Re: Leaking crankcase leads to overheat condition?

[johnyrude200]

After spending 90 mins on the water with the motor, my explanation for running hot is that it was probably the plugs. The J6’s were 1 range higher than the OEM recommendation of J4’s. Granted, this motor is going to be run at WOT quite a bit due to it’s application, but I guess the J6’s are really just for the put-put trolling fisherman with a few short WOT’s on the day. It was only running hot after sustained, 2-3 min bouts of WOT. And I’m talking 170° not super hot, but it would fall back to 145° reasonably quick. What alarmed me is the J6’s a pulled yesterday after using the motor for 90mins were crusty and had blisters on the tips. The cylinders were bone dry too. That was unusual. I ran a heat gun on it yesterday and today and closely monitors the head, cylinders, and thermostat cover to observe trends.

My boat is not lugging. It’s me on a 14′ aluminum starcraft with 180lbs of ballast at the bow. Gets up on plane quickly and I have the motor trimmed a couple of holes to keep it from sitting too low on the transom (long shaft motor, mini-jacker plate installed, ventilation plate is roughly even with the bottom of the boat give or take an inch).

I did switch to a regular prop and didn’t see a significant change in top end speed or RPM’s. I did remove the thermostat and normally wouldn’t run motors without a thermostat, but in this application, the motor only lost about 10° of running temp without the thermostat (115-135, previously 125-155~170 at sustained WOT). It ran fine at idle around 100-120° while at headway speed. So not too cold.

Maybe I was just chasing a ghost with this one.

Jeff Register: all of those things you brought up I already went through previous to the post.

Side question – the motor did develop a minor issue which I wanted to pick your brains about. The shift lever isn’t engaging the fast start safety lockout either at the rear of the manual starter (the black plastic piece which rotates to stop the manual starter if throttle all the way up – prevents accidental starting at WOT), and the shift lever which runs down through the pan and interacts with the actual shift handle to the gearcase. It isn’t hitting that brass ‘fixture’ that is attached to the mag plate, or just barely rubbing. I had this happen on a 20hp of the same era – any suggestions on how to fix this?