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Bad Coolant Sensor?

WaRrIoRs16

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Joined
Mar 23, 2008
Messages
373
Location
Ferndale, WA
When I start my car, the coolant temp will slowly rise, then at 127* it jumpts instantly to 212*. It remains there until my car is off and and has been completely cooled down. It does that every time. Also occasionally my temp in the gauge will start to increase pretty fast and will make it about 3/4 the way up on the guage. At this time, my coolant temp still reads 212*.

Are both the sensors going bad? My coolant is full and my heater blows hot.
 

Galactica

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Joined
Aug 23, 2011
Messages
103
Location
Beaverton, OR
Sounds like a bad ground that increases resistance with heat. /ubbthreads/images/graemlins/dunno.gif
 

Barnes

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Joined
Feb 9, 2003
Messages
6,249
Location
Richland, WA
Does the car start fine? Most common symptom I see from a bad coolant temp sensor is the car taking a LONG time to start when it is cold. Like 20-30secs of cranking.
 

WaRrIoRs16

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Joined
Mar 23, 2008
Messages
373
Location
Ferndale, WA
Where should I start looking for a bad ground? The car starts right up first crank, but it does have a rough idle until it warms up. I realized I have an extra DSM thermostat housing, so I'm going to try swapping in those sensor and see if it makes any difference. Thanks for the replies.
 

mikus

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Joined
Jan 11, 2007
Messages
2,763
Location
Aurora IL
^ infinite resistance will cause a -40 or something reading and thus the hard start condition. Sounds like OP has a way to read output so that condition would be apparant.

I had a sensor start to give wonky output recently, including skipping around -- but it wasn't consistent like you're describing. Unless wiring is really suspect, sensors are cheap & easy. There's a direct match replacement for like $20 at auto stores if you get the partno.

I believe coolant gauge and sensor are isolated BTW.
 

WaRrIoRs16

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Joined
Mar 23, 2008
Messages
373
Location
Ferndale, WA
Well I swapped all three sensors on the thermostat housing and had the same results. Started to warm up from 109* and right at 127* it jumped instantly to 212*. Only thing I accomplished was that I somehow made my dome light not turn on anymore.
 

desant78

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Joined
Jun 23, 2010
Messages
732
Location
Clarksboro, NJ
when the car is off what is the temp?

Also...the sensor does need one wire that goes to the ecu..and one that goes straight to ground. On 1662, as the manual calls, it was a black wire, but did not go to ground /ubbthreads/images/graemlins/frown.gif so that gave me trouble for a very long time.

Not sure if it helps but here is some random info

At 68F resistance should be 2.45 Kilo-Ohms (+- .24)
At 176F resistance should be 296 Ohms (+- 32)

^dsm 1g Manual as a reference. Maybe check resistance from leads to ecu when problem occurs? Good Luck!
 

Barnes

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Joined
Feb 9, 2003
Messages
6,249
Location
Richland, WA
Well, if you need an ECU or something to swap out, let me know.
 

mikus

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Jan 11, 2007
Messages
2,763
Location
Aurora IL
I'm pre-caffeinated so might not be thinking this through right, but what if the thermostat was sticking closed then popping? Someone that remembers sensor position relative to flow chime in -- not sure if this holds water... ha ha
 

WaRrIoRs16

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Joined
Mar 23, 2008
Messages
373
Location
Ferndale, WA
Well the other morning it was roughly 55* outside and my temp was at 76*. It warmed up to 127* and shot straight to 212*. Looking at my logs, early last week my coolant temps were normal, they did not have any jumps over two or three degrees all the way up to 192*. I can't think of any changes in my car since then besides my CEL from my knock sensor. I cleared the code and let the car warm up and it was still doing the funky jump 127* to 212*.

I did have a TPS CEL within the last two weeks at some point. I cleared it and it hasn't came back. It was acting weird, when I pressed the throttle the TPS would not go up linearly but rather jump around. Since I adjusted the sensor, it has behaved normal. I guess I will try and get a different TPS sensor. My knock sensor should be in tomorrow. I will have to check out the resistance on the sensors tomorrow and see how that looks. Thanks for the input.
 

broxma

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Joined
Nov 16, 2009
Messages
911
Location
San Antonio Tx
Check body ground point #7, lower passenger kick panel. All the sensors you mention ground to that point.

/brox
 

turbowop

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Joined
Apr 29, 2001
Messages
11,971
Location
Yakima, WA
I can't get my damn car to read over 177 even with cardboard blocking half the airflow to the radiator, so my gas mileage is suffering. Even with a new factory temp thermostat. I think I'm gonna replace my sensor because I know my car's factory cooling system isn't that awesome.
 
Last edited:

WaRrIoRs16

Well-known member
Joined
Mar 23, 2008
Messages
373
Location
Ferndale, WA
Is the body ground point #7 one of the two bolts that holds up ecu, the one with the black ground wire on it?

What degree thermostat do you have Mark? I can't even get under 200* in #796, that's with a 180* thermostat.
 

WaRrIoRs16

Well-known member
Joined
Mar 23, 2008
Messages
373
Location
Ferndale, WA
Hmmmm, that's odd. This weather is not going to help that problem any. Do you have any tuning abilities to create a coolant offset?

Well I'm a little baffled as to whats going on with my car. I should have mentioned that I bought have DSMlink v2 used and have it installed right now. I just put it in a couple weeks ago and I thought I changed everything on it back to stock, well I missed the coolant offset option. For some reason it was set to 200*, meaning my ecu would react as if the coolant temp was the actual temp plus 200*, for those of you without link that don't know. Well now I am seeing some normal coolant temperature values, good right? Well now all of a sudden my pocket logger, which is the only logging device I have been constantly using, is freaking out.

Sometimes it will connect but most of the time it won't(from my 2 hours of messing with it). When I did get it to connect, there was a 11* difference between the reading on the logger and the reading in link. Pocketlogger was 199*, Link was 210* for some reason. Link it connecting ever time and working just fine, but pocket logger was not, connecting rarely and sometimes showing only some parameters with complete wack values. Also my fan seemed to be going on and off randomly while link was showing between 206* and 213*. I will have to mess with it some more and find out exactly whats going on.

Thanks for all the help, I'm sorry I left out some crucial information.
 
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