Cooling problem with 1956 Merc Mark 30 Keikeifer

[WimbleG]

Goof evening,
First post i've done on here but I need some help.

I've got a 1956 Mark 30E. It was totally rebuilt several years ago by professional shop in Canada. Previous owner provided me with all receipts and list of what was done.

He also mentioned that the motor can run hot when throttled up. I have the motor on a 1955 Wagemaker Wolverine. Low to mid throttle, temp is fine. When throttling up, temp gauge climbs too high. If I throttle down, it cools back down.

I brought a professional who is very well versed in these old Mercs. He changed water pump impeller and ran in test barrel. Throttled up fine according to him and did not overheat. Put it back on boat and it did exactly same as my prior trip out...it goes into high temps. Will cool into normal operating range if throttled back.

The lower is in sufficient water. the intake holes are free of obstruction, and water is coming from pee hole on port side rear of Merc when under power. When motor was on stand, i blew air through intake holes on lower and felt it exiting pee hole.

Does anyone have a cooling system diagram or cutaway pic showing the water path through these motors. I'm stumped.

Thank for any and all help,

Greg

 

[jimmbo]

That engine has its water inlet behind the prop on the Exhaust Snout? When you say the Lower unit is in sufficient water, where is the Anti ventilation Plate with regards to the boat bottom height wise? Are all the passages between the water Pickup the water pump leak free?
the running hot might not be a water pump problem. other things thet can make a Motor run hot are; too Lean of carb, main jets, Improper Timing, wrong Oil or not enough oil. Build up of Salts/Mud/Corrosion in the Water Jackets, Exhaust gas getting in to the Water Jacket during High RPM operation.

If you blew air into the water intakes and it exited the the tell-tale, something is not right, as the water pump impeller would block the airflow

 

[Faztbullet]

Where is the sender mounted??? It is a line motor and temp is controlled by restrictions in block and passageways and temps will increase as you approach WOT. Now you need to know what temp is at WOT as it many not have a problem at all. Anything below 180° is good.

 

[WimbleG]

Temps get hot. Real hot. How hot? Hot enough that it blew one of the spark plugs along with the threads and part of the boss out of the #3 cylinder. So........ I had the boss rebuilt and new threads tapped in. I brought it to another who specializes in these old Mercs. Carbs & timing are good. He installed a new water impeller as well.Anti-cav plate is below waterline and sits just below plane of bottom side.
I just had the head plate off again to inspect jackets. The sending unit is in very top off block. Temps are fine to mid throttle. It’s above mid where she climbs.

Does anyone have the schematic for the water cooling system for one of these old Merck’s?