95 Volvo 850 T-5 Killed Another ECT 9186486

TheCynicalCanuck · Post by **TheCynicalCanuck** » 29 Dec 2016, 00:31

So, earlier this month I was having massive problems with my ECT. It thought it was warm when it was cold so it wouldn't start very well and would stall out pretty quick if you didn't hold the throttle down (was about -5C) and once it was warm it would think that was cold and would rev the engine to I assume try to warm it's self up (the ECT was reporting -40C). So I eventually got my thermostat housing off after dealing with a T40 that had effectively welded it's self and I replaced the ECT and thermostat. But now about two weeks later the problems are starting to come back. It's not as bad as it got before I replaced the ECT but the temp gauge will drop about half way and the engine will rev about 300rpm and the temp gauge will climb back up, only for it to do it again every 2-5 min.

The car needs a new battery as well so could it possibly be that? The interior dashlights also work intermittently.

I'm honestly at a loss, I really like the car but if it's just gonna keep killing ECT's then I just can justify committing myself to this car.

Post by **precopster** » 29 Dec 2016, 03:30

What brand of ECT did you use? Most of the non genuine ones out there aren't worth the time.

Also use OEM brand or GENUINE thermostat (Stant 48639 is the OEM) or by one in a Wahler box

TheCynicalCanuck · Post by **TheCynicalCanuck** » 29 Dec 2016, 03:34

I'm not sure the brand of the ECT. My stepbrother who's a mechanic ordered it on my behalf through his work. In his defense though I doubt a Kia dealer knows much about what kind of ECT a Volvo 850 needs.

Post by **misha** » 29 Dec 2016, 04:11

Just make sure it's oem Volvo (which is SWF Valeo btw)...or at least Vernet.
Nothing else will work in these cars.
Since you're allready in there....replace the thermostat too.

Post by **precopster** » 29 Dec 2016, 05:50

I have to disagree with Misha on the OEM thermostat brand as I've serviced Volvos that had a dealer schedule and they always had a Wahler in them with a Volvo stamp on the thermostat casting. Stant 48639 IS Wahler which is OEM. Nothing wrong with a Vernet or Valeo though

Post by **misha** » 29 Dec 2016, 08:07

Precopster...I was talking about ECT brand....not thermostat brand.
I know that Wahler thermostat is oem....of course.
About thermostat....i was just saying that it would be a wise thing to replace it while it`s in that area.

Post by **abscate** » 29 Dec 2016, 08:14

Battery voltage on any ECU controlled car is critical. You aren't saving money by not replacing a bad battery, so start there.

Post by **erikv11** » 29 Dec 2016, 08:26

The ECT is a simple thermistor, no mechanical parts at all within it. There is no way the car is "killing" them. Fix the battery and charging system first, then put the original ECT back in ad go from there. The ECTs do go bad but in all my years and P80s I have still not had it happen to me - it is not very common. I have a couple factory spares from the junkyard for when it does.

Post by **jimmy57** » 29 Dec 2016, 08:40

Well yes there is a way the car can kill ECT sensors. The ECM applies a current to the sensor and the voltage drop (and current amount) caused by resistance change is how ECM interprets the temp. Mot 4.3 and Mot 4.4 have two level ECT interpretation. Lower current up to about 50C and then higher current above that temp. At low applied current a 1 C difference in temp at 100C range is miniscule and decisions for cooling fan control and some other things is not as accurate. If you increase applied current then the incremental changes per degree are much greater. The problem is the higher current is tough on the sensor. If there is a bad ground or a faulty ECM or a low quality sensor then the failures are greater and more frequent.

The later Bosch systems use periodic higher current pulse to read temp with better accuracy. Denso systems don't seem to have any special tricks but still can interpret temp accurately. Maybe electronics improved in some way????

Post by **erikv11** » 29 Dec 2016, 08:51

With bad grounds in mind OP, one of the standard checks when there is ECT trouble is the wiring at the connector to the ECT, make sure it is not crumbling.