witchy woman
Cadet
- Joined
- Apr 13, 2009
- Messages
- 20
Sorry, this is a long one, but I've been chasing this rabbit for a few weeks now. Keep in mind that prior to this incident, the engine ran fine - but maybe hotter than it should have.
Engine is Mercruiser 2007 5.7L, 2 bbl carb. Sorry, can't tell you the serial number (it's not the original engine). Drive is Alpha One, gen 2. Bayliner boat if that helps. Original engine was a 1999 5.0L serial number 0L345352 and current engine is set up exactly the same way as the original.
Ran aground in the inlet about a month ago. Soft grounding, but the prop bumped in the sand enough that I wanted to pull the outdrive and have a look. I did and everything was fine, but while I was at it, I replaced the water pump in the lower unit, greased everything and put it back together. Outdrive joints, shaft, gimbal bearing and engine coupler appear to be fine. Good alignment - shaft slipped in like it had eyes of its own. Water pump was not damaged, but it was several years old so I replaced it while I had the thing apart. There was a pretty good pile of sand on the outside of the waterpump housing.
Since I was in inspection mode, I pulled the thermostat housing. It was clean. Moved on to the exhaust risers to see what condition they and the manifolds were in since it's getting about time for them to be replaced. Exhaust system looked much better than I expected, but I haven't run the boat much in the last 3 years (mostly haven't had the time). But I was surprised to find that the thermostat was a 140 degree, which I understand is correct for saltwater where I do most of my boating. I was surprised because my gauge always ran at 175 degrees. So I tested the thermostat per the Merc manual and it worked fine. So I put everything back together, new gaskets everywhere. The thermostat was in correctly. It's not possible to properly seat the plastic keeper in the housing if the thermostat is in upside down. I should also say that before this incident, the exhaust manifolds and risers never got so warm that I couldn't hold my hand on them (which makes me question the calibration of my temp gauge).
Now on muffs in the yard gauge shows about 165. Took the boat out and at anything above about 2000 RPM the temp gauge ran up to 175 then suddenly dropped off to 140, then repeated the cycle over and over. It looked like a sticking thermostat, so I put in a new 140, pulled the outdrive one more time just to make sure I hadn't missed anything and just for giggles, I put the old water pump back in. Now on muffs it was rock steady at about 165 degrees, so I put it in freshwater this weekend and the temp gauge did the same thing - up,down, up down. So I eased down the river for a while, anchored, cleaned the boat while kids swam, then decided to pull the thermostat out for the trip back - just to eliminate it as a source of the problem. When I removed the thermostat housing, it was full of water, so I felt confident that the outdrive was putting water into the system. Running (at about 3400 RPM) on plane back to the ramp the temp was pretty steady at 150 degrees and only wavered about 5 degrees up or down. At this point, I'm blaming the exhaust for not letting the water out because I felt like the temp should be lower than 150 with no thermostat.
But! About half way back to the ramp, we suddenly hear a rattling sound so I slowed and idled back to the ramp. Had no idea what this new problem was but it was not audible at low RPM. Well, yesterday morning, I wanted to start the process of elimination, so I pulled the supply hose off the thermostat housing and had it in a bucket to test the volume of water coming from the outdrive, but the engine wouldn't turn over. Hydrolocked. I pulled the exhaust off both sides, risers, spacers and manifolds, then began pulling spark plugs. Third one back on starboard side let out a gush of water. I'm fairly certain I have a blown head gasket - no water in the oil. Turned the engine over and oiled the cylinder several times to protect it until I can get to it. Next step is a compression check, but I think I know what I'll find. I set both manifolds upright and filled them with water and neither showed any leakage overnight. They're actually in very good condition and I no longer think they are at fault in this. The manifold to block gaskets were in good shape as well. I'm pretty sure the mysterious "rattling" sound was caused by the blown head gasket (at least I hope it's the gasket and not a cracked head).
So after all that, here's my 2 questions - 1)why is the engine temp fluctuating so badly? 2) why did a head gasket suddenly decide to blow (if it did - haven't confirmed that yet)?
I have a theory, but I'm long on theory and short on solution right now.
Engine is Mercruiser 2007 5.7L, 2 bbl carb. Sorry, can't tell you the serial number (it's not the original engine). Drive is Alpha One, gen 2. Bayliner boat if that helps. Original engine was a 1999 5.0L serial number 0L345352 and current engine is set up exactly the same way as the original.
Ran aground in the inlet about a month ago. Soft grounding, but the prop bumped in the sand enough that I wanted to pull the outdrive and have a look. I did and everything was fine, but while I was at it, I replaced the water pump in the lower unit, greased everything and put it back together. Outdrive joints, shaft, gimbal bearing and engine coupler appear to be fine. Good alignment - shaft slipped in like it had eyes of its own. Water pump was not damaged, but it was several years old so I replaced it while I had the thing apart. There was a pretty good pile of sand on the outside of the waterpump housing.
Since I was in inspection mode, I pulled the thermostat housing. It was clean. Moved on to the exhaust risers to see what condition they and the manifolds were in since it's getting about time for them to be replaced. Exhaust system looked much better than I expected, but I haven't run the boat much in the last 3 years (mostly haven't had the time). But I was surprised to find that the thermostat was a 140 degree, which I understand is correct for saltwater where I do most of my boating. I was surprised because my gauge always ran at 175 degrees. So I tested the thermostat per the Merc manual and it worked fine. So I put everything back together, new gaskets everywhere. The thermostat was in correctly. It's not possible to properly seat the plastic keeper in the housing if the thermostat is in upside down. I should also say that before this incident, the exhaust manifolds and risers never got so warm that I couldn't hold my hand on them (which makes me question the calibration of my temp gauge).
Now on muffs in the yard gauge shows about 165. Took the boat out and at anything above about 2000 RPM the temp gauge ran up to 175 then suddenly dropped off to 140, then repeated the cycle over and over. It looked like a sticking thermostat, so I put in a new 140, pulled the outdrive one more time just to make sure I hadn't missed anything and just for giggles, I put the old water pump back in. Now on muffs it was rock steady at about 165 degrees, so I put it in freshwater this weekend and the temp gauge did the same thing - up,down, up down. So I eased down the river for a while, anchored, cleaned the boat while kids swam, then decided to pull the thermostat out for the trip back - just to eliminate it as a source of the problem. When I removed the thermostat housing, it was full of water, so I felt confident that the outdrive was putting water into the system. Running (at about 3400 RPM) on plane back to the ramp the temp was pretty steady at 150 degrees and only wavered about 5 degrees up or down. At this point, I'm blaming the exhaust for not letting the water out because I felt like the temp should be lower than 150 with no thermostat.
But! About half way back to the ramp, we suddenly hear a rattling sound so I slowed and idled back to the ramp. Had no idea what this new problem was but it was not audible at low RPM. Well, yesterday morning, I wanted to start the process of elimination, so I pulled the supply hose off the thermostat housing and had it in a bucket to test the volume of water coming from the outdrive, but the engine wouldn't turn over. Hydrolocked. I pulled the exhaust off both sides, risers, spacers and manifolds, then began pulling spark plugs. Third one back on starboard side let out a gush of water. I'm fairly certain I have a blown head gasket - no water in the oil. Turned the engine over and oiled the cylinder several times to protect it until I can get to it. Next step is a compression check, but I think I know what I'll find. I set both manifolds upright and filled them with water and neither showed any leakage overnight. They're actually in very good condition and I no longer think they are at fault in this. The manifold to block gaskets were in good shape as well. I'm pretty sure the mysterious "rattling" sound was caused by the blown head gasket (at least I hope it's the gasket and not a cracked head).
So after all that, here's my 2 questions - 1)why is the engine temp fluctuating so badly? 2) why did a head gasket suddenly decide to blow (if it did - haven't confirmed that yet)?
I have a theory, but I'm long on theory and short on solution right now.
