Help, coolant leak on the back of the head with reroute
 

I've been putting my car back together after installing an IC to get ready for a track day. I was trying to track down why my radiator fan wasn't coming on when I started to smell coolant! I could see it dripping down the back of the engine.

From up top I located the leak as coming from a rubber plug at the back of the engine on the intake side. I installed a BEGI coolant reroute when I had the engine out about a year ago and remembered replacing this plug so I'm not sure why it failed so dramatically. I've done a couple of track days with the reroute before installing the turbo and one since the turbo with no problems. I did just have to mess with this area to install a new water temp sensor because the old one wasn't reading properly but I don't see how I could put a pin hole in it.

My questions are:
1) Why is this plug here and is it truly to hold in coolant or has something gone horribly wrong? (seems like a poor design)
2) is there a better fix than just another rubber plug (stronger, silicone, etc.)
3) anyone know the right size for this part?

Pictures and a video
https://www.miataturbo.net/attachmen...ine=1355904220
You can see the pinhole stream of coolant (sitting next to the sensor I mentioned)

Easier to see in video:
http://i925.photobucket.com/albums/a...BABAB51677.mp4

Yes it's just there to block coolant...not sure why. I've replaced them with generic parts store plugs and they only last a year or so. Haven't found a better solution. My heads off right now, I'm considering drilling and tapping for an NPT plug. I've had good luck pulling those pipes out.

Ahhhh . . . the "cursed water plug."

Like Curly said, the generic plugs don't last in this application. The OEM plug will hold up for about 3-5 years (sounds a lot like a warranty period, doesn't it)? I used to order mine from Rosenthal for about $4 each and got pretty good at replacing them. If you abstain from the worm clamp and stick to the OEM spring clamp, they are not too bad to swap out with a pair of pliers.

If you ever pull your head, tapping and installing a NPT plug is the permanent fix. Mazda used our engines in a variety of applications and put on these quickie plugs to simplify manufacturing. Hardly ideal. The other plug that would be good to tap and permanently plug is a on the intake manifold in approximately the same location. If it blows off under boost, it can cause a boost leak. Look hard, you'll see it!

I had severe problems with the BEGi spacer:
Had to belt-sand/clearance the part that mates to the trans
Had to seal all plugs with a hardening sealant
The CLT sensor hole wasn't cut deep enough to let the sensor flange bottom-out and use the washer to seal. I couldn't cut it deeper or no threads would engage, so I had to use black RTV to seal it up.
I used a silicone nipple back there. The next time it will get plugged or welded-up.

Have fun working back there.

I really wish I had known about this problem when I had the engine out of the car. I would have made a permanent plug!

Anyone know the size of this nipple? I'd like to search for a silicon one that might last longer.

Wow, that stream of coolant is pretty dramatic.

CAP, SEALING (FEA7-13-104) - $5.80 - FEA713104

COVER, BLIND (B660-10-328) - $6.54 - B66010328

Is it one of these two boogers? Should be available from the dealer, might be worth it for the short term. I can't see the OEM ones from the dealer taking too long to get, and then you'll have sizing?

It's the FEA7 part.

The B660 part is the blind plug that covers the turbo oil return port by the oil filter.

OP, I'd just pull the one you have and measure it if you want to do silicone. No sense spending 6 bucks + "shipping/travel to local dealer" for a plug you don't plan to use.

In the FWD variant of this engine, that port was used to supply water to the throttle body. In the RWD variant, it is not needed, so it is blocked off.

Just had the plug fail on me pretty quickly after a rebuild, I didn't drill/tap it like everyone else apparently. My "at the track and I need to fix it quick" solution was to get a short length of fuel hose, thread a bolt into one each then put a worm clamp on it. Then feed it on to the nipple at the back of the head and worm clamp it there as well.

The hot coolant has a lot harder time eating through the heavy wall of the fuel hose and pushing against a bolt doesn't wear out the end nearly as well as a regular plug does. Holding so far but I'll have to see how it works in the long run.

Idea is same as random pic below that I found

https://www.miataturbo.net/attachmen...ine=1355945422

Ha, I did that for another plug for quite some time. It still floats around my tool box on track days while I wait for the rear one to go. Forgot about that.