn't have enough carbon in it to respond to "heat treatment". (no matter how primative. BTW, it's "martensite" that someone was thinking of.)

It's worth the small amount of effort to install that fan switch, BTW.

Muskrat

what it is is a plumbers fitted tapered 5/16 sqaure head. you need to go to a plumbing supply store to get it or a snap on or mac truck i have the set from snap on.

HiRiser

I had to use an easy-out and an acetylene torch to get mine out after I rounded out the square plug. But at least I didn't have to pull the head, which was the next step. Good Luck!
BTW, the temp switch was the best mod I've done yet. Now I only look at the temp gauge for curiosity as I put in a GM switch with a 205 on and 195 off setting connected to both fans. There is nothing wrong with the size of the radiator, just the bone headed factory switch settings. :rolleyes:

Rich B.

What is that 205 On/195 Off switch out of? Do you still have the GM part #?

Cruz 86

Thanks guys for some good ideas. I tried grinding down an extension but it wasn't exactly the perfect fit and it started to bugger things. I guess I'll wait til monday and try to get the right socket from snap on or a plumbing supply house. Tomorrow I'm going to try to grind down some grade 8 bolts. The friggin' general could have made this a hell of alot easier if they just used a 3/8 plug that my extensions would fit. It's times like this when you want to abuse an engineer!

KYVette90

I had an old broken easy out that had a square end on it, most of them do, and put it in the plug and muscled it out with some vice grips on the easy out. It was in very tight. The fan switch is awesome. Good luck. :smash:

HiRiser

203 degree GM thermostatic switch (p/n 3053190) I bought the wiring connector a Carquest for like $3, I think it was called an A\C connector

vettenuts

First, don't bugger it up. If you can't find the socket, shoot me an e-mail and I will let you borrow mine. (I think my socket should put in for frequent flier miles :jester ) Last person I sent the socket to had a mechanic mess up the plug beyond removal. It is 5/16 according to the manual.

h rocks

Does anyone know if a replacement 180 deg fan switch (on at 200, off @180)is available from other than Hypertech etc.? I broke (and subsequently lost) the black plastic boss that the connector locks onto. I tried Autozone, and they (we) couldn't find any listing, or similar for anything. They are cheap if you can find them other than from Hypercrap.

Rich B.

HiRiser has a GM switch identified above (Thanks, HiRiser!).

Also, there's one available from MAD - part # 609-106, Fan Switch, on at 200*, off at 185*; $17.99 ea.

Ecklers has the Harness Repair, Fan Temp part # 29177 for $7.99 ea, if (like mine) your connector is shot. This splices into the single-wire connector that snaps on the fan switch.


[Modified by Rich B., 11:39 AM 9/23/2001]

Cruz 86

I finally got that little SOB out of there! This morning I ground down some grade 8 bolts to fit and tapped while applying force but the thing would not budge. The ground bolts were slipping out if I applied too much force. Time for desperate measures. I took my die grinder and ground a hole through the center of the plug. Then I kept grinding outward untill all that was left was a very thin outer shell. I then took a flat chisel and colapsed what was left of the plug allowing easy removal. If you ever have to resort to this method make damn sure you stop short of grinding to the threads! Thank god there was enough room in there the die grinder. The directions say "remove plug". Two words end up taking all day. Thanks for all the good advice and the offer to loan me the right tool! This forum is the greatest.

RED90SIXLT1

The same switch is about $8 at NAPA

paid4c4

Cruz;
I just completed the same project on our 90. Found the same problem. I filed down a small extension to fit the square hole and it worked fine. An old mechanic friend told me to tighted the plug just a little and then to remove the plug, I did just that and it worked fine the first try. Total time to have the fans turning was about 15 minutes and that included making a factory type wire loom for the wires. If you want to borrow the extension it's already made to order, let me know, send me your address. This has been the best change I've made to the Vette. The air box change and the air foil didn't seem to make much of a difference, this change was noticable the first time I drove the car.
Good Luck;
Bill