Mercruiser 260 alpha 1 temp gauge/sender does not work

[ddecoursey]

I have the 5.7 260hp mercruiser (1983) Temp gauge just sits on"C"
I used the recommended method
took wire off the sending unit and grounded that to the block and the gauge goes all the way up to HOT every one tells me this verifies that your wiring tothe gauge and the gauge itself is in good working order.

So I go out and get the new sending unit.

It will only scew about halfway in..I tried everthing to get it to scew in farther but, that is as far as it wil go the acutal sensor( inch long finger at the bottom of the unit) is certainly down in the water flow.
The old one was only half way screwed in also I used no dope or teflon.
Attached the wire lead back onto the top of the unit and IT DOES NOT WORK the guage just sits down on the letter "C" and as a matter of fact after I shut the key off , the indictor will climb up to the first hash mark.... but soon as you turn the key to the run position it goes down off the 1st hash mark to the letter "c" this must be the bottom most position.




So if that is all you can test : Guage / wiring /and sending unit ...and that
1st test validates the guage and wiring to the guage....and you put a brand new sensor...... what the heck else is left to troubleshoot ??


summer will be gone and I will have not used this boat once at this rate

ddec11@verizon.met

[mkast]

How long was the engine running when you tested the gauge?

[ddecoursey]

Well .... since the recommended method of testing the gauge was to ground out the single lead wire..... the engine was not run at all I just gounded that lead wire to the block...saw the needle pegged up to the hot which everyone saya indicates the gauge and wiring is OK

[towman818181]

how long did you let it run with the new sending uniit inplace without the temp guage moving is the question

[mylesm260]

You can also test the sending unit independently with a multi meter.

Even at ambient temp, it should provide you with a reading.

Something like:
1400 ohms @ 100 deg F. / 55 ohms @ 260 deg F.

A manual may give you the actual "scale" for you're sensor.

[rbh]

first, remember to put on the teflon tape or it will leak as it builds up preasure
next run the boat(on muffs if it is in the driveway). if the motor is not warm/hot it aint going to move the needle, as well you will have to wait for the thermostat to open.
rob

[ddecoursey]

whoa RBH,

I have been told all along to NOT put anything on the threads , dope or teflon, because these "single lead" units must groud to the block via the threads

I dont have a closed system...so how much pressure do I get???

I jsut got a new thermostat....hope this will be the end of this episode
wewill see

Thanks

[ddecoursey]

RBH......your pic looks like my boat I have a 1983 SeaRay SRV225

[rbh]

hey there-
its a 1985 270 sundancer,
I usually put just a little pipe dope on the threads and have never had a bad ground to the block, you can check for resistance with an ohm meter, outside sender to block.
rob