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PostPosted: Fri Jul 26, 2013 12:58 am 
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This issue is kicking our butts. Dan has a '96 1.8L Miata he bought in St. Louis last year. Over the winter we fixed a few minor engine issues, had the timing belt off so we replaced the water pump.

Once we got things back together and started it up, it ran great but once it got warm after idling just a couple of minutes, it started hissing and leaking coolant. The leak is driver's side, behind and / or below the water pump. It doesn't appear to be the inlet pipe, and I don't believe it's coming through the weep hole in the water pump.

We pulled it apart, cleaned it all up, put on new gaskets, switched from Blue RTV to Black RTV. This time it started dripping coolant as soon as we filled the radiator.

Pulled it apart again, new gaskets, another new water pump (this one's from Auto Zone, the other was form Napa), back to Blue RTV. Same thing.

Each time we're cleaning very well, using new gaskets, using a proper amount of RTV sealant, and torquing the bolts to specs.

I'm down to these causes:

- A leak in the inlet tube we're missing, but I don't think this is it.
- A leak or crack in the block. The water pump bolts don't pass through the block, but I guess it's possible that one could be cracked and leaking.
- The block is somehow warped, causing it not to mate with the water pump.

I don't believe there's a water passage below the water pump between it and the oil pump, and it looks like the coolant is coming from below / behind the water pump and above the oil pump. You can see pretty well between the water pump and the top of the block, and it's dry there.

We would welcome any ideas.

The engine is currently assembled, and can be started to demonstrate the leak. We're either going to see if someone can come look at it, or maybe tow it to a shop to have someone else look at it. (we have the tow dolly we use for the SM).


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PostPosted: Sat Jul 27, 2013 11:24 am 
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Location: Urbandale, Iowa
Can you pressurize the cooling system with compressed air and then trace the hissing sound?

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Greg S.
Swift DB4 - B Mod, 08 Yellow Chevy, 08 335i e92, 65 Mustang 2+2 GT, 70 Honda CL450


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PostPosted: Sat Jul 27, 2013 12:24 pm 
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That's a good idea...

Tried it out (just stopped by on my way past while I was running and errand), yep it makes it hiss and green stuff drip out. Dan's going to pull all of the timing belt covers off and see if we can tell where the leak is.


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PostPosted: Wed Jul 31, 2013 12:09 am 
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Found that it was leaking from the thermostat tube (aka the "dong" ) that comes out of the head, above the water pump, and running down around the water pump. Couldn't see that with the camshaft plate in place.

Some previous owner or a mechanic that shouldn't be allowed to work on a big wheel didn't get the o-ring in place - it was 1/2 out of the channel and cut into pieces. The only thing the saved it at all was the RTV that was around it.

We have the new o-ring, gaskets and thermostat ordered.

See example images:
Dong
Image
o-ring
Image


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PostPosted: Wed Jul 31, 2013 8:58 am 
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Throw the thermostat away. For our cars it is not needed. At MAM in June, my temps averaged 180-190 without it but still warmed up prior no problem.

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David Schroeder

2007 Red Acura TL Type-S
1993 Black Rx7
1996 Black SM/STL Miata


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PostPosted: Wed Jul 31, 2013 9:46 am 
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This is on Dan's street car, not the SM.

From what I understand, in SM you are supposed to have a thermostat, but it can be any temperature, which people interpret as meaning you can jam it open or even remove the insides all together.

We still have a stock thermostat in the SM, we have a nice Longacre temp gauge, at ISW we were reading between 175 and 190. From what I've heard, some guys run up to 250 F, not sure what they're doing different...


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PostPosted: Wed Jul 31, 2013 10:14 am 
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Oh just figured it was for the SM car.

And removal of the thermostat is allowed. Look at section 3 under cooling. Iowa was a pretty cool day though. Some of the hotter days will really push the cooling system.

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David Schroeder

2007 Red Acura TL Type-S
1993 Black Rx7
1996 Black SM/STL Miata


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