Hatrick10

we have a 2004 Mazda 3 hatchback and we are getting a check engine light and code is "coolant too cold " but temp gauge is normal midway between H and C and car seems to run fine

is this a faulty thermostat ? anyone had this problem ?

djs2571

can you give us the code #?
it could be a sensor, but if you have a lot of miles on it the thermostat could be stuck open too.

Hatrick10

thanks for the reply, don't have the code # as my friend an independent mechanic ran the code for us a while back, car has low miles 70k so maybe it is the sensor

thanks

Mark_ferguson77

I am very inspired with 2004 Mazda engines. It is very reliable and had Long Life as compare to others. what about you?

jp_fizzer

Hello, my '06 mazda 3 hatchback (50,000 miles) recently developed a P0126 code and the dealer has told me I need to replace the thermostat (which they quoted at $360 + tax). My concern is that the guage goes to the normal position within about 1-2 minutes of driving and the car will blow hot air in the same time frame. To me this does not indicate a stuck open thermostat or it would take much longer to warm up. In fact, it seems to me it is warming up too fast. However, if the thermostat was stuck closed, wouldn't the temperature guage continue to rise past the normal position? Also, after driving for about 15 minutes I felt the temperature of the coolant, it was barely warm. I'm not sure if that is usefull information at all as I am not sure whether the coolant in the resevoir would be expected to be hot/cold/warm? If I need to get the thermostat changed, I guess so be it. I just don't want to spend $400 if its not necessary or if the problem is something else. I am just confused why the temp guage would read normal, seems it should be either high or low depending on whether the thermostat is stuck open or closed?

thanks,
-jeff

djs2571

The book says the P0126 is a stuck open thermostat. The trigger conditions for that is the following:
ECT never exceeds 160F when the intake temp is above 14F and vehicle speed is over 3.7MPH

Basically the engine isn't warming up fully. i'm suprised the temp meter would go to a normal range... though it should be pretty much dead center in the full range of motion.

As for the overflow tank, this should remain barely warm, it only gets fluid sent to it as it expands out of the radiator. SO until the engine is warm it won't get any warm fluid, and the expansion of the coolant isn't a whole lot, i'm thinking maybe a cup of fluid that's warm mixed with the rest of what's in the tank.

$400 sounds quite high for a thermostat, if you're handy this is a good fix to attempt yourself. Though looking at the book it is only a hastle on the turbo model.

Good luck.

jp_fizzer

Thank you Dave, that is an awesome explanation for what triggers the P0126. It still seems strange though because the ambient temp is definitely over 14F and speed is over 3.7MPH so I wonder if it could be a problem with the ECT sensor? Is the ECT sensor the same temp gauge that displays the engine temp on the instrument panel? If so, then I am completely baffled because it definitely climbs to normal very fast (within 1-2 minutes).

One other thing that has me concerned is the temperature of my engine. After driving for about 15 minutes I used my IR thermometer to check various parts of the engine. At the rear of the engine the majority of it is around 200F but there are parts that are as high as 300F. 200F seems reasonable to me but the 300F has me very concerned. I felt the hoses coming into and out of the coolant overflow, one of them was cold and the other warm, which indicates to me that coolant is flowing, at least to the radiator. With the design of the water pump pumping out of the engine, I am not sure if it would even be possible for that return hose to be warm if the pump was not working.

This has me very confused, everything seems to be fine except for a P0126 code and my IR thermometer indicating a very hot engine.

I have done some simple work (brakes, starter, etc.) but this one looks tricky. It looks like the top two bolts are accessible (especially if I remove the tensioner pulley), but I am not sure how to get to that bottom bolt. I will take a look tomorrow to see what is involved in removing the radiator, if I can do that easily then the bottom bolt should be nicely accessible.

thanks for all help and advice,
-jeff

djs2571

From what you've said it does sound more like the temp sensor than the thermostat... i've used the OBDII data port and my engine temp was read at 192F-196F. I haven't looked with an IR gun, but the ~200F sounds just fine. One reason you may be getting 300F could be due to the emissivity of the material, or if you were close to the exhaust parts.
If the engine was actually running cooler, you'd see a drop in mileage too - not sure if you track that. In the winter on mine I get 28MPG average, and in the summer it's 32 (actual calculation, the trip computer says ~31.5-32.5 - not accurate.

To test the temp sensor, first you need to find it. The book has horrible diagrams, but it looks like it's on the drivers side of the car, pointed to the rear, and toward the engine block from the wire harness that is on that side of the block. It's a 2-pin connector with a white and a brown wire.
Resistance when at 68F = 35.48-39.20K
Resistance when at 158F = 5.07-5.60K
Resistance when at 176F = 3.65-4.02K
You have the IR gun, so you can get the temp that way. A multimeter is the second bit you need, and a third verification would be an OBDII scanner tool which should allow you to read what the computer is reading for the temperature.

The thermostat should start to open at 176-183F and be fully open at 207F - if you let the engine idle and monitor the temp with the IR gun, and feel the hoses to see when the coolant starts heading to the radiator, it would verify what's happening there too.

If you can do the starter, you can do the thermostat. The book says the tensioner pulley needs to come off, but nothing else - though the coolant needs to be drained too.

jp_fizzer

Thanks Dave, that is great detailed info on how to test the sensor, now if only I could find the darn thing. :-)

I actually borrowed my friends OBDII scanner/laptop, hooked it up and took it for a drive. The ambient temp was 55F, the air intake temp was 59F. First I let the car idle for about 5 minutes, the coolant temp got up to around 160F in about 2 minutes or so and then I took it out for about 15 minutes of city and highway driving. The coolant temp climbed and fluctuated between 168F and 174F depending on load and speed. I returned home and left the car idling and the temp started rising. I let it get to about 196F before I decided to turn the car off. I found it interesting that I could not discern any difference on the instrument panel gauge between when the laptop was saying 160F and 196F, it seems there should be some movement there. I let the engine cool down (took about an hour to get to 120F) and then turned the car back on and watched the laptop and instrument panel at the same time. There are 14 marks between cold and hot and it seems that each one represents approximately 5 degrees. It was around 130F at the first mark, then 135, 140, 145, 150, 155, 160 as it passed each subsequent mark. At 160F it gets to halfway between the 6th and 7th marks and stays there while the temp continues to climb. Is there something wrong with my instrument panel or does it get its reading from somewhere else or is this just the way it is designed to work? The only other temperature option to monitor (besides ambient, air intake and coolant) was something called the B1S1 Catalyst Temperature. I have no idea what that is but it is a very strange measurement, it gets up to rediculously hot temps (700F +) in a very short time and every time you touch the throttle it jumps another 20F.

On another interesting note, before I connected the laptop, the check engine light had gone out. I did not reset it with the computer ... honest! It pulled the codes and said that the status of the P0126 code was "stored". After driving it for a while and performing my various tests which involved starting and stopping the car many times, it was still reading the P0126 code as "stored". Then, the last time I ran the diagnostic, it came up with no diagnostic codes. I never intentionally pushed the "clear" button but perhaps I did without noticing because I don't know how it could just disappear like that?

As far as my mechanical abilities, I forgot to mention, all the work I have ever done (brakes, starter, etc.) was on a 1972 VW Beetle, probably the simplest car in the world to work on. :-) Changing the starter on my Mazda3 would probably be much much harder. I have never done anything on my Mazda3 or MPV.

thanks,
-jeff

djs2571

Good info on what you're seeing - though that made me go do some real work to see what's going on
See the chart below (more data in the pic attached) for where my temp indicator was as well as the engine temp. Mine also stuck at 6.5 ticks, and i also noticed it updated every ~10 seconds, you can see it 'surge' to different levels. This may be why it holds at one location for a wide range, so the drivers eye doesn't go to the gage moving back and forth when it changes temp - i've done that when it's warming up.

Ambient temp was about 36F, colder than your test, so it sounds like both our tests are pretty much the same temp rise.

inside fan set to min speed. 20mar2011 - 2007 M3GT, 41533 miles.

temp tick, temp (OBDII), time

cold 120 313sec
wide mark 126 364
1st narrow 131 420sec
2 135 ~470
3 140 528
4 145 590
5 151 648
6 155 700
6.5 163-180 838 sec
6.5 176 1100 sec

The check engine light may have gone off if the thermostat got unstuck, I haven't seen one fail, but if it did i'm sure it could come and go for a bit before dying completely... or if you poked around at the wiring and improved the connection on the temp sensor.

As for the catalyst temp, yes it's way high, think I saw mine in the 1200 range when doing a 0-60 run. Pretty sure that's built into the O2 sensor, we use a multi-wire heated version... and that's why those sensors are expensive, they handle a lot of heat & temperature shift in the exhaust stream.

I've got an excel file with my logged data, but it sounds like you're car is working fine at the moment. I'd keep an eye on the temp gage, and see if when the check engine light comes on, if the temp is at or below the 6th small tick mark - which is the 160F point.

djs2571

Oh, and here's the temp sensor - on the battery side of the engine, in line with the rear cam cover, and under a square black piece when looking at it from the front of the car.
The attached pic is holding the camera over the exhaust looking forward / left @ 45deg. It's a white & brown wire on the connector, toward the top of the spotlighted area.

jp_fizzer

thank you very much Dave, I was able to find the temp sensor after your great picture. So it seems that everything has returned to normal, it looks like the P0126 code only came up one time, when I was travelling at 60MPH and has subsequently cleared itself. I guess I will just leave it until it happens again.

I imagine you are right about the reason, they probably want it to stay at midrange (6.5 ticks) whenever the engine is within "normal" operating temperature. I assume it is designed that way but there must be a range (160F - ???F) at which it stays at 6.5 ticks and then some temperature where it continues to rise. Do you know what that temperature would be?

thanks,
-jeff

djs2571

I don't know the upper end, but i'm assuming in the 195F range, since i'm sure in the summer i've run around there and think it's the next tick higher. Then I don't know for sure, have to wait for warm weather to run that test.

Josue Santos

I have a 2007 mazda3 4 cylinder 2.0L with 125k now. i got my car about 3 years ago with 53k and recently as i was coming down the highway my check engine light came on and took it to Auto Zone and they diagnose my car with a PO126 Coolant Thermostat low operating tempature due to a low coolant level which is not true open or short circuit condition talking about air bags or having a faulty ECT sensor. they told me to wait and see if it went away which it does but then it comes again. my car is not stalling or anything temperature is normal midway for H and C. i just recently replaced my battery too and now my idling is a lil bit off i dont know if that has anything to do with it. does anybody knows what to do about this? should i replace my sensor? or the whole thermostat?? anybody? help would be much appreaciated

jp_fizzer

Hi Josue, I had a similar problem, P0126 kept coming on and going off. I left it for about a year after my posts earlier in this thread but then it came on and stayed on so I figured I would try changing the thermostat and see if that solved the problem. Sure enough it did. Really wasn't that hard of a job and the part was cheap ($45) from Mazdapart (part #LF7015170). It seemed much better quality that the thermostat that came out. You could probably leave it and wait until the CEL stays on but I probably should have just done it right away as I wouldn't take the car on long trips and was constantly watching the temperature guage worried. If I would have known how easy and cheap it was to do, definitely would have just done it right away.