Universal M25 Temp Sender Resistance

[newgringo]

I noticed the temperature gauge in our Universal M25 was reading kind of high at about 195 deg F but the engine did not feel that hot. My optical temp guage and a thermocouple confirmed the actual thermostat housing was 171 deg F. Not liking things that make me worry I decided to fix that too. Have started by buying a genuine Universal Temp. sender ($29 !)that screws into the thermostat housing. Then I thought I should get a temp versus resistance profile before I install it to help sort out the problem. Here is the datathe __ are to keep the formatting aligned)

__Deg F_______Ohms
___62_________930
___75_________880
___80_________652
___90_________473
__100_________405
__110_________327
__120_________270
__130_________216
__140_________184
__150_________155
__160_________135
__170_________116
__175_________109
__180__________95
__185__________93
__190__________88
__195__________77
__200__________76
__206__________73
__210__________69 (water boiling at 29.84 inch baro)

Now I don't claim this to be gospel but reasonably close using my Sears digital meter.
Jerry SV Raconteur Kingston, WA

 

[newgringo]

More info. The reason for my first post was related to resolving two problems.
1. The temp gauge was reading too high by about 25 deg F and
2. The engine was running too hot on higher power settings.
I based my actual engine temp data on the Sears Digital meter mentiond before which I believe to be accurate. The temp probe was located on the thermostat housing by the sender.
Resolution to the actual hot running engine was a good cleaning of the heat exchanger and replacement of the thermostat as well as all new hoses. OBTW - The thermostat is stamped 71C which equate to 160 Deg F. The engine now runs steady about 160 Deg F after 10 minutes of full power operation. So much for that part of my two problems.
The high reading temp gauge was also easy to fix. From the resistance curve of the temp sender it looked like I needed to add about 30 ohms resistance to the temp sender. Both the original and the replacement sender measured close th the same values with an ohmeter. I wired in 24 ohms and now the gauge reads with 7 Deg F of actual (actual=165, indicated=172). I'm happy with that.
Another OBTW - In the process of all this I located a source for after market heat exchangers. http://www.lencocoolers.com/index.html quoted me $295 for the higher capacity 3 inch diameter unit. Universal gets over $500.

That's all my news for now.
Jerry E32-3 SV Raconteur

 

[Geoff Johnson]

My gauge appears to read too low (about 145 degrees). The Teleflex web site said you could expect the reading to be off by about 15 percent so I never followed up on it. I find that expecting too much precision on a sailboat makes me "mental".