Temperature gauge issues? Can't get a temp reading?

[MarcelSydney]

Hi again.
Having trouble with my temperature gauge i just can't figure out. I can't get a reading on the temperature gauge.
It is a 1999 Maxum 1800 with a 4.3L V6 Mercruiser. Serial numbers are OL323311 (engine) and OL509362 (Transom).

I have done the following:
1. the gauge seems to work. When i ground it, goes to max.
2. I have changed the temperature sender with a quicksilver one.
3. If i take the sender out, ground the threaded part of the sender and put it in a hot cup of water, it gives a reading, so everything seems like it should work?
4. put it back in the boat and it doesn't ever give a reading. Stays on 0.

The manifolds and risers sit at a really comfortable heat range (i can rest my hands on them and they feel toasty warm. Water coming out the back of the boat is nice and warm.

Any ideas? i am stumped? I wondered if maybe water wasn't getting to the sender or an air lock so it isn't immersed? Could that happen.
Any ideas would be great. I'm stumped and it would be nice to have a working temperature gauge.

Thanks a lot.
Marcel

 

[Bondo]

Ayuh,.... Welcome Aboard,..... Is the t-stat housin' properly grounded,..??

 

[MarcelSydney]

Hmmm, that is a good question. Thank you. I didn't check that. It would have a gasket in between wouldn't it, so how would it ground?

 

[alldodge]

The Merc gasket as 2 brass rivets in it to help make electrical contact between the upper and lower. Take a jumper wire and clamp on side if the sender and ground it elsewhere to see if gauge works

 

[66stingray]

Need to get an infrared temp gun and take readings at the t stat housing to confirm temp. Might have an stuck open t stat and not get past lowest reading on the gauge

 

[MarcelSydney]

Thanks dodge. Ill try the grounding and revert.
Stingray, i don't have an infrared temp gauge. If not the ground, it doesn't leave a lot of other options other than the thermostat i guess???

 

[alldodge]

3. If i take the sender out, ground the threaded part of the sender and put it in a hot cup of water, it gives a reading, so everything seems like it should work?

Clarification please; when the sender was in the hot water where you measuring using the ohms scale? and did the resistance get less as the temp raised?

 

[MarcelSydney]

I didn't actually measure the resistance. It was a cup of coffee i had been drinking while thinking what to do next.
Ill have another go at it if the ground idea doesnt work and report back with some resistance readings.

 

[alldodge]

I'm wondering if you bought the water temp switch and not the temp sender. The switch is open until it gets around 200*F then it closes. The temp sender

 

[dingbat]

Ill have another go at it if the ground idea doesnt work and report back with some resistance readings.

Don't need a ground to read resistance through a sender with a meter

 

[MarcelSydney]

I'm wondering if you bought the water temp switch and not the temp sender. The switch is open until it gets around 200*F then it closes. The temp sender
View attachment 346362

Thanks dodge. Pulled the sender and tested it out of the boat in a cup of water and it gives readings around these results, so Im sure its the right part.

I also checked the ground between the thermostat housing and the battery negative as well as the body of the temperature sender and they are all definitely grounded.

I also started the motor on muffs to see if water was getting to the sender and it spurted out the hole as soon as i started it so its getting water.

Does that mean it is the thermostat is busted? would it be stuck open or closed?
The engine doesn't get especially hot anywhere really. I can rest my hands on the manifolds and the block no problem? Water temp at the moment is around 16C.

If it is the thermostat, which way does the water flow? I assume the thermostat is closed initially until operating temperature is reached, then opens to let it through the block. So if it is stuck closed, would the cold water temp explain why there isn't a reading? Although i don't understand why the engine wouldn't overheat if water can't get to the block so i might be wrong.

 

[Fun Times]

Does that mean it is the thermostat is busted? would it be stuck open or closed?

In your case with the things you've tested and done thus far seems to leave that there's going to be about a 95+% chance the thermostat is stuck open...Usually the thermostat is stuck open with debris such as small rocks, etcetera...It's time inspect the thermostat itself as a stuck open thermostat would keep a starting reading gauge of say 100 degrees fahrenheit from rising.

 

[MarcelSydney]

In your case with the things you've tested and done thus far seems to leave that there's going to be about a 95+% chance the thermostat is stuck open...Usually the thermostat is stuck open with debris such as small rocks, etcetera...It's time inspect the thermostat itself as a stuck open thermostat would keep a starting reading gauge of say 100 degrees fahrenheit from rising.

Thanks. Will pull it off, have a look and report back.

 

[MarcelSydney]

So, im not a mechanic but pretty sure this thermostat looks rooted. Isn't there meant to be a spring?? Where on earth would it have gone? Rusted away completely? Far out, wasn't expecting to see it this bad.
Im ordering a new thermostat. Will let you know if it makes the gauge work (and maybe the boat will run better if it warms up to a normal temp)

 

[Lou C]

I’ve never seen one that bad even here in salt water!
That looks like someone tried to use an automotive one in a marine application

 

[alldodge]

That's bad, the gasket has some kind of gunk on it which is having issue with the electrical grounding of it.

 

[MarcelSydney]

Just updating. Replaced the thermostat today with new gaskets (with the brass lugs) and the spacer per the parts diagram. Cleaned it back to bare metal.
At first I still wasn't getting a reading but after a few minutes t-stat must have opened and bingo, got a temperature reading. Eventually settled at around 160F.

Beautiful! Will water test tomorrow. Interested if a noticeable difference if the engine gets a bit warmer.

So, I'm still not sure if it was a bad ground or the engine just not getting hot enough, but hopefully this helps someone else.

Thank for your help.

 

[MarcelSydney]

Hi all.
So since this post, I've started having issues with my temperature gauge again. I think it's still a ground issue. It sits on 0 all the time.
I've taken the thermostat off, sanded down both the housing and engine side till it's shiny and reinstalled but no luck.
With the engine running and warmed up, if I quickly use a piece of wire to short the smaller threaded side of the sender unit to the block (so the temp gauge goes to max, then remove shorting wire) then it will settle back at the 160f temp on the gauge until I turn the engine off. Then same problem when restarting, no temp reading.
I used a Quicksilver brand temp sensor and it had red thread sealer on the thread? I'm now suspicious of the red thread sealer . It looked like this pic. Could this be the problem? Can I remove it with a wire brush or does it need to be there and isn't likely to be the problem. It's the only thing I can think if?
If that's not it, I'm thinking I'm just going to have to rig up an ugly/dodgy ground wire using a hose clamp around the body of the temp sender to the block.
Any ideas or something I'm missing?

 

[dubs283]

Your issue could well be a grounding problem. One thing you can try is to clean all the red sealant off the threads and install the sender. Mark the threads where they stop flush with the housing. Remove the sender and apply sealant on half the threads closer to the exterior (stud end) of the sender, reinstall and test.

This way you'll have bare threads making good contact with the housing and still have sealant to prevent leaks

 

[Scott Danforth]

stop over thinking it.

use a hose clamp to secure a ground wire the the hex of the sensor, run the other end to a bolt.

on all my sensors and light switches, I solder a lug on them to avoid grounding issues due to sealants and paint