So it's bone stock with a bigger intercooler blocking airflow, and it idles at 220° in 90° weather.
That sounds normal to me.

-Swap an aluminum radiator in. Doesn't matter which, just pick a good brand. Not mystery meat- eBay IOW.
-Reroute
-cut antifreeze to 5%
- vent hood
- seal gaps around radiator

Should then idle at tstat temp, only get to 215 when you lean on it and quickly drop when you ease off.
Will cruise below 210° on hot days with A/C on.

None of these recommendations are clever or new info. Just SOP for a car like yours.

Thanks. Yep, this is what I've seen from reading around online so no surprises there. The MSM is somewhat of an odd bird however with it's fan set up and the IC pipes getting in the way of stuff, hence me framing this thread from the angle of the MSM's oddities.

Brb doing some shopping.

So your fans are off when temps are good on the highway right?

I'm guessing things aren't sealed well enough to pull enough air through the system when your fans are on. If things are stock ish then I doubt the fans are the main issue. Is the ebay intercooler covering up more surface area in front of the radiator than the MSM one?

How's your undertray looking? Any holes /damage?

Edit: phone didn't show me emilios response till I posted...

Hard to tell if fans are off cruising on the highway but yeah, they should be off unless I have the AC on. The car holds tstat temp or very close to when on the highway or anytime i'm basically cruising along at anything over 25-30mph. Only in stop and go traffic do temps start to climb. They generally don't go over 220f or so, as that's about the temp the MSM triggers the fans to go to high speed.

Basically, i can let the car idle and watch the car go from tstat temp to about 220f, watch the fans speed up, car quickly drops down to about 212-215 and then slowly heat back up and the cycle repeat itself. Effectively, the system is "working" as intended, but 220-225f is hotter than i'd prefer.

I agree, you should not see temps that high when just idling. My car runs in between 88-94C doesnt matter if I am idling, driving highway, backroads. All I have are stock fans and a Ebay 55mm just like Concealer does. I have minimal ducting in place.I did seal the fans to the radiator with some weatherstripping stuff I found at Home Depot. I run a approx 80/20 water/AF mix.

Additionally in terms of DPE, when i did install the Ebay 55mm radiator with Mishimoto fans/shroud, the car took foooorrrrreeeevveerrrrr to kick on the fans at idle or low speeds, if it ever did.

But would get hot on the highway. Like, too hot.

A panicked call to FM during the middle of my wedding trip net me a "ah yeah that's normal for aftermarket fans on MSMs." Turns out it's not an uncommon anecdote among MSM owners and FM in particular to see these cars using the fans more often at highway speeds than they do around town. Actual good fans got me sorted out, and i could watch them kick on and off at highway speeds, which again, isn't uncommon for these cars. An MSM with an upgraded intercooler w/ AC, stock ducting/undertray, and stock hood has absolutely HORRID airflow through the radiator at speed. Pressure builds up and creates this nice cushion in front of the car which not-so-conveniently gets all your air going around the car instead of through the opening.

General consensus around various other MSM owners seems to be that it's on the higher end of normal, but still normal for an 100% stock cooling system. I'm sure there's some variance between cars as well.

I also dont have an MSM, maybe the MSM is just a different animal.

I found your thread on your experience with that setup in digging around here. Seems like my situation is exactly the opposite. I drove the car 30 miles south to work today and the car held right at 195-205 the whole way down cruising at 70mph. It's when i got stuck waiting on the train to pass and idling for 5-7 minutes that i saw the car creep up to 217 if i recall correctly. Conventional wisdom would indicate better fans would do the trick here, but i'd rather completely bulletproof the cooling system and be able to drive the car as intended without keeping my eyes glued to water temps.

I agree with "you should bulletproof it." It's easy. It's just money, you can always make more.

Sounds like you know the way forward either way. :)

220F at Idle is a bit high for a stockish MSM . Is this a new issue? Any cause and effect analysis here? When did you install the Ebay intercooler? Some of these Ebay intercoolers block more air than they allow through. Makes for a crappy intercooler and limits air reaching your radiator.

Next, some second owners of MSMs have reported a similar issue as you where the radiator had been replaced by the previous owner using a new factory radiator which was the NB non MSM model (there are different OEM radiators for MSMs and NBs). This was hard for the second owners to diagnose as their cars had "new" factory radiators. The MSM forums were moved to miata.net but there has been good discussion regarding how to tell if you have a MSM OEM radiator : https://forum.miata.net/vb/showthrea...t=msm+radiator

If you have a OEM MSM radiator and it is not clogged or damaged, then you have an airflow problem. Sounds like you have confirmed factory fans are running correctly is that right? If yes, look to how your airflow is reaching your radiator. Another mistake discussed on the old MSM forum is that folks had a rise in temps when they put some type of wire mesh in the bumper opening to "protect" the intercooler and AC condenser from rocks/bugs. The mesh limited airflow just enough to cause idle temps to rise. The goal is to always have unrestricted flow entering the bumper opening and then to force this air through the radiator not let it move around it. This is where sealing up gaps with foam tape around the radiator and making sure the undertray is in place become important. Switching to a 95%: 5% water : coolant will also help as water exchanges heat much better than coolant. Switching to an ebay aluminum radiator may actually exacerbate the temp issue if you are replacing an OEM MSM radiator with a brand that does not have comparable heat exchange capabilities. If a radiator change is warranted, the Supermiata, FM, or Trackspeed crossflow models would be a better solution as they are more efficient than the OEM radiator and are not made with plastic end tanks like the OEM model.


Hope this helps.

Thanks for the feedback. It's always idled around 220f with the AC blasting in ambient temps of 85+ even before the intercooler install. Doing a bit of searching around online seems to lend itself to this being in range of normal. If i shut the AC off, temps start to drop and will settle at around 205-210f. Once the car is in motion and moving over 25-30mph, temps quickly drop down to tstat temp so it's getting airflow at motion. I've always theorized that this increase in temps with the AC on is mainly due to the car idling up slightly when the compressor engages + the additional load on the motor. My daily driver lexus is the same way and runs a little hotter with the AC on.

I confirmed it's the correct MSM rad and i don't have any mesh grilles blocking the mouth opening. Seems this is just normal operation for these cars. Will be throwing some money at a new rad and reroute in the coming days and the longer term plan is to do some ducting to make sure i'm getting every bit of airflow to where it needs to go.

You were right :(

Passenger side cooling fan was intermittently failing. Hadn't noticed it since every time i checked they were spinning, until one day I saw temps creep up at idle, popped the hood and saw the passenger fan off. getting it started by hand or hitting the shroud with a wrench got it going again, but it definitely wasn't running at the same speed as the driver fan and looks as if it's off balance. OEM MSM fan operation runs both fans at the same time, so pretty much confirms the passenger fan is bad. Ordered the FM fan kit and crossflow to start and the reroute will come next pay cycle. Going to completely bulletproof the system