Not bad for $50ish in materials and some handiwork! That's honestly incredible you can snag an assembly like that for $20. I kinda felt the same way when I put together the digi dash for my last car. Woulda guessed even basic computer components, displays, etc. had a higher cost of entry.

What you said about your wheel lock is exactly why I swapped back to standard 6-point lugs. Flat-spotted my front tires at a track event a couple years ago and split my wheel lock in two while rotating them to the rear. So much for that lol.

Pouring one out for your dead tire

 

No photos or videos, but the car and I had our best showing together last weekend. Took 7th/8th raw times and 11th/13th PAX out of ~85 drivers. No issues with the car the whole weekend aside from a tuning bug.

The car felt slightly sluggish on Saturday morning. I pulled the onboard logs from the Link at lunch and after picking through them I realized that I hadn't changed the Y axis value for the boost target tables, which was causing it to do some weird things with the boost controller duty cycle. It might not have been as big of a deal as I originally thought, because I was looking at the "Boost Base DC", which I found out is different from the commanded duty cycle, which I wasn't logging. I'm still getting some oscillations, so I'll revisit the PID settings at some point and possibly switch over to the mode which uses a set value once you're close to your target (stage 3 of boost control), as opposed to updating the duty cycle throughout stage 3.

I was only 0.1 seconds away from the class win, which ended up going to a car which is basically a slightly under prepared DP ND Miata that is driven by a guy who's won nationals before, so I'm going to take that as a win.

Another XB driver who has a turbo'd NA blew a brake line on Sunday morning. Thankfully he was able to get the car stopped safely, but he was going to be done for the day, so I offered him a codrive with me in the afternoon. Certainly not the hottest day, but even with a pretty quick turnaround between runs the car seemed to be peaking around 94 C after a run, with a max for the day around 98 if I remember correctly. I'm still not convinced the car won't have some cooling issues in the hottest summer months, but it's nice to see that the current setup is working. The switch I threw in to force both fans on also seems to be helping a good amount. If I leave that on in grid the car will get down to ~79 C (IE thermostat temp) between runs.

Well, the weekend was uneventful, but my grocery store trip afterward wasn't. Still not sure what happened here, but I ran over to grab a 3d print, stopped at the grocery store and then drove home. ~20 minutes on the freeway each direction, cruised at 80, nothing out of the ordinary. I pulled back into the garage and went to do a quick chore and when I got back into the garage I noticed that there was a bunch of coolant in the engine bay. I was actually going to go take a photo of my overflow tank which always seems to leak a bit at autocross. I was curious if people thought it would be leaking due to a bad seal, or the fact that, as far as I can tell, there is no venting built into the overflow tank. Usually the leaking is from the cap, which drips onto the top of the tank and then rolls off into the engine bay. You can see streaking in the photo below, which is usually what the tank looks like after it's leaked a bit at an event.

I took the car around the block and got into boost without issue. When I came back to the garage it wasn't leaking at all.

When I did the throttle body swap I did disconnect the factory coolant lines and spliced them together. That connection was dry, as well as the hose and fitting that go into the overflow tank. I did top off the overflow (to ~2/3 full) and bleed the system recently, but I'm not sure that would cause any issues. I'm wondering if the radiator cap failed or there's a small crack in the overflow which is only leaking when things are hot and expanded.

I went back out to the garage this morning and the ground was dry. The overflow tank still has some coolant in it. Anyone have any theories? I might run over to the parts store today or later this week and get a tester to pressure test the system (and the cap if I can).

 

Nice work with the ESP32 gauge so far. I'll be watching how you finish it and how it works in practice for you. I wouldn't mind swapping my setup for one with more flexibility.

Congratulations on the weekend results all around!

Bummer about the coolant. Was the source of the leak above or below the expansion tank? I'm thinking if above, then maybe your rad cap opened and pushed a bunch of coolant and it came out the tank, but if below then maybe there is a crack as you said. For me the overflow pukes coolant on hard turns because it has no baffles, but that's a rather large amount of coolant for that to be your issue.

 

Thanks man, I was actually picking up a 3d printed case for the ESP32 last night before the coolant started leaking. I found some photos of the BMM Kan gauge and confirmed that it's also using an ESP32. Not sure if I'll be able to leverage anything from that, but it's at least a confirmation that what I'm hoping to do is possible.

Usually it seems to leak out the cap and drip down the sides, which is what I'm pretty sure happened yesterday. Still not sure on the root cause though. I ran (walked actually) over to O' Reillys at lunch and grabbed their pressure testing kit. I figured if nothing else it would give me some peace of mind and I could try a new diagnostic. I put 20 PSI on the system and it dropped maybe 1 PSI over the course of ~10 minutes. Considering I just did a leakdown test a week or two ago and saw good results, I'm going to assume the leakage here isn't a major issue and is likely coming from the tool and or coolant lines swelling from the pressure.



While I was doing this I turned to the overflow and possible issues there. Well, I figured if I could pressurize the radiator and cooling system, I could pressurize the overflow as well. I pulled the overflow hose off the radiator and rigged it up my tire inflator with a nozzle. I set that thing to 5 PSI and let it eat which revealed 2 things. First, the overflow definitely vents through the cap. I'm not sure that's intentional, but around 2-3 PSI the pressure starts leaking out the cap. Good to know, as I was about to figure out how to add a vent to it. Second, the tank doesn't seem to be cracked. I even added some water to see if it would leak when there was more fluid in it, but it held fine. I did pull that water back out after testing. I've found that a turkey baster is surprisingly handy for fluid jobs.



I'm still not really sure what to make of that. I couldn't test the rad cap since the kit didn't have the right sized adapter for it. I do have an old stock one laying around, so maybe I'll throw that in the Miata's trunk toolbag. Maybe I just overfilled the overflow and everything's fine

 

That's an interesting issue then. Maybe you did overfill it some since the coolant system checks out. Keep observing it and see what develops. I leave the overflow empty or pretty close to empty for track duty, then put a little in the tank for street driving, otherwise I get coolant in the undertray. At the track I see it rise up to the sight glass when I shut down the engine and goes back down to empty after a bit. I had a friend comment that I would get air in the system doing this, but I've been doing the same for a couple of years now and no issues. Maybe I've gotten lucky.

 

That's pretty much what my plan is at this point. I was mostly letting the car idle between runs this weekend and was kicking the fans on, so maybe it just had more time to cool down before I shut it off. Still seems weird that it would wait until yesterday to overflow, but I guess we'll wait and see.

 

Late to the party, but congrats on the finish last weekend dude! ND's are proper fast right out the gate. That's sick you were hanging with one piloted by a proper driver.

I've no worthwhile insight on the coolant overflow leak in addition to what you and Ricardo have already mused over. How long did you leave the pressure tester on? We usually test em for a 3-4 hours, and in certain cases will leave them pressurized overnight (though only to test for the semi-common cracked cylinder wall issue in some of the older 4 cyl ecoboost engines. I digress...)

 

Thanks Z!

I actually went back out yesterday and threw it on for 20 minutes. It sagged about 1 PSI in the initial minute or two and was stable after that. However, I took the car to our SCCA meeting and was hooning a bit on the way home. Parked it in the garage and came back out to this.




I didn't investigate last night, but I'll probably take another look tonight to try to see where it's coming from. Of course I didn't check when I parked the car, so it could've been leaking as I drove.

I did throw on an old OEM rad cap that was laying around, so we'll see if that makes any difference.

 

Ahh shucks, I forgot you said you weren't able to test the rad cap with the parts store tester. Let us know how the OEM cap works. Wouldn't surprise me if that's the culprit, assuming you don't find the overflow leaking from somewhere else.

 

I just ran out to the garage and pulled the overflow off the car. It doesn't look like it leaked from the cap since the last time I wiped it down (no coolant streaks on the top).

I filled it up with coolant and set it on the floor of the garage. I'll see how it looks in a couple hours and go from there. I do still have my stock overflow tank as well, so as much as I like the look of the aluminum one, I can always throw the OEM one back on if it is leaking.

 

The UV dye works well for leaks.

 

That's a good point Six, I'll keep that in mind depending on how the next bit of diag goes.

The cap on the overflow isn't sealing nearly as well as I expected, but I still don't think that's the root cause. The overflow tank was fairly empty yesterday when I left home, so I don't think it should've leaked that much just from sloshing around.

I think I'll run it with a different radiator cap and if it's still leaking then I'll swap the old OEM overflow tank on and go from there. The OEM one would be better for diag anyway since I can actually see the coolant level through the plastic.

 

I don't understand why you'd want a sealed overflow tank.

The radiator cap opens at ~16psi (or whatever it's rating is) and bleeds the extra pressure (and hopefully any air in the system) to the tank. if that tank is sealed then that tank will be pressurized during this.
the more the tank is pressurized, the higher the relief pressure of the radiator cap will be.

then when cooling, the radiator cap opens and allows coolant back into the system (when pressure in the system is below ambient). if the tank is perfectly sealed then that pressure in the tank would vent back into the radiator and all "should" be fine.
But if the tank leaks even slightly, and especially intermittently, the tank will be drawn to a vacuum at times, but not others.


Logically, either use a Vented tank with a regular radiator cap.
OR, use a proper expansion tank with it's own radiator cap, and do not use a cap on the radiator.

 

What Iron said. Overflow should not be sealed. If we fab one at work, we have to gut the rad cap so it doesn't seal. If your over flow is empty when hot, it'll suck up air once it cools, so make sure it's between the low/high mark, low when cold, high when hot. Expansion tanks are different from over flow, Miatas aren't designed for an expansion tank, I wouldn't try to do that.

 

I think there was some miscommunication. I do not want a sealed radiator overflow! I originally threw this cheap aluminum one on without thinking about it, but recently when I looked at it I noticed that there wasn't any venting (at least none that was obvious) built into the overflow tank. The reason I tried to pressurize it was to see if it had cracked and was leaking fluid. When I did that I was pleased to see that the pressure was bleeding out of the cap, so it is not sealed like I originally worried.

I was debating on adding some sort of breather tube for the overflow, but after seeing that the cap wasn't sealing like I thought, I don't think it's an issue.

Also, I swapped the rad cap yesterday and took the car to my buddies. No leaking from the overflow going there or coming home, so I think the issue was likely just a bad rad cap which seems fairly common for Mishimoto. I originally got their radiator because it was a bit cheaper than some of the other options and had a lifetime warranty. Looking at it now, I'm pretty sure they'd charge me $40 to warranty the cap... Should've just gone with one of the crossflow options, but I guess that's a lesson learned. I'll reach out and see what they can do, but I'm not expecting much.




Also officially over 10K miles on the engine build finally.



Bonus photo since I didn't know SuperMiata was making pizza ovens @turbofan .

 

So basically more expensive to warranty the rad cap than buy a new one, got it

Congrats on hitting 10k on the motor. It seems like yesterday you were worried the injector tick might be something bad going on inside the engine haha.

 

I'll second the 10k milestone. I remember not trusting my car to drive it around town, now I'd drive it across the country in a heartbeat. Reliability hasn't been my concern for longer trips, just comfort. Feels good. I hit 20k on mine last year.

 

Thanks guys. Yeah, aside from some of the smaller issues and endless tinkering (which is self imposed mostly), it's been pretty reliable (knock on wood). As much as I still want a tow rig for track days I fully plan to roadtrip to our out of state events this year. Hell, our Winnemucca event is about a month away now.

I reached out to Mishimoto to see what they'll do about the cap. If they don't send me one for free I'll probably grab a FM one or similar. I'm pretty done with Mishimoto's hyper aggressive advertising bs.

 

No real work on the car this weekend, but I did get together with my buddy to run up to the local ski hill. I'd been wanting to take the Miata's up all season and closing weekend was finally clear enough and warm enough. We dropped the tops and cruised up to get some final runs in and watch the pond skim. Rowdy weekend where half the people on the mountain were wearing something ridiculous. Traffic was terrible, so it wasn't the best cruise, but that was expected given the season.

 

You’re really gonna give us that post and not show a pic of the car with the skis mounted!?

Haha good stuff man. Glad top down season is finally reaching you guys. Did Mishimoto end up telling you to f*ck all the way off?