BF115 Headcover getting hot

I was having an overheating issue, so I started researching , and wound up removing the water jackets to find that it was completely blocked off by corrosion and salt build up(btw--saltwater run only motor). Don't know why the overheating alarm never sounded. Cleared the obstruction, and cleaned the backwash relief valve as well as the relief valve in the water jacket. When I took it out for a run, the motor stayed cool at low speeds, but after putting the boat on a slide for about 5 minutes (still NO alarm), piss stream started getting warmer, so I popped off the cowl, and the head cover felt hot to the touch(motor was steaming a little while idling), while the rest of the engine felt cool(waterjackets, head, and intake manifold). Could only keep my hand on the head cover for about 5 to 8 seconds(not sure how hot 160F feels like). Wish they just put a gauge on it instead of an idiot light. I found that when the piss stream gets warm the motor is getting hot, or so it seems, due to it being a t'd off passage. I've seen it stay cool while motor gets hot(running on water muffs). Does the headcover even have water passages in it? Is there a way to test the alarm sensor to see if it is still good? I would like to try to retrieve the codes using the shunting method discussed in other threads, but not sure where the connector is that i need to shunt. Can I change out the sensor sending unit for a gauge sending unit? The thermostat was removed by the previous owner, could that be the issue? Does the thermostat have to be in these engines to operate normal? Any help on this issue would be greatly appreciated. Thanx for your interest.

It is imperative that you have a thermostat in an efi motor or it will always run very rich and use excessive fuel.The thermostat also creates back pressure on the cooling system thereby evening out the temp within the engine. It is fairly safe to say that if your alarm beeps twice when you turn on the ignition that the warning system is functioning.There is nothing wrong with the Honda warning system, it is activated long before any engine damage occurs.It is normal not to be able to keep your hand on a block that is at 60 degrees, that is the temp of hot water from your hot tap at home. I would install a new thermostat, make sure the alarm is functioning as described and take it for a run and see if it overheats. If it does, you will have to try and descale using vinegar or one of the commercially available treatment.

By experience on my Bf130 which is exactly the same as the Bf115;
I would descale the engine by removing the lower end, connecting a hose to the water inlet and connecting a bilge pump or a powerful aquarium pump to the hose.
With the thermostat removed for better flow I would run descaler through the engine.
You could use vinegar or you could use Barnacle buster 1to4 ratio and flush the engine.
There are 2 Temperature sensors;one on the top back of the engine port side and one on the top starboard side behind the intake manifold near the oil pressure sensor.
You could try replacing them but I would recommend fully descaling the motor.
My 130 was always weakly dribbling through the telltale until I descaled it....and believe me the vinegar turned gray from all the salt scale .

This is a good suggestion, might be a worthwhile thing to do at annual services for motors run in saltwater since salt build up is such a common cause of overheat issues.

Fished the boat for 3 days , and it did heat up to what i thought was getting hot, again, once or twice. A day later, I was able to get my hands on a temp gun. I felt my trucks engine while running around town, which guage said was round 170F, and couldn't touch it as long as i could the head cover. Gun said it was 178F in that spot, so I very well may have been being paranoid about it after finding that completely clogged water jacket passage. Going to take the gun with me on next run, and check. Meanwhile, i should still probably do the descaling you guys mentioned, as well as get the thermostat to put back in. Changed the plugs and oil today, and it appears (from lookin at the plugs) that it may have been runnin a bit on the rich side. Another issue is raising its head now, but I think that needs to be another thread, in case the info can help someone else, they can find its heading.. Thanx guys , for chimin' in.

Running rich because it's running cold, fit the thermostat

A Temp gun on the cylinder block from top to bottom will show a temp difference in readings if you have blockages in the head or block.
Usually the lower part starts to block due to build up.
When taking temp readings your temp values should not have much difference.