Heater Core Replacement in the ’93 Mazda Miata: Part 2

Last we left off, your intrepid garage hack was somewhere in the process of replacing the engine compartment coolant hoses, as part of a heater core replacement on his 1993 Mazda Miata. In this installment, we will provide an update on the progress of said hoses.

You may be saying to yourself, “the blog post is entitled ‘heater core replacement’, but there are nary few words so far about the actual core”. This would be an accurate observation, as in fact, the heater core has been removed from the vehicle, but I am not quite ready to begin the installation of the new part. Instead, I’m documenting the work that’s been done most recently (the hoses), and will soon be writing more about the core. At least I certainly hope I will be, as it’s almost June and I haven’t driven this car since last fall.

Intermediate pipe, painted with high-temp paint, was cured with heat gun
Intermediate pipe, painted with high-temp paint, was cured with heat gun

Back to the hoses. In Part 1, I gave mention to a “heater hose kit” from Moss Motors. The kit comprises of 7 hoses: 3 larger-diameter pieces, and 4 smaller-diameter ones. The larger hoses are your typical radiator-to-engine coolant hoses, excepting the fact that Mazda has a 3-part lower setup, with a rubber hose running to a metal intermediate pipe, followed by another rubber hose. But it was the 4 small ones which threw me the curve ball, as I had no idea that the car had these additional coolant hoses. As Moss did not provide a diagram, I also had no idea where in the engine compartment they were.

The two hoses, running parallel between intake and valve cover, are coolant hoses
The two hoses, running parallel between intake and valve cover, are coolant hoses

Poking around the area of the thermostat housing, I found two; the other two were over at the intake manifold. The function of these hoses seems to be to provide a “warm engine temperature” signal to the idle control and the radiator fan control. I didn’t research it further as I wanted to devote the time to getting the spring-loaded hose clamps off.

Note clamps under and to the right of thermostat housing
Note clamps under and to the right of thermostat housing

These clamps were not only difficult to reach; the clamps ears in some cases were rotated away from what might be the most accessible positions. It is possible that these were built up as subassemblies before the engine was dropped into the car. In any event, they had not been touched since the car was built, and I needed to get them off. Using various shaped pliers, including needle-nose, curved nose, and slip-joint, most of them eventually came loose. One clamp in particular, under the thermostat housing, was twisted back and forth until it broke off (I was very mad at it). Like many other underhood jobs, components which were in the way were removed for better access.

Old and new hoses side-by-side. Old ones were hard but not leaking (yet)
Old and new hoses side-by-side. Old ones were hard but not leaking (yet)

Besides the clamp which was twisted to death, there were two other casualties: the A/C-power steering belt was removed with a hacksaw, because I intend to replace it anyway; and the fan temperature sensor switch in the top of the thermostat housing fell victim to an errant wrench. New parts have been ordered and are on their way.

Switch is NOT designed to be removed in this fashion
Switch is NOT designed to be removed in several pieces

As of today, the upper radiator hose, lower rear hose, and all four smaller hoses have been replaced. On the smaller hoses, several spring clamps were replaced with screw clamps for easier installation. With this part of the job basically done, we’re soon moving back to the heater core.

 

All photographs copyright © 2016 Richard A. Reina. Photos may not be copied or reproduced without express written permission.

 

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