DT100TC V4 water warning

[malcolmh]

My 1990 DT100 was beeping last time I was out and the starboard water warning light was on. The rev limit light came on when opening the throttle.
Strong flow out of the tell-tale and no sign of overheating.
I brought the boat ashore and removed the lower leg. All ports are clear and the impeller is as good as new.
Next, I removed both cooling water sensors from the cylinder head.
The port one was clean but the starboard one had a significant crop of salt crystals on it and also on the casing adjacent to it.
Are these crystals the likely cause of the warning light, or should I be investigating further before I reassemble?

[Solarman]

If you have a sub-water cooling system, usually includes a stainless tube running through a grommet to just below the water pump (cavity where water enters to supply the water pump), from a screen just above the prop, in the cavitation plate. Then you should inspect that grommet for looseness/or being excessively burned (not clean and firm, similar to a new firm rubber grommet). This sub-water cooling pipe sends additional cooling water through the exhaust channel to that water pump cavity on some models. If those grommets are damaged, or loose generally it will cause overheating at higher rpms due to higher exhaust pressures blowing past those weak/loose grommets interfering with the water pump picking up exhaust gases instead of water. Not all motors have this tube, and not all those suffer this problem, but simply inspecting these grommets when down for a new impeller, could save multiple teardowns.

I suspect before teardowns for overheating, a good saltwater/ corrosion flushing with vinegar or other corrosion flush fluid would prevent some of these same problems you might be seeing?

Good luck, post back on what you find.

[malcolmh]

Thanks Solarman. The grommets you describe are all in good condition and I couldn't find anything else amiss at the bottom end.
Cleaning the salt crystals from the starboard sensor seems to have done the trick. The engine ran for 10 minutes on the muffs without beeping or showing the warning light.

[Solarman]

This could also mean you should flush that motor with a corrosion flush solution, or a vinegar water solution for a good hour to clean any other build up inside some of the passages?

Good luck, post back on what you find out.

[Murray]

Some reading material.

https://www.thehulltruth.com/boating...m-vinegar.html