I like the concept, but I don't like the number of parts required/adding hoses/etc. Especially on the hot side of the engine compartment.

Still, interested in the results. No reason why it shouldn't work well.

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.

I think I found it on m.net somewhere and verified that it was correct. I forget exactly where.

Andrew and Emilio. How can you tell the difference between a regular 99-00 head vs a MSM head? Besides the differences in water ports, was there a difference in visible casting numbers? BP4W 2-? vs BP4w 4-?

There is a casting number difference in the head, but I forget what it is. I don't have an MSM head in the shop right now.

Intake cam and exhaust valves are different part numbers. Otherwise the same AFAIK.

Totally different final machining on the casting, though. The MSM heads have the same coolant port pattern as the VVT heads.

"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.

edit: sorry, like 5 posts behind :) news to me though. I'll grab the casting numbers off my MSM head over the weekend for posterity's sake.

Personally, I feel its solid data and belongs here. This is the consolidated cooling thread after all. :bigtu: As we've now seen, head gaskets are going to be a big part of how the system functions.

Does this happen with a bp6d bottom and bp4w head?

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.

sorry, I used the wrong codes in my initial question. I was referencing bp4w head correctly but meant bp-z3 01-05 block.

In practice, the BP6D's whether running the NB1 or NB2 head gasket, run much cooler with a reroute. We have raced a bunch of BP6D engines. Some were bone stock with 6D gaskets, some were blueprinted or full race builds with 4W gaskets.

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

For the purposes of this conversation, the blocks are all identical from 94 to 2005. The issue comes in the cylinder 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".

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.

Indeed, I designed it as a true bypass thermostat housing. When it reaches temperature, flow through the heater core is cut off and coolant may only pass through the radiator. Is there a good simple way to reduce the heater core outlet size on the BMW Thermostat without using 12 different adapters? I'd prefer to minimize the number of possible failure points.

Not really, no. For me, it was more proof of concept. I ran it briefly, verified it worked then started looking for a vendor that could build the rear adapter and remote tstat.

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.

FWIW my VVT head with modded 99 head gasket runs noticeably cooler than my 99 head with 99 gasket. I added holes... documented elsewhere.

I remember that post. Inline image links of the modded gasket please sir.