'87 Merc 165 3.7 runs 20 minutes dies then hard to crank

[BeaverLakePete]

Hell fellow boaters! First post here needing some help. I've spent the last 2 days reading through the forums. Think I have an idea where to start, but would greatly appreciate any experience y'all have.

Just purchased '87 Dynasty Apollo Luxury Ski with Merc 165 3.7L Alpha 1 Gen 1. Around 15 minutes into the test ride the throttle froze in the carb. Got a good price break, bought it, put a new carb from flying fish on, started right up. Put in the water, ran about 20 minutes (idle, wot, idle, wot) then sputtered out and died. Went to restart and it would barely turn over. Put it back on trailer, pulled it home, went out next afternoon and it fired right up...

Going to 1. Clean ALL electrical contacts 2. Remove and test starter 3. Replace coil (I think that's why it died)

FWIW temp was 140-175° max , around 140° when it died, and yes, blower was running...

Any other suggestions?

 

[turand]

I'm still very much an amateur, so I'd get some other opinions, but I took a brief look at your service manual and it says your thermostat should be opening up at 143F, same as mine. If your temp is getting as high as 175 and the motor is quitting, sounds like it could be overheating and I'd be starting at that thermostat. If you are overheating and you solve that problem, I'd be running some compression tests to see if you damaged the head gasket.

I don't think the blower does much for engine temp, that is to evacuate flammable fumes that can gather in the bilge for startup and below cruise speeds.

 

[nola mike]

I'm still very much an amateur, so I'd get some other opinions, but I took a brief look at your service manual and it says your thermostat should be opening up at 143F, same as mine. If your temp is getting as high as 175 and the motor is quitting, sounds like it could be overheating and I'd be starting at that thermostat. If you are overheating and you solve that problem, I'd be running some compression tests to see if you damaged the head gasket.

I don't think the blower does much for engine temp, that is to evacuate flammable fumes that can gather in the bilge for startup and below cruise speeds.

The stat on that motor is 160, the gauge temp is notoriously inaccurate. Blower running will probably change what you're seeing on the gauge. Barely turn over like a dead battery? If so, first thing I'd check is water in the cylinders causing a hydrolock.

 

[BeaverLakePete]

@turand
Stat is confirmed as a 160° and I only saw 170-175 ish after about a 8-10 minute wot burn. I believe the blower can affect the temp in the engine compartment, which in turn the affects the engine as well. It circulates air through the engine compartment, fumes out=fresh air in=cooler air...

 

[BeaverLakePete]

@nola mike
Hydro lock was my first thought, until it cranked up with zero hesitation next day. No oil in coolant, no milky oil. Going to put it back in the water today. Taking tools, a volt meter, and an IR gun. If it happens again gonna check temps, pull plugs and check for water, and/or check voltage drop and amps on Starter... Anything else?

 

[nola mike]

@nola mike
Hydro lock was my first thought, until it cranked up with zero hesitation next day. No oil in coolant, no milky oil. Going to put it back in the water today. Taking tools, a volt meter, and an IR gun. If it happens again gonna check temps, pull plugs and check for water, and/or check voltage drop and amps on Starter... Anything else?

The water will leak past the rings if allowed to sit The blower running didn't actually affect the temp. If your wiring is older the extra resistance created by turning the blower on can make the gauge read higher. You didn't confirm if slow cranking was the problem?

 

[BeaverLakePete]

The water will leak past the rings if allowed to sit The blower running didn't actually affect the temp. If your wiring is older the extra resistance created by turning the blower on can make the gauge read higher. You didn't confirm if slow cranking was the problem?

I had no way of checking voltage or anything the night it happened. It was dark by the time I got home and just covered it up until the next afternoon when it cranked up fine. Didn't die or even get warm running on the muffs. As far as the blower goes mine did lower the temp a few degrees after being switched on...

 

[BeaverLakePete]

The water will leak past the rings if allowed to sit

Also I did run it for 30 minutes on the muffs that next day, checked the oil after and absolutely no signs of water in oil