Joe I don't know what that's supposed to mean. Has this place really changed? It used to be common to discuss ways to make our cars better, without all the crap I'm getting. I'm all for constructive criticism and a discussion on why something sucks if it does in fact suck.

Will someone do the math on how much cooling capacity at full load is actually lost by having the heater core return to the mixing manifold.

The upper radiator hose is like 3 times the size of the heater hose. But I don't know how to calculate anything else.

Yes. See the part where I specifically discuss HOT SPOTS and unwanted uneven temperatures within the engine due to lack of circulation.

The ideal cooling of our engines is a constant, even, full flow of coolant over all parts of the engine. A coolant reroute to accomplish this is the way we corrected the error that Mazda made on the Miata cooling system.

Imagine a loop of water pushing to the front of the engine, traveling through the head and along the cylinders at a high Reynolds number, out the back of the engine, through the heater core, back to the pump, and continuing the cycle.

Now, when the engine reaches optimum temperature, the thermostat allows a little bit of coolant to exit this loop and go to the top of the radiator, which draws in cooler coolant from the bottom of the radiator. The flow through the engine in a correct reroute is increased slightly at this point, but not substantially since the water pump is almost at capacity forming this loop of water through the engine.

As the temperature of coolant flowing in the initial loop increases, the thermostat allows more water to exit to the top of the radiator, allowing more coolant to enter that loop to control the heat being removed from the engine and keeping the engine at a correct operating temperature.

When the thermostat has opened completely and the full flow through the radiator is available, the fans will cycle to regulate the coolant temperature until the load on the system is too much for the radiator to remove and the system needs augmentation.

This augmentation is accomplished with more efficient radiators, better ducting, etc, but not by bastardizing the basic system

This is the optimum system for all driving conditions on our cars short of an auxiliary water pump. Don't fuck with it and you won't have problems.

Great post.

Pat, two questions:

1) which coolant sensor is reading those temps?

2) can you take some pics of your reroute?

Regards,

Rafa

Just some short and quick math.

I have a Stant SuperStat thermostat to measure since that's what Emilio recommends. Supposed to be the highest flowing thermostat on the market.

It has a 22mm opening. I don't know how far it goes back, but I'll just assume it goes back far enough that the limiting factor is the 22mm size.

Heater core hoses are 11/16 by my measurements, which is 17.5mm.

Area of thermostat = 380 mm^2
Area of heater hose= 240.5 mm^2
Total Area = 620.5 mm^2
Rough numbers, but a start.

% flow area for thermostat = 380/620.5 = 61.2%
% flow area for heater core = 240.5/620.5= 38.8%

Obviously if thermostat doesn't open as much as I assumed then less goes through thermostat.

Also thermostat is just a restrictor where as the heater hoses are several feet of pipe with that ID. So even if you cut the flow of water going through the heater hoses in 1/2, that's still right at 20% going through heater hoses with a 100% open thermostat.

No Reynolds numbers, no friction factors, blah blah it's rough math to put things into perspective since you asked. If anyone really wants it I could actually do some more accurate math but this is ballpark and it shows that yes, a significant amount of water goes through the bypass.

But the thermostat and upper radiator hose flow more water than the heater hoses? Even though there is a restrictor (thermostat) doesn't flow depend on the whole system? I never took a fluids dynamics class though.

Yes it depends on whole system. To do the math perfect, would take forever, because the system has many pieces.

To get a ballpark, you look at what the major losses are going to be. For thermostat side of things, that's the thermostat. The one I measured has a 22mm ID, and a piston behind it that forces the water to turn to go through that. Everything before and after it is larger ID, and much less significant. If you included radiator hoses, bends, etc, the numbers would change + or - 10-15%. Both parts have to flow water through a radiator too, so that's kinda equal.

Heater core is all the same ID, and several feet, so you'll have more pressure drop than if it had say 1" hoses with just one tiny spot that dropped to 11/16".

Rafa,

1) The coolant sensor I used during this testing was the OEM sensor, located on the back of the cylinder head.

2) Here's a few pics. It's basically just a rear spacer with hose barbs before/after the thermostat, then a hose that goes to the front like normal.

Attachment 184244

https://www.miataturbo.net/attachmen...ine=1427039728

https://www.miataturbo.net/attachmen...ine=1427039728


http://i231.photobucket.com/albums/e...psdkx40nml.jpg

http://i231.photobucket.com/albums/e...psnudfwinv.jpg

http://i231.photobucket.com/albums/e...ps5umwv4d1.jpg

I have a much better understanding of your situation after viewing your pictures. Two things stand out to me:

1. You have voluntarily added more potential points of failure in your upper radiator hose than I have in my entire cooling system.
2. You chose a supercharger over a turbo.


Seeing that you made these decisions of your own volition and without coercion, I don't believe rationalizations and advice offered by anyone else will be heeded.

I el oh el at the Supercharger Hate :)

But yea. The cooling system on these cars with a decent radiator, water pump, standard re route, High Quality fan and shroud and simple ducting is more than enough. No real need to re-invent the wheel to cure a problem that doesn't exist at this point.

1. True.
2. I've had been driving a turbo miata since before you registered on this forum. I'm now building a supercharger setup. So what? :bowrofl:

You can believe anything you like, and post whatever opinions you like. Neither of the above 2 points from your last post have anything to do with improving the cooling on a miata, or the math I recently posted. Feel free to look at my math in post 46 and let me know what you think.

I have posted real testing, data, experience, and simple math in this thread regarding the topic of improving the cooling capabilities of miatas. I've gotten some good feedback. But it's sad how much BS ended up in this thread. Half the people that posted said to put the car back to stock, don't bother trying to improve anything/test anything.

You are right that I'm not going to take the advice of "give up because I said so". Several people were quick to jump in and state things that were False, like saying the car would overcool at any cooler temp, or the heater won't work, or using a restrictor won't work at all, or saying now the thermostat won't work at all. In fact Sav himself said, in the same post, that I now have so much water going through the heater core that the engine is going to overcool if it gets any cooler outside, while simultaneously, I don't have enough water going through the heater core to get hot air from the vents. That would be post 38, paragraphs 1 and 2 assuming he does not edit them. Clearly it can't be doing both! I didn't say anything at first, but nobody questioned him and his post is flat out impossible. No fancy math or thermo required to see that.

But I do thank those who have posted info that is actually relevant to improving the cooling system on a miata, your feedback is appreciated.

I have done everything you said before. Problem is I have an A/C condenser blocking airflow to my radiator, and I don't have a vented hood. This is a street car. No doubt if I wanted a race car I could pull the A/C, move the intercooler, put some hood vents in and never worry about cooling problems again.

I said the radiator would overcool it, not the heater core. You were too busy falling over yourself at the giddy thought of proving me wrong to actually read the post you were trying to pick apart.

Having now seen the amount of money and effort you appear to have expended on your upper radiator feedline, I can understand why you are resistant to criticism about the design of the system as a whole.


edit: seeing your radiator with the stock plastic tanks reminds me that mine is probably getting to be due for replacement. The upper tank is heavily discolored around the neck to which the cap attaches, and that's often indicative of impending failure.

I'm not proving you wrong, your statement I refereed to is in fact wrong. It is impossible that I could have enough coolant flowing through the heater core (and radiator) to both simultaneously not supply heat to the heater core (too little flow), while overcooling the engine (too much flow). This is simple. One or the other could happen, but not both at the same time, which is exactly what you wrote.

The system isn't perfect. Six shooter correctly pointed out how many connections I have in the upper radiator hose. It's embarrassing, I think there's 10 or 12 connections! It's alot! Like he said, they're all failure points too. And silicone is heavy too.

If the oil cooler works as intended in that location, (have not tested yet) I will have to make a set of hardlines to reduce the number of connections. I've never used one of these oil/water oil coolers so I don't know if feeding it hot radiator water will be enough to keep oil temps in check. If it's not, it will get moved to lower radiator hose or something different put in its place all together.

So heating the water right before the mixing manifold is OK now?

Steve, I just want the car to go fast and not break, not overheat, and be reliable. If the oil cooler works where it's at, it stays. If it doesn't, I'll do something else. I have not tested it yet. If it needs cooler water to work correctly then yes it's going in the lower radiator hose. But I already know it probably won't fit there anyway as this oil cooler is very long.

It is actually in a reasonably good position where it is, if you must use it. The oil is usually much warmer than the water when under a load. Getting that additional heat into the coolant prior to the radiator will cause the coolant to be at a higher temperature differential with the air flowing through the radiator, allowing it to remove heat more quickly. If placed in the bottom hose, the temperature of the coolant would likely be raised too high reentering the engine to be suitable for cooling. It would also cause the oil to be below optimum temperature at light loads, causing greatly accelerated wear.