Water Temperature Probe

[Christian Fish]

I had my engine coolant analyzed and it came back saying the coolant had no freeze protection or boil over protection. So I took it to NC Power Systems (the local CAT maintenance shop) in Tukwila, WA for a flush and fill and thermostat replacement. Driving home I noticed the water temp was all over the place ie, normal until about 188 then up 10 to 15 degrees in about ten seconds and back down 5 seconds later. Prior to the service the temperature indication was very reliable. It’s been back at NC Power for 2 weeks. They say the temperature probe is bad but they can’t seem to find the proper replacement. They informed me the thermostat housing isn’t a CAT part so they have no part numbers to look up and have been buying various probes from NAPA hoping to find one that fits. Does anybody know the part number for the probe?

[Richard Davis]

Christian
I have an '06 Monterey with the Cat C9.  The gauges in my '06 are a Beede product.  Beede has been purchased by Faria.  Faria is not real good about supporting the older Beede products, but I would certainly give them a call and see if they can give you the information on the temp sending unit.  The temp sending unit is installed in the thermostat housing.  I would check to see if they tightened the small nut that holds the wire to the sender when they reassembled things.  Good luck.
Richard

p.s.  The sending unit provides a stepped Ohm connection to ground depending on the temperature of the coolant.  Also, did they "burp" the air out of the thermostat housing?  If there is an air bubble in that housing, you will get false readings until the air dissipates.

[Christian Fish]

I finally got it back. It took them 3 weeks to finally get the right probe. They got it from Beaver Coach Sales & Service( I should have thought of that.) It didn’t fix the issue, ie the water temperature indication normal until approximately 188 and then erratically moving up to 195 then down to 180 within 15-20 seconds. The steam gage on the dash shows normal temps.

Any ideas on what could cause this?

I also bought and installed the metal expansion tank fromBCS.

[Steve Huber Co-Admin]

Christian,
Check the sensor connection at the thermostat housing. The dash readout is stable so that indicates the fluid temp is stable and the dash sensor is separate from the Aladdin readout which comes from the ECU signal. I suspect the shop damaged the connector when they first removed or reinstalled it. Try contact cleaner first to see if it is just dirty/corroded. The connection is probably getting intermittent when the housing gets hot.
Steve