Engine Air Lock, Engine Heating Problem?
Original Message:
Engine Air Lock, Engine Heating Problem,
Hi --I changed my coolant just before lay-up last season. The
engine wanted to overheat, but I shut it down before that happened,
and decided to deal with it during spring commissioning. This is the
first e-mail I received on this topic. Could you "fill" me
in on the details of what happened and what the cure is? I'd
appreciate it.
Pete Lyssa, #393, PSmullen@connstep.org
Subj: Re: Engine Air Lock, Engine Heating Problem,
After you drain the internal coolant (50/50 Prestone and water),
you will probably experience an air block in the hose that goes
through the water heater (which is a heat exchanger) causing the
engine to overheat.
Although the Universal Operators Manual tells you how to purge the
system, I found an easier, faster method.
- Remove the "radiator cap" and fill the reservoir
with the coolant mixture.
- Then remove the hose from the water heater return to the
bottom of the thermostat housing.
- Connect a small hand pump, like the PAR Pump ("Handy
Boy", Boat U. S. Item # 162003), and pump the coolant from
that hose into the open reservoir until you get all of the air
out of the system.
- Then reconnect the hose (with your thumb capping the top of
the hose until reconnected) to the thermostat housing.
- After reinstalling the radiator cap, start the engine.
- If the temperature starts to go up to fast periodically open
the butterfly valve on the top of the thermostat until you get
the juice squirting out and then close it.
This should have eliminated the air block and the coolant should
flow freely.
I also use this PAR pump to bring up water to the raw water-cooling
pump (Oberdorfer) after changing an impeller. It's much easier on
the engine pump impeller to have the water "right there."
If you don't have a coolant recovery system, you may want to install
one. See MAINSHEET article Aug 1990. The Par pump is one item that I
consider a must item on any sailboat. I suck out over filled
transmission fluid or engine oil with it.
Your engine temperature should be running at about 160 Degrees
Fahrenheit. The range of the error for the Teleflax engine
temperature gauge at 180 degrees Fahrenheit is + or - 3 degrees. FYI
71 degrees Centigrade or (159.8F) is stamped on the thermostat
(MAINSHEET Aug 1992).
Ron Hill, Apache #788, Ronphylhill@erols.com
Subj: Re: Engine Air Lock, Engine Heating Problem,
Dear Ron:
Thank you for your reply and the "CURE" I didn't have a
small hand pump so I used a 50 CC (ml) BD hypodermic syringe without
the needle to suck out the coolant from the small hose to the
thermostat assembly. After a few attempts, it worked. Our water here
in Monterey Bay runs about 53 to 58 F and my normal engine
temperature is about 160F Again.
Many thanks, Howard Robinson
Subj: Re: Engine Air Lock, Engine Heating Problem,
I have found the following way is the most effective way to get
air out of the entire fresh water system. I fill the water tank with
50/50 then open the petcock on the top of the thermostat, which is
on the top of the engine.
The next step is to crack open the water heater, heat exchanger,
line that is located at the engine compartment access door in the
aft cabin. You will see the two water lines with a connecting
fitting. I open the return line fitting and start the engine. When
the air is purged, fluid will start coming out of this line. Tighten
the fitting and go to the petcock. When the fluid comes out of the
petcock tighten that up. Refill the water tank with 50/50 and let
the engine run for a while. Make sure you run the engine above idle.
If you can, run the engine while the transmission is in gear. This
should bring the operating temp to a more realistic level. Before
you go on that long trip make sure you take the boat out for a test
run, and be ready to solve an overheat during the test run.
Rich Dwyer, Rebellious #328, RPDIII@aol.com
Subj: Re: Engine Air Lock, Engine Heating Problem,
I fully agree on the PAR pump. I have had one for years, and use
it to change engine fluids. With a long pickup hose, removing
transmission oil is a piece of cake, and a funnel with a long hose
makes refilling just as easy.
Pete Lyssa, #393, PSmullen@connstep.org
Subj: Engine Air Lock, Engine Heating Problem,
The air lock could be in the lines that run from the engine to
the hot water heater and back. What I have done in the past is start
the engine and, one at a time, remove the lines from the top of the
engine (not from the hot water heater) until antifreeze comes out of
the top of the engine (beside the thermostat) and then replace them.
After this is done, open the petcock on top of the thermostat until
antifreeze comes out. This should take care of the problem.
Hope this helps.
Chap Hodges, Kemosabe #344, kemosabe1@home.com
Subj: Engine Air Lock, Engine Heating Problem,
Well, I put this off long enough but it is time to tackle my
engine overheating problem. I have an '85 c-30. Starting last summer
I noticed the higher the rpm (above ~2000) the hotter my m-25 would
run. It could keeps a steady temp of 180 at 2000 rpm
- The raw water pump impeller is good.
- I have never lost any impeller blades in the engine
- The raw water intake hose doesn't collapse at any rpm
- The raw water strainer is clean.
- I have a good stream of water from my exhaust.
- I get the same temps with the thermostat in and out.
- No other noticeable changes in engine performance
Michael.Fair@hboc.com
Subj: Engine Air Lock, Engine Heating Problem,
My first thought is the heat exchanger (it has the older smaller
one). Can anyone suggest some other things to look at if it checks
out OK?
I have an 86 Cat 30 with M-25 engine. I fought overheating problems
for 5 years (bought boat a neglected repossession in 90).
Do you have the hot water heater mounted in the port cockpit
lazerette?
Do you have the fresh water (Prestone) overflow tank in the cockpit
lazerette?
Do you have the Rube Goldburg plumbing/bypass valve mounted under
the heat exchanger that controls the amount of engine cooling water
going to the hot water heater?
You are on the right track with the heat exchanger. Lime and salt
deposits lower its efficiency. Take it to a radiator shop and have
it boiled out.
Another major problem is zinc tips. The small pencil zinc eats
through in the middle. The tips drop off and will plug the water
passages lowering the efficiency of the heat exchanger. Take it off
and shake it hard. If it rattles you have zinc tips. They are
difficult to get out because the old heat exchanger only has an
access cap on one end. (The wrong end for zinc’s) If you pound and
shake long enough you can get them out through the zinc-mounting
hole.
Another major source of problem is air locks on the fresh water (Prestone)
side. Air locks are a problem because the filler cap is NOT the
highest point in the system. (If you have the hot water heater in
the cockpit lazerette). The hot water heater is. Catalina recognized
this as a design problem and moved the heater to in front of the
fuel tank in about 87-88. However, moving the hot water heater is a
major project. (You have to move the fuel tank back and the new
design is slightly smaller I think). There are several things you
can do.
1. Take out all of the Bypass water heater rube goldburg
plumbing. Plumb the heat exchanger direct. Plumb the hot water
heater to the little tiny hose that bypasses the thermostat (it’s
on the thermostat housing on the front of the engine-top). Simply
remove the little hose and hook up the input and output hoses of the
water heater to the connections. You will have to get some hose size
reduction couplers. Catalina also made this change in newer boats.
2. If you have the overflow tank back in the lazerette, there
will be a little check valve between the overflow tank and the hose
leading to the hot water heater. This check valve is black plastic
about 2 inches cube. This check valve is NOT designed for Prestone
and is probably not working properly. (It’s supposed to help get
the air bubbles out of the fresh waterside.) West marine carries
them in the catalog. You can try cleaning if you want but the rubber
is probably shot and swollen from the antifreeze. Both of these
actions will help prevent air locks and poor circulation on the
fresh waterside.
You said the impeller "is good". Do you mean it
"Is good" or do you mean it "looks good". The
blades can get stiff and not seal well even though it looks ok. If
the impeller is more than 2 years old, I would recommend you replace
it even if it looks ok.
Bottom line. The older heat exchanger system is marginal and has
very little reserve capacity. You could have one major problem or a
number of little things all lowering the efficiency enough so that
at hi power; the system can’t quite hack it. Catalina recognized
this and went to the bigger heat exchanger. I recommend that too.
Georgeg305@home.com
Subj: Engine Air Lock, Engine Heating Problem,
Finally plucked up enough courage to attack my heat exchanger.
Pulled it out of the boat and flushed it internally. After
reinstalling it, I was unable to put back all the green (antifreeze)
water. I have read everything in tech talk and discovered that each
boat is set up differently. The boat would run for hours at about
165' now I can get it up to 180' at the dock in about ten minutes.
It would seem to me that there is air in the system, and I'm also
assuming that it is at the pump, as I'm not feeling any heat at the
heat exchanger or the lines going to it. The only bleed point I can
find is on top of the thermostat housing.
What temp should the thermostat open? I was wondering if I needed to
run the temp up higher to open it, and maybe the air will vent that
way. I do have a small water heater but can only find something that
looks like a pressure relief, no vent plug. This is a 25XP engine.
Ian "Repose", #5125, SW FL, igfowler@gateway.net
Subj: Engine Air Lock, Engine Heating Problem,
I don't think that my story relates directly to your problem,
but just in case . . . I had the same problem some time ago and I
tried, with no luck, almost everything listed in the previous
letters: changed impeller, removed the water heater from the
circuit, cleaned the (small) exchanger, etc.
Finally, I called a good local mechanic to request his services
fearing the worst (valves, injectors, compression, etc.) but he
suggested to first check the bottom and propeller for rope, growth,
etc. A bottom-cleaning job performed by a diver solved the problem.
The anti-fouling paint had protected the hull but the prop and shaft
were heavily coated product of a warm winter and not enough use. He
also changed the zincs. Overall, a bargain
Enrique, Argentum, 83 C-30 #3221 TRBS, Houston, TX, danlives@swbell.net
Important: The opinions expressed here are
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the Catalina 34 National Association or Catalina Yachts, Inc.
Additionally, this material has not been reviewed by Catalina
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suggested modifications or upgrades. Please obtain assistance from a
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