Temp gauge not working

[gleavens]

Mercruiser 3.0L 140hp in a 1986 Chris Craft Scorpion. I have continuity in the light brown wire to gauge, I have power @ the gauge, I have Ground @ the gauge. When I ground the light brown wire ( disconnected) @ sender the gauge pins all the way right. I ohmed the sender ( wide open ) threw it in the trash, went and bought a new sender ( had resistance) could not remove old sender so I put it in the hole next to the sender where a plug was. STILL NO gauge. Then I thought the water from my hose was too cold to register on the scale so I went to the lake........nope................. No water in there? Cracked the small plug on the top of the housing, plenty of water in there.
Where do I look next? Thermostat? ...???

 

[achris]

Re: Temp gauge not working

Check the thermostat housing has continuity to ground.

 

[gleavens]

Re: Temp gauge not working

it does indeed

 

[OldNBold51]

Re: Temp gauge not working

I've this same problem on my 7.4L. I've changed the sender, checked the ground, pegged the temp gauge needle , checked the resistance of sender in heated water and still no temp reading. I'm grasping at straws on my next thing which is to put a small piece of foil in the cap of the wire to the gauge (at sending unit head) to see if I've a connection problem.

I'm keeping an eye on this thread. Let me know if you find your solution.

 

[CheeseCutter]

Re: Temp gauge not working

You don't have teflon tape or something similar around the threads of the sender, do you? With the sender installed, test for continuity from the base of the sender to a known ground. Also compare the known resistance of the sensor (the reading you took before installing it) to a reading, after installing the sensor, from the probe to a good ground. They should be the same.

I was having similar issues, tested everything as you have, but no luck. Cleaned the threads because they were rather rusted/corroded and the PO seemed to have used some type of thread compound at one point. Cleaned up all the threads and all was good.

 

[gleavens]

Re: Temp gauge not working

I did check those ohm readings at the locations you suggested and I did get similar readings. The OE Mercruiser switch I installed does indeed have some sort of thread sealer on it (red) I'd assume they would know what they were doing on that. I decided to check the thermostat ( why in the name of all things holy does it even have one) and to my surprise did not find one in there even though the manual calls for one. So, off to the marine parts store to purchase a new stat to see if this does anything for me. I'll post the results after the next trip to the lake ( whenever that will be)

 

[OldNBold51]

Re: Temp gauge not working

I did check those ohm readings at the locations you suggested and I did get similar readings. The OE Mercruiser switch I installed does indeed have some sort of thread sealer on it (red) I'd assume they would know what they were doing on that. I decided to check the thermostat ( why in the name of all things holy does it even have one) and to my surprise did not find one in there even though the manual calls for one. So, off to the marine parts store to purchase a new stat to see if this does anything for me. I'll post the results after the next trip to the lake ( whenever that will be)

I thought mine didn't have a thermostat in it as they usually (auto) are mounted with the base in the intake manifold. The marine thermostat is mounted in the housing, not the intake.

 

[gleavens]

Re: Temp gauge not working

the stat in this 3.0L is located on the water outlet
much like a passenger car, remove two bolts, pull up and there it is (or isn't)
I only know that because of all the spare parts i have for this 3.0L, I had a spare housing that had the stat installed in it. In any case I'm going to fire this thing up tonight after work in the driveway, I'll see if anything different happens. ( I also removed ALL thread sealer from the sender)

 

[gleavens]

Re: Temp gauge not working

It appears there is "some" movement in the gauge. It looks to be about 120 degrees, won't go any higher than that. Maybe the water from the hose is too cold? I'll have to take it to the lake, will post results by the weekend.

 

[gleavens]

Re: Temp gauge not working

Whether it was removing the thread sealer from the sender or installing a thermostat where there was not one before, my temp gauge IS now working. Reads about 130-140 out on the lake, around 120 on the muffs, I guess this is about right?

 

[CheeseCutter]

Re: Temp gauge not working

I average about 130 on my 4.3LX according to my gauge. I got a similar reading using an IR temp gun pointed at the base of the sender. Merc specs a 140 thermostat for my setup, so that temp is resonalble for mine. You have a 140 or 160 thermostat?