temp gauge reading too low?!

[boatdetective]

Hello- I've changed out the temp sender (tempo) & made sure that it matches the gauge (NOT factory merc). The engine is running at normal temps, but the needle on the gauge does not seem to budge much past 120. I've changed out the gauge too- same ting. Of course, I've checked contacts & all seems good. Vot giffs?

 

[Don S]

Re: temp gauge reading too low?!

Get a cheap Temp Gun and verify the temperature where the sender is located on your engine.

 

[boatdetective]

Re: temp gauge reading too low?!

Thanks, Don. I have a raytek and have gunned the block all over. It's running at normal temps- but the gauge is just reading too low. If i had a logic tree of how to work through the system one by one, I might be able to figure it out.

 

[Don S]

Re: temp gauge reading too low?!

Ok, then lets start from the beginning. What engine, what year, what make etc.
Do you have raw water cooling or a closed cooling system. Do you have a water heater or a cabin heater installed in the system, if so, how?
Just a couple of easy questions.

 

[boatdetective]

Re: temp gauge reading too low?!

Sorry- it's a 4.3- late model (I replaced the block sev. seasons ago). full Merc. fw cooling unit. I/O installation. Nothing else tapped into system. It's stuffed in a little 20' Bertram. It's odd, I know. Everything seemed fine. I first noticed it after my mechanic changed out the block. The gauge worked fine before that. I assumed he had used a merc sender in the new block, so i changed it out to a Tempo (as I had before & it had worked fine). No dice. Hmmm

 

[Don S]

Re: temp gauge reading too low?!

Try this. Check the voltage at the purple wire on the temp gauge. Make sure it's the same as the purple wire on the ignition switch.
Now, disconnect the wire off the temp sender and gauge. Either do an ohms check on the wire between the sender and the gauge or put a temporary wire between the sender and the gauge and see what the reading is

 

[Reel Poor]

Re: temp gauge reading too low?!

Teflon tape on the sender could also be the culprit. Check the hex part of the sender to ground for continuity.

 

[Don S]

Re: temp gauge reading too low?!

Teflon tape on the sender could also be the culprit.

Good point. Teflon tape is the DIYers Swiss Army Knife for everything (Like WD40 is a top penetrant, corrosion preventer, lubricant, fish catcher, etc). Teflon tape shouldn't even be allowed on boats. Creates more problems than it cures.