Miata cooling system thread
08-07-2014, 04:30 PM
#122
The BMW tstat wasn't the basis for the M-Tuned, just a validation of sorts. Most DIY reroutes back then used a Kia or B6 outlet on the back of the head with Jackson Racing tstat spacer. One needed to cut a step into the spacer. Bulky and precluded the EGR pipe. I built one and didnt like the packaging
When Marc at Mtuned asked my opinion on a possible reroute, I voted for a remote tstat based on my experience with both variants.
The BMW is a bypass type. I plumbed that to the heater with a restrictor IIRC.
When Marc at Mtuned asked my opinion on a possible reroute, I voted for a remote tstat based on my experience with both variants.
The BMW is a bypass type. I plumbed that to the heater with a restrictor IIRC.
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08-07-2014, 10:54 PM
#128
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"Sokath, his eyes uncovered!"
This answers a question that had been bugging me for a while, namely why on earth the M-tuned package went with the extra hardware of the remote thermostat rather than duplicating the original FWD config. I've done a number of rear-thermostat reroutes (one with a spacer I made on my lathe, the rest with the piece that Bell sells), and I just realized that they've all been on either 1.6 cars or on turbo 1.8s from which the EGR system has been removed due to installer laziness.
Peripherally related: Does anybody remember that guy in Port Charlotte, FL who was building and selling a hotside reroute kit c. 2009 or so? I wonder what ever happened to him...
Anyway, I feel like I drifted the thread a tad with this talk of heads and gaskets. Just felt that the BP-Z3 comment merited elaboration, as I've recently spoken to some folks who were unaware of the changes to the gasket and head porting.
This answers a question that had been bugging me for a while, namely why on earth the M-tuned package went with the extra hardware of the remote thermostat rather than duplicating the original FWD config. I've done a number of rear-thermostat reroutes (one with a spacer I made on my lathe, the rest with the piece that Bell sells), and I just realized that they've all been on either 1.6 cars or on turbo 1.8s from which the EGR system has been removed due to installer laziness.
Peripherally related: Does anybody remember that guy in Port Charlotte, FL who was building and selling a hotside reroute kit c. 2009 or so? I wonder what ever happened to him...
Anyway, I feel like I drifted the thread a tad with this talk of heads and gaskets. Just felt that the BP-Z3 comment merited elaboration, as I've recently spoken to some folks who were unaware of the changes to the gasket and head porting.
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news to me though. I'll grab the casting numbers off my MSM head over the weekend for posterity's sake.
08-08-2014, 01:16 AM
#130
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As we've now seen, head gaskets are going to be a big part of how the system functions.
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08-08-2014, 08:21 AM
#131
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I haven't heard of that testing done either. I will say that Thumper uses a BP6D gasket (01-05) and a reroute and it hasn't blown up in spectacular fashion yet. 
One more note on the differences between VVT heads and '99 heads. When Mazda changed the head gasket design, they added several cooling ports to the surface of the 01+ head (including the MSM). As a (likely unintended) result of this, nearly every coolant port on a 99-00 head ends up blocked off if you use a 99-00 head with an 01+ gasket. Out of 17 total ports, eleven of them end up blocked, with cylinders #1 and #2 sharing a single coolant port between them. Not good at all.
The ports in red are blocked:
If you were thinking about using a BP6D gasket on your early engine to forego a reroute, don't.
One more note on the differences between VVT heads and '99 heads. When Mazda changed the head gasket design, they added several cooling ports to the surface of the 01+ head (including the MSM). As a (likely unintended) result of this, nearly every coolant port on a 99-00 head ends up blocked off if you use a 99-00 head with an 01+ gasket. Out of 17 total ports, eleven of them end up blocked, with cylinders #1 and #2 sharing a single coolant port between them. Not good at all.
The ports in red are blocked:
If you were thinking about using a BP6D gasket on your early engine to forego a reroute, don't.
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08-08-2014, 08:57 AM
#132
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No, I'm fairly certain that the configuration of the coolant ports in the block didn't change much at all between the BP-6D ('94-'97), BP-4W ('99-'00 and MSM), and BP-Z3 ('01-'05). So as far as putting a '99-'00 head onto a '94-'97 bottom end, this is safe. Mazda even used the same head gasket for those two engines.
It should be noted that MSM engines, despite being superficially identical to a standard BP-4W, used the same head gasket as the BP-Z3, with similar cooling ports in the head.
Essentially, what all this boils down to is the following: When Mazda turned the B6 engine sideways and stuck it into a RWD car, they made a design compromise with the cooling system which ultimately proved unsatisfactory*. They perpetuated this compromise, unremediated, through the next two major engine generations, and did not get around to fixing it until 2001. Model year 2001 and later engines, due to the revised head gasket and port design, don't really suffer from the fundamental problem which rear-thermostat reroutes solve in other engines. So while I can't tell you with absolute certainty that doing a rear-therm reroute on an '01-'05 engine is going to harm it, I can say with a reasonable degree of confidence that it's not really going to benefit much either.
It should be noted that MSM engines, despite being superficially identical to a standard BP-4W, used the same head gasket as the BP-Z3, with similar cooling ports in the head.
Essentially, what all this boils down to is the following: When Mazda turned the B6 engine sideways and stuck it into a RWD car, they made a design compromise with the cooling system which ultimately proved unsatisfactory*. They perpetuated this compromise, unremediated, through the next two major engine generations, and did not get around to fixing it until 2001. Model year 2001 and later engines, due to the revised head gasket and port design, don't really suffer from the fundamental problem which rear-thermostat reroutes solve in other engines. So while I can't tell you with absolute certainty that doing a rear-therm reroute on an '01-'05 engine is going to harm it, I can say with a reasonable degree of confidence that it's not really going to benefit much either.
* = After the explosion and meltdown at the Chernobyl nuclear power plant in 1986, the first Russian television broadcast to acknowledge the event used the phrase "an unsatisfactory condition exists..." in describing the worst radiological disaster in human history.
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08-08-2014, 11:40 AM
#134
What we generally see is, regardless of gasket or head casting, that the system does a poor job of getting all the hot coolant out to the rad efficiently without a reroute. Manifested as coolant temps far higher that rad core temps. On reroute cars, the core is a tad hotter, the ECU/gauge temps are cooler. Lower delta between the core and ECU reading indicates better scavenging and utilization of the heat exchanger with a reroute
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08-08-2014, 11:49 AM
#135
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No, I'm fairly certain that the configuration of the coolant ports in the block didn't change much at all between the BP-6D ('94-'97), BP-4W ('99-'00 and MSM), and BP-Z3 ('01-'05). So as far as putting a '99-'00 head onto a '94-'97 bottom end, this is safe. Mazda even used the same head gasket for those two engines.
It should be noted that MSM engines, despite being superficially identical to a standard BP-4W, used the same head gasket as the BP-Z3, with similar cooling ports in the head.
It should be noted that MSM engines, despite being superficially identical to a standard BP-4W, used the same head gasket as the BP-Z3, with similar cooling ports in the head.
94-00 head with BP26 94-00 head gasket: OK
01-05 head with BP26 94-00 head gasket: OK
01-05 head with BP6D 01-05 head gasket: OK
94-00 head with BP6D 01-05 head gasket: Not OK
The MSM head is a freaky one - it can be accurately described as either "a '99-00 head with 01-05 coolant ports and a unique intake cam" or "a 01-05 head without VVT and a unique intake cam".
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08-08-2014, 12:27 PM
#136
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Unique intake cam, 01-05 coolant ports, and 01-05 COPs. Although technically that's just the valve cover.
I feel like vvt head without vvt and with a unique intake cam is less of a mouth full.
I feel like vvt head without vvt and with a unique intake cam is less of a mouth full.
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08-08-2014, 02:39 PM
#137
(I can't tell from the picture if yours seals off the mixing manifold port when the radiator port opens fully)
Bypass thermostats are indeed the best of all possible scenarios. No need for a mixing manifold. If you really wanna get fancy, do the same on the heater core outlet. Note that the aftermarket units above are not equal to the BMW part.
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08-08-2014, 02:54 PM
#138
On race cars without heaters, we run the reroute with a restrictor in the heater bypass. Usually a piece of fuel hose stuffed inside the 5/8" heater hose.
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