My 90 has been running/driving great with barely any fluctuation in the temp gauge, even after 8 autox runs in 90+ degree temps. However twice now - both at the McDonald’s drive-thru - the temp gauge has climbed very near the “H” mark while waiting in line.
I’ve jumpered the fan & made sure both it and the relay are good. Ive jumpered across my new thermoswitch, and confirmed it’s grounded, yet the cooling fan has never turned on. At what point(ish) on the temp gauge should I expect the fan to kick on?
The coolant temperature gauge is a dummy gauge, only goes above halfway when you’re on the verge of overheating.
IIRC the fans on my 92 kick on when the coolant hits around 210 degrees.
In reply to ShinnyGroove :
I thought the early NA6 had a real gauge? It seems to vary a bit, especially once it starts climbing past normal.
Pete Gossett said:
In reply to ShinnyGroove :
I thought the early NA6 had a real gauge? It seems to vary a bit, especially once it starts climbing past normal.
They’re heavily damped around the 210F area, kinda like the rotary ones that indicate your engine is done once they move. There may be a “fix” for that but that is one of the reasons that my 90 is getting a proper gauge.
Ok, so if the gauge can’t be trusted, I’m not sure how to find out if my cooling fan will kick on when needed - especially since it didn’t today. Yet it seems to test ok?
It's the coolant switch that's right on the top of the thermostat housing, single wire. If you've grounded that single wire and it turned on, replace the switch. Should be less than 20 and take about 5 minutes to do.
If the 90-93s are dampened around that point, it's not much. I routinely see the gauge fluctuate a bit around the middle on my 91. Even on the 94 it seems to match the aftermarket guage fairly closely.
In reply to WonkoTheSane :
The switch is new & I’ve confirmed it’s grounded. I’m just not sure how soon after the needle climbs past 1/2-way before the fan should kick on?
I think there’s a FAN jumper in the diagnostic box, you should be able to jump it and see if the fans come on. If that works, and the temperature switch is confirmed good, then you should be OK.
In reply to ShinnyGroove :
The fan works & the switch is new. I’d expected it would have kicked on when the gauge climbed so high, but it didn’t. I’m hoping another NA6 owner might be able to tell me whether it should have kicked on by that point, or if it doesn’t until the needle is right at the “H”?
Quick MS Paint diagram showing where my '91 usually operates. 90% of the time, the gauge rests on the lefthand orange line. Intermittently, the temp gauge will float up off that line, sometimes getting all the way to the right most line before the cooling fan kicks on. It moves most aggressively when sitting at traffic lights after getting off the highway. My particular Miata has a thick all aluminum radiator, a single aftermarket pull through fan, and IIRC the PO said it had a 180 or 185 degree thermostat. Otherwise, it currently has stock hoses / routing, and possibly original water pump (I have a replacement and new lower rad hose, but haven't felt up to draining the system yet). Personal opinion here, I feel generally comfortable with how it has been operating, though if the gauge climbed higher than the right hand line I would definitely be concerned (since that would be beyond normal operating parameters). In the long run, I intend to lower under hood temps and improve instrumentation to be safe (assuming I keep the car).
In reply to MrRobogoat :
Thanks, that helps!
Mine generally is at the same point on the left at a hot idle, or just between it and the “thermometer” when it’s really hot out. Yesterday it was a bit more than a needle width before the thin line before the “H” in the McDonald’s drive thru. That’s when I turned the heater on max, and the gauge remained there for about 5 minutes. As soon as I was a 1/4-mike down the road it was back to the normal location.
It sounds like the fan likely would have kicked on if it had gotten much hotter, but with no frame of reference I was worried of it overheating.
I would've expected the fan to turn on at that point. That seems to be rather high.
How new/good is the thermostat? The thermoswitch for the fan is after the thermostat and the temp gauge is getting its reading from a different place. That might explain what's going on.
In reply to BoxheadTim :
Thermostat is new, as is the water pump, hoses, and aforementioned fan thermoswitch. The radiator is old, but the temp is fine everywhere besides the McDonald’s drive thru - though I’ve not yet tried any other fast-food places to see what happens.
Sorry, traveling yesterday so I couldn't GRM at all :(
That was going to be my suggestion, try BK :)
If I recall, the fan switch is somewhere around 205-210. If you're relatively comfortable with a meter, check the continuity between the thermostat housing and the engine block, it's possible that corrosion around the two bolt holes has prevented the fan switch from properly grounding out?
My 1.6s always responded like MrRoboGoat's.
The gauge is totally legitimate. If it's moving, your cooling system is struggling. If it's not, everything's good. Far from a dummy, it tells you exactly what you need to know without being difficult to interpret. Normal is just below 12 o'clock for US cars. Interestingly, Canadian cars have the normal just above 12 o'clock. This tells me that Americans are scared of overheating while Canadians are scared of freezing to death 
You really shouldn't ever see it climb off normal. As far as we know, it starts to move at 230F. I think MrRoboGoat has a lower efficiency radiator and an unshrouded fan which is causing his car to run a little warmer.
If the fan isn't turning on with a 1.6, there's a really simple test. Unplug the wire from the thermoswitch and ground it. Does the fan turn on? If yes, then the problem is the switch. If not, the problem is in the fan or the relay or the fuse. Only the driver side fan will run, the other side is triggered by the AC. It's possible to do a fairly simple rewire to run the AC fan along with the primary to improve cooling if necessary.
Thermoswitch operates between 194 and 207 according to the manual. Below 194, it's open. Above 207, it's closed. In between is apparently a quantum state of some sort. But in normal operation, the fan will be cycling before the gauge moves.
In reply to Keith Tanner :
Thanks Keith! The fan operates when I ground the wire, and I verified the thermoswitch & thermostat housing are grounded, so it sounds like my new switch is either bad, or the wrong temp range.
IIRC I got it from eBay. Do you guys sell the switch, or should I try a dealer?
We don't sell it. Dealer is always a solid option, but I haven't heard of problems with bad aftermarket units before. The temporary workaround for a car with a bad thermoswitch is to just ground the fan wire so it comes on with ignition.
You can also hit the AC button to turn on the AC side... I did that for a summer before I got around to installing my new fan switch.
In reply to WonkoTheSane :
I still need to rehab my a/c, or just remove it completely, though I’m still leaning toward keeping it.
Keith Tanner said:
It's possible to do a fairly simple rewire to run the AC fan along with the primary to improve cooling if necessary.
Since it came up in this thread... I have a no-A/C car, and I installed the passenger side fan and wired it in parallel with the primary fan, for extra cooling capacity. Now that I'm older and wiser, I realize I probably didn't help anything for my application (80% track/ 20% street), and I didn't really have a problem in the first place, but I've been running this way for two years with nary an issue.
Recently someone told me that I shouldn't have done that because it draws too much current off the relay, and that there's a different way to wire it. My question- should I even bother? Trying to buck my past pattern of fixing things that aren't broken.
WonkoTheSane said:
You can also hit the AC button to turn on the AC side... I did that for a summer before I got around to installing my new fan switch.
But that "turns on" the heat exchanger in front of the rad, which pumps heat into the air and decreases the efficiency of the radiator. I know some of the guys with MSMs were pulling the plug on the compressor to force their fans into high speed mode - but in the case of an earlier car, it's probably easier to just do it right.
ShinnyGroove said:
Keith Tanner said:
It's possible to do a fairly simple rewire to run the AC fan along with the primary to improve cooling if necessary.
Since it came up in this thread... I have a no-A/C car, and I installed the passenger side fan and wired it in parallel with the primary fan, for extra cooling capacity. Now that I'm older and wiser, I realize I probably didn't help anything for my application (80% track/ 20% street), and I didn't really have a problem in the first place, but I've been running this way for two years with nary an issue.
Recently someone told me that I shouldn't have done that because it draws too much current off the relay, and that there's a different way to wire it. My question- should I even bother? Trying to buck my past pattern of fixing things that aren't broken.
Fans have a big start-up surge, so you're more likely to blow a fuse than overheat a relay. If it's working, I'd leave it. If you put in a stronger fan in place of that AC fan, then you'll want to look at upgrading the wiring.
You still need fans on the track, the amount of airflow through the nose is surprisingly small. You definitely need fans on the street.
Keith Tanner said:
WonkoTheSane said:
You can also hit the AC button to turn on the AC side... I did that for a summer before I got around to installing my new fan switch.
But that "turns on" the heat exchanger in front of the rad, which pumps heat into the air and decreases the efficiency of the radiator. I know some of the guys with MSMs were pulling the plug on the compressor to force their fans into high speed mode - but in the case of an earlier car, it's probably easier to just do it right.
Right, but if you find yourself overheating because the primary fan didn't kick on, it's a far sight better than doing nothing :) My fan switch decided to die between run #3 and #4 @ an autocross where we did back-to-back runs. I noticed that he gauge was on the "H" when I was lining up for my second run. Unless you're in an excessively hot environment or on the track, it seems like it has ample capacity for puttering around town in this mode, which is why it took me so long to fix my fan switch. I was only driving that Miata once every week or so for 12 miles at a time :)
