Diameter of the "Cursed water plug"
 

I need to know the outside diameter of the water fitting at the back of the 1.6 head that has the rubber cap on it. Anyone?

Main diameter of the tube is .322", didn't measure the lump on the end to keep the cap from pulling off.

That's the measurement I was looking for, thanks.

Damn, 8mm. That's a bit too small for feeding the heater core. Looks like I'll be drilling after all.

summoning this thread from the grave...

Some people have mentioned using a reducer in the heater hose in order to get the car to come up to temp properly. If we use the cursed water plug as the heater feed, would that be roughly the same thing? I remember someone else on here ran it off that port, and didn't have any issues with it. Not sure what combination of search terms would find that post though.

yeah, pretty sure I've fit a 5/16 hose on it. I looped mine back to the IM port on #1 after it blew the second time.

We may be speaking at cross-purposes here.

I have, in the past, postulated that a restrictor might be inserted into this line when the heater core is removed entirely, not to ensure quick warm-up, but to prevent too much water from bypassing the radiator when the thermostat is open. The purpose here being simply to simulate the restriction of the now-absent heater core.

Adding additional restriction to this line when the heater core is still present, which would include taking water from the Cursed Water Plug to supply it, might well result in too little coolant flow through the engine when the thermostat is closed. This is, of course, only a guess. I have neither empirical data nor a comprehensive education in thermodynamics to back it up.

got it. What about the big line with the cap on it near the oil filter? Is that even coolant? Looks like it could be a potential place to tap for the heater if so.

That goes right to your oil pan. It is an oil return line. I wouldn't connect any water there.:giggle: It is sometimes used for turbo oil return.

Yup.

My understanding is that in the original (323 GTX) application, that port was used as a vent for a breather / oil seperator. It was NOT the turbo oil drain port. (The FWD/AWD engines had a different oil pan with an MSM-style oil return port on it.)

you are correct joe, the FWD variant used a different pan with a drain. im trying my damdest to place this "big line with a cap near the oil filter" anyone have a picture?

on topic. with the FWD configuration of the coolant inlet and outlet we delete the heather core and just loop the lines with no ill effect even on the high HP guys. no clue if this helps.

In this picture, it is below and to the right of the oil filter. It is covered with a rubber cap held in place with a metal snap-ring:

https://www.miataturbo.net/attachmen...ine=1349299884

In North America, this appears only on the '90-'93 1.6l (B6) engine blocks. It is not present on the later engines. I have no idea whether the Jap / Euro 1.6 engines from '94 onward had it or not.

yeah the older B6t GTX had it capped as well (atleast all the ones ive seen)