Messages

Derek, by scalding hot are you saying the water heater temperature exceeds the engine coolant temperature?

Jon - I should have been more clear...the hot water in the heater matches the coolant temp, around 195 degrees.  Sometimes I'll see steam coming out from under the sink.

Stu - good copy on the thermostat...will do, thanks!

Thank you all so much for all of the suggestions!  This will definitely help focus my troubleshooting efforts.  My next step will be to completely recheck every aspect of the raw water system from thru-hull to exhaust outlet to definitively rule out a blockage/restriction issue.

I used Ron's hand pump method when I refilled the coolant and I'm fairly confident it's not an air lock issue.

Stu - I did not replace the thermostat.  My thinking was that since I could watch the temp slowly rise and then hold steady at 165 for several hours, that the thermostat was doing its job.  But admittedly, I don't know much about thermostats.  Is there a test I could do to verify it's working or should I go ahead and replace it just to be safe?

As for the oil in the bilge...I'm not sure how much got in there, but it was enough to turn the water in the bilge black and send me into sheer panic (the bilge water was from the water heater pressure release valve).  Oil was spattered around the engine, e.g., on the alternator, the upgraded alternator bracket, the front of the engine and below it.  I couldn't identify from where the oil escaped the engine.  I drained the oil that night and gave it an oil change...there was no water or coolant mixed in with the oil that came out of the engine.

Ron - in the 6 months I have with the boat, the engine has always done this.  Holding around 2700 RPMs it'll heat up to 165 degrees...hold there for a couple hours...and then slowly start making its way up to about 195.  The water in the water heater will get scalding hot and will start spilling out the pressure release valve.  The previous two owners did not run the engine enough to replicate the issue, so it's hard to say when it started.  If I back down the RPMs or run it at idle the temp goes down.

Noah - awesome tips for the non-raw water related possibilities, thanks!  I'll go down that road after I double-check there's no raw water system blockage.

I'll post some pics and report back what I find next week.

Thanks again, you all are a wealth of knowledge!
Derek

Thanks for the replies!  Let me try to elaborate on your questions...

Air block - when I refilled the coolant I used a hand pump to circulate the coolant from the thermostat hose to the coolant reservoir until the coolant flowed smooth without any air bubbles.  It did take some time and initially I didn't have enough coolant in the reservoir to prevent introducing new air bubbles into the system.  Topping up the reservoir did the trick and I pumped until I didn't see any more air bubbles.  I did not remove or check either of the hoses going to/from the water heater.  I'll add those checks to my list.

Belt slip - the belt looks to be relatively new and in good shape.  It was a little loose when I first bought the boat but I tightened it up to about a 1/2" deflection and it looks like it's holding well without any slip.

Exhaust outflow - I tried to find specifications for my Johnson water pump on how much outflow I should expect at certain RPMs but I struck out and couldn't find any info.  When I visually compare outflow with other boats around the same size, it looks pretty normal, maybe a bit on the low side...not steady or constant, but it'll blow out a bit of water every 5 or 10 seconds or so.  I'm considering replacing the Johnson pump with an Oberdorfer, but that's an expensive troubleshooting experiment.

Heat Exchanger - no blockages or calcium buildup in the HX.  I did find some calcium buildup in the vented loop and the hose from the vented loop to the exhaust riser combiner...I replaced both the vented loop and that short hose.

Thanks again,
Derek

Good evening everyone!  I bought my first boat, a 1987 C34, about 6 months ago and I've put her through the wringer with an ICW passage south, Bahamas cruising, and then back to the Chesapeake.  I'm embarrassed of all the stupid mistakes I made along the way, but the journey gave me a great chance to get really intimate with all of the boat's systems.  I can't put into words how incredible of a resource this forum has been in every respect.  Seriously, thank you!

Currently, my most pressing issue is that the M-25XP w/ 3" HX seems to be running hot and there is constant white smoke out the exhaust.  I've had two mechanics take cursory looks, and both said that the engine was running fine and there was no immediate concern, although neither could pinpoint the root cause.  I'm hoping you all might be able to give me some advice to help me troubleshoot the problem and work toward a solution.

PROBLEMS: 
1) Constant white smoke from exhaust, regardless of RPM or engine temp.  I hate to say that I slightly overfilled the oil about a half a centimeter over the fill line on the dipstick and it was two days later that I first noticed the white exhaust smoke.  Upon further inspection I discovered that oil had made its way to the bilge, presumably through a pressure release valve on the engine.
2) Cruising around 2700 RPMs, the engine will get up to 165 degrees and hold steady for a couple hours.  The temp will then slowly rise before it levels off around 195/200 degrees.  If I back down the RPMs or put it in neutral, the temp will go back down.  Maybe this is normal and expected once the hot water heater has absorbed all the heat it can, I'm not sure?

WHAT I'VE DONE SO FAR:
1) Raw water seacock clear.
2) Raw water sea strainer clear.
3) There was a hard 90 degree turn in the hose from the sea strainer to the raw water pump and it looked like the hose was slightly collapsed.  Based on a post from Ron, I installed a 90 degree elbow to prevent the hose from collapsing...that seemed to slightly improve water flow out the exhaust but did not impact the engine temp or white smoke.
4) Replaced raw water impeller, it was showing signs of cracks (I've got a Johnson water pump)...no impact.
5) Removed HX, cleared out a couple pieces of what seemed to be old impeller bits, and gave it a muriatic acid bath...no impact.
6) Blew out or replaced 5/8" raw water hoses...no impact.
7) Installed new vented loop on raw water line...no impact.
8 ) Cut out the rigid hose from the exhaust riser to water muffler and replaced it with a hump hose...no impact (the original hose didn't have any blockages in it).
9) Flushed the exhaust hose out with a water hose from the water muffler outlet to verify that it had good water flow and there wasn't a wasp nest or something in the exhaust hose.  Water flow was good...no impact.
10) Verified that I'm not losing coolant...the level is holding steady.
11) Verified that I'm not losing oil rapidly...I have to add a couple ounces every 50 hours or so, but I suspect that's normal.
12) The HX and coolant hoses are hot to the touch; the hot water tank gets the water scalding hot and will spit some out of the pressure release valve into the bilge.
13) Replaced the fuel injectors based on a mechanic's advice...no impact.

Apologies for the long-winded post, I'm just trying to be as concise as possible and not miss any details.  Anything that can help point me in the right direction would be greatly appreciated.

Thanks again!
Derek