1998 V70 Overheating Due to Bad Temperature Sensor

Post by **Eddystone** » 28 Oct 2022, 14:47

This is for the record in case anyone is searching with this problem. In a recent thread, I thought I had solved my problem with a new radiator coolant tank cap from Gates. The cap needed replacement, but the real culprit was a bad temperature sensor.

NOTE #1: If you notice that your engine temp gauge usually reads exactly halfway up and suddenly stabilizes and indicates somewhat below halfway, your temp sensor is probably bad.

Two functions of the temp sensor are to feed the temp gauge on your dash and IMPORTANTLY it tells your radiator fan when to turn on. If it's reading low (for example, the coolant is at 217 F and the sensor reports that it is at only 180 F), your fan will not come on when it should, and your engine will overheat. A sensor costs about $20 and is a bear to get at. If you remove the thermostat housing, it's possible to get it loose with a clawfoot wrench. Or buy the specialized 19mm tool.

NOTE #2: If you have the Torque app on your mobile phone and a Bluetooth OBDII device, you can read your engine temperature in degrees AS REPORTED BY THE SENSOR. With the defective sensor, the OBDII was reporting only 180 F when the car was boiling over. The new sensor read much higher AND it activated the the radiator fan properly. On MY CAR (and your mileage may vary) the radiator fan switches on at an INDICATED 217 F degrees and runs until the temp drops to about 208 F within a minute and switches off.

Note that just a little bit of air through the radiator makes a big difference, especially when you are idling an engine that was blasting down the freeway two minutes ago. My original problem was that the temperature stayed stable below the boil-over point whenever the car was moving, but it would then boil over if I had to stop and let the car run at idle. The temp sensor was incorrectly measuring the temp and reading low, and at idle the radiator fan never came on, so the car boiled over.

Post by **Sveedy** » 28 Oct 2022, 19:05

You can use a grinder to notch an old socket. Worked great when I had to do mine.

: IMG_20221028_182038213.jpg (507.56 KiB) Viewed 367 times

Post by **Eddystone** » 29 Oct 2022, 08:57

Very nice, Sveedy. I was actually able to JUST get a clawfoot wrench in there between the sensor and a bracket, and it just happened that the orientation allowed me to unscrew it about 10 degrees after which it unthreaded very easily. I have to admit that I used a couple of different pliers to tighten the new one sufficiently. Needed to get that job completed.

Post by **scot850** » 29 Oct 2022, 10:17

Eddystone, you mention the 19mm specialized tool. Is that a Volvo specific tool or something like the O2 sensor tool?

I had a look at pulling a spare ECT one time at the junkyard but gave up as I could not get to the lower bolt for the housing with what I had there.

Thanks,

Neil.

Post by **Eddystone** » 29 Oct 2022, 11:19

I think it's exactly like an O2 sensor tool in design due to the wires, but I'm not sure if it is the same size. You can always just search Amazon or Google for an image.

Post by **abscate** » 29 Oct 2022, 13:47

22 mm for OXS

You can also de mount the PS pump to get good access to the ECT sensor . No need to remove the lines

Post by **Eddystone** » 29 Oct 2022, 14:06

abscate wrote: ↑29 Oct 2022, 13:47 22 mm for OXS

You can also de mount the PS pump to get good access to the ECT sensor . No need to remove the lines

Too much work. Easier to buy or modify a tool. A few more millimeters of clearance, and it would be a five minute job.