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Old 10-24-2008, 05:18 PM   #1
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Unhappy Coolant pipe leak

Hello Miata Turbo community - you can read some (really old) stuff about my '91 at Mike's Miata's Homepage - not much has changed, except that I've been using the Miata as a daily driver for the last 8 years or so, and not working on it much other than for maintenance.

So, after driving home the other night, I noticed a little puddle forming more or less under the master cylinder on the floor, smells like coolant... look under the hood - hey, coolant leaking from the bottom end of the leftmost heater hose - no biggie, order up some heater hoses from the dealer and wait...

So, while I'm taking off the old heater hose, it doesn't seem to be in bad shape at all (pretty remarkable after living that close to the turbine exit for 11 years, but I guess that heat shield worked...) the heat shield did, however, seem to have a LOT of corrosion under it where it was on top of the metal pipe. Hoping that the corrosion just pushed a leak open under the hose (yeah, big hope.)

So, got it all cleaned off, got the new hose in place, and voila' same leak, but this time I can see it - it's coming from a pinhole on the inside of the bend in the coolant pipe (the one on the engine side of that leftmost heater hose....)

So, here's the question: just how hard is it to replace that pipe? I see that the exhaust manifold has to come off - is that it, or are there other gotchas? I'm assuming with all the turbine exit heat running around this forum that someone else in here has seen this particular problem before?

Or - another route - does anyone know of a good (trustworthy, does quality work) mechanic for turbo Miatas near Gainesville, Florida? I have done most of the work on my car myself over the years (except the initial turbo install) - and when I get something done by a "professional" (other than the turbo install) I generally get really disappointed to see that they slap something together 5x faster and twice as sloppy as I would have done myself.

Thanks in advance for any useful advice.
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Old 10-24-2008, 06:02 PM   #2
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The exhaust manifold does not have to come off. You're talking about the pipe that returns water from the heater core to the mixing manifold at the water pump? It pulls out of the mixing manifold. It's got an o-ring so pull hard. then just push a new one in. Not easy working under the turbo but definitely doable. I removed/replaced mine to modify it with the BEGi S kit in place.
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Old 10-24-2008, 06:10 PM   #3
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Yeah I've removed that pipe on my 99 with the stock exhaust manifold still bolted to the engine. On my 99 there's a bracket coming off that pipe that goes to the exhaust manifold where it bolts to steady the pipe. You just take that one nut off the manifold, slide the bracket off the stud so now it's free, and then wiggle and pull and the pipe will snap out of the mixing manifold as Paul described. When reinstalling use plenty of lube on the mixing manifold and o-ring so you don't damage it and get a leak. Also makes reassembly easier.
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Old 10-24-2008, 07:29 PM   #4
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Cool! Yeah, I can get in there, I've got the bracket bolted on in-between exhaust outlets 3&4, I've got reasonable access a normal 14mm open end wrench gets in there ok, having no power steering pump helps... soaking in PB Blaster now, will call for parts in the morning (I'm sure this will be another special order.)

Thanks!

Last edited by Mangocats; 10-24-2008 at 09:07 PM.
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Old 10-24-2008, 10:54 PM   #5
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1.6 and 1.8 pipes are of different length. Make sure you specify the year of the Miata when ordering.
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Old 10-25-2008, 09:58 AM   #6
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Update: pipe is out, nut wasn't too tough after soaking overnight - it's actually cheaper than the pair of hoses ($33.91 for the pipe, hoses were a bit over $40) - have to specify that you want the $0.21 O-ring to go with it - old O-ring actually looks in good shape, but at 18 years since the factory made it, I think I'll replace it anyway.

The local dealer takes the last 8 of the VIN before discussing anything about parts, so I hope their system can hook me up with the right parts (my engine matches the original VIN...)

Unfortunately, it wasn't this obvious until after I replaced the heater hose:


Last edited by Mangocats; 10-25-2008 at 05:59 PM. Reason: Add photo
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Old 10-25-2008, 10:16 AM   #7
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How far down the pipe was the pinhole? If it was just an inch or so after the hose ended, I would've just found a slightly longer hose and covered the pin-hole with it that way.
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Old 10-25-2008, 04:44 PM   #8
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Originally Posted by KPLAFIN View Post
How far down the pipe was the pinhole? If it was just an inch or so after the hose ended, I would've just found a slightly longer hose and covered the pin-hole with it that way.
It is over an inch past the hose stopping kink... even with a custom hose, I don't think I'd try that now, the pipe is very corroded where it was exposed to the turbine glow....

The pipe lasted 18 years, 11 with turbo, not a bad service life. I just hope the new one is made the same as the original, I've noticed lots of factory parts getting more cheaply made over the years.

The offending hole is damp in this photo:


Last edited by Mangocats; 10-25-2008 at 06:00 PM. Reason: Add photo
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Old 10-30-2008, 12:17 AM   #9
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Update: new pipe is in, and incase you're wondering... yes, it did need to be re-bent to clear the BEGI downpipe by more than 1/4". Putting it inside a bigger pipe and pulling did the trick, having the old pipe as a reference made it fairly painless to get it "close enough" before installing, then after tightening it to the manifold, a final bend (probably of the bracket) got it to a good spot.

The original re-bend job is probably what led to the leak, I did a nicer bend in that location, but put more of a kink near where the hose attaches - I think it should last at least another 10 years.

If you get into a job like this, remember to lube up with dish soap - almost everything that was a problem was solved with dish soap, especially slipping the old spring clamps into place.

Does somebody know of a source for new spring clamps? Almost everyone in town just stocks the worm gear type clamps, which make a hard job harder, and I don't think they are the ideal solution for clamping onto those copper heater core pipes. The 18 year old spring clamps are still working, but the one that lived by the exhaust manifold is pretty rusty now.
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