Rotrex cooling issue
 

I just had a new Rotrex kit installed on my 2001. Car still has AC, power steering, Koyo radiator and dual Mishimoto fan shroud system. a Rev build MS3 and just had a newer engine installed (bent a rod on the old engine). When the engine was out I had the installer tap a hole and install a temp sensor on the water line coming out of the back of the engine. Also have a Mustang GT500 hood vent installed. Car runs so hot I can't track it and barely can drive it on the street. Temps approach 230 when driving. Looking from the front in, the stack includes: Kraftwerks intercooler, Kraftwerks oil cooler, AC condenser, radiator. No reroute but thinking about it. Also just thinking I'll pull the Rotrex and go back to NA. It's ducted up some but doesn't seem to do anything. Need help...

Found your problem. I bet you will get much better temps when you actually get coolant flowing at the back of the head.

I don't think that's his problem. and 01 HG doesn't play nice with a re-route

To amplify the above:

Mazda changed the design of the head gasket starting in the '01 model year. They blocked off all of the coolant ports around the #1 cylinder, and some of those around #2. The effect of this is to force coolant to flow towards the back of the engine, then up and forwards once the thermostat is open. This was done specifically to address the poor and uneven cooling performance in the previous engines, which used the same head gasket as their FWD counterparts.

It's not a perfect solution, but it's a significant improvement over the earlier design. And, most critically, doing a rear-therm reroute on this engines can actually make matters worse, by creating a stagnant area around the #1 cylinder which experiences virtually no coolant flow at all, whether the thermostat is open or closed.

A "perfect" solution is to replace the head gasket with the '94-'00 design and also do a rear-therm reroute. This is quite a bit of work, of course. The stock design should work adequately in most applications.

"Approaching 230°" is warmish, but not meltdown-temp.

What sort of ducting, if any, exists to seal the path between the nose inlet and the outline of the radiator? With all the stuff in between the two, you need to make sure the air has some encouragement to flow through the path of most resistance.

Your fans are awful and worse than stock, which is exactly what you don't want in a forced induction situation with another extra echanger stacked in front. You should replace them.

Also, the Mishimoto fan shrouds and fans have gotten poor reviews -- I have no personal experience with them though. You've got quite a heat exchanger stack and may need some powerful fans to pull air at low speeds.

Is your undertray still relatively intact?

Running the Cobalt stainless steel undertray.
https://www.miataturbo.net/attachmen...ine=1441937385

The multi-pass radiators available from TSE, FM, and 949 (and probably others) work much better than the simple large-core single-pass ones do.

--Ian

Could the tune be running a little lean? That will raise the temperature as well.

I'd start with the garbage mishimoto fan/shroud stuff and troubleshot from there
To give you a reference point: my MSM with a FMIC and AC never went over 209 in CA 90-100* weather

I've never tried this product, but I strongly suspect that the OEM undertray is far more effective at promoting radiator airflow.

So, yank out the Mishimoto fans and go back to stock? I can pick up a set of used OEM fans relatively cheap. Will look for an OEM undertray at the same time.

Stock would be a step in the right direction. Loading that shroud with some SPALs would also be a good move.

Stock undertray a good idea.

New OEM under trays are cheap from Mazda, like $30 the last time I bought one. I guess people destroy them a lot, so they have a relatively high sales volume.

--Ian

I get just about the same problem with my VVT swapped and Rotrexed NA.

- temps rising rather fast up to 110°C - as soon as I give the car some throttle
and even at light throttle at 4.500-5000rpm in 5th gear at the German Autobahn
- go down equally fast, when I let go of the throttle

- setup is nearly equal to the one above (intercooler, big IL Motorsports aluminium radiator, 2 spal fans on DIY shroud, no AC though)
- no coolant reroute due to the 01 head gasket problem
- already changed the thermostat
- no water loss, no white smoke - so I still guess the HG is okay
- OEM undertray with intake for engine oil-cooler on steering rack

At first I suspected that there is still air in the coolant system - but this should be long gone...

So I will be watching this closely...

Its a radiator on the front of a car, the shrouds and big fans only serve to slow airflow through the radiator when you are doing 100mph.

So you suggest to remove the shrouds?

From the Miata Cooling System thread in the Race Prep area:
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Head gasket
Mazda recognized the cooling issues and altered the head gasket in the 01-05 "NB2" VVT (BP6D) engines. This change restricted the coolant flow to 1-2 cylinders thereby increasing flow to 3-4. Bandaid fix that doesn't really solve the problem of the backwards coolant flow. It's OK to use a reroute in an NB2 engine. If you have the engine apart already, further improvements in flow can be made by swapping in the 94-00 # BP26-10-471 head gasket. We run this HG on all of our VVT engines.
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I looked because I just swapped in a NB2 with reroute and didn't want to crack it open to swap headgaskets.




OP- to keep my Rotrex car cool on track I've done the following:

-Coolant reroute
-Big radiator (trackspeed)
-Big oil cooler (trackspeed)
-Remove A/C condenser
-Seal all gaps around radiator
-NO fan shrouds- just one stock fan

This keeps my car cool on hot days (90 f) at 5000 feet elevation where the air is thin and dry (bad for cooling)

The exact same person that wrote that, admitted:
...so I guess we're both right. or wrong. lol

True. I'll see how it works out soon enough... Track day coming up in a few weeks on the new motor. :party: