temp spike

[SilverBulletES]

So I'm sitting at a traffic light today and I look down and my needle has climbed very close to the H!

A scary sight to me since I'm not used to my Protegs temperature gauge budging at all from a few degrees left of center (same thus far with the 600ish miles I've put on the Miata).

Also weird because I wasn't running the car that hard (and I have) and it was "only" 95 out (not bad for Vegas right now).

Anyway.... when I pulled away from the light the temperature gauge went quickly down (I watched the needle move) within 30 seconds.

So, could I need a new radiator or fan? How long can the needle stay near H before the car truly overheats? I reckon mine was only up there for a minute or less...

 

[kcbhiw]

Check the fan and check the sensor on the thermostat housing first and foremost - it's easy and free.

To verify the fan and wiring, with the key in the run position, remove the plug on the temperature switch located on the t-stat housing and short the wire to ground (using a short peice of wire). If the fan starts, it and the associated wiring is good. I'm not too sure on how to test the temp switch itself other than possibly process of elimination. Obviously, There might be an issue elsewhere. How old is the thermostat, itself? What's the quality of the coolant - does it look rusty? Is there a significant number of bent fins on the radiator by chance?

If the car ran that hot for only a minute or so, it's fine. Though, you need to diagnose the problem ASAP

 

[SilverBulletES]

Thanks a bunch Kevin. Will check all that....

 

[MiaTurbo]

As Kevin alluded to, it sounds like electrical. Once you started moving, and got airflow accross the radiator, it started cooling.

FYI: That fan switch is about $40. I broke mine when I was swapping motors :|

 

[SilverBulletES]

OK, here's the re-diagnosis. Radiator seems good, fan seems good, coolants seems good.

The "spike" happened again tonight and again this morning. Both times in much cooler weather. (Maybe this has happened before but it happens so quickly that I never noticed.) It seems to happen 5-6 minutes after starting a cold car. Needle begins to head towards H (but doesn't hit H or leave the "normal operation temp"? markings... for sure I get NO overheat light), hangs there for 15 seconds, and then quickly backs down to the normal position left of center-- where it remains firmly parked. (Even after I drove the car hard to be sure). So it's weird-- the gauge instantly recovers (instant being 15-20 seconds) and then is fine. It's almost like I have a faulty gauge that continues to (erroneously?) climb after the car is warming up.... then it settles back down to the true temp. Thoughts? Is it just a whack gauge?

 

[MiaTurbo]

possibly an air bubble in the coolant. The sensors are pretty high in the engine, so an air bubble could also cause momentary spikes on the gauge.

 

[SilverBulletES]

possibly an air bubble in the coolant. The sensors are pretty high in the engine, so an air bubble could also cause momentary spikes on the gauge.

Sounds like that.... but I ordered a $15 new OEM thermostat off eBay to be safe. Seems easy to replace off miata.net. At least will be a good learning experience.

My Protege is in the shop getting 3 electrical problems fixed under warranty right now....will pick up tomorrow. I asked the mechanic about the gauge thing.... he said it could be a sticky thermostat, which seems like another possibility.... so that's what I'm dropping 20 bucks to just replace. It's a 17 year old car after all.

It did it briefly again tonight on the way home from work.... I'm talking just barely up the scale. Then back down again. I put the car in neutral and the gauge went down even faster. But get this right..... once the car's running, the gauge doesn't budge from normal.

Anyway, thanks for the thoughts.

 

[MiaTurbo]

if the t-stat housing bolts have never been off, be very careful with them. They are steel, and bolt to an aluminum housing. they may be stuck. Be very careful...

When you put it all back together, fill with a 70/30 mix of water/coolant. What I normally do is drive the front wheels on ramps, and let the car run without the radiator cap (might be a good idea to replace it too..) for about 10 minutes. once you see a steady stream of coolant , and no air bubbles, you should be fine. If there is air, it will naturally want to rise up, so the car kjacked up will help get rid of it. Also if there is any, it will be present as a 'surging' in the radiator.. Put the cap on, fill the resevior, and go for a drive.

 

[SilverBulletES]

Thanks for the tips. Got the new thermostat. Will replace it, flush the radiator, and see if it makes a difference.

 

[SilverBulletES]

OK-- update. Last weekend I replaced the thermostat and put in a new one. Took all of ten minutes. No more temp spike -- always left of 12 o'clock now -- towards the C. For the record, I never overheated -- it just climbed high and stayed there a few seconds until it became unstuck. But I guess it was running hotter than it should once a run, unfortunately.

 

[MiaTurbo]

glad you got it fixed

 

[Mazdaspeedgirl]

I know I am late on this, but mine overheated when the thermostat froze shut a few years ago. I dropped it in a pot of boiling water afterward to confirm the faulty thermostat. Sure enough, it never opened up.

I also had to replace the water pump a little over a year ago. It did not overheat, but coolant was found dripping from the "weep hole" on the pump.

Big tip: if you are ever to replace the timing belt, for the love of God replace the water pump at the same time! (lol) I had to replace the water pump not 3000 miles after I replaced the timing belt!

 

[hustler]

btw, the temp gauge has a dead spot from just left of center to "H". Its not very accurate.

 

[drivethruecp]

Same thing happend to me today! I was driving and all asudden noticed my engine coolant gauge spiked all the way past H. It would fluctuate with these random paterns between normal to as far as it could go. So you would all def say it is the thermo? I drove it over 150 miles yesterday...and it was so random of that to happen. It scared the s*** outta me cuz I was on the way down the shore...so there was no turning back.

 

[drivethruecp]

Where is the fan switch!? It's not my thermostat...changed it.

 

[Pitlab77]

thermometer??? back of the head where the coolant exits???

 

[kcbhiw]

The thermoswitch (fan switch) is located on top of the t-stat housing.

The thermosensor (temp sender - green plug) is located on a housing on the back of the head just below the CAS.

 

[drivethruecp]

I replaced both my thermostat and the cooling/ temperature sensor ($80) right to the left of the air intake where the anitfreeze goes to the engine. I am still having trouble. When I drive my temp climbs still. I dont see any fan switch on top of the t-stat housing...would you mind posting a photo of it with an arrow pointing it out.. Do you think it could be this...and whats this about the thermosensor...is that what I already replaced? Its a brass thing that screws down and has a connector plug that connects two wires to it. My issue is that I believe the fans don't turn on. So my temp goes to H and stays there. All of three days ago I have never ever seen my temp go above halfway (right between C & H) Please help! I need my car for class and work...and already bought both of those parts. I need to be sure the next part I replace is the right one. My Dad is worried that I warped the head gasket or something...

 

[drivethruecp]

Bump! cuz getting rides to skl and work sucks asss

 

[kcbhiw]

I replaced both my thermostat and the cooling/ temperature sensor ($80) right to the left of the air intake where the anitfreeze goes to the engine. I am still having trouble. When I drive my temp climbs still. I dont see any fan switch on top of the t-stat housing...would you mind posting a photo of it with an arrow pointing it out.. Do you think it could be this...and whats this about the thermosensor...is that what I already replaced? Its a brass thing that screws down and has a connector plug that connects two wires to it. My issue is that I believe the fans don't turn on. So my temp goes to H and stays there. All of three days ago I have never ever seen my temp go above halfway (right between C & H) Please help! I need my car for class and work...and already bought both of those parts. I need to be sure the next part I replace is the right one. My Dad is worried that I warped the head gasket or something...

Yes, the thermosensor has two wires.

Since you didn't post what year car you have, I assumed you had an early NA. The 94+ Miata's do not have a thermoswitch as the fan operation is controlled by the ECU.

Have you checked that the fan is good? Unplug it and place 12 Volts across it while observing the proper polarity.