73 Z with SU's. The water tube that goes between the front and rear E-36 intakes has a leak where it meets the rear manifold. There are hex nuts at each end of the tube. Don't know much about it so don't want to mess it up worse. Want to keep using the water tube. It's a small leak but I want to fix it before it gets worse.

Temporary and/or permanent fix?

Never had one of those off, but I assume that tube is just a straight piece of tubing with flares on the ends. Not sure if they are single, or double flares, but flares of one sort or another. If that's the case and you have the means, you could replace just the tube part by using the correct size of tubing, moving your flare nuts to the new part, and then flaring the ends.

Is the part is NLA at the dealer? You can't just buy a new one?

I thought that everyone south of the Ohio river just plugged those things...

I didn't take mine apart when I had it off. (It gets cold here so I hooked it back up) Have you tried snugging the hex nut? The other option if it is a really small leak is to try some stop-leak in the radiator. On some of my older cars I have been able to plug small leaks with the over the counter stuff.

Doubt if the water tube is available - Z therapy might possibly sell me one though. ZT website implies I don't need it which may well be correct. No stop leak in my new radiator. Possibly JB weld on the leak as a temporary fix. Before I start messing with it I'd like to assemble the hardware I'll need to plug the water system just in case - the Z's my daily driver and I expect to need the car this weekend. Wonder what size plug would fit the opening on the thermostat housing, maybe 1/4" BSPT? And what to plug the other side by the heater hose, maybe braze the unused end of the fitting?

It only seems to leak when the engine's cold.

BTW, it's a E46 not a E36.

Where is it leaking, between the tube and the fitting or around the threads on the fitting. I've seen any number of those fittings at the shop when removed, that are pretty severely scoured out from water flow over the years and dangerously thin in spots. To my way of thinking that whole system, at this point in the life of those cars, is just ready to leave you standing beside the road the day it does start puking.

Hi Bruce. Don't know, I'll get a look tomorrow with the magnifying glass.

Every one I've taken apart has been severely corroded, as mentioned above. It could not be salvaged/reassembled in a fashion that I thought would be reliable. You would have to build something from scratch or source a less corroded tube and fittings. Living in CA I don't bother replacing them and just run a AN -4 bypass line from the outlet at the back of the head to the inlet on the bottom of the thermostat housing.

Every one I've taken apart has been severely corroded, as mentioned above. It could not be salvaged/reassembled in a fashion that I thought would be reliable. You would have to build something from scratch or source a less corroded tube and fittings. Living in CA I don't bother replacing them and just run a AN -4 bypass line from the outlet at the back of the head to the inlet on the bottom of the thermostat housing.

Damn, that's a great idea!

EDIT: I have mine blocked off with BSPT plugs, don't remember the size though. I got them from McMaster.

Edited March 22, 201311 yr by LeonV

Every one I've taken apart has been severely corroded, as mentioned above. It could not be salvaged/reassembled in a fashion that I thought would be reliable. You would have to build something from scratch or source a less corroded tube and fittings. Living in CA I don't bother replacing them and just run a AN -4 bypass line from the outlet at the back of the head to the inlet on the bottom of the thermostat housing.

Does running the bypass line provide better coolant flow than just plugging it? How did you run the line, under the intake manifold or behind the balance tube? Looks like you could do that with heater hose, although steel braided would look way better and be less likely to leak.

Took a better look, it's leaking behind the nut, maybe evidence of some previous leaks between the nut and the tube at both ends. Also a leak at the back or the rear intake where the short hose it attached. Basically leaking all over the place. Guess I'm over having it there. Maybe I'm over having the heater, too, but I like the defroster.

Wonder if the aluminum tee (that bolts to the right rear of the engine) it thick enough to tap some threads into. Looks sort of thin.

Here's the definitive thread on cooling the L6 engine:

Head cooling on cylinder #5 - solutions? - L-Series - HybridZ

Wow, 24 pages on the cooling system. Back to school. Don't think I'll do any mods like that to the head, I'm already running cool enough for Pike's Peak (the drive, not the race).

Just need to dump the goner water tube in a functional and "cool" looking way.

S30 coolant plumbing.pdfHere's a pdf, some sketches to help me understand coolant flow with various setups, based on the hybrid Z thread John posted.

That thread is about coolant flow, not heating the carbs, but it answered my question about John's setup. A lot of that thread is about high horsepower Z cars that are tracked - I left those setups out since they're over my head. Also I left out conditions where there's heater with a closed valve and a carb heating tube with a closed thermostat (in the tube) since not much happens.

Fig. 1:Stock setup, heater on. Improves circulation at cold start (see that 24p thread for why it's important, esp for racing) and helps cool rear cylinders.

Fig. 2. Stock, heater closed. Same as plugging outlet D and branch of tee F.

Fig. 3. Heater hose looped, carb heater tube remains. What I've got now. This setup gets bad press because it sends hot coolant from the head back to the intake, but it helps cold start circulation and helps equalize engine temps.

Fig. 4. Heater hose looped, carb heater tube gone. Helps equalize temp and improves cold start circulation. Proven to raise coolant temp, but maybe because more is circulated at rear of engine.

Fig 5. John Coffey's setup if I'm correct. This is what I want to do with mine. Improves circulation at cold start and helps equalize engine temp.