I need the number to a good mercruiser engine place. I have been chasing a problem for 4 months. I am near chicago il. My issue is on my 500hp carbed. The gauge does not mimic the temp of the engine. My last try involved the following. I have replaced the sensor (located in the intake manifold behind the t-stat housing) and i have replaced the guage. I shot the engine with my laser temp gun just below the t-stat housing and it reads 152* but the guage reads 190*. I have two small holes drilled in my t-stat for water to my risers because i have a water crossover and my risers are at 90deg. And no the crossover has nothing to do with my false temp readings so you cant blame it all on the crossover as some do. Like stated the motor seems to be running perfect temps and all but i cant get a solid reading, any ideas guys.

Buy an inexpensive mechanical coolant temp gage and compare. I would at this point believe the senders and look for what is making it run hot. In that vein, I would first consider a lean condition.

I can put my hands on the risers no problem and the motor is no where near the 190 the gauge is reading as i can put my hands on it for a bit and the laser says 150ish. The motor is definitely not running hot. Next ??

Are you sure the sending unit is the proper one for the gauge? Causing it to give a false reading.



Darrell.

There can only be 3 things wrong if its not actually running hot.
guage, sender or wiring.

is the crossover you are running have a bypass ? should have to run a t-stat I'm running the same set-up, crossover w/bypass merc 140 stat with 4 1/8 holes drilled, runs 135
Rob

I had the same problem in the spring with my new engine,gauge read 190,temp laser gun at the the t-stat housing read 150 all the time,i replaced the sender with a new merc sender,still the same thing so i bought a new auto meter gauge kit that comes with a sender and installed the gauge and the sender using my factory wiring and it works perfect,reads about 160 all the time after warmed up.

I ordered a sensor from merc and the gauge from advantage, maybe thats my problem. I will give advantage a call and get a sensor from them and see if that works with there gauge. Does this sound right or are they just going to give merc a call and give me the same temp sensor.

With the ignition on ground out the sender. I like to use a remote starter switch so I can see the gauge. If the gauge goes to the highest reading, (pegs), the wiring and the gauge should be okay and the sender is probably suspect.

Don't forget, there are two senders for temperature: one for the gauge and one for the engine overheat warning buzzer. The overheat buzzer sender is just an ON-OFF switch that should activate about 195 degrees. If you ground out the wrong sender, you'll hear the buzzer.

That was also what i wanted to mention,make sure you are looking at the temp sender and not the overheat buzzer sensor,the wire to the temp sensor is one colour and the buzzer is a colour with a stripe ,i forget the color off hand but could check for you if you need,as far as matching the gauge to the sender,that could be a problem,someone mentioned that to me but i never checked into it.