When you turn up the HEAT, ya gotta keep it COOL!
After adding the FM3 turbo kit, my engine temperatures became a real problem. The intercooler with the kit is quite large and blocks the majority of the front surface area of the AC condenser (and thus the radiator). Since I had previously removed my splash pan and nose shroud, air rushing against the front of the car really was not strongly forced into the intercooler/condenser/radiator area. Instead, the air could easily blow around these heat exchangers, and reduced amounts of heat extraction would occur.
To further complicate the heat dissipation issue, the Garrett turbo included with the kit utilized a water cooling jacket-which heated the coolant further. Running the engine harder with high amounts of boost also contributed to added heat.
All of these elements contributed to a major problem. On a 80 degree F day, I was seeing considerable overheating while cruising above 70mph. This was truly a serious problem that could not be neglected.
To remedy the problem, I made a few relatively cost effective modifications which have (so far) completely eliminated all my overheating issues. All of these items were done at once so I don't know for sure which one made the biggest impact:
Re-Installed the Nose Shroud
Perhaps the most effective fix to this problem was re-installing the nose shroud. This turned out to be easier than I expected, but it required lots of trimming for my intercooler. Below is a picture of the result. Notice how the plastic nose shroud mates up right against the lower end cap of the intercooler (please ignore all the bugs stuck in the IC. Poor little suckers).
Having this shroud in place prevented air from rushing underneath the IC. By forcing more air into the IC, more air was forced into the AC condenser and radiator. I also fabricated a couple small aluminum pieces on the sides of the IC to further force air into the IC, but they didn't turn out real well. I need to redo those pieces.
My first instinct when the overheating issues arose, was to upgrade the radiator. Although I now think focusing on air flow was the key improvement, upgrading the radiator was certainly another contributing factor in fixing the problem.
I really wanted a nice, all aluminum radiator which not only works well, but is a work of art by itself. The only problem was the price tag. At about $500 for a quality unit, I just didn't have the funds to commit to it. Enough was already spent on other things.
As an alternative, I was fortunate to have been directed from another miata enthusiast about a company that created an all metal (copper) dual core, high efficiency unit that was claimed to extract as much as 40% more heat than an OEM unit. The best part was the price tag... $185 from Hughs Radiator in California. Below is a picture of their product.
The radiator showed up well packaged and in great shape. All that was required of me was to remove the old radiator, transfer a couple mounting posts from the OEM unit to the new one and install it. I am quite pleased with the quality of this unit for the price I paid for it.
While refilling the system, I felt this was another area to focus on. The heat transfer characteristics of a coolant mixture can be improved by leaning out the mixture with a higher water:antifreeze ratio. I filled the system with approximately 80:20 water:antifreeze mixture. Heat can transfer better along a water to metal surface interface than antifreeze to metal.
In addition, I also add a bottle of Redline Water Wetter to further promote better heat exchange from the metal to coolant surfaces.
AC Fan Modification
This turned out to be a really easy solution! Since I have air conditioning, I have two fans behind the radiator. Many miatas are equipped this way; one fan is called an AC fan, the other is a COOLING fan. Whenever the engine water temperature reaches a certain "hot" temperature, a thermal switch above the thermostat closes and causes the cooling fan to come on. The AC fan, however, does not come on due to high water temps.
Whenever the AC system is on, the AC fan periodically comes on. When this fan comes on, the cooling fan also comes on.
Why not have both fans also come on whenever the water temps get high? Good question! There is an easy fix to this. Simply cut the hot wire going to the AC fan (Black/Blue). Tape off the harness side of the cut wire (it will have no future need), and splice the AC fan side of the cut wire into the hot wire going to the COOLING fan (Yellow). It is important to do the connections this way; if you don't cut the AC hot wire, you'll have problems. For some reason, the AC hot wire gets grounded whenever the car thinks to turn the AC fan off. If a wire was simply spliced from the cooling fan hot wire to the AC hot wire, there would be a short whenever the AC fan is off and when the cooling fan tries to turn on.
Now whenever the AC is on or when the water gets hot, both fans come on simultaneously.
To top it all off, I bought a new radiator cap for the new radiator. The stock cap is rated at 13psi pressure. I found one from a local autoparts store that fit the same, yet at a 16psi level. By increasing the cap pressure, the coolant in the system is also regulated at a higher pressure. By increasing the pressure, the coolant mixture will boil at a higher temperature. It is very important for the coolant not to boil; once the coolant vaporizes, there is less liquid to metal contact and thus less heat extraction. The 16psi cap is just a little over the stock regulation pressure; not a huge amount. If pressures still build above 16psi within the system, the cap acts as normal and allows boil over to spill into the overflow tank.