Overheating mysteries solved (I hope)

[Claygr1]

Since we bought our boat in 2006, the engine temperature has consistently been in the 180-190 range and even up to 200 with extended motoring.  Reading through the postings on this site and the technical notes, I decided that this was the year to bring the engine temperature down to 160 range.  You might be interested in our experience because it encompasses a number of problems that have been written about on this site and in the technical notes. 

We started out by checking the thermostat.  It turns out it indeed had failed so we replaced it.  This brought the temperature down to the regular range of about 180 degrees.  We next opened up the end of the heat exchanger.  About five large chunks of old zincs fell out.  A ha!  We started up the engine and it ran back up to 180.  Not wanting to take the entire heat exchanger off, we next tried two separate treatments of pouring  Limeaway into the water pump output hose and letting it sit for an hour.  We started up the engine and again it ran back up to 180 degrees. 

The next step was to open up the raw water pump and inspect the impeller and the water pump gasket and cover.  The gasket and cover looked fine but the impeller had a tiny crack in one of the vanes.  After struggling to remove the impeller, we inspected the elbow of water pump where the water is expelled.  A ha!  There, lurking in the corner, was a big black piece of impeller.  Apparently, PO thought that impeller pieces disappear when the impeller shreds.  That was cutting off at least a third of the water output from the pump.  We ran the engine and it went right back up to 180.  Insert much foul language here to get the full effect. 

Thinking about this some more, I figured that if PO was careless enough to not track down one piece of impeller, there may be others stuck in the water output hose or the heat exchanger.  Biting the bullet, we took the heat exchanger off.  Keep in mind that I have no doubt that this heat exchanger, and, more importantly, the coolant and water hoses to the heat exchanger, had not been disassembled since hull #871 left Woodland Hills in 1989.  After many scraped knuckles and a thorough dousing in coolant, we got the heat exchanger off.  I felt like I was opening Al Capone's vault when I slipped the socket wrench on the end bolt.  All of this work paid off, though, because there were two nice big fat pieces of impeller in the first quadrant of the heat exchanger.  Otherwise, the heat exchanger looked to be in pretty good shape inside.  Our boat has always been in Lake Michigan, so we don't have the issues presented by salt water.  Regardless, we poured in radiator cleaner and let it sit overnight.  We flushed it the next morning and reassembled the next day. 

This time, thinking that we must have solved the problem, we started the engine and watched anxiously.  The first thing we noticed was that we had considerably improved the water flow from the exhaust.  The next thing we noticed is that the engine temperature ran up to 180.  At this point, kayaking was starting to look like a good hobby. 

I read through the various postings on this topic as well as the technical notes on dealing with overheating issues.  I came to the conclusion that this likely was an instrumentation issue now.  Keep in mind that the water temperature in Lake Michigan is 56 degrees right now and we we're shooting a lot of it out the back of the boat. 

We noticed late last summer that the voltmeter, fuel and temperature gauges would occasionally (i.e., every thirty seconds) "jump" in unison.  At the same time we were working on the overheating issue, I had sent a post to this site to see if anyone had any ideas about the possible cause.  The two consistent responses were "sounds like a bad ground connection" and "have you done the wire harness connection upgrade yet?"  The answer to the latter question was "i've bought the kit and it's on the list of things to do. . . ."

Well, in a "Serendipity must be trying to tell us something" moment, we went to the boat last weekend to go for a sail, turned the engine key, and got absolutely nothing from the tachometer, voltmeter, and fuel and temperature gauges.  Dead as a doornail.  We did have power to the glow plugs and blower and the engine started up just fine.  We ultimately determined that yes indeed, it was a bad ground connection somewhere in the damned rubber plugs either at the instument or engine end.  We ran a new ground connection and the instruments powered back up perfectly plus our "jumping" problem was gone. 

So, the conclusion you all have been waiting for - we took out the boat last night and motored for an hour and she never got above 160.  Ah, sweet satisfaction. . . . it feels so good when you stop pouding your head against the engine block (metaphorically and literally speaking). 

To forestall the many replies I would get otherwise, the wire harness connection project begins tomorrow morning. 

Thanks to all of you who posted in reply to my pleas for help plus the many contributors (Ron and Stu particularly come to mind) who have written on these topics over the years.  I don't want to even think about owning a "seasoned" boat without these types of resources and support. 

[Ron Hill]

Clay : Thanks for being a "living testament" that reading the posts/projects/Mainsheet tech notes, can make you a wiser, happier and smarter C34 owner.  Good Luck in the future!!!