Merc 4.3L No Temp Reading / One Manifold Cold

[agrifab]

First time post and need some expertise.

2007 Merc 4.3L Carb
Serial #: 1A078893
95 Hours

Started to use the boat for the 2nd time this year and noticed the temp gauge has no reading. Tested the wire from the sending unit by grounding it and it pegged the gauge. Replaced the temp sending unit but still no change. Let the boat idle for about 5-10 minutes and noticed the port side exhaust manifold was warm, but the starboard side manifold was not increasing in temperature at all. I had the boat professionally winterized and I know for sure the temp gauge was working when it first went in the water because I always let it get up to temp before pulling out of the slip.

Thoughts, suggestions?

 

[Don S]

Re: Merc 4.3L No Temp Reading / One Manifold Cold

May be nothing more than a thermostat stuck open. It's normal for one manifold to be warmer than the other at idle.

Get an IR temp gun and test the temp right next to the temp sending unit to verify the temps the gauge sender is seeing.

You also have two temp senders on your engine, one is an alarm switch ( Tan/blue striped wire) and the gauge sender ( Tan wire).
Did you replace the right one?

 

[agrifab]

Re: Merc 4.3L No Temp Reading / One Manifold Cold

I did replace the gauge sensor...the one with the single tan wire connecting to the stud of the sensor. I did not replace the other sending switch with the two-wire plug as someone told me that this fed the computer. I am hoping it is just a thermostat. Called the dealer to see if they had one in stock. Told them my issue and they said it could be the manifold is cracked on that side. :blue:

 

[Don S]

Re: Merc 4.3L No Temp Reading / One Manifold Cold

Told them my issue and they said it could be the manifold is cracked on that side.

:facepalm: :facepalm: :facepalm: No, it's not a cracked manifold. Cracks cause leaks, not temperature differences.