The car is a '99. It use to run like a champ in the summer here in Texas with the AC on. No longer being stock, that has changed. Car has a rotrex supercharger (no offense...) with TDR's intercooler. Over time I have added an old style FM radiator, as well as their fan kit and a coolant reroute. Somewhere along the way, the car's cooling system has been hindered, and as the weather is starting to warm up, it is becoming evident. First noticed several days ago when my reverent built MS started flashing my check engine light. This occurs when the computer sees ~210*F coolant.

Pulled the laptop out and drove around looking at numbers. Roughly 70*F outside and the car will run 205*F cruising @ 60mph on the highway. Put the car under any stress and it sees 210+. These numbers by themselves aren't necessarily out of the miata's operating range, but for these circumstances, I believe they are. And adding another 30*F outside through the summer, and kicking the AC on, I am thinking I will have a real problem.

With the car sitting idle, it will go up to 200*F, kick the fans on, and over the course of 5 or so minutes, retreat back to 190*F. This seems to be quite a bit longer if I recall correctly than when everything was stock. Decided to pull the fuse for the fans and go for a cruise, and all my numbers were the exact same. So basically at cruise on the highway, my fans are on 100% of the time and doing nothing as far as cooling.

I am running the stock belly pan. My coolant mixture is ~60% water to 40% coolant. 16PSI radiator cap. The mouth of the car is shrouded with the pieces from the intercooler kit. Alot more air is going through my heat exchangers as opposed to when it was stock. Water pump was replaced roughly a year ago.

Anyone have any ideas as to what my problem could be here? Possibly a flow restriction somewhere? Anyone direct me to possible trouble shooting something like that? All thoughts would be appreciated.

Thanks,
Luke H.

 

What coolant reroute did you do? It sounds like blockage. Is your T'stat opening all the way? Is T'stat in back of head or remote?

 

BTW, for a reference point, my water temps are running ~180-185°F. I'm using the BEGI spacer/Kia waterneck/GM truck hose reroute. Stock radiator and shrouding, but no intercooler for the moment. I would think yours should be around this temp also.

 

That way too much coolant, but this should work.

You say "the mouth is shrouded". Does this mean you have the TDR plastic stuff or did you totally shroud the radiator to the bumper mouth so that air is forced to go through the radiator? Putting plastic bits on there to "direct air" doesn't work, it must be sealed.

A fan shroud hurts cooling when the car is moving.

 

Best cooling is 10% coolant and 90% water, correct me if i'm wrong.

When it was 110* outside my temps were around 190* all the time. I had the begi reroute, bigger radiator with no shrouds and no ducting and I still had low temps.

I'd check the stat like hornetball has suggested, just to be safe. How thick was the old style FM radiators?

 

100% water is best, maybe some water wetter or DEI stuff to lube the pump as I've heard but not an expert on that.

I ran one 103*f day for about 40-minutes tucked behind a Panoz at 250whp and never went north of 199*f on the water.

 

Track car yea, the 10% coolant just helps keep corrosion out of the system like you said.

His problem sounds like a clogged system to me

 

M-Tuned coolant reroute. It hasn't been in even a year yet, so hadn't thought of the thermostat being stuck. Had a friend's shop install it. Would it be possible that the original thermostat was left in also? The stock thermostat is in the back of the head, correct?
Thanks,
Luke

 

No, the stock thermostat is inside the fitting which attaches to the front of the head, which is the source of the prolem which the reroute corrects.

Thus, assuming that there is no longer a hose running from the front of the head to the upper radiator pipe, the stock thermostat is no longer in place (or if it is, it's een capped off and is thus irrelevant.

*disclaimer: The key on my keyoard etween V and N has stopped working. Imagine that letter existing in the places in which it is oviously asent.

 

EXACTLY what I suspected.

Luke, when you were stock, you probably noticed that little bleed line in the stock T-stat housing. Costly little bandaid. You can bet Mazda had a good reason for it. Why was it there? So that the thermostat would actually see the temperature of the water in the block and head. If not for that bleed line, the temperature seen by the T-stat would be quite a bit less than actual.

Enter the M-Tuned reroute. Like the stock system, the T-stat is remote (even more remote in this case). Is there a bleed line? Is it open and functioning? If not, there is no chance in h*** that the T-stat is seeing the real water temperature -- in your case, you seem to be getting about a 15° offset.

 

Just to satisfy my own curiosity, I checked on the M-tuned reroute installation instructions. The M-tuned reroute supples a 190° T-stat that has a bleed hole drilled in it (see pix). It is important that the bleed hole be open and located at the top of the housing for air bleeding and T-stat response. I think the first thing to do here is check the T-stat. This could have been easily missed by a flat-rate mechanic in a hurry.

I personally prefer having the T-stat in the head. That's really how the cooling system is designed to work.

 

I had talked with my friend who had done the install on this a couple days ago. He ordered me a cooler t-stat, and said to make sure the little hole is at 12 o'clock, so I assume it was done correctly. Hadn't installed it yet, not being sure that this would resolve it. Reading what you said, perhaps it might...?

Now with the thermostat being remote, would it really hinder the entire cooling system as much as it has in my case? In my logic(which isn't very reliable), it seems that this would simply delay the thermostat going full open, which it eventually should. Would the water be cooling so much from the back of the head, to the thermostat, that the thermostat isn't going full open?

Will pull it apart after work this evening and double check the positioning.

Edit- Should it simply be needing a cooler thermostat... Why isn't everyone having this problem who uses the m-tuned reroute?

 

This, no doubt, provides the most optimum flow path, and best replicates the original OEM cooling system design. When the thermostat is located at the back of the head itself, all of the bypass water going to the heater core flows directly past the wax element.

Placing the thermostat aft of a spacer located at the back of the head is the most common arrangement in DIY-style reroutes, and is the design used by the Bell system as well.

 

Based upon the decent radiator, etc. and the mild days we're having, it seems most likely that this is a control issue rather than a genuine lack of cooling issue. But I can't really answer that question -- a lot of people use that reroute. Is it possible to pull out the thermostat for a test run without causing housing leaks? If so, that would definitely tell you whether there is a problem with any other part of the system.

If it is an offset being caused by the remote mounting, then a cooler thermostat should take care of the issue.

 

I just recently picked up a scan tool for home use that I've been messing around with on the mazda. I was surprised to see that my ect readings were also staying around 199-205F once fully warmed up. It's also a 99 but with a larger aluminum radiator, new water-pump and stat with no belly pan. The cheesy temp gauge on the I/P shows it right in the middle if not slighty less. It never climbs above halfway even in 90F weather.

I don't think that 200f is anything to be concerned about, but in Michigan it's like 32f outside and I'm seeing these temps.

I have always just went off the I/P gauge and never thought twice about overheating but I'll definitely be paying more attention to it now.

 

Well I pulled the thermostat housing apart. The stat was cocked to about 11 o'clock. Also, there is a strange wear mark directly infront of where the air opening in the thermostat is on the housing. This is on the half thats closer to the radiator. This new thermostat is also offset slightly lower.
Left is new stat, middle is old stat, right is the housing half that is closest to the radiator with the weird wear mark...

 

I still think it's a ducting issue.

OP - when your temps go up to 210*f, do they seem to stay/hover around 210, or do they go to 210, then back down to 190, then back up to 210.....forever oscillating???

 

They would go to 210 when under load and back to 205 when cruising. No oscillation. Just correlates with my driving.

Put the new 160* thermostat in and so far it looks good. Let it warm up on an incline and burped it, then took it out and hammered on it shortly and never got above 195. Will do some more driving and see how it goes.

The "ducting" that came with the intercooler kit forces more air through the mouth then when things were stock, so I am pretty confident in ruling that out. Along with running hot even when sitting still at idle and both spal fans pulling.

 

Couple things.

a) the ducting. I have looked at the trackdog instructions before but it's been a while. As mentioned by others, they need to actually be sealed as much as possible so that all air is forced to go through the heat exchangers. Then your intercooler needs to be sealed to the radiator. The basic goal is for all air entering the mouth to go through every heat exchanger into the engine bay because you leave it no choice.

b) Radiator fan shroud. Do you have one? If so you should remove it, and attach the fans directly to the radiator. All it is doing is creating a huge air dam at speed, obstructing airflow through the system.

c) your fans should easily keep the system cool at idle. If they are not, then either your radiator is losing efficiency or you've got poor coolant flow for some reason or your fans are borken. Easy to test the last, and I assume they are not.


I have gone from FM Stage II airflow kit (two spal fans + shroud sealed to the back of the radiator) to just the driver's fan attached directly to the radiator. After mostly sealing the airflow paths the car now runs cooler at highway speeds than it did before. The single fan has no trouble pulling the coolant temp back down to 195 when the ecu kicks it on at 204.

 

Dear Sir,

When it comes to ducting a car miata, "more of it" does not equal "all of it".

And

When it comes to ducting a car miata with an intercooler added, "less than all of it" is roughly equivalent to "none of it".

And, if changing your thermostat from 185* to 160* really did drop your temperatures from 210* to 195*, then your temp gauge is reading incorrectly.