2009 Mercruiser 4.3 Temperature Gauge Sometimes Working

[desertjack]

I have 2009 Larson Senza with a 4.3L Mercruiser with and Alpha one dirve. I just bought it used and the problem that I'm having is that the temperature gauge sits at zero most of the time (below 100 which is the lowest temp on the guage) and once in a while shoots up to 160, 175 for a few seconds and then back to zero (below 100). I've tested the gauge itself and it works fine. The connection/wire between the gauge and the temp sensor is all ok. I've removed the sensor and cleaned it. I put a new thermostat. Installed a new impeller. Still doing the same thing. I believe that the gauge is reading the correct temperature at the sensor. When it is at zero, the thermostat housing and all of the hoses coming into it near the sensor are fairly cool. The thing that I noticed is that when the gauge suddenly starts working for the 2 or 3 seconds, I notice the sound of the engine change and idle a little lower. I figured that thermostat was sticking or something, that is why I changed it and installed a new sleeve, gasket, and ring as well. Could it be something electronic? or possibly the engine pump? FYI, when I had the thermostat replaced, the mechanic said that he flushed a lot of rust out of the system. I guess the guy before me did not flush the engine after using it in salt water.

 

[achris]

Re: 2009 Mercruiser 4.3 Temperature Gauge Sometimes Working

Ensure you have good continuity between the thermostat housing (where the sensor screws in) and the engine block. The OEM gasket has a couple of rivets in it for continuity... If you disconnect the sender wire and ground it the gauge should peg HOT.... If it does.. You have a sender grounding problem or a faulty sender...

 

[Don S]

Re: 2009 Mercruiser 4.3 Temperature Gauge Sometimes Working

First, check that the wiring on the gage is giving good 12V on the purple, and a good ground. And that the gray wire is clean and tight.
With the engine warmed up to operating temp, remove the wire from the temp sender on the engine, turn the ignition key to the run position (engine does not need to be running) and touch the sender wire to a good clean ground and see if the gauge pegs to full hot. If it does, the gauge is working. Replace the sender.

 

[desertjack]

Re: 2009 Mercruiser 4.3 Temperature Gauge Sometimes Working

Thanks for your responses. I've previously grounded the brown wire of the sender on the side of the sender and the temp gauge maxes out hot, which means that there is continuity for the ground from the block through to the t-stat housing and into the sender. I don't think that the problem is with the sender or the gauge. I have a feeling that the problem is somewhere between the engine water pump, the engine block, and the thermostat. Either the pump is bad, or rust in the block or something around the thermostat. The reason why I say this is because after I installed the new t-stat yesterday I took the boat for a test drive. The temp gauge did the same as before, did not work most of the time and the t-stat housing was always cool, but when I put my hand on the engine block directly below the t-stat level, it was hot (which is normal). But when I shut the engine off and let the boat sit for about 10 minutes, the t-stat housing and the water sitting in it heated up because of the heat from the block. I then turned the key on without starting the motor, the temp gauge worked and gave me a reading of 170-175 and stayed there, until I stared the engine again and the cold water reached the sender, it then dropped back to zero and the housing was cool again. That's why I believe that the sender is working. Could there be something with the water pump that might cause this kind of behavior, or could the t-stat or the spacer below it be installed incorrectly? Anyway, I'll order a new sender just to rule that out before I start digging deeper into the engine. Also, I'm thinking of removing the t-stat and running the motor without it for a test. If the gauge starts to work without dropping to zero, then the problem is somewhere around the t-stat area. What do you guys think? Any other suggestions?

 

[ENSIGN]

Re: 2009 Mercruiser 4.3 Temperature Gauge Sometimes Working

Without a t-stat installed you probably won't get any reading on the gauge.It sounds like the sender is acting more like a on-off switch instead of a variable resistor.

 

[desertjack]

Re: 2009 Mercruiser 4.3 Temperature Gauge Sometimes Working

I finally got the temp gauge to work. I decided to remove the t-stat housing myself and take a look inside. Apparently, the idiot mechanic who installed the new thermostat, istalled it wrong. He had the t-stat sitting on the bottom on the intake manifold side ant the plastic spacer was in the t-stat housing. The correct way is to put the t-stat in the housing first and then the plastic spacer under it. Now the water coming from the engine reaches the sender and it's finally working fine. I just bought the boat and I guess the previous owner had the t-stat replaced and it was installed incorrect then. When I had my EX-mechanic!!! install the new thermostat and spacer, he just installed it the same way the old one was. I tested the boat out today and the gauge worked fine, but there was one thing I noticed. At Idle, the temp was 175. When I drove the boat around at higher speeds it would go up to just below the next notch (which I guess is 200, 0r 210?) and then drop back down to around 180 and 175 and then back up again and down. But at Idle it would stay at 175. Any idea what may be happening there?

 

[Don S]

Re: 2009 Mercruiser 4.3 Temperature Gauge Sometimes Working

Get yourself an IR temp gun and verify the temps.
175 to 180 at idle sounds a bit high.
Take the engines temp right next to the sending unit and see if the two match.

 

[desertjack]

Re: 2009 Mercruiser 4.3 Temperature Gauge Sometimes Working

That's what I thought too. I'll try and get my hands on an IR temp gun. Thanks for the assistance.

 

[Fun Times]

Re: 2009 Mercruiser 4.3 Temperature Gauge Sometimes Working

The correct way is to put the t-stat in the housing first and then the plastic spacer under it.

Actually the correct way is to put the cork looking gasket inside the T-housing first, then the t-stat, then the plastic spacer. If that gasket is not in place or damaged, missing, etc, the temp will do weird things like your seeing still.

See item number 7, And don't go by the "photo" in the parts diagram below, it shows the gasket in the wrong spot as well, But the numbering is right.
http://www.mercruiserparts.com/Show...r=12833&bnbr=170&bdesc=Thermostat+and+Housing

Good luck.

 

[desertjack]

Re: 2009 Mercruiser 4.3 Temperature Gauge Sometimes Working

Thanks Fun Times for the info. I installed the cork looking gasket when installing the t-stat but did not mention it in my earlier post. I also figured out what was causing the engine temp to go up and down like I had mentioned. There were chunks of rust stuck in the spring of the t-stat probably making it harder for the spring to open at 160 thus allowing the temp to go higher before it could open. So, I shoved a hose in there and openned up all of the drain plugs on the block, headers, hoses, etc. and flushed the hell out of the system. Lots of small chunks came out. Boat seems to be running better (temp wise) now. Does not fluctuate as much. Is there some kind of treatment that I can pour into the system to clean and slow the rust?