I’ve encountered a problem with the temperature readings on the boat which have me completely stymied and confused.
Late last season the temperature gauge intermittently “pegged” at the highest reading (240) several times. The first time I shut the engine down immediately, but the engine had not overheated. Coolant levels were normal. The high temperature alarm did not sound. Water was circulating thru the system normally. Temperature readings with an infrared thermometer were normal.
After varying periods of time (generally an hour or more) the gauge would return to normal.
My initial thoughts based on reading Calder’s “Boat Owners Mechanical & Electrical Manual” and checking ohm readings was that the temperature sensor was bad, but I don’t know if his number was correct for the M35B sensor. I purchased what was supposed to be an aftermarket compatible product which I installed this spring before launch. I have had high readings since launch with the new sensor in place. I've checked connections and bled water from the housing and there was no indication of an air bubble.
Catalina Direct has a good outline for troubleshooting the temperature gauge and sensor which I followed. Their “Test Procedure for Temperature Gauges Used by Catalina Yachts” eliminated (1) the Gauge, (2) the sender wire, and (3) proper grounding of the sender to the block. By process of elimination the problem is therefore assumed to be the sender.
I ordered a new Westerbeke sensor using the part number (#035109) from the parts catalogue that came with the boat when we purchased it new. Installed it this morning, and I have the same problem. I followed the Catalina Direct trouble shoot again, and again it still seems to point to a bad sensor. I’ve run the engine for about an hour today monitoring it closely and the engine was not overheating.
When I start the engine, the temperature gauge immediately reads 180 degrees (plus or minus) and quickly pins at 240 degrees as the engine warms up.
I can run a direct wire from the sensor to the gauge, an additional check to rule out wiring and connections. Other than that the only options would seem to be the gauge or sensor, and what are the possibilities of three bad sensors? If running a direct wire does not work, I’m thinking about ordering a gauge next.
Any thoughts or suggestions would be appreciated! Obviously not a situation I am comfortable with and need to resolve ASAP!
Bob Chase
2003 C36 MKII 2138 "Change of Heart"
Laconia, NH - Sailing Lake Champlain
Runnig an external wire or at least jumpering the harness at the terminal block on the wire harness to eliminate a high resistance connection. The temp gauge is simple volt meter reading voltage through a a resistance coil (temp xducer). Can not remember which way resistance drives the gauge, up or down. Grounding sensor lead will drive gauge full scale one way or other. If it indication goes down when grounded any resistance in circuit will give a higher reading.
You have replaced multiple probes, have you checked all connections at gauge to make sure there is no voltage drop from the ignition switch to the gauge?
The gauge and control panel are more exposed to the elements and are more prone to corrosion. A gauge may be the next step.
Cepheus dream
C36 MK I # 825
MK I Tech Editor No Mas
Bob, hopefully you resolved your issue and can share what the solution was....
The Catalina Direct procedure is good, except it does not test the calibration of the temp gauge or the sensor. As a final test, you could remove the temp sensor from the water jacket, connect a ground to the threaded part, and dip into a container of water that was just boiling. [COLOR="Blue"]See enclosed picture. [/COLOR]Since water boils at 212F, depending on the volume of water and how long it was removed from the heat, you would expect the gauge to read something like 200F. If you want ultimate accuracy, have a meat thermometer dipped in as well. [B]NOTE: [/B] This is a last ditch effort as removing the temp sensor from the water jacket entails proper re-installation and proper coolant loss recovery.
Although engine dependent, the temp sensor, temp switch, and oil switch are three distinct units. Make sure you're working with the correct one. [COLOR="Red"]The high temp alarm is something that is critical and should be periodically tested.[/COLOR]
If you don't have a high temp alarm, strongly consider installing one.
Nick Caballero
Retired C36/375IA Mk II Technical Editor
Nick, thanks for this testing procedure. I'm going to test my gage, as it suddenly began reading 180-185 deg (typically 160)
Ive boiled out the HX, replaced the raw water pump impeller, replace the temp sending unit and thermostat, checked the raw water strainer and thru hull, checked hose blockage between the two. Replace numerous hoses while I had all this apart.
I even bought a heat temp gun, aimed it at the thermostat housing after warming engine, said 160.
So my last focus is on the actual temp gage.
Steven Jones
C36/375IA FaceBook group administrator
C36/375IA Jib Sheet Editor 2012
Seal Beach, CA, USA
C36 #2164 Maléna 2003 Mk-II SRig/FullK, Long Beach, CA
stevenjones21@gmail.com(link sends e-mail)
The temperature gage if grounded the needle pegs to the right or high temp. the low temp is at 240 ohms of resistance. You can buy a potentiometer and connect, as you vary the resistance at the middle of range should read 1/2 the range. It is likely to be the sender unit at fault.
Sail La Vie 1999 Catalina 36 MKII,(link is external) M35B-17031, Coyote Point, San Mateo, CA (link is external)
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