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Coolant Temp Sensor...

Help and Advice on Volvo's extremely popular car line, powered by Volvo's nearly indestructible, versatile inline 5-cylinder engine.
1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

Coolant Temp Sensor...

Postby rspi » 16 Jul 2012, 15:32

Ok, I'm getting confused. Is this the engine coolant temp sensor that causes the car to have hard starts? I thought this also sent the temp signal to the ECU and gauge in the dash?
http://www.fcpeuro.com/products/volvo-e ... 90-9186486

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The sales page indicates it's purpose is to control the fan. :?
'95 855 T-5R, Panther - 21/27 mpg
'98 S70 GLT, Lil' Red
--------------------
Volvo's of past: '87 740 GLE, '79 262C Bertone, '78 264, '95 960, '97 960, '98 S90, '98 S70 GLT, '95 850 T-5R Yellow
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Re: Coolant Temp Sensor...

Postby jimmy57 » 16 Jul 2012, 15:43

Beginning with the 850's and then on all new model Volvos since, the engine has one coolant temp sensor. The sensor is wired directly to the ECM. The ECM controls the fan for engine temp and sends a signal to the cluster and to the climate control if car has ECC.
Cluster uses the signal for gauge. ECC uses it to regulate a nicer programmed feature to blow windshield with lower blower until water temp gets warm enough to feel nice on our feet at which point a transition form defrost to floor in a few stages occurs (assuming you have fan and mode both on "AUT".
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Re: Coolant Temp Sensor...

Postby rspi » 16 Jul 2012, 15:50

Good. It threw me a little when they called it a "Engine Coolant Fan Temperature Switch". I got one from FCP about a month ago and it has already failed. Left my daughter stranded with a dead battery. :x
'95 855 T-5R, Panther - 21/27 mpg
'98 S70 GLT, Lil' Red
--------------------
Volvo's of past: '87 740 GLE, '79 262C Bertone, '78 264, '95 960, '97 960, '98 S90, '98 S70 GLT, '95 850 T-5R Yellow
ABS Light? - My Volvo Video Channel
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Re: Coolant Temp Sensor...

Postby jimmy57 » 16 Jul 2012, 16:59

When the sensor fails you get a 6 minute (varies a bit on some models) afterrun of the engine cooling fan. Did 6 minutes of fan running kill the battery?
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Re: Coolant Temp Sensor...

Postby byeboy » 16 Jul 2012, 17:04

I'd like to suggest that what the failure was is the two wire connection plug. If the sensor is not completely and properly connected, it causes the fan to run in default "high" mode, plus run for six minutes after engine shut down. (Your daughter probably would not ave noticed this). Separate the plug, slide the plastic parts down the wires, use baking soda paste to clear out any corrosion (mine had plenty down in the lower "tube" parts), and use bulb grease or vaseline on the connection to keep corrosion at bay.

I know this because I experienced exactly the same thing, and used my AAA to tow me back home, at which location JImmy57 zeroed in on the cause...'been doing great since then.

That fan draws heavy amps. I had my three year old battery checked, and its still in very good condition, so the amp overnight charge was all it needed to make it happy again!
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Re: Coolant Temp Sensor...

Postby rspi » 16 Jul 2012, 17:20

jimmy57 wrote:When the sensor fails you get a 6 minute (varies a bit on some models) afterrun of the engine cooling fan. Did 6 minutes of fan running kill the battery?


I think it ran longer than that but maybe that was it. The problem is that her normal commute to work is only 3 miles, about 8 minutes so the battery is likely 1/2 drained anyway. So you drive 8 minutes, cut the car off, then the fan runs for 6 minutes, that'll kill any battery.

I got one out of a junked car and all is well.
'95 855 T-5R, Panther - 21/27 mpg
'98 S70 GLT, Lil' Red
--------------------
Volvo's of past: '87 740 GLE, '79 262C Bertone, '78 264, '95 960, '97 960, '98 S90, '98 S70 GLT, '95 850 T-5R Yellow
ABS Light? - My Volvo Video Channel
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Re: Coolant Temp Sensor...

Postby jimmy57 » 16 Jul 2012, 18:03

Byeboy's post covers a VERY common failure on 850/s70/v70 gen 1/ c70 gen 1
The terminals in the plug that goes to the pigtail on the ECT sensor are potted with a clear plastic that disintegrates. You plug it together but the plastic that should be positioning the terminals in the grey (maybe black) connector body are crumbled and the terminals don't actually end up slid onto the bullet terminals in the pigtail.
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Re: Coolant Temp Sensor...

Postby cn90 » 16 Jul 2012, 18:13

Interesting! I still have the original ECT and car runs fine at 120K miles.

Question: is this a problem with the ECT itself or the Connector?
1998 S70 GLT 150K+
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Re: Coolant Temp Sensor...

Postby byeboy » 16 Jul 2012, 18:30

cn90 wrote:Interesting! I still have the original ECT and car runs fine at 120K miles.

Question: is this a problem with the ECT itself or the Connector?


Well, all good hope rides with it being the connector...and cleaning it is free ad easy...so think of that as Step1! The dried "stuff in the lower tbe parts was like candle wax...wood Skiskabob Skewer worked well to push it out, and clean up the bore. :)
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Re: Coolant Temp Sensor...

Postby j_cd » 16 Jul 2012, 23:36

Interesting. I replaced my thermostat recently, as it was acting sluggish. I was going to replace the ECT sensor at the same time, but my intake manifold spacer pushes the manifold out just far enough to make it impossible to get a wrench on the sensor. After reading this thread, I'm not sure whether or not I should replace it when I have the manifold off for this valve job. The original is still working perfectly. The replacement part I have is the aftermarket one from fcp. It looks fine, but who knows.
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Re: Coolant Temp Sensor...

Postby rspi » 16 Jul 2012, 23:43

Our's didn't work right after the car overheated just once. The new one worked good for 2 weeks but after I changed the head gasket it only worked for 2 days after that. I was thinking it was messing up because it was burping air but it stayed bad for a week then caused our battery issue.
'95 855 T-5R, Panther - 21/27 mpg
'98 S70 GLT, Lil' Red
--------------------
Volvo's of past: '87 740 GLE, '79 262C Bertone, '78 264, '95 960, '97 960, '98 S90, '98 S70 GLT, '95 850 T-5R Yellow
ABS Light? - My Volvo Video Channel
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rspi
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Re: Coolant Temp Sensor...

Postby jimmy57 » 17 Jul 2012, 00:13

cn90 wrote:Interesting! I still have the original ECT and car runs fine at 120K miles.

Question: is this a problem with the ECT itself or the Connector?


Connector.
Usually occurs due to it being unplugged or any work in that area where the connector could be disturbed.
I suppose road salt spray could give you issues if the plastic disintegrated and fell off with time.
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Re: Coolant Temp Sensor...

Postby JimBee » 17 Jul 2012, 01:11

When I went through the 850 connections prior to a trip last summer I struggled to get that one apart. When I finally succeeded it was obviously corroded, so I took my dremel tool with a tiny wire brush to clean it up as well as possible, then a pick with a barb on the end to scratch the insides of the tubes, before putting it back together with some dielectric grease. I've pulled a couple from wrecks and they always seem corroded. If that happens to mine again, I might just cut the pigtail and put in some new connectors that are more protected from the elements.
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Re: Coolant Temp Sensor...

Postby erikv11 » 17 Jul 2012, 06:25

Do some reading, you will find the aftermarket ECTs are notorious for failing. I consider this a dealer-only (or junkyard-only) item.
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