1993 Mariner 75hp high pressure tell tale, not heating up.

[j_k_bisson]

I recently purchased a 1993 Pro V with a 1993 75hp Mariner 3 cylinder on it. I have worked thru all the other issues with a motor this old; carb rebuilds, link and sync, faulty coils, new water impeller, new fuel lines, removal of oil injections system, etc....

My current problem is a rough idle. I have traced it back to the block not heating up and an excessive amount of water coming out of the tell tail. Also i mounted a water temp Gage on the motor. The temp Gage is not registering any temp at all. I have tested it with a heat gun and it works, I have also replaced the sender 2 times thinking it was a bad sender.

I have also puller the t-stat and diaphragm . The Diaphragm was not sticking, and the T-stat dis work. I replaced it with a new one and went with a 145 degree. Thinking that this will increase the head temp. It did not make a difference.

So My question here is, what else to look at. I check the factory service manual for a water flow diagram and there was not one like the Johnson factory service manuals.

1) Does anyone have the water flow diagram for this motor and can share it with me.
2) What other possibilities could it be that is causing the water pressure to be high? Possible some plate flipped upside down when changing the water pump impeller? Blocked let off hole in the water pump, etc.....

The motor is running not bad at idle, a bit shaky and occasional kick back. I am trying to make this motor run like a new one. Compression is 125-124-125 top to bottom.

Looking for any and all possibilities for this issue.

 

[j_k_bisson]

Just following up on this thread.

I finally figured out what was going on. Don't buy temp gauge and sender that's max reading of 280 because its on sale. 100-120 degrees is only a blimp on it. Buy a proper gauge for the application. A max 150 degree outboard gauge. That any temp reading that is low - shows.....

My loss, posted - lesson learned....

 

[Texasmark]

Your compression is "above the bar" per the service manual. Ok fine.

Water pressure, monitored at the ⅛" pipe tap port on the rear of the block's water jacket cover, per the manual is around <5 at idle up to >15 psi at WOT. The engine block proper has a cooling loop controlled by the Tstat up to 2500rpms and the popoff for larger, non-controlled water temp/flow above that. I have a water temp gauge in my current 115 and at low speeds it moves up to the pellet stamped temp of 125. When I get on plane and rpms get above 2500 the gauge immediately drops back to the ambient water temp plus a little for engine added heat, well below 125. The pellet on my 90 triple was stamped at 143 so you are right on with the Merc. spec, temp gauge for that engine. Why my 115 has what it has I don't know. PO doings and it works so I leave it be.

On later engines, probably yours too, the exhaust cover plate was the source of water for the tell tale....follow the hose. The exhaust has to be cooled if the engine is running. Therefore the exhaust is on a separate loop, uncontrolled, and flow is available as soon as the water pump can get water up there and is proportional to engine rpms. I don't know what you mean when you say "excessive" TT flow.

Couple ot things you missed were fuel pump kit and new engine fuel filter. When/if you replace the fuel filter, cut open the old one and see what's there. If full of tan chips, replace your tank to engine fuel line too. You didn't mention changing plugs either.

Last trick that might help is to tilt the engine up in the rear 10-15* when running at low speeds and see if that helps with your problems there. Being intermittent makes for confusion in chasing the source.....leads me to crud in the fuel lines rather than electrical problems.