Risers are staying very cool.

Im going to put in a 140 thermostat, with relief holes in it, and either find fittings and a hose to make a bypass with what I have...or just get that Hardin/CPP kit you linked. I like that their kit has a larger 1" bypass hose where if I got fittings to make a bypass of what I currently have, it would be smaller and more restrictive than their 1" bypass.

The kit is a good plan.

I have used the Hardin Marine Tstat housing and it works well. If you look at the cut away of the housing, there is a divider inside that helps keep the cold water from affecting the Tstat function. I was skeptical at first but my water temps are rock solid at 150 degrees and the Tstat begins to open as quickly as it ever has.

Troy

Thats great to hear. I have the Hardin kit on the way to me now. Will try to install next week and give it a try. Thanks again everyone.

OK I just installed that nice Hardin kit, so now I have a crossover WITH a bypass, so the exhaust always has water even when thermostat is closed. I used the 140 marine thermostat that came with the kit, which already has a hole in it for steam.

Took it for a spin today. Water I was boating in was 65-70 degrees. While trying to warm it up and idling through the no wake zone, temp gauge never rose off 100. I then went to speed, about 40-50MPH and drove for a while. Temp gauge never rose off 100. As mentioned before, I dont think the gauge is bad because when I took the wire off the sender and grounded it, the gauge pegged. After driving for a while, I stopped and shut down the engine. Risers are staying cool to the touch. Crossover tube was cool-ish also, except the starboard side was a bit warmer than the port for some reason.

Anyway, I let it sit for a while with no water flow so the engine could absorb some of the heat. I then keyed my ignition on to check the temp gauge and it finally moved, granted it did not show more than 110-120. Again, this was after I shut the engine off and let it absorb some heat. Engine on, it dropped back to 100 and stayed there.

Think my temp sender at the intake manifold could be bad?
Im also going to remove the thermostat and heat it in water to be sure its opening at 140 and working correctly. But, I assume it is opening because if it wasnt then my temp gauge should've shot up...unless the sender is bad of course.

I've got the same Hardin set up. I have not had the boat out since but on muffs both motors will register almost 140 degrees at 3lbs water pressure at an idle.

You definitely have a sender or gauge issue. Unless your dumping water out of the block some other way it's got to come to temp at an idle or running.

His system is plumbed correctly for what it is. Its a crossover system with no bypass and that is how they are plumbed.
The 4 hose type of Tstat housing has not been used since the late 90's. The newer ones have 2 hoses that go to lower exhaust manifold inlets and the Tstat housing has an internal bypass.
ALL Merc black carbed raw water cooled engines used 140* T stats as do all Merc Racing Carb engines and even some of the EFI ones.
The Merc black 454/502mpi's that use the 2 hose Tstat housing use 160* Tstats

Like SB, I'm not a fan of crossovers. I would have gone back to circ pump and 2 hose Tstat housing with a 140* Tstat

Thanks for the replies, everyone. And, I agree with this, thanks for confirming. It must indeed be a sender or gauge issue, as the water inside block has to be coming up to temp now that I have a thermostat in there. The water has nowhere else to go until the tstat opens, so it must be getting hot.

My existing sender was installed with loctite by a previous owner. Going to take a heat gun to warm it up and unscrew. Since Im going to put a heat gun to it anyway, I might as well heat it up to 180 or so and then key my ignition on to see if the temp gauge reflects accurately.

From everything I've read, if I ground the sender wire and the temp gauge pegs (like it did), that should mean the gauge is OK, right? This is reason Im thinking sender issue.

have you tried grounding the body of the sender, with all that goop on the threads it might not be making contact, I didnt read the whole thread

I have not tried grounding the body of the sender. Is it as simple as using a wire and touching one end to the sender body and the other end to ground? And that should peg the gauge also right?

If it doesnt peg then bad sender?
If it does peg, then the sender just isnt making good contact to ground?