MazDilla

iTrader: (7)

Yes, which means your heater source and return are on the same side of the thermostat. Which means there is little difference in pressure between those two points. Coolant won't flow from one point to the another without a pressure differential.

Due to it's proximity to the water pump the pressure may be higher at your new plumbing point relative to the stock outlet at the back of the head. Thus reversing flow through the circuit.

Curious to see what our learn'd friends think.

Joe Perez

iTrader: (8)

I realize this wasn't directed at me, but having read all of your posts, the entire solomiata site, and pretty much every word that's been written about the Miata cooling system over the past few years, here are my observations:

1- As MazDilla astutely notes, the fact that your heater core return is plumbed into your thermostat housing means that you are going to have virtually zero flow through the heater core when the thermostat is closed, and relatively little flow through it when the thermostat it open- the thermostat itself is a restriction which will create a localized high pressure area relative to the radiator, resisting the flow of coolant from the heater out to the radiator. The pressure in the back of the engine would have to be higher than the pressure in the front in order for coolant to flow through the core, but in reality there will be very little pressure differential between the two points. Both ends of the heater are connected to points in the system that are on the discharge side of the pump, and thus at relatively equal pressure.

2- Because of the above, you are also going to have relatively little circulation of coolant through the engine in general when the thermostat is closed. The only means I see for water to circulate anywhere when the engine is cold is from the thermostat housing through the turbo and back into the water pump. There will be significantly uneven heating of the engine, with localized zones of varying temperatures.

3- Since there is no incentive for water to move through the heater core (which in both your design and the factory design is the only way for coolant to flow through and exit the back of the engine) the coolant in the back of the engine is going to be relatively stagnant, even when the thermostat is open. The difference is that since the factory put the heater return at the pump inlet, at least coolant flowed through it, even if much of it went right back into the engine without being cooled. The predominant path of the coolant in your system (when the thermostat is open) is going to be from the water pump outlet, up through the front of the block, and then directly out the thermostat into the radiator. As a result, the front of the engine is going to be cooled properly, while the back of the engine is going to overheat.


You've actually made the situation far worse. Relocating the heater return to the thermostat body means that very little coolant is actually going to circulate through the engine itself. Sure, eliminating the mixing manifold means that the coolant itself is going to be quite cool indeed. It's going to come in from the radiator, be pumped up into the front of the engine, and then go right back out the thermostat without absorbing any heat from the engine.

Braineack

iTrader: (62)

that's the point...you put the heater core return behind the thermostat....it will only flow when the thermostat is open.

Joe Perez

iTrader: (8)

...And very poorly even then.

There is no incentive for coolant to flow all the way through the engine, from front to back and bottom to top, then out through the heater core, and then all the way back around to the thermostat housing. The path of least resistance is straight up around #1 and then right out the front.

johndoe

iTrader: (5)

Irony is the word that comes to mind here.

Hyper with ADD

not so fast buddy.

A variation of this setup not yet discussed on my behalf easily is done by simply putting a freeze plug in front of the engine and keep the same setup you all see on the pics. The choice will be to use bigger coolant lines from the back of the head or just keep as it is without any thermostat in the back since coolant will be forced to exit through the back of the engine and will be exiting without any issues.

A simple add on of a freeze plug in front of the will create greater flow of fresh coolant from the water pump all the way to the back to the to the heater core wich will eliminate any of the concerns raised by Mr. Joe Perez. At the same time to hot coolant and fresh coolant will not be mixed anymore. At the same time, it makes more sense to me to run a thermostat in the front or a modified thermostat in the front as I already said before.

The idea I talking about may be misunderstood here, but for sure with the freeze plug any issues raised by Mr. Perez regarding coolant exiting from the back of the engine through the heater core through the front thermostat as you see on the pics should be no problems at all.

Joe Perez and group do you understand?

Joe Perez

iTrader: (8)

Where precisely would you place the freeze plug, relative to the outlet on the front of the head, the thermostat housing, the thermostat itself, etc?

(Also, don't get too riled up just yet. We're open to new ideas, but some convincing is required when they run contrary to the sum of our previous experience.)

Hyper with ADD

i not looking for ideas from anybody as you can see the idea, the concept is already done.. the freeze plug will be placed as it comes in all protege engines. in front of the cylinder head ,it makes more sense for me toleave the thersmostat in the front as i already said.

Joe Perez

iTrader: (8)

A bit late, but I just noticed something here. The way I see it, the turbo is actually going to be fed with the hottest coolant in the system, given the rest of your configuration. Since the front thermostat housing it the "last stop" in your system before the radiator, and this is where you're taking the coolant from for the turbo, you've preheated this coolant by passing it through the engine.

From a practical standpoint, pretty much everybody has their turbo water lines plumbed the same way you do. In the factory configuration, there's a little water outlet on the bottom of the thermostat housing, and a rubber hose that goes to the mixing manifold. This was done so that when the thermostat is closed, there is always some coolant circulating around the bottom of it, to ensure that it opens when the average temperature of the coolant in the engine warrants is.

This spot happens to be a tremendously convenient place to plumb the turbo in, and it's one that has an excellent pressure differential across it. Check out the installation manual for FM's turbo kits and Bell's turbo kits to see what I mean. On the first page of FM's manual, there is a high-resolution picture of the overall system that shows these two coolant lines quite clearly. I've highlighted them for you in this image:

Joe Perez

iTrader: (8)

So let me be sure I've got this, because I don't want to misinterpret you. You're saying that you'd drive a freeze plug into the opening at the front of the head, and then mount the thermostat housing over top of it, leaving everything else exactly as it is in your pictures, yes?

Hyper with ADD

sir your r basically completely wrong on that comment. the turbo lines were istalled accordingly as the miata cooling and turbo system flows. i know it is difficult to see on the pics but the lower braided line feeds the turbo with fresh coolant and then exists to the top line in thermostat housing

Hyper with ADD

yes, difficult to digest si? but that's it

MazDilla

iTrader: (7)

I think you are confused about the direction of flow. The lower braided line does not feed the turbo. It's plumbed to the water pump INTAKE (suction side), drawing water from the thermostat housing through the turbo.

matttheniceguy

Hyper, it is your digestion, or rather your entire understanding of the Miata cooling system, that needs to be corrected.

You have a line running from the water pump inlet to the turbo. The pressure here is very low. You have another line running from the thermostat housing (pre thermostat) to the turbo, the pressure here is fairly high. Water will flow from high to low pressure, so the water is actually flowing the opposite direction from what you think. The water in those lines will be flowing from the thermostat housing through the turbo, and into the water pump inlet.

If you stick a freeze plug in the front of the block with your setup, your flow will look like this:

With the thermostat open: Water flows through the water pump, out the back of the head, through the heatercore, through your lines, through the housing, through the thermostat, to the rad, and back to the waterpump. This circuit is very long, and very restrictive. Your car will overheat running like that, there won't be enogh flow through the rad.

With the thermostat closed: water won't flow at all, aside from the small amount through the turbo, and through the intake and EGR stuff depending on the year. Your heatercore won't work, your head will have virtually no coolant flow, and you will have localized boiling and overheating in the head.


Your current setup is bad. There will be very little flow to the back of the head and you will have localized boiling there, and I would expect the entire engine to overheat because you have damaged the efficency of the cooling system so much. Your proposed reroute with the freeze plug is worse.

leatherface24

iTrader: (10)

I am so shocked at how nice everyones been on this thread. Eli, I'm confused as to where this freeze plug your talking about should go. What I'm seeing is that your acknowleding that putting a freeze plug would be better than what you currently have yet your stating also that the way things are now is best?

MazDilla

iTrader: (7)

Wait for it...

leatherface24

iTrader: (10)

I'm curious as well as to what your last setup was like. The one where you kept overheating and how this one is an improvement. Also, did you ever actually get your car running again to actually test this idea of yours out?

m2cupcar

iTrader: (5)

That's the return according to Mazda (and their diagram)... maybe they're wrong.

I don't get your concern for coolant temps at the turbo. Did you measure the coolant temp there? did it exceed spec for the turbo?

It seems like you've done a lot of hard work without any data to solve a problem that doesn't exist.

Joe Perez

iTrader: (8)

I think you may be looking at this backwards. Here's an image you posted earlier which clearly illustrates both sides of the turbo's water feed:


As we can see, one side of the turbo is connected to the thermostat housing (before the thermostat) and the other side is connected to the Protege pump inlet, which is where the lower radiator hose attaches.

You seem to be of the opinion that coolant is going to come out of the Protege fitting, flow through the turbo, and then return to the thermostat housing. In reality however, the opposite is occurring. The Protege fitting is on the suction side of the water pump, and the thermostat housing is on the discharge side of the pump. Therefore, the pressure in the thermostat housing is always going to be greater than the pressure in the Protege fitting whenever the water pump is turning. As a result, hot coolant from the thermostat housing will flow into the turbo, and then hotter coolant will flow from the turbo into the Protege fitting and be drawn back into the pump without ever passing through the radiator. The Protege fitting is now a mixing manifold.

Fortunately, the turbo is symmetrical insofar as the water jacket is concerned- there is no distinction between the "in" and "out" fitting. And since the volume of coolant flowing through the turbo is relatively small, the overall effect this bypassed coolant will have on the system is relatively small. As I said earlier, Bell and FM turbo kits are plumbed in exactly the same way (as are most water-cooled DIY setups) and this does not present any significant problems so long as the rest of the cooling system is operating nominally.

Unfortunately, as I said before, your routing of the coolant return from the back of the head, through the heater, and into the thermostat housing virtually guarantees that the rest of the cooling system is not operating nominally. The turbo itself (and the forward portion of the engine) will be adequately cooled, however the rearward portion of the engine will experience relatively little coolant flow and thus tend to run much hotter.

No, I just wanted to be certain that I understood you, to leave no room for misinterpretation.

The setup that you describe here (with a freeze plug blocking the forward outlet, and the thermostat housing mounted over top of it) is a definite improvement over your current design. In fact, it is functionally similar to the reroutes being done presently, where the thermostat is relocated to the back and the heater return is left plumbed into the mixing manifold. (At least, when the thermostat is open)

With such a setup, proper warm coolant flow through the engine is restored, since the only avenue for water to exit the engine is through the fitting on the back which feeds into the heater core. Assuming that the heater core continues to be returned to the thermostat housing (on the front), then when the engine is cool and the thermostat is closed, this coolant will exit the thermostat housing via the turbo feed, pass through the turbo, and be drawn back in at the Protege fitting. When the engine is warm and the thermostat is open, most of this coolant will exit to the radiator, with a smaller portion of it continuing to pass through the turbo and back into the Protege fitting, having bypassed the radiator.

I expect that the cooling performance of such a setup would be comparable to that of a rear-mounted thermostat and mixing-manifold returned heater core. In your setup, the rear outlet is considerably smaller than that of a rear-mounted thermostat (thus presenting a restriction to flow through the engine) however the bypass line (through the turbo, and back to the Protege fitting) is also smaller in diameter than the stock heater lines.

On a warm engine, I expect that the ratio of flow through the two avenues would be similar to what is seen in a rear thermostat application, although the total volume of flow is likely to be less, as the water pump is working against a greater restriction. When the thermostat is closed, the total flow through the system will be considerably less than stock (nearly 100% of the coolant must now flow through the turbo) which will not significantly harm the engine, although during the warmup period you may have some degree of uneven heating until the thermostat opens and the temperatures equalize. The back of the engine will still run a bit hotter during this time. Another potential issue is that you will greatly increase the pressure inside the heater core when the thermostat is closed (as it's trying to drain into a significant restriction) and thus increase the probability of the heater core bursting.


I think you really need to sit down a draw a diagram of your current system, as well as any proposed systems. In them, carefully consider the pressure differentials which will dictate the amount and direction of coolant flow through each portion of the system. You may find the results enlightening.



[edit] I'm taking too long to write these and everybody is beating me to the punch.

Splitime

iTrader: (24)

Ok.. is this backwards day or something crazy? Why is everyone being so subtle and nice.... I'm scared....