[C320-list] Faulty Temperature Sender

[Scott Thompson]

Dennis, this does not directly answer your question (for which I would 
call Catalina), but the following info might be helpful...

According to the Yanmar service manual the standard 3GM30F engine has an 
overheat temp switch that is either on or off. Such a switch could not 
give you an actual temperature reading, and the standard Yanmar engine 
control panels for this engine (not used by Catalina) do not have 
temperature gauges.  So I suspect that Catalina (not the PO) introduced 
the sensor in question into the coolant circuit as a factory addition. 
I'm pretty sure I have the same thing, although I'm going from memory.

I can't find any reference to the specific temperature sensor part in my 
Catalina manual. The manual does have an engine wiring diagram that 
indicates that the temperature sender  wire should be blue at the 
sender, transitioning to brown in the instrument pod. The temperature 
"switch" (the Yanmar overheat sensor) should have a white/blue wire at 
the sensor transitioning to tan/black in the pod. Apparently these 
circuits are separate.

There is a picture of the overheat temperature switch in the Yanmar 
service manual, but I can't find any indication of where it is located 
on the engine.

BTW, did the test you did on the gauge also trigger the overheat alarm? 
I'm guessing not, since that appears to be a separate circuit.

Let us know what you find please.

Scott Thompson
Surprise, #653 (1999)


On 6/23/2020 4:07 PM, Dennis Cookson wrote:
> That’s very helpful, Larry. Yes, I have the Yanmar 3GM30F engine on which the fittings are largely metric, but the T could be anything!
>
> Dennis Cookson
> #577
>
>
>> On 23 Jun 2020, at 17:31, Larry Frank <WindSwept at stx.rr.com> wrote:
>>
>> Hi Dennis,
>>
>> I just replaced my sender on WindSwept (#246) which has the Westerbeke.  From the photo and hull number I assume you have the Yanmar.  However it appears that a PO has modified how the sender is mounted given it is now in a hose run.  I don't think this would be typical.  My guess is that all of the fittings are NPT pipe threads and that nothing is metric.  An 11 mm wrench is nearly identical to a 7/16 wrench (which is 11.1 mm) so it would seem as the correct size and probably work just fine.  Senders are normally specified by their resistance and the NPT size.  The resistance has to match the guage and this is pretty much a standard item.  So that leaves the thread size.  I was able to measure the OD of the threaded section of the sender and looked this up online to determine the size.  I don't remember what that was but yours would be different.  I was able to buy one locally and if it did not fit I could exchange it.  If you cannot measure it you could buy a couple of pipe nipples at a hardware store and compare their size to the sender.  You should be able to find the correct sender at a lock boat parts store that has engine parts or online.  I used a wet vac to suck as much engine out of the radiator before removing the old sender and did not spill a drop.  You will need to decide if this will help you by checking the elevation of the T where the fitting is installed with the radiator.
>>
>> Larry
>> WindSwept C320 #246
>>
>> On 6/23/20, 9:25 AM, "C320-list on behalf of Dennis Cookson" <c320-list-bounces at lists.catalina320.com on behalf of dennis at cooksons.net> wrote:
>>
>>     Our temperature gauge has not worked since acquiring our C320 last year, and fixing it has been on my to-do list for a while now. Today I finally managed to disconnect the wire that is normally attached to the sender and conduct a resistance test, which confirmed that it is open circuit.  Despite appearances, the sender body was making good contact with the engine ground.  Connecting the wire to ground swung the temperature gauge needle fully over, so both the wiring and the gauge are ok.
>>
>>     I don’t know if this temperature sender was an original fit by Catalina, or a subsequent addition, but it is plumbed into a T-piece that leads from the thermostat area to the water heater. It seems to be a relatively small device screwed into a brass adaptor, which in turn screws into the T-piece.  I’ve uploaded a picture here <https://c320.org/mediagallery/media.php?f=0&sort=0&s=20200623135307185>.
>>
>>     Can anybody help me identify this device, particularly the thread as I would prefer to do a quick swap to a new sender without draining the coolant. It looks like it will unscrew with an 11mm socket.  There is an article on c320.org <http://c320.org/> that mentions a Stewart Warner, 240-33 ohm device, but there are several different sizes. The suggested replacement on Catalina Direct doesn’t look much like the unit I have, but the notes suggest that it should have a metric thread.  But perhaps the adaptor converts the thread?
>>
>>     Grateful for advice,
>>     Dennis Cookson
>>     #577
>>
>>
>>
>>
>>
>>

-- 
Scott Thompson
Surprise, #653