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Old 08-09-2015, 03:51 PM   #1
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Question FMII 1995 Miata Heat Management

Hello everyone!

I bought a 1995 Miata a month ago now and it was prepped well for AutoX by the previous owner. For me, this is my new AutoX and HPDE track day car. I am retiring my DD '12 Mazdaspeed3 from racing.

Here's the list of mods the car came with:
-FMII Turbo kit - Hydra Nemesis ECU
-FM turbo shield
-FM chassis braces
-Racing flywheel and clutch
-Over-sized Aluminum Radiator
-Sway bars
-Tein Flex coilovers with two sets of springs
-3 sets of wheels and tires: track, summer street and snow.
-Torsen LSD
-I'm sure I'm forgetting some stuff.

Anyways, the car was sold to me with some known problems that I have been trying to work out and my biggest concern with the car is the excessive heat from the turbo. Before diving into the heat, let me talk about some of the problems as there may be related issues:
-ECU boost target of 12psi is not met, and the computer seems to be doing nothing to manage boost - all mechanical right now.
-When the car is shut down hot, and restarted immediately or 15 minutes later, it will not idle smooth; revs oscillate from 400-1,500rpm and settle down after 20 seconds to ~800rpm. Behaves much like an low-dampened control system oscillation that overshoots and then smooths out. This can also happen without shutting the car down on a hot day.
-Compression isn't perfect: Cyl #1,2,&4 are about 180psi, Cyl #3 is 160psi. (dry) Leak down test is next on the list.

Those are all the known issues at the moment. Now lets talk about heat. Last night I took the Miata for a short cruise, getting into boost here and there, in 70*F weather. When I got home, I parked, immediately popped the hood, and sat next to the turbo listening... After about 40-60 seconds of silence, I heard the radiator cap release some pressure and coolant in the turbo coolant lines started percolating. To me, it appears like heat is soaking into the coolant from the turbo, and starts to exceed the 16psi cap, so pressure is released and then low enough for the coolant to start to boil.

The cap that came with the car was a 16psi Stant, but the rubber was cracking and it was not holding pressure. I replaced it with a new 16psi Stant 10233 (Napa #703-1712) and pressure seems to be holding. The percolating was much worse with the old cap, so once replaced I flushed the coolant and burped the air out of the system.

Should I be using a higher-pressure cap? Should I do something to make the radiator fans run after shutting down the car?

Two more notes:
1. The under-body panels, the "air diverter" in front of the radiator and the panel under the engine bay are missing. I plan on replacing them to get proper air flow through the radiator while driving.
2. The stock hood is unmodified; no vents or hood risers and still has the rubber seal on the back edge. I bought a second hood and plan to vent the front center between the lights, as it seems to be the consensus on these forums as the best location for an extraction vent.

Sorry for the life story guys, but I thought I should put everything on the table. Out of all this information I've given you, I would like to focus on the heat management. However, if you have some ideas or tips for my other problems, please feel free to share, I just don't plan on solving them in this thread.
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Old 08-09-2015, 04:10 PM   #2
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I wouldn't worry about a bit of percolation a minute after shutting down. You have no water flow at that point, and some local boiling should be expected -- but your expansion tank should catch all of it and return the fluid after cooling further.

Keeping the fans on won't help much unless you add an auxiliary water pump to circulate the coolant.

Bottom line, this doesn't indicate a problem. What we care about is coolant temps while operating.

An OEM air guide probably no longer fits depending upon the location of your intercooler. I built my own. https://www.miataturbo.net/build-thr...8/#post1244564
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Old 08-09-2015, 05:09 PM   #3
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Wow, nice work! You are correct - the OEM part would not fit. I was thinking about doing something similar to yours, or hack up the OEM one. I don't have the parts to play with and not sure if those two parts are the only ones I am missing...

So percolating coolant near the turbo after shutdown is perfectly fine and common in most turbo builds?

This just seems wrong to me... And I could very well be wrong here and just paranoid, but wasn't the point of turbo-timers and such to keep the turbo cool after shutting down? Once the water boils and the water vapor hangs out inside the turbo, there is no limit to how much heat soaks into the oil, bearings or inlet side of the turbo. I haven't seen any accessories or anything like this for a turbo Miata, so perhaps I am just paranoid.

A simple design solution (on paper, or in a car with more space) in my mind would be if the turbo was placed vertically between the inlet and outlet of the radiator/thermostat, so the steam/hot water would rise to the thermostat and water could naturally want to flow through the turbo. Right now the turbo is about level with the thermostat and both coolant lines run below both, trapping the water vapor... Of course changing this is not simple: there is no room in the Miata and therefore no manifolds would be made to place the turbo there.

So am I just paranoid and have absolutely nothing to be worried about? Or should there be some concern and perhaps an auxiliary water pump would be a good thing?

In my mind, I am trying to get this car ready for a track day... Heat and boiling will only get worse.

Thank you!
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Old 08-09-2015, 08:59 PM   #4
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Good read, especially the section about clocking turbo chra such that the coolant will naturally circulate post shut-down.

Garrett Turbos White Paper Water
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Old 08-09-2015, 11:22 PM   #5
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<p>The water boils, and rises, leaving cooler water to take its place. One of the big merits of water cooling.</p><p>Hot restarts: what injectors are you running?</p>
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Old 08-10-2015, 12:19 AM   #6
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Do you have an AFR gauge? The hot start issue could be heat soak.
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Old 08-10-2015, 12:54 AM   #7
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Quote:
Originally Posted by Chooofoojoo View Post
Good read, especially the section about clocking turbo chra such that the coolant will naturally circulate post shut-down.

Garrett Turbos White Paper Water
Awesome, thank you Chooofoojoo!

Being that the turbo center section is about the same height as the thermostat, there unfortunately isn't a great place for the outlet hose to go. The only coolant line higher than that are the heater core lines... Should I tie into one of those instead so the hose can raise to that without dips?

Quote:
Originally Posted by aidandj View Post
<p>The water boils, and rises, leaving cooler water to take its place. One of the big merits of water cooling.</p><p>Hot restarts: what injectors are you running?</p>
Yes, assuming the center section is 20* as the white paper mentioned, and your coolant hoses don't both go way below the turbo and up to the motor as directed by the FMII manual install guide.

I believe the injectors are the one that came in the FMII kit: 550cc/min.

All mods to this car were done in 2008 when the car had 51,000 miles. The car has 67,000 miles now. Everything is still pretty new.

Quote:
Originally Posted by Ted75zcar View Post
Do you have an AFR gauge? The hot start issue could be heat soak.
I do not have an AFR gauge. I have taken some datalogs to watch the AFRs and see how the computer sees the engine running.
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Old 08-10-2015, 01:08 AM   #8
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Quote:
Originally Posted by MechE View Post


I do not have an AFR gauge. I have taken some datalogs to watch the AFRs and see how the computer sees the engine running.
and...

If they are lean during the rough start-up, could be heat soak of the IAT sensor. The funkiness while running is odd, I presume this is the root of the injector question. I would be surprised that an FM kit would be prone to heat soak.
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Old 08-10-2015, 04:33 AM   #9
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Quote:
Originally Posted by Ted75zcar View Post
and...

If they are lean during the rough start-up, could be heat soak of the IAT sensor. The funkiness while running is odd, I presume this is the root of the injector question. I would be surprised that an FM kit would be prone to heat soak.
I haven't logged to see what happens at that event in particular yet. Really I've just made sure I can talk to the ECU and see what information it can see, and try to understand the UI.

Looking through the three logs I took one night, I think I may have captured the event... The RPMs are a little high, so I may have rev'd upon restarting the car to get it rolling. Either way, the AFRs are pretty low there. See attached screenshot.

Thanks!
Attached Images
File Type: png LowAFR.PNG (112.1 KB, 10 views)
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Old 08-10-2015, 09:52 AM   #10
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I don't think there is enough there to diagnose. Try to get the whole transitory to steady state shot from key-off to smooth idle, and keep your foot off of the pedal.

I am not a Hydra guy, but if you can enable additional columns that show AFR target, fuel compensation, battery voltage, ...
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Old 08-11-2015, 01:17 AM   #11
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Thanks for the suggestions. I'll try to see what I can add to the log and catch this issue later this week.

Now to circle back to the turbo coolant lines... How should I route them to get the best possible flow after shut down? Tie the hot outlet side to the heater core line? Or clock the turbo 20* and fab a metal line to be nearly perfectly level right into the thermostat housing?

Thanks!
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Old 08-12-2015, 02:39 PM   #12
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^ Garrett approved thermal siphoning

More in here: https://www.miataturbo.net/diy-turbo...cked-up-77029/
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Old 08-16-2015, 09:56 AM   #13
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I don't think you need to worry about any heat effects on the Garrett turbos as long as the system is lubed with synthetic. In my view, the turbo timers do not offer any value.

corky
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Old 08-16-2015, 01:13 PM   #14
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FWIW, my car has been boiling coolant in the turbo after shutdown for a minute or so the entire time I've had a turbo on it. That's about 12 years and 60K miles at this point, so I wouldn't worry too much about it.

What version of the Hydra do you have? There are big differences between 2.5, 2.6, and 2.7

--Ian
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Old 08-17-2015, 01:43 AM   #15
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Thanks for all the replies, guys!

After reading through the suggested thread from Vuti and all the other forums and threads I've read about the issue, I'm comfortable ranking the routing of the coolant lines a little lower on my priority list right now, and feel a little at ease about the boiling in the coolant lines.

I do think the upper line could be routed a little better and will give it a shot. I agree with some of the arguments that clocking the turbo will reduce the effectiveness of the oil cooling and lubrication, so I will simply just move the "outlet" line and test it out.


Regarding the engine idle issues, I've started a new thread to keep the threads focused and concise. The engine issues and datalogs are in this thread here:
https://www.miataturbo.net/prefabbed...5/#post1257398

And to answer your question, codrus, I am running Hydra Nemesis Version 2.5 R15


Thank you!
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