Or the original thermostat has a flow problem. Having it open at 160 vs 190 should make no difference once coolant is past 190.

 

This.

Take, for instance, the Stant SuperStat. We know, from rigorous scientific testing, that the Superstat does not open as fully as the "regular" Stant model.

In theory, an engine equipped with a SuperStat would experience less flow through the radiator and more flow through the heater core, thus having less cooling capacity overall than one equipped with a "regular" thermostat of the same rating.

It is possible that similar discrepancies may exist when comparing other thermostat brands, including the twin-element thermostats which were OEM on these cars.

 

Sounds to me like Joe needs to make a series!

 

I'm having a(nother) beer, because there is now incontrovertible proof on the interwebs that I said something, and Joe Perez quoted it, and said "This."

 

Had the new thermostat in last night and drove it home.. Was unable to take the laptop to monitor actual numbers. Nothing really different according to my highly calibrated and scientific stock dash temperature gauge. However, driving to work this morning during the first 5-10 minutes of warm up, the temp gauge creeped up past 12 o'clock, to the point where the CEL stopped flashing and stayed solid(near 230*F, come to f ind out). Went for another drive after things had cooled down to get a fresh start with laptop monitoring. Temperatures rose and kept going, temps ended up at 227*F, then within literally 1-2 seconds, dropped to 178-182*F. Stayed there the rest of my 10 minute drive, regardless of simply cruising or repeatedly running through a couple gears.

Not really sure at this point how to explain the spike/drop. Will monitor for the next several warm ups. If the spike persists, I will run it through a few scenarios to try and get some more info and possible cause...

Thoughts?

-Luke H.

 

Ducting? Do you have pics of what you have now?

 

Bubble?

 

This is pretty much the exact definition of lag in the operation of the thermostat. It's what happens when the thermostat is located some distance away from where the action is happening, buffered from the engine by a column of relatively stagnant water.

It is also the thing that M-tuned said wouldn't happen when we questioned the remote placement of the thermostat several years ago during the initial design.

I am not implying that these two things are related, just making an observation.

 

Step 1 (if possible): find a way to move your thermostat *closer* to the engine.

Step 2: put the higher temp thermostat back in, but drill the hole out to the larger size like you did with the lower step thermostat. Drill the hole too small and your temps will continue to slinky back and fourth, drill the hole too large and your temps will never climb high enough for the thermostat to open in the first place. The problem of needing a hole in the first place is associated with the remote thermostat mounting.

 

This.

And, I'll elaborate.

Let's say you had the stock thermostat setup, and you took your car to a hack shop for a timing belt/water pump service. The hack mechanic decides that you don't actually need the bleed line that goes from the bottom of the thermostat housing to the inlet of the water pump, so he inserts a bolt into the line and tightens a clamp around it.

Now, every time you start the car from cold, the temperature gauge nearly pegs . . . but just before it pegs it immediately drops to the center of the range. Fast. Like 1 or 2 seconds.

Sound familiar? The above was what happened to me in 2005.

Or another common occurence . . . where that same bleed line gets filled with crud causing the same symptoms. Look it up on miata.net (cooling system maintenance page).

This is a common issue with our cars, and it is purely a symptom of the remote thermostat.

Now, look at the M-tuned kit you bought. Remote thermostat, no bleed line. Hmmmmm. How do they get around it? They drill a large bleed hole through the thermostat. Not as good as a bleed line to the intake of the water pump, but apparently good enough.

Now, look at the picture you posted of your original and new thermostats. See a difference? That's right -- the bleed hole in your new thermostat is tiny compared to the other. The problem you're having was entirely predictable and I apologize that I didn't post this earlier.

I think you know what you need to do. It involves a drill bit. Keep in mind that no matter what you do, this setup will never control as well as putting the thermostat in the head.

 

Beat me to it! BUT, I still had the cool story about the hack mechanic.

 

A viable alternative to the need of a "hole" would be to drill and tap the thermostat housing directly in front of the engine side face of the thermostat for a nipple and run a new small water line to a low-pressure area of the cooling system - perhaps its possible to add a "tee" to the heater core output line - this would serve the same purpose as mazda's solution to the stock remote thermostat at the front of the engine where a narrow coolant line is run to a low pressure side of the cooling system.

 

Sounds like it would work. However, I think I will just pull the thermostat, pull out that brass tab, drill the hole out slightly, and be on my way home in the next 30 minutes.

 

^^Should work.

Another viable alternative: Sell the M-tuned reroute, buy the BEGI spacer and a GM truck hose, and pocket the difference (or buy beer with the difference so that installing the BEGI spacer is tolerable).

I did mine while the engine was out . . . thank goodness.

 

Good catch- I didn't even open the picture he posted to see that the new thermostat still had the jiggle pin in it.

 

Having all the same issues. 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. 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...

 

When I put together my own reroute, I agonized over putting the thermostat remotely (so it would be easier to access for maintenance) or in the back of the head (so it would be exposed to the coolant in the head directly). I reasoned that I've had approximately one thermostat failure over the past 15 years and it wasn't even in the miata and I'd rather not have issues with it activating. Also, removing the coilpacks at the back of the head to go the COP route frees up a lot of space to access the rear thermostat housing.