I feel this overlooked item should be given the spotlight. Out of my two 12a's both rear intake o-ring gaskets were compromised. I plan to plug (20mm).

 

Yep plugging them with a freeze plug is the way to go.

 

Block your ACV port as well! People always forget that this causes the manifold to heat up without the benefit of coolant running through it.

 

Dumb question, but why plug them, I assume they are like that for a reason? I just replaced mine, kinda a pain to do, but the old ones lasted 34 years and should outlast the engine.

 

I agree. Either block both the coolant and the ACV for "performance" (cooler running manifold), or don't block them at all.

 

Mazda recognized that these cars would be driven in some cold country. Cold intake temps tend to cause rich mixtures (high air density) which can also cause poor atomization of the fuel and inefficient burn. By routing hot coolant through the intake, it brings some engine heat into the air path leading into the combustion chambers, helping to atomize the fuel for better combustion. The -SE has a separate heater hose which runs from the back of the water pump to the Throttle Body and then back to the block which also serves this purpose, even though the engine is fuel injected right at the ports, but the hot coolant route is used to operate the Vacuum Secondary Throttle plates which function as chokes for cold, cold weather startup. Also, the function of the Thermowax pellet relies on this hot coolant to set a cold start throttle hold to build engine (and cabin heat) more quickly for passenger comfort, then allows the throttle to return to normal operation after the engine is warmed up.

Where I live (Sonoran Desert), there's no need to add more heat to the Throttle Body, but it also doesn't hurt anything other than possibly increasing intake air temp a bit more than ambient. Regardless, the intake air temp sensors account for that differential and adjust injector pulse to match for proper Air/Fuel Ratio. The -SE also doesn't have the ports on the intake manifold to worry about leaks, so that's probably the main reason why people plug them - to avoid having coolant leaks into the air path.

 

It was not used so much for fuel atomization more for intake icing or throttle plate icing. In certain conditions ice can form inside the intake or around the throttle body while driving the car. One way to combat this is with heat, so they used hot coolant to prevent the chances for formation of ice. Gasoline has been reformulated over the years to have properties to help prevent this.


There is a good article in hemmings. https://www.hemmings.com/magazine/hc...g/3747511.html

 

This is great information, thanks. I always like to know the "why" behind quirky engineering. Lord knows my F-150 has more than it's fair share of quirkiness too.

 

The other reason is it makes it easier to swap intakes. You don't have to drain the coolant to just pull the intake off. Not a big issue until you start messing with modified intakes or carbs, then it becomes a real issue.

 

At least mine is done now, it will out last the car living at the beach. I foresee a lot of rust in my future...