Hello all.

I recently purchased a 97 1.8 with a FM 2560 based turbo kit, running on a Haltech Elite 1500. Running low-boost right now right around the 10psi range with a very safe tune, but the car runs very well overall. My goal for the car is to be a dual-duty auto-x and track-day car, with the occasional nice-weather drive to work. So far I had never experienced any overheating issues with it over maybe 150 miles of street driving, and one auto-x event. It sits around 180-190 all the time while moving, and will also hold there with the fans on at stoplights.

I took the car to a track-day at Thunderhill in N. California yesterday, and had some major overheating issues, including having the car not cool down virtually at all when completely lifting off and coasting for entire laps.

Cooling System:
Supermiata re-route, with 185 degree thermostat
Mishimoto radiator, with shroud and dual SPAL's (Fans are on manual switch)
Coolant currently in the car is 50/50
No ducting, and no undertray (both are in the works)



The car was at 230 degrees within 2-3 laps all day. Ambient temps were 60-80 throughout the day, so should not have been a factor. Two recent changes to the car just before heading to the track-day were the addition of a couple hood vents, and a water-pump install by a reputable shop that I trust. (Needed to do front-main and camshaft seals, and had them do the water pump/timing belt while in there). While at the track yesterday, I did surmise that they might've not fully bled air from the cooling system. I cracked the bleeder and it did seem to let out a decent amount of air before spurting solid coolant, so I figured the problem was solved. However, it did not change the overheating issue in the slightest. I also removed a SPAL from the shroud, and then ended up taking the entire shroud off and running fan-less. Neither setup made a lick of difference. I also tried two different rad caps, again, with no effect. After doing the 2-3 laps that I could do each run-group I would lift and coast for an entire lap and not see any significant cool down. Once back in the paddock coolant was boiling out of the overflow tank each time.

I'm still trying to figure out if this is an airflow or coolant flow issue. It seems like the car should've cooled significantly when coasting and off-throttle, and because it didn't it makes me think that it might be a coolant flow-rate issue? IE, either my new thermostat is not opening enough, or the brand new water pump is not functioning 100%. My only other thought is that the addition of the hood vents somehow altered the flow of air through the radiator. I plan to test the thermostat, and also do a road-test and see if it holds temp on the road, (had not driven the car since the water pump change).

I am doing another event in about 10 days, so I need to find a solution ASAP. Beyond building ducting I have even considered full-removal of the t-stat to see if that addresses the issue, but I know that is not generally advisable, and can actually exacerbate overheating when ambient temps are high.

Anyways, looking to see if any of the knowledgeable folks here might have any insight or ideas! Thanks!

 

Start with ducting. You will never cool a turbo miata without ducting, or an undertray at the very least. Been there, done that. Couldn't even do a mild 20 minute part throttle canyon driving without overheating without the undertray. And that was with a big alum rad, coolant reroute, etc.

 

I have a similar setup and use. I have had to extensively improve the cooling since I have retained the AC system. The AC condenser is very restrictive and gets hot when the ac is on.

I would start with a 25/75% coolant/h20 mix with a bottle of redline water wetter. I made gaskets from Harbor Freight grey foam floor mats. The gasket goes around the rad and is just a thin piece except in the corners. The top plates that seal between the rad and support are a good investment. I installed a new undertray and air guide in front of the rad since both had to be cut for the IC plumbing. They are cut accurately and seal well. I run without the tray occasionally, after I change the oil etc and don't see much benefit from it. Its the most recommended part, but from testing its not a huge factor. I'm currently running the FM oil cooler which did help and is a worthwhile investment. Although I would build my own if I did it again instead buying the FM kit. The oil temp is never over 260F and usually runs around 200-210. The biggest improvement was installing a big Spal fan that I'm controlling with a PWM controller from a C6 vette or ford fusion. I would eliminate any shrouds or restriction other than the fan. Shrouds work when stopped but hurt moving performance.

 

Thank you both. Yes, I agree with doing away with the shroud, and plan to just run fans straight to the rad. I also forgot to mention that my car has all HVAC removed, so no condenser, nor any lines going to the heater inlet/outlet piping.

While I agree I need to do some work to address airflow, the lack of any cool-down when idling around at 50-60mph is still very concerning to me. Reading different threads about overheating, it seems like those suffering these issues generally see temps drop quickly as soon as they get out of it. Since I'm not seeing that, it makes me think that coolant may not be flowing at sufficient volume. I'll dig into it tonight and see if I can pinpoint if that is true or not.

 

Definitely ducting (including the shroud after the radiator), but make the air keep to the ducting by sealing ALL the gaps, including into the front bumper skin. Just sit there, look at the inlet, and think about all the 'escape routes'. Remember the rad offers resistance to the air, and that builds pressure in front of the rad, and any avenue of air avoiding the rad will be utilised.

Those bonnet vents are probably a bit too far back, the rear of them at least is in a high pressure zone - you want them closer to the front, they are supposed to let air out, you don't want them pressurising the engine bay.

 

Hi there! We were paddocked across from each other yesterday and spoke briefly about your issues. I’m glad to see you getting input here.

Some engine bay pictures would be helpful here, your setup is a little bit unusual.

In addition to the sealing and ducting already mentioned, and getting rid of the fan shrouding, my next area of consideration would be that honking big Mishimoto radiator. I’m personally not a fan of the brand, and I’m not sure the extra thickness is helping much, but I’ll defer to others for further input.

I think I mentioned it yesterday, but I’ll reinforce that given your exhaust plumbing, I strongly encourage you to insulate the heck out of your brake master reservoir.

It’s a sweet ride, I hope to see you out again soon!

 

Good point, and it was great to meet you out there this last weekend! I plan on being at the next Sonoma event (at least on Friday), so maybe I'll see you there.

Here are some pics of the engine bay and from the front.

The PO had an external wastegate with a dump out the hood that I was never a fan of, plus its not really practical on a track-car anyways. I just went ahead an removed it, and will go back to an internal gate. Boost creep is probably going to be present, but I'll just set baseline boost a little lower, and make sure any spikes aren't out of control. I may plumb the external gate back into the downpipe/exhaust someday, but for now this will work. I've also ordered a replacement FM heat shield, as I believe the trimming that was done to the existing heat shield for the external setup is also heavily contributing to high under hood temps, and heat soaking everything on the exhaust side of the engine bay.

I did drive the car last night in it's current configuration, (without any fans), and it held stead at 190-200 on the highway and a little spirited country road driving. However, it was late, and ambients were in the high 50's or low 60's, so it wasn't stressing the cooling system at all.

Anyways, I'll duct everything over the coming days, and am going re-work my intercooler positioning and mounting to minimize the flow restriction as much as I can.

Thanks all.

 

IMO you should not have cooling issues. Low boost, re-route and aftermarket rad should be working well enough. Maybe not ideal, but adequate for the application. What are you using for measuring the temps? Have you checked to make sure the system is holding pressure? You need at least 10psi and 18-20 would be better.

 

I run a Haltech IC7 dash in the car that is setup to display coolant temp. It also still has the stock cluster gauge, and they largely agree, (stock gauge seems to peg right about when 230 is indicated on the IC7).

I will see if I can grab a coolant system pressure tester from a local autoparts store later this week, but I do not have any coolant leaks anywhere, (at least none that are obvious).

 

I disagree. With a FMIC, A/C condenser, and no undertray that car has no hope of staying cool.

Just coming from experience, without undertray my turbo car couldn't even stay cool under part throttle uphill drives. And that's without A/C. The same setup with undertray, and proper ducting stays cool for 20 minute track sessions at WOT. Night and day difference. The fluid dynamics behind it are pretty simple, there's barely any air being forced through that radiator. And that's not easy track driving, PB is ~3 seconds faster than SM record (not bragging just a frame of reference).

 

No A/C condenser on my car, but your point is taken, and I hope you are right!!

One thing you can't really make out in the pictures is that my FM I/C is not straight, it sits at an angle to the right. I'd surmise this isn't helping with airflow either, as the air flowing in is likely partially deflected, and what does go through it is bouncing off the inner core, and then traveling towards the radiator in the redirected orientation. I plan to rectify that while constructing my ductwork.

I think the only other possible issue is with a possible thermostat constriction. I will pull it out and test it, but does anyone have input as to if it's worth trying to run without? I've had good luck with built side-by-sides, and motorcycle powered racecar applications running much cooler without the t-stat in place, but know that it is generally frowned upon, and can also potentially cause overheating by not allowing the coolant sufficient time in the radiator for heat-exchange in some applications. Thoughts?

 

Thank you all for being kind to me and not calling me out for not finding the dedicated Miata cooling system thread before posting mine.

https://www.miataturbo.net/race-prep...-thread-79930/

Lots of good info here, and I'll employ all the tricks it describes and report back. Looks like there is a lot of improvement to be gained by addressing the airflow situation.

 

The undertray is behind the radiator and the air guide is in front. I happen to have mine off now and it has little effect on cooling. Since the start of this thread I have done a bit of testing just to confirm. There might be a few reasons that this is the case for my application. One being that I have a bit more of an airdam and also Im running the singular hood vents. I will post some picts of my setup shortly. Its similar to the OP's except I'm running more boost, output and have a functioning AC system.

 

I only asked about how you were measuring the temp because there are many ways to do so and some might just be using the factory gauge which is not accurate. My IC is angled a little which is common for the FM mounting system. The FM IC is not the best design.

 

Here are some picts of my setup. Look at the top of the rad how the corners and gaps are sealed with the foam mat. The mat is bent at the corners to produce a radius. IC is slightly angle like yours. I'm running a stant 180F therm which will not decrease the max temp but allows me to target a lower normal temp which nets more head room. I target 185 and will allow it to run up to 200 before the fan is on at 100%. My fan turns off above 80% throttle so the temps will climb to 210F on a hotter day under high load at full throttle, but as soon as the fan comes back on the temps go back down. When the car is not moving the fan has no problem controlling the temps. It will usually return it to 185 and turn off.

 

A little update-

I ran Track Night in America with SCCA yesterday evening at Thunderhill West, and still experienced very high coolant temps over sustained runs.

Over the last few weeks I've:
- Purchased and installed a cover plate sealing in the hood-latch area
- Built an under-tray, (1st edition is only about as wide as the motor/radiator, and I plan to make another that more comprehensively blocks pressurization of the engine bay. It ties into the front bumper, intercooler, and subframe. It does still have a several inch gap to the bottom of the radiator that I need to fill in.)
- Bled 100% of any air trapped in system using a funnel-bleed cap and elevating the nose of the car
- Permanently removed the radiator fan shroud, now running only one 12" fan by itself on the back of the rad
- Built ducting louvers that come off side of the rad to the front bumper. Not fully sealed, but approximately 6" long, and should duct a significant amount of air toward the rad
- Went to a CSF rad cap just like the one on the green car posted above
- Went back to an internal wastegate, and bought a new turbo heat shield from FM, since mine was cut-up for the external gate.
- Cut three 3" holes in the front bumper fascia, with direct flow to upper part of radiator

I'll post pictures up when I can get some to show some of these things, but I was really surprised my efforts didn't yield substantial results. Within 3-4 laps I was pegging 230-235. The straights would particularly heat-load the car, with temps generally going up about 5 degrees by the next corner. Temps seemed to sustain around this area, but as soon as I saw anything exceeding 235 I backed out to full lift and coast mode, (PB was 1:26, and I was coasting around doing 2:00). Very strangely this didn't really cool the car down, and was still 225 after several laps of idling around.

Realizing there are still some air-flow improvements to be had, does anyone have any other insights? I do plan to go to a remote thermostat so I only have to mess with the SM reroute once. I'm going to try running without any thermostat, and have also ordered a 170 degree unit to try. I also think the FM intercooler isn't doing me any favors as far as IAT's, and will likely look towards a larger, (longer) intercooler.

Anyways, more to come! I would really like to get this thing to the point where 20-25min track sessions are sustainable.

 

Sorry to hear you’re still having issues. You’re past my point of expertise now, but hopefully someone else can chime in.

Tear out all that turbo stuff and do a K-swap, that’s the easy answer. (Kidding x1000)

 

Cutting more holes to let air in is pointless if you are not using the air that is already getting in through the mouth. Ducting, ducting, ducting .... Sealing, sealing, sealing, sealing ....

Then made some modz to let the air out - as stated earlier those bonnet vents are probably either not doing much at all, or acting as inlets to pressurise the engine bay. This time put them much closer to the front of the hood, where pressure is either negative or lower than at the rear, and therefore they act as intended - outlets not inlets.

Burping a BP is an artform, read up on it. If you have air in the system you will have overheating.

Until you have done all the above, playing around with thermostats is not addressing the fundamentals. Get those right, and I doubt you will see a need for mucking around with different thermostats.

 

Just checking because I think you are mixxing up incorrect terms:

That is just front ducting. The stock undertray is the first picture below. The gap below the radiator is also not helping. Air takes path of least resistance, and I remember some V8 guys saying they had to *reduce* the miata front radiator opening to an inch gap because using the entire opening was overcooling their engines. If you have that big of a gap it is not going though any of the heat exchangers.

Any part of the cooling system, Radiator, Oil cooler, AC condenser, Intercooler, any heat exchanger, etc it is all down to pressure differentials. If you have X about of pressure in front of the radiator, and the same behind, you will have 0 air flow, no matter how much ducting you put, fans, etc, 0 pressure difference is 0 air flow.

Fans should never be the primary way to cool the car at speed, it should be completly passive with airflow though the heat exchangers. Fans are for idling or stop and go traffic driving under 40-45 mph

Your hood vents are very far back where it is likely picking up the pressurized air from the hood/windshield interaction (the HVAC intake uses this pressure and why cowl induction works on cars) and the front part bordering the 0 and positive pressure hood bump, they needed to be mounted almost 12 inches forward of where you have them for best air extraction. You are likely pressurizing your engine bay and making it harder for the air to pass though the heat exchangers with those vents and lack of undertray creating a high pressure area instead of a low pressure for extraction. (see second and third images)

This bit, and how far back it goes is what creates the low pressure zone behind the radiator giving that pressure difference. if you make a custom one, sealing it with tape helps a ton. I layer mine with one strip of duct tape, and then aluminum tape over it. When I do the duct tape, I form a buddy tab that is just a folded over end of the tape, so later on, it is easier to pull off instead of trying to pull up a stuck edge.












I have AC, Three pass radiator, front ducting, undertray and WRX vents mounted in the lowest pressure zone on the hood, and have driven at speed with the AC cranked though Death Valley during the summer without it going over 190 before it dropped again. I tested every one of my modifications by literally sticking a manometer with a length of tubing into the engine bay and seeing the pressure difference from the changes while I was making mine. I had a cam cover seal leak at once time that the drip was being pulled forward on the cam cover and then was being sucked out the vent.







I would recommend putting some string tufts on some tape and putting them on your vents to check their airflow direction. I do not think they are helping creating a low pressure zone under the hood and is likely making it worse. If you get a manometer, see if covering the vents all the way or partial makes a difference.

 

Certainly worth doing, but this is unlikely to affect the engine temperatures. Turbo heat shields are more about not melting the master cylinder, they don't really affect coolant temps much.

I would second the idea of modifying a stock undertray (they're pretty cheap) rather than trying to build your own. You want to seal up the sides to the chassis as well as along the bottom. And yes, the goal is that every molecule of air that comes in the nose goes through the radiator without any way to sneak around it.

All of that said, IMHO the Mishimoto radiator isn't doing you any favours. My car cooled just fine at 340 rwhp with simple ducting, reroute, modified stock undertray, and no AC using a TSE radiator (no hood vents). Unfortunately those aren't available any more -- I'm not sure what the best on the market is right now, maybe the supermiata one?

--Ian