I just replaced my temperature gauge and sender on my M25xp. I replaced both the sender and gauge head were standard Teleflex units. The sender has standard 1/4 inch male pipe threads.

The only problem I had was removing the temperature sensor from the thermostat housing. It seemed to be corroded in place. I got it out by draining the antifreeze down to just below the thermostat housing, and then applying a little heat to the old sensor with a small Bernzomatic torch. I did not have to get the old sender very hot, and was able to unscrew it.

When I tried to screw the new sender in, it would not fit. I cleaned the threads up with a 1/4" pipe tap, and the sender fit perfectly. The tap went in fairly easily, and did not remove any metal, so the problem must have been some of the old corrosion products left in the hole.

As I recall, the temperature gage was about $30 and the sender was about $12 from a local marine store.

Good luck with the change.

I replaced my guage and sender with units from FW Murphy. This was a pricy option......but.....the guage I bought has an adjustable switch which can activate an alarm for over temp. I set mine at 195 which is well above the temp it normally operates at. You would need the guage, the sensor and an adapter for the sensor as this is metric threaded. All this is available at your FW Murphy dist.
This will direct wire with the existing harness but will need either a 2 input alarm or another alarm horn. For me knowing that an alarm will sound long before I start to lose coolant is great oeace of mind. I have had both a broken fan belt an a clogged raw water filter and would have been alerted much sooner had I had the alarm.

I am glad this topic came up. I have a question. I have a MK1 from 1984. The control panel has (I think they call it custom)
RPM
Oil Pressure with alarm buzzer
Temp
voltmeter
blower switch
glow plugs
start switch
key on off

Does this have a high temp alarm? Seems like I read in the manual that the buzzer is for oil or temp. How can we know if our overtemp buzzer works?
I dont want to find out the expensive way that the buzzer doesn't work for temp.

[QUOTE=mike37909;20756]I am glad this topic came up. I have a question. I have a MK1 from 1984. The control panel has (I think they call it custom)
RPM
Oil Pressure with alarm buzzer
Temp
voltmeter
blower switch
glow plugs
start switch
key on off

Does this have a high temp alarm? Seems like I read in the manual that the buzzer is for oil or temp. How can we know if our overtemp buzzer works?
I dont want to find out the expensive way that the buzzer doesn't work for temp.[/QUOTE]
Mike -
From the description, sounds like the same panel as our similar vintage boat ('85 Mk I); apparently there was no overtemp buzzer that was installed back then as part of the factory set-up. Catalina Direct sells a retro-fit kit for this, which consists of a replacement thermostat housing tapped for an overtemp sensor, see [url]http://www.catalinadirect.com/index.cfm/product/2433_382/high-temp-alarm..., and separately sells a 2-tone buzzer that one wire in to indicate oil pressure or overtemp problems separately. We installed that setup on ours, although in hindsight I think we could have done it a lot cheaper by simply drilling and tapping in the second sensor on the existing housing (Tom Soko apparently did precisely that, and has an illustration of it in his photo-documentary of improvements here: [url]https://julandra.shutterfly.com/93[/url] ).
As to how to test, if I recall correctly the temp sensors work by closing a connection to ground, so you could test by taking the wire off your temp. sensor and touching it to the engine block to see if it sets of a buzzer (should make the temp gauge max out).

Matthew is correct. Another "philosophical" approach is to never depends on the buzzer, since sometimes when the engine is running and tunes are cranked up you may not hear it, although the new buzzers are much louder.

Then, one DEPENDS on regular checks of the temperature gauge, which is why it's there. :cool:

We don't have an over-temp alarm either. One day, while motoring up to an anchorage, The Admiral noticed the temperature rising. Rapidly. We shut down the engine, unfurled the jib, sailed into the anchorage, dropped the hook, let the wind set us back on the anchor, made sure it was set, and started looking around.

Here's what happened (click on the link for the full story):

[url]http://c34.org/bbs/index.php/topic,5078.msg31079.html#msg31079[/url]

Those "Critical Upgrades" are just as applicable to your boats.

Good luck.

I think Neil Roach, above, has the least expensive and simplest way to add a high temperature warning. After reading his post, I ordered a Murphy temperature switch gauge, and sending unit for my M25xp. The gauge was $68.75 and the sender was $26.25, plus shipping. My sender required 1/4 pipe threads. I still need to purchase an alarm buzzer, but I know they are not too expensive.

I ordered online from a company called Pitt Auto Electric Company. I am not sure what threads the M25 has, but Pitt lists a lot of senders with different size pipe and metric threads.

I have not received the system yet, but I expect installation to be very simple.

Thanks all. I have to say that Julandra is the most tricked out boat I think I have ever seen. Must be a true labor of love! So let me know when you want to sell her.

Mike,
You missed your chance four years ago and three years ago. The couple I sold her to was getting back into sailing after a 20 year hiatus. I guess it didn't work out, as she was sold again to another couple a year later. I see her occasionally in eastern Long Island Sound. She still looks pretty good!

Bumping this thread.  I need to replace the temp gauge on my '85 C36.  I replaced the entire panel 5-6 years ago with a new one from Seaward, but Seaward seems to have been acquired by Whale Marine Products and don't sell those panels anymore.  Anyone know which gauge would be a like-for-like replacement?

[quote=rjmcclemens]Can anyone recommend a temperature gauge and sending unit for the M-25?[/quote]

I approached this a little differently.

I took the 1/4" MNPT sending unit out and swapped it for a 1/4" MNPT Temperature Switch, where the old 1/4" MNPT sending unit used to be located.

Then I added a 1/8" MNPT Faria Temperature Sending Unit in the bleed hole on top of the thermostat housing.

No holes to drill; no tapping needed. But the trade off is the hassle to burp the system from the top of the thermostat housing by removing the new 1/8" sending unit.

I also added a red LED/Buzzer combination alarm to the 1/4" MNPT Temperature Switch.  So at 200˙ the switch will activate and sound the alarms.
 

Faria Marine Temperature Sender
Mfg.# TS26631
Temp Sender 1/8" NPT Single Standard.
Universal sender unit for most gauges and instruments.
AFCO
85286 Electric Fan Switch
200 Degree On & 185 off
1/4 NPT

I also added a raw water low-flow switch to my alarm panel -  along with a red strobe light that flashes down below in the galley area.

So if I lose my raw water flow in my raw water pump circuit, an alarm sounds with an accompanying red strobe light, which is bright enough to illuminate the interior of the boat - even on a sunny day.
 
I'll also post the wiring diagram for the strobe and the raw water low-flow switch.
 

Mitch,
Interesting idea.  If what I see in the pic is what I think I see, you may have a problem.  Most engine switches work by grounding the sending wire to the engine block.  If you have teflon tape on the switch threads, it may be a problem.  You might want to take the teflon tape off the threads.  Just a thought.