1998 V70 Coolant Cap? Overheating? Something? Topic is solved

[Eddystone]

Gates 31329 Coolant Reservoir Cap

Installed this Gates 31329 cap today and everything seems to be nominal. My large radiator hoses were in the 200-205 F region before the fan turned on. The new cap sealed very well and was also easier to get on and off.

So, this was one of those cases where the simplest solution was the correct solution.

NOT TRUE!!!!

See below two posts down.

[454cid]

Gates 31329 Coolant Reservoir Cap

Installed this Gates 31329 cap today and everything seems to be nominal. My large radiator hoses were in the 200-205 F region before the fan turned on. The new cap sealed very well and was also easier to get on and off.

So, this was one of those cases where the simplest solution was the correct solution.

Good to hear.

I'm curious if my upper hose gets that hot, now.

[Eddystone]

CORRECTION TO SOLUTION!!!

The coolant cap was bad, BUT the real problem was that the coolant temperature sensor next to the thermostat was bad and reading low.

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 fans 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 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 185 F when the car was boiling over. The new sensor read much higher AND it activated the the radiator fan. On MY CAR (and your mileage may vary) the radiator fan switches on at 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. 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.