Funny logger temps.. Guru's Look here!

[JLangevin]

Ok, so because of another problem, I decided to start logging my car closely this past week when I noticed something odd. The ECU Coolant Temp readings are all over the place... but mostly very hight.

Here is some background; The car jumped timing about 10 months ago, and obviously had a new head (mine was toast) and gaskets all around. The temps this summer according to the dash gauge have been very nice, even with the A/C on and sitting in traffic on a 110* day. The temps never rose about the half way mark, and if they even started to move, the needle would drop quickly. Even when I would get on it, the temps would never really move, and sat most of the time just below half on the gauge...

So, when tracking my O2 this past week, I noticed the cars temps would read as high as 222*f WTF - Whats even more funny is that the cars dash gauge was sittle just below half when this happened. The logger has showed temps all over the place, from 199* to 222* and in a matter of 1-minute could rise 15* then drop back, and rise again. So, here is what I did.

-Radiator very clean, no deposits and only a couple months old
-Flushed coolant (was extremely clean, not a spec of deposits)
-Replaced Thermostat (factory 180*)
-Checked fans (both come on when AC is on)
-Pressure checked (Radiador cap was bad, replaced)
-Purged air from system
-Pressure cleaned the AC and radiator

So, yesterday I button it all up from the freshened system, and go for a drive, its rougly 100* outside, and the car rises to 203* in a matter of 2 minutes, and stays there, sometimes jumping to 206 or 210, then back to 203.... WTF WTF WTF - Ok, now Im pissed... why isnt the dash gauge showing this? Then I remembered that the ECU and gauge have their own sending units...

Is it possible that the ECU sending unit is bad? I had one go bad in my Camaro before and where as my dash gauge showed damn near 240*f at times, my Autometer showed 190*f. I know over time (11yrs) sensors can get out of spec. Does this sound like my case? Whether is 60*f outside (morning) or 105*f (way home from work) the temps show the same, 203-222. I dont get an engine lights for temps, and I do not have a thermal laser gun to test the water neck for temps.

Here are some pics from my logger. You can see in a matter of a minute, it has fluctuated quite a bit, and this is while on the freeway. Yet, the dash gauge never moved. On the logger pic, the low was 203 and the high was 222. AS you can see on the gauge to the left, in both pics, it wasnt reading the same temps.

 

[bmwisthekey]

I'm not exactly sure if anyone has figured out how the factory temp guage is supposed to read according to certain intervals on the gauge ( there are no tick marks on the gauge either which makes it kinda difficult)

My guess is that the 20 deg variances you are seeing on the logger would barely be enough to change the needle position on the factory gauge, example (200deg on the gauge could read just a smidge below exactly halfway and 220f might just ever so slightly go to the exact halfway point on the gauge.

 

[JayRolla]

Yes you are right. The factory gauge is not sensitive enough to change. Ive noticed when a radiator hose blew I was at 230 and the factory gauge did not budge but after that it started to go up.

 

[JLangevin]

This sucks, I mean. I dont know where to go from here. With the cooling system being practically brand new, and the pump good, presurizing, no leaks, good compression, etc... is it still possible that the ECU sending unit could be bad? I mean...

When I was purging the system of air, I noticed that with the radiator fill neck cap off and idling the logger would soar right past 180, then 190, then 200, then 206 before I saw any coolant flow in the neck... the fans also didnt come on when the logger hit around 210... if the ECU sending unit is off, I have no idea where Im looking at... if 206 is really 180ish, then thats 26* off... when is the first fan supposed to come on?

 

[JLangevin]

Another thing I noticed is that in the manual, it says to make sure the jiggle valve is pointing "up" in the housing... I dont recall checking, I just put it in with the new oring and let her fly... I didnt even check if the old one was pointing up... would this have that much of a difference? Whats that got to do with flow? Never heard that before actually... insight?

 

[donmagicjuan]

It's true that the stock temperature meter is notoriously unresponsive in the middle of the range. Many people have reported temps upwards of 230F on their loggers with the stock meter holding rock-solid at the halfway mark. My car behaves very similarly to how you describe yours (after your changes), so I would not worry about the coolant temperature sensor.

Just my .02...

 

[bmwisthekey]

Yes the jiggle pin should be up(on a 1g) and pointing torward the rad hose on a 2g because it sits in there sideways. If the thermostat is installed backwards, it would have to wait for the coolant in the lower radiator hose to get up to temp (180) before the thermostat opens, when installed correctly once the 180f is reached inside the water neck ( engine side) then the tstat opens and the coolant flows into the lower radiator hose and gets pumped through the radiator

 

[JLangevin]

ITs quite strange that either the lower OR upper hose would both be in contact with the Tstat.... but, having it installed upside down or sideways WOULD effect my temps?? I will check it when the car cools a little.

You are saying that your car shows the same coolant temps with your logger? I would be worried seeing as my car does it too even in cool climates. A fellow local DSMr only shows around 190-195 on very hot days, and even has a front mount and stock cooling system pushing about 350hp.

 

[bmwisthekey]

I installed mine in wrong and didnt catch it for quite awhile heres a link to an old post i made about it, defiant gave me a good reply

http://dsmtuners.com/forums/showthread.php?p=1567348#post1567348

 

[donmagicjuan]

Actually, I missed the part in your post that said you are still seeing temps as high as 222F. That's a bit on the high side, especially if you don't have a FMIC. I have a large FMIC with no ducting (yet), and I see roughly 203-210 on the highway. Those temps were logged with an air temp of roughly 80F.

Coincidentally, the fan will kick on at a logged temp of 203F when the car is just warming up.

 

[bmwisthekey]

The spring on the thermostat should be on the engine side ( opposite the radiator hose side)

 

[bmwisthekey]

I guess you could check the coolant temp sensor, unplug it , plug it back in make sure its not loose. See where that gets ya.

If that didnt help, there is a procedure outlined in most manuals how to test the coolant temp sensor, involves checking the resistance of the sensor prongs at cold engine temp, and operating temperature

 

[JLangevin]

I installed mine in wrong and didnt catch it for quite awhile heres a link to an old post i made about it, defiant gave me a good reply

http://dsmtuners.com/forums/showthread.php?p=1567348#post1567348

Your post mentions staying too cool, my car has no problems warming up, and does so rather quickly... as for the thermostat not being for cooling, thats not entirely true... its also the thermostats job to keep the coolant in the radiator long enough to cool it down... those who remove their thermostat do see overheating problems as well.

I know well about cooling systems, I just dont know if I truely have a cooling issue, or a faulty sending unit.

 

[JLangevin]

I guess you could check the coolant temp sensor, unplug it , plug it back in make sure its not loose. See where that gets ya.

If that didnt help, there is a procedure outlined in most manuals how to test the coolant temp sensor, involves checking the resistance of the sensor prongs at cold engine temp, and operating temperature

You may have misunderstood me, Im talking about the jiggle pin on the top of the tstat, not the spring. The Thermostat will only fit in one way anyways, its impossible to installt it backwards...

 

[bmwisthekey]

In my post i only noticed something outta the ordinary while driving in cold weather conditions, wouldnt get up to operating temp, i almost froze to death because i couldnt build up enough heat for the heater to get warm. It did warm up ok in warm weather and never got too hot. I know the jiggle pin is on the opposite side of the spring on the thermostat. I know 1st hand that the thermostat can be installed backwards i did it myself and yes it fit in the housing.

However im not totally familiar with the 2g thermostat housing/water neck , the 1g tstats dont have an o-ring, so if it cant be installed backward on a 2g someone chime in.

 

[JLangevin]

On the inside of a 2g water neck, it immediated bents at a 90* angle and points down, its also tapered on the inside to smooth water flow... there is not enough room for it to fit. What I need to know is what the normal logger temps should be... whats too cold, and whats too hot?

 

[donmagicjuan]

If you have a Haynes manual, try performing the check of the engine coolant temperature sensor in accordance with section 6-9. It basically consists of checking the resistance across the terminals while heating the sensor in a pan of water with a thermometer.

 

[JLangevin]

No Haynes, I have a Chiltons which by far, is quite vague with diagnosis procedures. What is normal for the logger to see? Both on freeway and traffic? What do you see?

 

[donmagicjuan]

My numbers are likely a little above normal with my FMIC, but as I mentioned I usually see 203-210F on the highway. I think it's usually in that ballpark in traffic as well.

I'll go take a look at some of my logs from before the FMIC on the laptop and edit to include those numbers as well.

EDIT: Well, with a virtually stock setup and air temp of ~75F, it seems like it was pretty normal for me to log temps of 200F on my WOT runs. I'm not sure if that helps at all, but I would definitely still check the sensor to be sure.

 

[JLangevin]

Thanks for all your help, since my last post, here is what I did...

-Checked T-Stat (It was sideways, corrected the angle)
-Refilled coolant and added Water Wetter
-Started the logger, and the car

Car started logging ast 150*f, 160, 170, 186 (stat has not opened) 195, 199, and at 203-206 I got a whirpool in the radiator neck.... so to me, that means 206 on the logger is really 185ish... then, at 213 on the logger, the first fan turned on, then the temps in a matter of 20 seconds, dropped back to 206...

Can someone verify the stock cooling fan temp? I am leaning towards a faulty sending unit since the thermostat would have definitly opened before 203... sure, the stat doesnt COMPLETELY open at 180, but by 190, would have.. So that difference in the logger and tstat operation leads me to believe the unit is off... now if someone can verify the temp the cooling fan turns on, I can triangulate that information with the other data and think I have found my culprit... (yes, insert cheesy cool smart sounding lingo here)

 

[donmagicjuan]

You can't diagnose a faulty temperature sensor in this manner. The ECU is going to start the fan when it sees a value from the sensor that exceeds the setpoint. It doesn't matter if the actual coolant temperature is 190F or 490F when this happens; the fact is that your fan will always kick on when your logger reads 213F. That is the value that corresponds to the voltage setpoint in the ECU. The only way to tell if the sensor is reading inaccurately is to track its resistance against the table of values for known temperatures.

EDIT: Sorry, I should have elaborated slightly. Your logger displays temperature based on the reading from the engine coolant temperature sensor, which is the same device used by the ECU to control functions such as the fan operation. The setpoint for the fan is stored in the ECU, so the calibration of the temperature sensor has no bearing on the value you see on the logger when the fan turns on. The coolant temperature sending unit operates the meter in the dash.

 

[JLangevin]

I think I see what you are saying... if the sending unit was showing a hotter value than is actual, then the fans would turn on prematurely, rather than late...

I would love to diagnose the sending unit, but which unit does the fan and ECU get operated by? The smaller or larger unit in the thermostat housing? According to Chiltons, there is a fan control switch located on the radiator, but does not tell me if thats the NT or Turbo model.

No one has yet told me when the fans are supposed to turn on, yes, a predertimined voltage, but also that voltage relates to a temprature. Has always been that way in every car I have built. For instance, in order to keep my 480whp Camaro cool, I needed a larger radiator, 160 thermostat, and 170 fan switch.

I need this value turned into a temprature. Bottomline, I know that the fans are to turn on well before 213* by engineering design. No engineer in their right mind would set the thermostat to open at 180, and the first fan to turn on 33* later... So, tell me the proper way to diagnose this, since there isnt even a Cooling Tech section.

 

[donmagicjuan]

I think I see what you are saying... if the sending unit was showing a hotter value than is actual, then the fans would turn on prematurely, rather than late...

Yes, that is right.

The only thing the turbo cars have is a couple relays to control fan operation. The signal to actuate these relays comes from the ECU and is based on the output from the temperature sensor. I'm not sure about the N/Ts.

Here's what I think. You said when you observed the car warming up, the temperature log rose to 203-206F and held steady. I would assume this correlates to your thermostat setting of 180*. In that case, the fan kicking on at 213F on the logger would be roughly 190F actual. The temperature sensor for the ECU is the larger one mounted on the back of the thermostat housing. If you want to check it, I can give you the resistance values that I have from the Haynes manual (if you don't already have them).

 

[JLangevin]

I dont have them, Chiltons doesnt provide them... if you could also relay to me the proper test points... Im assuming its probaly resistance between prong and copper body? I will need to test hot and cold based on your previous post?

 

[donmagicjuan]

Place the sensor probe in a pan of water with a thermometer and connect an ohmmeter between its terminals (only 2). Heat the water and compare the resistance readings on the ohmmeter with the values listed below:

32* - 5300-6700 ohms
68* - 2300-3000 ohms
104* - 1000-1500 ohms
176* - 300-420 ohms

These values are actually under the intake air temperature sensor resistances, but since they're the only values at the beginning of the chapter, I believe they are the same for the coolant temperature sensor. I'll double-check to make sure they're correct.