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850 Turbo Coolant Temp Sens, or Sensor Connector ?

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo 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
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Nick777
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850 Turbo Coolant Temp Sens, or Sensor Connector ?

Post by Nick777 »

Ok, so heres the symptoms and my reasoning:

My Temp gauge has been acting crazy shortly after I purchased the car. The needle would at times seem to act normally, rising normally to just a hair beyond mid-line, only to plummet to Zero, then rise back to approx mid-line, then plummet, repeat and repeat (I know its not a malfunctioning cluster gauge because I could hear and feel the engine adjusting when the Temp needle would plummet). So clearly something is off - but is it the sensor or the connector?

But yesterday the sensor did something Very interesting. Upon starting an absolutely cold engine, the Temp shot right up to mid-line, right away. Now given that these sensors are Negative Temp Coefficient sensors (the Resistance goes Down as they heat up), the fact that the needle shot up right away tells me that it can't possibly be the sensor connection. Reason why - any kind of connector issue would cause an Increase in resistance (corrosion, crud, partial open), yet the sensor is acting right off the bat as though there's a resistance Drop. This, along with the fact that there is NO evidence that the gauge in the cluster is malfunctioning tells me that it is HIGHLY likely to be the sensor itself.

Furthermore, although I will change the thermostat because I don't know how old it is, it would be physically impossible for even a trashed thermostat to cause a reading of instant heat on a cold engine.

So it MUST be the sensor!

What do you guys think?
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abscate
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Re: 850 Turbo Coolant Temp Sens, or Sensor Connector ?

Post by abscate »

Pull off the connector and check the pins for corrosion. Then pull the part number,search forum here for that part number and the resistance table, and confirm it Errors of about 10% are ok

The new part is about $50

Pick and pull less

I think I have one of my 1998 parts car , too. If you are tapped out and fighting the man, it’s free, otherwise market value or something in between.
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Re: 850 Turbo Coolant Temp Sens, or Sensor Connector ?

Post by RickHaleParker »

Nick777 wrote: Sat Nov 16, 2019 1:25 am So it MUST be the sensor!
Intermittent electrical shorts will lower the resistance. Conductive corrosion in parallel with the temperature sensor will lower the resistance.
1998 C70, B5234T3, 16T, AW50-42, Bosch Motronic 4.4, Special Edition package.
2003 S40, B4204T3, 14T twin scroll AW55-50/51SN, Siemens EMS 2000.
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Nick777
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Re: 850 Turbo Coolant Temp Sens, or Sensor Connector ?

Post by Nick777 »

Abscate - thanks for the info and especially for the offer! I'm not quite in financial dire straits (yet!) so I'll save your offer for if and when I really need it!

RickHaleParker - very interesting! I wasn't considering that there could be conductive corrosion, even though I'd imagine that resistive corrosion is far more likely. As to intermittent shorts, also another good observation. As a matter of fact i wonder if that is in fact going on in my situation - on one occasion I observed the temp needle shoot all the way to the tippy top even though the engine was clearly not overheating (just started more or less). An intermittent short would plummet the resistance to near zero, which would explain the needle jumping to the top like that!
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Re: 850 Turbo Coolant Temp Sens, or Sensor Connector ?

Post by RickHaleParker »

Nick777 wrote: Sat Nov 16, 2019 10:26 am
RickHaleParker - very interesting! I wasn't considering that there could be conductive corrosion, even though I'd imagine that resistive corrosion is far more likely.
Resistance also has conductance. Resistance is some where between a perfect insulator and a perfect conductor.

Resistance and Conductance are reciprocals of each other, like Yin and Yang there is some of the other in each.
1998 C70, B5234T3, 16T, AW50-42, Bosch Motronic 4.4, Special Edition package.
2003 S40, B4204T3, 14T twin scroll AW55-50/51SN, Siemens EMS 2000.
2004 S60R, B8444S TF80 AWD.
2005 XC90 T6 Executive, B6294T, 4T65 AWD, Bosch Motronic 7.0.
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Re: 850 Turbo Coolant Temp Sens, or Sensor Connector ?

Post by abscate »

Isnt resistance more Buddhist, like Ooooohhhhhmmmmmmm?
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Re: 850 Turbo Coolant Temp Sens, or Sensor Connector ?

Post by wizechatmgr »

abscate wrote: Sat Nov 16, 2019 5:17 pm Isnt resistance more Buddhist, like Ooooohhhhhmmmmmmm?
You're baaaadddddddddd =P
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Re: 850 Turbo Coolant Temp Sens, or Sensor Connector ?

Post by erikv11 »

If you need to buy another ECT, this is another part for which the cheap aftermarket ones often don't work.
'95 854 T5-R, Motronic 4.4, 185k
'96 855 NA, 145k
'98 S70 NA, 220k (living out west)
'98 V70, T5 tune-injectors-turbo, LPT engine, 293k
'06 S60 R, 167k
'99 Camry V6 :shock: 130k
gone: '96 NA 850 210k, '98 NA V70 182k
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Re: 850 Turbo Coolant Temp Sens, or Sensor Connector ?

Post by abscate »

Driving through NJ all week MON TUES. WED

Give me a PM and see if we can connect
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