NB Miata Cooling Issues | Lack of under-tray?

So my 2001 Miata has been giving me cooling issues recently. 

First I found that the main cooling fan (not the A/C fan) was not working. -Replaced it and it is working now.

Then I was still having cooling issues so I replaced the Thermostat. The old one did appear corroded and possibly didn't open as far. Cooling issues persist. 

I have been watching the temps on my OBD2 device and here's what it does. I'm driving home (it's kinda hot out) and the temps creep up. On the drive in they never got above 208*, but on the way home it got as high as 220*. So I opened the windows and cranked the heat, and it cooled down and stayed under 200* and closer to 190* the rest of the way home. 

I know that my miata does not have the plastic undertray, could this cause this much of an issue giving the radiator less airflow?

When I ran my Spec Miata without the undertray, I could get about four laps, then had to back off (was renewing my SCCA license on the short course at Daytona).  Made a crude undertray out of plastic and was able to almost go the whole session without creeping temps.

Dude, my miata stays around 200 highway, and gets to 240 in traffic. Only has one working fan. At first, I had no undertray, then I had an undertray, and now I’m back to no undertray. My obd2 tool showed no change. 

In reply to _ :

240 doesn’t worry you?!?

Yes, put the undertray back on. You can get a new one cheap from the dealer, at least you used to be able to. 

It will make a difference. 

AWSX1686 said:

In reply to _ :

240 doesn’t worry you?!?

I know, right? I have my ECU set to go into limp mode (Edit: really just catch my attention with a 5krpm limit) at 215 and shut the engine down at 230!

The undertray will make a difference at higher speeds and is totally worth having, but it sounds like there's some other problem involved, even without an undertray you shouldn't see such high temps in gentle street driving.

GameboyRMH said:

AWSX1686 said:

In reply to _ :

240 doesn’t worry you?!?

I know, right? I have my ECU set to go into limp mode at 215 and shut the engine down at 230!

The undertray will make a difference at higher speeds and is totally worth having, but it sounds like there's some other problem involved, even without an undertray you shouldn't see such high temps in gentle street driving.

Yeah, 240 degrees in traffic does not seem right at all. My car, back before the new engine and supercharger, on a stock radiator and fan, with A/C and no undertray never went above operating temp in traffic. 

NickD said:

GameboyRMH said:

AWSX1686 said:

In reply to _ :

240 doesn’t worry you?!?

I know, right? I have my ECU set to go into limp mode at 215 and shut the engine down at 230!

The undertray will make a difference at higher speeds and is totally worth having, but it sounds like there's some other problem involved, even without an undertray you shouldn't see such high temps in gentle street driving.

Yeah, 240 degrees in traffic does not seem right at all. My car, back before the new engine and supercharger, on a stock radiator and fan, with A/C and no undertray never went above operating temp in traffic. 

Was that monitored by the gauge in the dash, or an OBD2 reader?

The undertray won't do anything in traffic. That's all fans for airflow. There's no reason why a 1.8 Miata should only have one functioning fan. 240 is a little high for traffic.

If you don't have an undertray and you drive your Miata at speeds exceeding a walking pace, get an undertray. It'll only help. They're inexpensive via Mazda's Team Support program (every Mazda owner on the GRM board should be a member), or you can get them from Flyin' Miata for a pretty good price.

AWSX1686 said:

NickD said:

GameboyRMH said:

AWSX1686 said:

In reply to _ :

240 doesn’t worry you?!?

I know, right? I have my ECU set to go into limp mode at 215 and shut the engine down at 230!

The undertray will make a difference at higher speeds and is totally worth having, but it sounds like there's some other problem involved, even without an undertray you shouldn't see such high temps in gentle street driving.

Yeah, 240 degrees in traffic does not seem right at all. My car, back before the new engine and supercharger, on a stock radiator and fan, with A/C and no undertray never went above operating temp in traffic. 

Was that monitored by the gauge in the dash, or an OBD2 reader?

Gauge in the dash. It was pre-OBD (1990), so there was no OBD2 reader on that. 

NickD said:

AWSX1686 said:

NickD said:

GameboyRMH said:

AWSX1686 said:

In reply to _ :

240 doesn’t worry you?!?

I know, right? I have my ECU set to go into limp mode at 215 and shut the engine down at 230!

The undertray will make a difference at higher speeds and is totally worth having, but it sounds like there's some other problem involved, even without an undertray you shouldn't see such high temps in gentle street driving.

Yeah, 240 degrees in traffic does not seem right at all. My car, back before the new engine and supercharger, on a stock radiator and fan, with A/C and no undertray never went above operating temp in traffic. 

Was that monitored by the gauge in the dash, or an OBD2 reader?

Gauge in the dash. It was pre-OBD (1990), so there was no OBD2 reader on that. 

Is that an accurate gauge? Mine doesn't mive from normal unless it's MAJORLY hot. 

One of my buddies has an undertray, so I'll grab that tonight.

AWSX1686 said:

NickD said:

AWSX1686 said:

NickD said:

GameboyRMH said:

AWSX1686 said:

In reply to _ :

240 doesn’t worry you?!?

I know, right? I have my ECU set to go into limp mode at 215 and shut the engine down at 230!

The undertray will make a difference at higher speeds and is totally worth having, but it sounds like there's some other problem involved, even without an undertray you shouldn't see such high temps in gentle street driving.

Yeah, 240 degrees in traffic does not seem right at all. My car, back before the new engine and supercharger, on a stock radiator and fan, with A/C and no undertray never went above operating temp in traffic. 

Was that monitored by the gauge in the dash, or an OBD2 reader?

Gauge in the dash. It was pre-OBD (1990), so there was no OBD2 reader on that. 

Is that an accurate gauge? Mine doesn't mive from normal unless it's MAJORLY hot. 

It's a useful gauge. If it's not moving, you have no problem. If it starts moving, take action.

Keith Tanner said:

 There's no reason why a 1.8 Miata should only have one functioning fan. 240 is a little high for traffic.

I was told on ancient Miata forums that the Miata only has one functional fan. The other fan is for AC. 

_ said:

Keith Tanner said:

 There's no reason why a 1.8 Miata should only have one functioning fan. 240 is a little high for traffic.

I was told on ancient Miata forums that the Miata only has one functional fan. The other fan is for AC. 

The other one also cycles on when the temp hits 230ish degrees, as I was led to believe. I just wired the two together when I put the new engine in so that they run at the same time.

In reply to NickD :

 Are you OBD two? I seem to remember reading something about blowing fuses if you wire both fans together. Then again, maybe that was if you turned the AC on, and maybe that was if you had an OBD one vehicle. 

_ said:

Keith Tanner said:

 There's no reason why a 1.8 Miata should only have one functioning fan. 240 is a little high for traffic.

I was told on ancient Miata forums that the Miata only has one functional fan. The other fan is for AC. 

That is true for 1.6 cars, but has not been true for 26 years :) And the AC fan is functional, it's just tied to the AC. We sell a wiring kit to gang them together (and feed the right power to the AC fan with a dedicated circuit breaker) if you want to more than double your airflow. 

The 1.8 cars have both fans under ECU control.

In reply to Keith Tanner :

See this is why I come ask here first. Thank you!

You guys are living in the past.  190? 200? Maybe for a small block chevy.  On a newer Ford 5.0(coyote) the cooling fan doesn't even TURN ON until 217 degrees!

Many newer engines run at higher temps to make them more efficent(gas mileage, emissions)

On anything newer than 2000 I would expect 215-220 to be normal.  At 235-240 I would be worried.

The BP engine found in NA and NB Miatas is not a newer engine. It dates back to the 70's and even a 2005 Miata is still basically a 1990 with some upgrades.

Keith Tanner said:

The BP engine found in NA and NB Miatas is not a newer engine. It dates back to the 70's and even a 2005 Miata is still basically a 1990 with some upgrades.

Alright, you win

....this time!  *dum dum dum* (dramatic drum beats)

Keith Tanner said:

The BP engine found in NA and NB Miatas is not a newer engine. It dates back to the 70's and even a 2005 Miata is still basically a 1990 with some upgrades.

Even so, I'm betting that the highest fan setting won't turn on until 215 or so.  I would not be worried with a BP at 220- we used to run all of our engines that hot back then, too.  240 is hot, but not so much to freak out over.  

Given that the early ZTEC 2.0l is very similar to a BP- cast iron block and aluminum heads- 220 isn't something to be scared about.  And the ZTEC is a 4V version of the SPI motor that dates back to the early 80s in origin.

Not to say that you should ignore cooling problems- fans should be coming on at the right time.  And for most cars of the late 90's and on, the high speed fan is the same as the one used for a/c.

Well, happy ones don't run at 240. So if that's happening, then it's indicative of a problem. 240 is a long way from thermostat temp. You won't pop it there, but you should be taking steps to stop the temperature gain. You have to try really hard to blow a Miata head gasket, but we've found that if they climb to 240 they'll probably keep climbing.

Just so nobody reads this and generalizes "all Miatas use the AC fan for high speed", here's a little more info:

1.6 Miatas (specifically 1990-93 North American cars, I don't know about later 1.6 Miatas overseas) have the primary fan triggered by a thermoswitch on the thermostat housing and the AC fan triggered by the AC. No interaction at all.

1994-05 Miatas (non-MSM) have ECU control of both fans. I don't have the exact trigger temps on hand at the moment.

2004-05 use two two-speed fans under ECU control. They'll change the speed of the fans depending on the cooling requirements instead of just turning individual fans on and off. They have the most efficient stock radiator (better than most "race" replacements) and the best factory fan system, which is surprisingly complex electrically as it includes some relay logic in the system.

For this NB product, what I personally would expect given what all cars do around the turn of the century- when the A/C is turned on, all of the fans are also turned on.  

For earlier cars, I have no experience with pre-92 cars.  

And in that era of cars, the first stage of fans turn on above 200F and the high setting is somewhere between 210 and 220.  Which allows cars to run hotter than they normally would when they are on the FTP, which then results in higher fuel economy.  We would regularly see 220 F on a gentle cycle, and then on the tough cycles, which has a much more powerful fan, they would run close to 190.

So driving slowly in traffic, I would not be stunned by seeing anywhere between 210 and 220.  But moving down the freeway, it should be easily capable of 190.

If the fans are not turning on properly, then that needs to be addressed.  If the car is still running on the fans when going 50mph (w./o A/C), then something needs addressed.  

Somewhat related but may be partially off topic - when do you start to worry on a turbo track car, Keith? Running my car at Atlanta Motorsports Park I was seeing mid-220's after about 15 minutes of hard track driving in 90 degree Atlanta (humid) heat. It drops back down quickly once I let off but I am a little too scared of hurting something to push it any further.