Universal 35B Intermittent Overheat

A

adelboat

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Oct 12, 2012
15
Catalina 36 East Greenwich
Hi, all - hope you are enjoying a great season! A bit of unseasonal weather this season in NE, but always great to be on the water!
I have a wonderful 2001 36 MKII with a Universal 35B with only one issue: there is some air blockage in the engine cooling circuit to the potable water heater. If I bypass the circuit it works fine. If I funnel engine coolant into the hose, burp the coolant, and purge the petcock on the engine top, then also fine. It seems, tho, like I should not have to do this (and get hot water)!
We have had the boat for 6 years. The first three - perfection. At the end of season four we replaced the water heater. Had no trouble the rest of that year, but experienced intermittent overheats the start of last year. We used the same exact replacement heater, in the same exact location - have not changed the position/elevation of the water heater relative to the engine. Any thoughts? What are we doing wrong?!
 
jviss

jviss

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Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
Why do you think the overheating is related to the water heater? Could be something else entirely, like a clogged heat exchanger, broken impeller, clogged strainer, etc.
 
A

adelboat

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Oct 12, 2012
15
Catalina 36 East Greenwich
Yes, indeed! Should have added: when taking the water heater out of the equation, the engine runs perfect all season - cool and calm, just like like the captain!
 
A

adelboat

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Oct 12, 2012
15
Catalina 36 East Greenwich
Had a great cruise to Westport this summer - awesome harbor (once you are in)!
 
jviss

jviss

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Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
adelboat said:
Had a great cruise to Westport this summer - awesome harbor (once you are in)!
Click to expand
Yes! It's a beautiful harbor, but at times challenging. The CG has trouble keeping up with the shifting sand, in terms of buoy placement. The rocks don't move year to year!
 
jviss

jviss

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Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
adelboat said:
Yes, indeed! Should have added: when taking the water heater out of the equation, the engine runs perfect all season - cool and calm, just like like the captain!
Click to expand
I have a C36, too. I replaced the water heater maybe five years ago. I have a bypass that adjustable, but set and forget - never an intermittent overheating problem. Maybe you still have an air bubble in there?
 
kloudie1

kloudie1

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Nov 6, 2006
9,893
Hunter 34 Mandeville Louisiana
A bad "radiator cap" might be letting in enough air to re-start the problem after you've burped it..
 
jviss

jviss

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Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
kloudie1 said:
A bad "radiator cap" might be letting in enough air to re-start the problem after you've burped it..
Click to expand
Good catch.

Is there a coolant recovery tank? Is there coolant in it?
 
A

adelboat

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Oct 12, 2012
15
Catalina 36 East Greenwich
Really good catch - will replace the cap! Yes, there is a coolant recovery tank (plastic), with coolant in it, but there does not seem to be good communication between the hose and the fitting in the neck of the radiator - was nervous about "cleaning" out the fitting that connects the overflow hose to the radiator....
 
jviss

jviss

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Feb 5, 2004
6,745
Tartan 3800 20 Westport, MA
This isn't mine in the pic, but it looks exactly like this:


There's a pipe with connections for the engine coolant hoses and heater hoses on both ends. If the valve in the middle is closed, all of the coolant flow is forced through the water heater. This can lead to overheating. If that happens, you open the valve some, to allow some coolant to bypass the water heater, increasing the flow.
 
RoyS

RoyS

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Jun 3, 2012
1,742
Hunter 33 Steamboat Wharf, Hull, MA
Is your water heater higher than your heat exchanger?
 
A

adelboat

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Oct 12, 2012
15
Catalina 36 East Greenwich
Thanks, all - "it takes a village"!
Yeah - I know how to burp it, just wish't I did not need to! Was thinking about replacing the heater hoses to the water heater - and replacing the hose clamps. Water heater is lower than engine - same location as original.
I guess the confusing part, to me, is the intermittent nature of the problem. I have fixed many problems on boats over the past 35 years. I can either fixit or not - unusual to get this correct (last season) and to have it overheat this year. The common sense and Forum consensus is that air is getting in somehow: leaky radiator cap, hose clamp, possibly worn hose not readily visible.
Guess we know what 'we' are doing this weekend!
 
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