3 thermostat's at the back of the head
 

Our Roadrunner SR2, which is NA 1.6 powered has 3 thermostat's at the back of the head

1 temp for dash
1 for the ECU
1 to switch on the electric fan

Is that right? Or is there a way to streamline the setup?

It has a manual override switch for the fan, so we could eliminate one stat and just use the manual ooverride. But I'm not sure that's wise..

I'm looking to return the turbo water back there, so the hot water then goes straight to the rad.

I was with you until I got to the end of your post. You say you want the turbo water to go back to the radiator. How do you propose to do that? The line between the back of the head and the radiator is the highest pressure area in the system aside from within the block. After the radiator and before the water pump at the mixing manifold is the lowest pressure area.

Yeah, I don't know what I'm doing.. :facepalm:

I started this thread some time ago asking about the turbo water feed. Pulling water from the mixer, then returning at the back of the cylinder head.
https://www.miataturbo.net/diy-turbo...stalled-99082/

time ago is this a bad way forward?

for info the car has no outlet at the front of the cylinder head, hence thinking the back of the head would work

https://farm8.staticflickr.com/7894/...6948e02d_c.jpg

What you drew will work fine. The water will come from the back of the head to the turbo and then to the mixing manifold at the inlet to the water pump.

That's good then.

I thought the flow would be the other way though. From the mixer, to Turbo, the head, back to rad. That's the way the water flows but if it'll work either way then that'll do me.

So, what about the 3 thermostat's in there - is that how it needs to be? Is that how all your cars are?

I think you mean 3 temp sensors?

You can use an NB sensor (two resistive temp sensors in one physical unit) to feed the dash and the ECU. The "dash sensor" half has the same resistance curve as the NA6 dash gauge sensor. Most people here are using their ECU to control the fan, either by using a standalone ECU or by owning a Miata newer than an NA6.

While I agree in principle, the thermostat itself is the greatest restriction in the system, whereas the radiator itself presents very little restriction to flow. I'll bet that if you were to measure the pressures before the thermostat, after the thermostat but before the radiator, and after the radiator but before the mixing manifold, you'd find that the pressures before and after the radiator are nearly identical, relative to the difference between them and the difference between either and the pressure before the thermostat.

I didn't reply earlier because I'm having a hard time satisfying myself as to whether adding a significant coolant bypass around the thermostat would significantly affect warmup times, presupposing that said bypass flows through the core of a turbocharger.

That being said, I agree with you in practice. IMO, it's far more important to route the lines such that convection occurs after the engine has been shut off. The best way to do this is to route one side of the turbo to a point high in the system (eg: the top of the head) and the other side to a point low in the system (eg: the mixing manifold / lower radiator hose.) Having water flowing through the turbo center section of its own accord after the engine is shut down and oil flow has ceased (due to hot stuff rising and cool stuff descending) is the most significant benefit of a water-cooled turbo. It helps to prevent the stagnant oil stuck in the turbo from cooking after shutdown.

Yes, I do. Not sure why I was calling them thermostat's now!

We have a standalone ECU, so with that I should be ok to remove the fan temp sensor and switch it on through the ECU. Though it doesn't sound like it'll be wired up to do that.

With all this said.. I don't think the car has a thermostat at all. I can't recall seeing one inside the neck at the back of the head. And if it was there, the temp sensors are fitted after it anyway!

Does it matter being a track only car? We warm the car up before hooing with pulling it off the trailer, noise tests, steady green flag laps etc

Joe, nearly identical is a relative term. Flow obviously occurs between the upper and lower radiator hose regardless of the presence of a radiator. My point was that the concept of direction of flow the OP held was erroneous and needed to be corrected.

Most of us use the ECU to control radiator fans.

Do you have the upper radiator hose on the front of the head or coming from the back of the head?

Looking back at the first few posts, I just realized that I was erroneous in assuming he meant to return the turbo water post-thermostat. From the image he posted, and the original description, it appears that he intends to return the water pre-thermostat.

You're correct in that this will result in zero flow through the turbo.

If it were returned to the upper radiator hose post-thermostat, he will get good flow, and also create a bypass around the thermostat which may delay warmup, depending upon how much heat the turbo actually puts into the water during low-throttle operation, which is something I have no data on.


He clarified that in post #3: "for info the car has no outlet at the front of the cylinder head, hence thinking the back of the head would work"

I don't think the car has a thermostat at all. I can't recall seeing one inside the neck at the back of the head. And if it was there, the temp sensors are fitted after it anyway!

Does it matter being a track only car? We warm the car up before hooing with pulling it off the trailer, noise tests, steady green flag laps etc

https://cimg3.ibsrv.net/gimg/www.mia...7a78dba756.jpg
Here's a photo which may not help at all

?!

Please provide a photo of the back of the head, where the upper radiator hose attaches.

Here you go. The neck has been rotated 180deg so the main water flows down the inlet side as opposed to exhaused side as seen here, but other than that it's like this


https://live.staticflickr.com/7889/4...524ecfff_b.jpg

IMG_4343 by Phil Grayston, on Flickr

I'm going to step away from offering advice in this conversation now, as you have a cooling system configuration which is... unique.

No no, please say what you think

it's been setup like this for a long time now, done many trackdays and hasn't overheated. I'm unraveling it a little while I learn where the turbo water feed can start/end

If there's anything we can do to improve this then lets hear it.

My uneducated guess would be that the two temp sensors on that... T-...thing... are going to have wildly inaccurate readings because there is no flow back there. I'm sure there's more to it then that though. Depending on what sensors are feeding what, this could cause bad readings on your gauges, or an exploded engine.

What's your solution?

A sandwich plate back there to eliminate the T thing? Like this?
https://live.staticflickr.com/7921/4...44e473b482.jpg

spacer plate by Phil Grayston, on Flickr

I think you just have a spacerless reroute. Google it, you probably have a thermostat under the 2 bolt neck there. Unplug the grey connector on the T, and see if you can still turn on the fan with your ecu. If you can, ditch it and put the green sensor where the red/white wired sensor (which I’m guessing is an aftermarket gauge) and put the red/white wired sensor in the thermostat cover. This will require some drilling/tapping/adapters.

Or buy one of those spacers you listed which all have a 1/8npt port for aftermarket sensors, and a hole for the oe ecu sensor (green plug in your pic).

Thanks for that Curly. I’ll get one of those spacers to sort it out.

I’ll check if there’s a thermostat inside too, and if not I guess it wants one fitting.