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troubleshooting engine overheating problem

Sep 25, 2008
108
Catalina 30 MKIII Beach Haven
OVERHEATING CAUSES AND TROUBLESHOOTING FRESH WATER COOLED ENGINES
· Engine overheating can be a common problem on sailboats with diesel engines. If the engine overheats excessively, shut it down ASAP or damage could occur to the impellor or engine.
· Check the antifreeze level in the overflow reservoir. If empty, there may be a leak of antifreeze. Check the bilge for any antifreeze. If so, check hoses for leaks. Always carry spare antifreeze onboard your vessel. Once the leak is found and repaired, refill the reservoir. Let the engine cool then remove the pressure cap to check antifreeze level.
· If coolant is replaced, air can be introduced into the system causing an air block. If air gets in the cooling system, the system needs to be bled. This can be done by opening the coolant bleed valve (sometimes located near the thermostat housing) or with the engine running at high RPMs, remove the pressure cap. Refer to the engine manual to properly “burp” or “bleed” the coolant system.
· Overheating is frequently caused by an external blockage to the seacock intake or debris into the seawater strainer. With the engine shut down, close the seawater intake seacock and remove the strainer to check for debris.
· If the strainer is clear, momentarily open the seacock to see if sea water comes through. If so, the seacock is clear and most likely not the problem.
· Remove the raw water hose momentarily exiting from the heat exchanger to make sure raw water is flowing to the riser.
· Check the exhaust to make sure a steady stream of water flows from the exhaust pipe. If not, there could be a hole in the riser allowing gases to escape or a blockage in the exhaust hose.
· If the raw water system seems Ok, check for debris in the heat exchanger. A common problem is pieces of the zinc can break off inside the heat exchanger. This can cause an intermittent problem as the pieces can shift around inside the exchanger tube. To check this, remove the end cap and look inside for any debris.
· Other possible causes for overheating can be a bad impellor, loose or faulty belt, thermostat, low engine oil, clogged or faulty heat exchanger, bad riser and even the pressure cap or anti syphon valve. The sender or temperature gauge could also be bad.
· There could also be a bad hose or blockage in the hose. Check these hoses for leaks or blockage.
· If everything checks out OK, there could be something wrapped around the prop causing excessive stain while motoring under load.
 
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Feb 26, 2004
21,004
Catalina 34 224 Maple Bay, BC, Canada
· If coolant is replaced, air can be introduced into the system causing an air block. If air gets in the cooling system, the system needs to be bled. This can be done by opening the coolant bleed valve (sometimes located near the thermostat housing) or with the engine running at high RPMs, remove the pressure cap. Refer to the engine manual to properly “burp” or “bleed” the coolant system.
Good point. The REASON this occurs most times is the line from the engine to the water heater, which needs to be completely filled to avoid an air bubble.

Engine Overheating 101 - How to Burp Your Engine (Reply #6) http://c34.org/bbs/index.php/topic,4518.msg26462.html#msg26462

IN many cases, these types of instructions are ENGINE SPECIFIC, too. Yanmars and Universals may be different.
 
Apr 13, 2015
1
Catalina 30 Point Roberts
depending on the year of your boat, i have a 1986 and the cooling system is different there is a mixing valve and the tank is in the cockpit. Look on image to find the instructions. The previous burping do not apply
 
Nov 12, 2016
8
O'Day 302 Sarasota
I have an enigma when it comes to overheating... I own a Hunter 376 with a Yanmar 3JH2E. The other night, I had to pull up anchor at midnight and when I started the engine (relatively) cold, the overheat alarm went on and never ceased. Knowing the motor is not hot, I kept going. Went like this for 45 min. Next morning, ran it again for an hour with no problems, and alarm went on again as soon as I started.
Note: I personally changed the impeller, mixing elbow and checked the exchange heater about 6 months ago. Water is coming out under out of the seawater drain. Is this an overheat sensor issue? If so, what is the PN and where is it located? The Yanmar manual does not specify.
Thank you.
 
May 20, 2016
2,911
Catalina 36 MK1 94 Everett, WA
I have an enigma when it comes to overheating... I own a Hunter 376 with a Yanmar 3JH2E. The other night, I had to pull up anchor at midnight and when I started the engine (relatively) cold, the overheat alarm went on and never ceased. Knowing the motor is not hot, I kept going. Went like this for 45 min. Next morning, ran it again for an hour with no problems, and alarm went on again as soon as I started.
Note: I personally changed the impeller, mixing elbow and checked the exchange heater about 6 months ago. Water is coming out under out of the seawater drain. Is this an overheat sensor issue? If so, what is the PN and where is it located? The Yanmar manual does not specify.
Thank you.
Follow the wires.... most likely it’s towards the front by/above the waterpump or thermostat. It will usually have one wire going to it.