First a sad story, then the questions:<br /><br />I've only had my 1990 Sea Ray a few months. It has a 1990 135 Horse Mercury on it. I've had it out several times and had no problems. We were going out today, but the boat had sat idle in the driveway for about two months because of my wife's back injury. Anyway, before heading to the lake I decided to make sure the battery had the juice to start the motor. All I wanted to do is see if it would fire up and run for a couple of seconds.<br /><br />It did not...so I hooked up some jumper cables to the battery (using my pickup as a source) and tried to crank it again. No fire, just crank. Next I squeeze the bulb a few times thinking the pump needed some priming. The bulb was hard almost immediately. Tried cranking again. Turns over good, but no fire. By now I have cranked the motor about 60 seconds total. I finally decide it either has no spark or no fuel. After digging around in the garage a while, I find my timing light and clip it on a spark lead, and the wife cranks the motor for me. Aha! I have spark. So I now start looking at the fuel lines, etc. I removed the fuel filter and checked it. Seems fine. Squeeze the bulb again, good fuel flow. So I decide there's something not letting fuel into the carbs. I look at the driver's side (right-hand) of the engine, and there's a device with two wires coming from somewhere and it also has two small hoses going to/coming from it. And it has a small pushbutton-looking thing on top of it. I have the wife hold it down while I crank the motor, and it fires right off. Whoopie. I kill it and put the cowl back on and we go to the lake. It gets better.<br /><br />So we are at the lake, the wife gets in the boat, I back it down into the water, she cranks it and floats off the trailer, and I drive away and park. Within three minutes I am on the boat, which has sat there idling in the meantime. But a horn is going off, the same one that chirps when I turn on the ignition. My wife thinks the engine is smoking too much. We kill it, and as I stand there thinking about it, I realize I have forgotten to put the plug in! Yeah, yeah, I know...but hell, I just forgot!<br /><br />Anyway, I jump out of the boat and run to the pickup and get the trailer back in the water pronto, and we manage to get the poor boat back on the trailer before she sinks. I was amazed at how much water she took on in just five or six minutes! Anyway, I install the plug and we launch again. And again, the alarm is sounding when I get back down the dock and into the boat. This being my first boat, I am informed of the oil system alarm, but all that smoke...I stand there thinking, and ask my wife what the water temp gauge says. "Oh, the thing is pegged." Sure enough, nothing from the peehole. We kill it again, and we recover again, but unfortunately had to use some motor power to get back onto the trailer. So, we go home...and tonight, I decide to check on-line to see what I can find out, and I find this site. Okay, so at least ONE good thing happened today! And in this forum I read about there being an overheat alarm. So I suppose that's what was going on.<br /><br />So, now my questions: first, how likely is it that my motor is damaged from overheating? And what was the device on the engine that seems to have cut off fuel flow to the carbs? Will cranking a dry motor, even briefly, destroy the impeller? How long can you run an outboard dry without hurting it, and what is the damage that can be done other than burning it to cinders?<br /><br />By looking at other threads, I already know I will have to drop the lower unit and replace the impeller and check for pieces of it in the cooling system if it is mangled. But I want to know about these other things too, so here I am spilling my guts. Please don't call me an idiot because that word has been ringing in my head all afternoon and night. Thanks for responses, in advance.
I've heard/read that 5 seconds dry running is enough to thrash your impeller. Be safe, and always hook up water before cranking/starting. Can't help with the other questions, will leave to others more familiar with your motor and with overheat problems in general...