In adding to the turbo coolant question, after noticing a boiling sound near my turbo, even after a 5 minute idle after only a mild street drive, I instrumented my turbo outlet line. If I stopped the engine for 2 minutes, when I started it back up the turbo coolant line was reading 120C!

I was confused when on track, my coolant temperature from the turbo was reading less than the main coolant temp reported by the ECU. But now that I've measured a difference front to back of head in terms of coolant of 5-7C hot, this makes more sense as this would suggest 3-5C rise in the turbo coolant temperature as it passes through the turbo.

https://cimg6.ibsrv.net/gimg/www.mia...2042abddf1.png

It does seem that the logical thing would be to take a little amount of post water pump but pre block coolant that is cold and high pressure and return it to the head, pre stat, that way it can get controlled by the stat and go to the radiator. Has anyone tried this?

Also, how much heater coolant flow is there even with a fully open thermostat? It looks to me like there would be quite a lot. Can anyone quantify how much? A thermostatically controlled heater valve seems like it would make sense to improve radiator efficiency. (the one that measures the difference between heater outlet and inlet, and if both are hot and not delta, shuts off flow).

Flow through the engine is maintained with the heater circuit when the thermostat is closed. This is important to prevent stagnation and resultant hot and cold spots.

Yes, but I thought there was a heater flow control valve that was both thermostatic (ie it won't open until the engine stat opens) and it also only closes when both the heater lines are at the same temperature, ie it will open if the heater is on and the coolant in the heater out is cooler than the heater in.

I'm not suggesting anyone block off their heater lines entirely!

I'm not aware of any heater coolant valves in the NA/NB.

Coolant boiling in the turbo after shutdown is pretty normal as the heat soaks out of the exhaust housing/manifold, etc. AFAIK the only way to avoid it is an electric coolant afterrun pump like some OEMs use.

--Ian

On an entirely separate note, I just wanted to thank you for your contributions to the forum. You research, ask questions, have good knowledge of certain areas, collect and share data and are open minded to options for setting up your project.
So few that come here are willing to actually work to gain an understanding and just want to be spoon fed. You seem to contribute as much info as you gain. Welcome.

/drift

I recently also confirmed this suspicion, during some dyno runs in another car with no reroute the temp sensor at top radiator hose was measuring ~2-3C lower than ECU at idle with no load, as soon as temperature started climbing during pulls, the delta increased to 5-6C (and this was only at 95C at the back of the head), It would probably increase a bit when near overheating at ~108C)

Gaining that extra delta at the top of the rad is great.

Also, no miata has a valve for the heater, its always-on, although some people do rig valves (manual or otherwise) to bypass it for various reasons (reducing cabin heat in the summer or on track for instance, since the heater isnt perfectly sealed to the cabin)

RE: thermostat, I actually see below opening temperature (~87-88C) after a while of cruising on the highway, with oil temps ~90C on a ~24C ambient day using QMAX, good ducting and ebay 52mm rad. When speeds drop it quickly shoots up to 91-92C.

I do like this thermostat on the street, especially with the stock engine as you are running the engine within the optimal temperature for the tolerances it was designed with (reduced blowby etc..),

The 180F has a few advantages on track for those with insuficient cooling capacity (not everyone is willing or able to run one or more of: crossflow/hood vents/reroute), this thermstat will allow a cooling lap to reduce temperatures well below 91C to allow a longer run time before needing to do it again (and for 20m sessions, perhaps one lap is enough).

It is true that running a 180 tstat will give a car that tends to overheat, a great greater "thermal battery" capacity. But because of our background in longer events, we have always engineered for steady-state capacity which means not allowing it to overheat, even for short bursts.

According to our Garrett contacts, the water flow through the turbo isn't all that important during operation - and after shutdown, the water circulates by thermal siphoning. Thus the noise. What would be really interesting would be to cut off off the water flow to the turbo during operation and only open it up (pumped or otherwise) after shutdown.

Thank you, it's good to hear that my contributions are welcome. There's a large choice of Miata/MX5 forums and after reading a lot of them, I chose this one due to the very high SNR. It's surprising how many forums (and especially facebook groups!) just respond with hostility when data is posted that goes against perceived wisdom.

My car is an awful lot better than it otherwise would have been thanks to this forum (and a lot of your contributions), so sharing my data and helping others to do likewise is the least I can do. Also, finding like minded individuals is nice bonus. I should probably start an actual build thread to keep the information in one place.

We be loving build threads around here

And/or an expansion tank. The expansion tank needs to be the highest point in the system. A line from the turbski runs to the inlet of the expansion tank and allows for natural convection and the tank deaerates the coolant. When you shut the car off you can hear bubbling in the expansion tank.
A properly configured cooling system with an expansion tank also has the advantage of eliminating coolant flow drop at high TW. The outlet of the expansion tank outlet should connect to the water pump inlet and the air volume is in the expansion tank. The cap only acts as an emergency bleed, and it's the defined air volume in the exp. tank which regulates the system pressure. As the coolant heats up it expands and also heats up the air. Since PV=nRT, the volume is fixed so the pressure must increase if temp increases. This applies pressure at the water pump inlet, which is where the cavitation is occurring. Curiously, I've seen a few OEM's use an expansion tank and not take advantage of this. Depending on the cooling system, you can see as much as 20% flow drop due to cavitation between like 80C and 115C.

This. I added an expansion tank in the cowl on the MZR swapped car, that motor has worse coolant routing than the BP but holy crap it made bleeding so easy. Just connect the top turbo line to the tank with a T and the T the tank into the lower rad hose and also do a take off of the highest point in the coolant lines if that isnt the turbo. Just add water there and heat cycle it, no need to use Husters Magic Funnel. The tank doesnt have to be that big or crazy. I welded mine up with a spare piece of 2.5" IC piping and a cut up aluminum rad for the rad cap mount. You just need to remember to never ever open the cap on the rad (and remember to tell that to the buyer of your car, unlike me).

My current cooling system- Stock WP, 20psi radiator cap, FM crossflow from 2016, FM Stage 2 Fans, OEM 2002 coolant routing, minimal ducting but aluminum under tray is installed, 70/30 distilled water/coolant, 185F thermostat

Problems- My car runs generally hotter than I would like to see city driving (210-220) and will hit 230 in stop and go traffic when using AC.

Upgrade path:
1. FM reroute, leave everything else the same.
2. TSE radiator and the recommended single spal fan for ac cars.

What route do you think I should take here? I don't mind spending the cash on the TSE I just cant believe I don't see other people having this problem. Maybe less people have AC turbo street cars than I think.

Thinks I wont do:
Hood vents

How do you burp the coolant? Those temps seem way high for what you are doing.

My assumptions would be one of the following
1) Air in system
2) Head gasket
3) Bad radiator cap
4) pinhole leak somehwere

Are you losing any coolant? When's the last time you checked.

I totally agree they're way too high. I burp the coolant using on of those radiator filling funnels. I let the car idle with some periods of holding the rpms at 2000 with the funnel attached and filled up the whole time. I will usually then let the car cool down and repeat for another heat cycle.

A mechanical problem has crossed my mind before as-well.

1. My burping procedure is as above so I think I should be air free, also with a few thousand miles since I last flushed coolant I would expect any minor bubbles left to have been worked out.
2. No signs of a head gasket. Oil comes out coolant free, coolant in overflow is clean and car makes good power. No white smoke out of exhaust.
3. Just swapped from the one FM supplies to a 20PSI CSF unit same results with both.
4. I'm not loosing any visible amount of coolant. No spots under the car ever, no signs of it in the engine bay, overflow pretty much always at the same level.

I should mention crusing the highway or backroads is fine the only time I experience these heat issues is when using the AC in stop and go traffic. Even on track my temps stay pretty cool for a long time and improving that is just a ducting issue which I am waiting to address.

Edit: To confirm the pinhole leak/headgasket theory I'll rent a radiator pressure tester this weekend and see if it holds pressure.

HF sales a radiator pressure testing setup for a reasonable price.

For burping my cars, I jack up the front as high as I can. I then put on the magic funnel and fill it mostly up. Then run the car until the fans cycle on and off 3 times. Then I let the car cool. Once cool I put the radiator cap back on. Then I usually cycle the fans a few more times and check fluid levels.

If you are going to ad a reroute I would suggest the QMax. Mostly because I have found it the easiest to install on a miata with the engine installed.

This diagnostic question should be broken off into a new thread pretty please.

This is the [re]route I was going to take. The last 2 track days my temp floated between 202-207F on track. One day the weather was 98F and this last weekend it was 65F. Everything is stock and this was with generic green coolant.

This winter I was going to do the QMax and switch to DH20 and wetter water

You need a coolant reroute, that's the first thing a Miata needs after turbo.