autox/track appropriate thermostat?

[OZMDD]

Ok cool kids, I need the lowdown on the best thermostat temp for Dallas summers and autox. I typically go cooler, but that's not always best. Running a standard 1.8 NA motor with good fans and radiator.

[Walsted]

I don't autocross, but I believe conventional wisdom is that the thermostat limits how cool the car gets, and the radiator and fans determine how warm the car gets. If you need to stay cool, focus on the radiator and/or fans. I have run larger than stock radiators on both of my cars and on my wife's current car, and the only cooling problems I have regardless of load, outside air temp, or traffic is when there is a leak in the cooling system.

Others can probably give better advice. If you need to stay stock, the radiator and/or fan mods are probably out of the question, and the advice above is probably useless.

[Davidss]

Many enthusiasts believe that a lower temp thermostat will give them more power but the opposite is actually true. A significant amount of energy is wasted as heat into the coolant jacket. So if the coolant is hotter there is less loss and vice versa. This is one of the reasons you see newer cars with extreme high coolant temps as engineers are trying to increase power and efficiency.

There is also the issue of engine bay temperature and although I am not certain I could theorise that a lower temp thermostat could actually hurt you there as well.

Ultimately my recommendation would be OEM temp. The stock computer makes serious adjustments based on the coolant temp not limited to fuel, timing, and open/closed loop. So unless you really know what you're doing I would stick with stock.

[cone-cerned]

I'm with Davidss, run the OEM temp.

[OZMDD]

Good info. I wasn't really thinking power, as miata has so much to spare. I was mainly concerned about overheating, but the rad and fans are <1 yr old. Thanks, Dave. Anything new on the CRX to share?

Mike - not limited to stock parts on this build, not going to be scca-limited. Hopefully will be codriving a proper car for their events. The majority of clubs are using a displacement/tire system these days. If I do run it for SCCA/ER, it will be in one of the silly classes. Main limiting factors are cost and effort.

[Davidss]

In the event of an overheating scenario the thermostat would be wide open. So the only advantage to a lower temp is a few seconds of additional time in which you 'might' be able to catch it. That is not realistic protection IMHO. A much better investment would be an over temp alarm, and there are a few ways to do one of those.

Nothing really new on the CRX. We sold Kim's RX8 and bought a BRZ.

[jrj512]

I was mainly concerned about overheating...

As long as my OEM cooling system is functioning properly, I never overheat at an AX. People with (naturally aspirated) Miata heating issues that start installing bigger rads and fans are usually masking the true issue.

Pressure test the cooling system.

[hornetball]

This is NA6/NA8 info.

A lower temp thermostat reduces your cooling capacity because there will be a lower temperature difference between the coolant and the air at the radiator. That's why you often see a higher-temp thermostat as part of a trailer-towing package. So, stick to the OEM t'stat.

A good undertray is key. A brand new one is <$60 and worth it.

A coolant reroute is a great thing to do on early Miatas. Cools #4 and also increases the amount of coolant going to the radiator vs. going to the heater core (once again, this increases the "capacity" of your radiator).

I run a stock radiator, unmolested undertray, OEM thermostat and reroute. Car runs cool on track in August at 10psi boost. The only time I get hot is stuck in traffic with AC on full blast. That's an airflow issue though (my fans are the originals from 1990). As soon as I'm up to 20mph or so, car is back to normal.

[OZMDD]

Thx. Been looking at the Coolant reroute, so it sounds like a good pressure test, system maint and OEM t-stat ought to be sufficient prior to the reroute.

[TexasStig]

Did you modify the fans to run in parallel? That's the only cooling mod I did and never had an issue at TTs or AutoXes.

Nope. I just lied... I also used a RX7 O'Reily's radiator cap. Something about a couple bar pressure difference with the RX7 helps but damn if I can remember the science behind it. Probably read it somewhere on the web, so it must be true.

Technially, I also replaced the radiator with a OEM knock-off, but that was just a precaution b/c I didn't know the car's history.

[OZMDD]

Higher pressure basically raises the boiling point of the coolant by creating a greater resistance to the kinetic energy of the liquid molecules trying to change state, in an oversimplified way.

I have not modified the fan wiring at this point. Might look into it, but the reroute solves a design issue with the way the BP motor was altered from a fwd design, so it makes good sense to me regardless of how well the rest of the system is working.

[EricJ]

I had some high temp issues last summer. I got a hole in my stock radiator and overheated coming back from Hallett, I put in an Automatic radiator, but failed to change the thermostat. On track, the temp would go above 12 o'clock after 4 or 5 laps. I went from 50/50 to water wetter only. Still the same issue. I finally put in ta 37mm Koyo and new thermostat. No issues since. In retrospect, if I'd put in a new thermostat and maybe added aluminum tape to plug up around the radiator it probably would have been fine. I'm using 160o's based on the recommendation of one of the local Miata shops.

[lostlorin]

Higher pressure basically raises the boiling point of the coolant by creating a greater resistance to the kinetic energy of the liquid molecules trying to change state, in an oversimplified way.

I have not modified the fan wiring at this point. Might look into it, but the reroute solves a design issue with the way the BP motor was altered from a fwd design, so it makes good sense to me regardless of how well the rest of the system is working.

So what you are saying in a shorter oversimplified way is that the higher pressure raises the boiling point of the coolant?
?

[cone-cerned]

Yes, he is.

[lostlorin]

I got lost when the moles were moving to Oklahoma.