Tracking a Miata in desert temperatures - do I need an oil cooler?

One of the items on the todo list before the next PDX at the local track is to figure out if I need an oil cooler. According to some of the regulars, it's not unusual to see temperatures on the wrong side of 100F there, in the shade if there was any.

I'm a little concerned about oil temps in this heat (and probably water temps, too).

Car has a stock engine with a stock cooling system with the FM lower hose and fresh OEM thermostat.

What say the audience - uprate the cooling system, stick an oil cooler in it or just leave it as is?

BTW, what's the recommended oil viscosity in these temps? 0W50? 15W50? In the UK I did tend to run 15W50 Mobil 1 on the track, but if it hits 100F over there the roads start melting. No, seriously.

I'd say the more the merrier, but I'm not a pro.

I run my Miata in Florida. I've done several 1 1/2 hr. enduro's on Labor Day at Sebring, where it gets to 99 degrees with 95% humidity. For a while, I even had the stock radiator in there. If you're close on budget, I'd say you can hold off. If you want the extra protection, it certainly couldn't hurt.

Actually, high humidity is bad for people but good for engines. The dry desert air makes cooling more difficult. Bonus points for altitude as well.

The weakest point might be the rad. A stock 1995 radiator is made of brittle 17-year-old plastic. When you start to stress it, it's liable to crack.

Make sure you've got a logical coolant mix in there (no need for 50/50 when it's 100F outside!), pressure test the cap and radiator, and give it a shot.

As for the melting roads, that's a matter of specifying the correct oil mix in the asphalt for the temperatures. Different climate, different oil.

Keith wrote: Actually, high humidity is bad for people but good for engines. The dry desert air makes cooling more difficult. Bonus points for altitude as well.

The track is "only" at 4500-ish ft, but I guess that's high enough.

Keith wrote: The weakest point might be the rad. A stock 1995 radiator is made of brittle 17-year-old plastic. When you start to stress it, it's liable to crack.

Radiator is only a few years old, but it's an auto stock radiator. And the duct is damaged somewhat, too...

I think I better try to get as much air to the radiator as I can and take it from there.

Keith wrote: Make sure you've got a logical coolant mix in there (no need for 50/50 when it's 100F outside!), pressure test the cap and radiator, and give it a shot.

Well, it does have fresh 50/50 mix in it. I guess I can always drain part of that.

New 1.1bar cap on it, too.

Listen to Keith. I could waste words here but he's right. At stock power levels I never had a problem tracking any of the 3 Miata's I owned. All NA's. Hell, I could track the last one at 5lbs boost with a new rad and thermostat in a VA summer without much issue. Once I started to overheat I installed a mishimoto large rad and those problems went away. Another thing you can do to help, completely optional, is seal up the nose so that all air is going through the rad instead of leaking around the sides.

Does the undercarriage plastic cover in the front affect cooling? Mine's missing...

Don't forget... it's a "dry heat."

So is that good or bad for oil cooling ?

Use of a synthetic racing oil might be good insurance.

I was thinking of pouring it some Mobil 1 racing 0W50. It's due an oil change before the next PDX anyway.

Dry heat is bad for cars.

Ducting into the rad is useful, although getting the air out afterwards is possibly more important. Put the plastic under tray in place. Make sure your fans are working, even at speed they're critical. I've seen some people pull the plug off the AC compressor and turn in the AC to trigger the second fan - Mazdaspeed cars seem to appreciate this.

If you do buy an aftermarket rad, pay attention. We did a bunch of dyno testing, and the design of the core is really important. Some of the aftermarket rads were worse than stick, even if they were shiny.

50/50 is way too much antifreeze. That stuff is good at preventing freezing, but has a lower heat capacity than water. Increasing your water content is a great way to improve your cooling for cheap.

Keith wrote: Dry heat is bad for cars. Ducting into the rad is useful, although getting the air out afterwards is possibly more important. Put the plastic under tray in place. Make sure your fans are working, even at speed they're critical. I've seen some people pull the plug off the AC compressor and turn in the AC to trigger the second fan - Mazdaspeed cars seem to appreciate this.

Both ducting and under tray are in place, both however are somewhat busted up from the previous owner's offroad excursion with the car. I guess I better make sure I replace both (was on the list anyway).

Both fans are working, I wouldn't go near the track without that. Would the FM fan shroud make a big difference on a stock rad?

Keith wrote: If you do buy an aftermarket rad, pay attention. We did a bunch of dyno testing, and the design of the core is really important. Some of the aftermarket rads were worse than stick, even if they were shiny.

I'd either get the FM crossflow or a 37mm Koyo...

Keith wrote: 50/50 is way too much antifreeze. That stuff is good at preventing freezing, but has a lower heat capacity than water. Increasing your water content is a great way to improve your cooling for cheap.

I guess once it gets proper warm out here I can drain the antifreeze, put it away until autumn and run distilled water + water wetter in the summer.

Keith wrote: Bonus points for altitude as well.

Does this make a noticeable difference in cooling on track?

Lets say the air is 90% as dense as seal level.

90% air density = 90% the power created by the engine (NA engines) 90% power = 90% heat out the radiator

Seems like the altitude wouldn't make too much of a difference since power output should drop by the same amount as cooling capacity.

So is there really any point in performing a coolant re-route (using either the FM kit or another kit) if the car is tracked? What about street driven? I was considering that modification but the responses in this thread seem to indicate that it may be unnecessary. It certainly seems like there may be better areas on which to spend $200-$300, at least right now.

iceracer wrote: Use of a synthetic racing oil might be good insurance.

I agree with this. Synth is going to stand up to extreme heat better than dino.

Keith wrote: Ducting into the rad is useful, although getting the air out afterwards is possibly more important. Put the plastic under tray in place. Make sure your fans are working, even at speed they're critical. I've seen some people pull the plug off the AC compressor and turn in the AC to trigger the second fan - Mazdaspeed cars seem to appreciate this. If you do buy an aftermarket rad, pay attention. We did a bunch of dyno testing, and the design of the core is really important. Some of the aftermarket rads were worse than stick, even if they were shiny. 50/50 is way too much antifreeze. That stuff is good at preventing freezing, but has a lower heat capacity than water. Increasing your water content is a great way to improve your cooling for cheap.

1. Ducting is EXTREMELY important. I've seen turbo cars over heat. Cut a hole in the hood behind where the rad is placed letting air flow through the rad and out the hole. Worked wonders. For fans I personally wired both fans to the one cooling circuit. I used Spal fans. Two of them filling the back of the rad. Worked for the time I tracked the car. You may overload the stock relay but I never did. YMMV

2. Good point Keith. I never tested the Mishimoto rad except on track and it worked out for me ok. But I'll bet some of the stuff from Ebay is complete junk. The good thing about FM products is you know they're tested and FM will stand behind them.

3. I thought a lot of tracks were specifying water as coolant these days. The reason being safety as spilled antifreeze is very, very slick. Water spilled on track will evaporate and not leave a slick surface. In either case water is a better cooling medium.

Winston wrote: So is there really any point in performing a coolant re-route (using either the FM kit or another kit) if the car is tracked? What about street driven? I was considering that modification but the responses in this thread seem to indicate that it may be unnecessary. It certainly seems like there may be better areas on which to spend $200-$300, at least right now.

When my car hit 7-8lbs of boost I used a coolant reroute. I routed my heater core outlet back into the top rad hose using some pipe and a threaded nipple. It worked alright. Not well, just alright. It would keep the water temps down for about 5 minutes more on the track. The car would still overheat but just later in the session. That's when I threw in the towel and got a bigger rad and double the fans. I will defer to Keith for any other data on this. I'm sure he has more experience in talking about coolant reroutes, the cooling design compromise of taking a FWD motor and making it RWD, and the beating the #4 cylinder takes from being last in line for coolant.

RossD wrote: Does the undercarriage plastic cover in the front affect cooling? Mine's missing...

Yes it does, you should replace it. the presence of the undercarriage cover helps create a low pressure area behind the radiator which helps pull more air through (similar effect to jacking up the rear of the hood).

On pop-up light cars you can also improve cooling by making a sheet of plastic to keep air from escaping over the top of the radiator. You can buy them for Miatas but that's not very grassroots

That plastic piece above the radiator isn't stock? I assumed it was.

Oh dunno if any came with one, but I've seen some people running aluminum ones with flashy aftermarket names on them.

As with everything else, maximizing your cooling depends on what's holding you back. The world's greatest radiator won't help if you don't have air moving through it, for example. If your cooling system is doesn't properly circulate water through the engine, pulling heat out of the coolant won't help.

I've become a big believer recently in fans after seeing the effect they've had on a few cars. Problems that were resisting different radiators (including, in one case, an enormous fat crossflow setup) can be vanquished by a good fan setup. Airflow across the rad is critical, and the problem isn't usually getting air to the front but getting it through the core. Xceler8x dealt with that by putting a hole in his hood to drop underhood pressures. If you're not willing to get out the saw, a good set of fans on a good shroud (and there are some on the market that are useless) will have a big effect. Contrary to popular perception, the air underhood is almost stagnant even at speed. Stay away from "slimline" fans, as they usually don't have enough torque in the motor to pull significant air through multiple heat exchangers.

My order of operations - assuming a healthy OE radiator - would probably be fans, radiator then coolant reroute. If the car's got a budget aftermarket radiator, I might address that first. Getting rid of the heat is usually a bigger problem than the internal coolant flow in the engine.

ProDarwin, altitude certainly affects cooling. We deal with turbo cars, which can make pretty similar power at altitude as they can at sea level - but in order to do so, they generate more heat. So, less efficient heat exchange AND more heat. Bad combo.

If you're going to run pure water, throw in a bottle of Redline Water Wetter. That'll help prevent corrosion as well as keep the water pump happy.

I thought antifreeze raised the boiling point, making it less likely to overheat (as in boil over).

The part about not spewing it on the track makes sense however.

How about install a real water and oil temp guage to see if you actually need it.

Antifreeze will reduce the tendency for the coolant to boil in pockets inside the engine, although I'm not sure if that's due to boiling point or surface tension alterations. But with a lower heat capacity, antifreeze will get hotter for a given amount of energy absorption. Water wetter gives you the same benefits without the drawbacks, so it's a better choice for a desert race car. Not a sub-freezing desert, though.

Another data point is that water under pressure boils at a higher temperature. That's why cooling systems are pressurized.

Source

Huh. Now, I'm no mechanic, but I would think the Spec Miata guys would have some light to shed on this. :-)

We didn't run an oil cooler. I had a big Ron Davis radiator, raced it in the deserts of Arizona and southern California, shifted it at the fuel cutout. It was fine all that season and after.

But I didn't do a teardown to find out what the internals looked like afterward.

David