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Overheating issues, it can't be this hard!

Jun 1, 2019
19
Oday 30 Saugatuck
Hello again my beloved Sailboat Forum,

I'm having an issue with my engine overheating. After getting towed in (again) and my own troubleshooting, I am stumped:

I have a 1980 Oday 30 with a Universal Diesel engine M20 5416. I recently discovered that the exhaust piping coming from the manifold lead to nothing (the pipe was missing). Apparently there are downsides to buying a cheap old sailboat. Always ran fine despite the carbon monoxide we were probably breathing in.

I replaced all the pipe with galvanized piping leading back to the water locker. The fresh water intake went through the engine and to the water locker as always. After replacing the pipe, filling the coolant with proper fluid, sealing off any leaks, I am still overheating. I did the normal trouble shooting. No issues with the impeller, water still exiting the stern of the boat, it sounds like a coolant issue.

The coolant does travel through the engine and goes to a non working hot water heater (I don't know why). Perhaps I didn't bleed the line correctly but there are no bubbles coming from the line as discussed in previous threads on this page.

Any advice would be much appreciated. Thank you for your help as always.

Jim
 

senang

.
Oct 21, 2009
200
hunter 38 Monaco
Check that the thermostat is functioning correctly. Take it out and put it in a pan of water on the galley. Use a thermometer to check opening temperature.
 

BarryL

.
May 21, 2004
827
Jeanneau Sun Odyssey 409 Mt. Sinai, NY
Hi,

Troubleshooting overheating can be complicated because there are two separate water systems and both must work correctly.

First go through the raw water (sea water circuit). Make sure the raw water pump is working correctly - it is sucking up sea water and sending to to the heat exchanger and then out of the exhaust. If you see good water exiting with the exhaust then this is probably working correctly.

Next check the engine coolant system. This should have an automotive type antifreeze coolant. You need to make sure the water pump and thermostat (if present) are working. Since you have a water heater this gets a little more complicated. Trace the coolant hoses. They should go from the water pump to the water heater then to the heat exchanger and then to the coolant tank. When the engine is running the hoses should be HOT and you should be able to feel coolant moving through the hose. Squeeze the hose and see if you can heel coolant moving through. With a water heater it is EASY to get air in the system and an air lock that prevents water from flowing. You may need to remove the hose and 'burp' the line a few times.

Good luck,
Barry
 
Jan 4, 2006
3,820
Hunter 310 West Vancouver, B.C.
Antifreeze cooling systems can be a bugger if you get air bubbles in them when changing the coolant.

Ensure that both your overflow tank (normal level) and your coolant reservoir (full to the neck) are at the correct levels. Run your engine at the dock (cheaper than a tow) and VERY CAREFULLY check your idling engine to see if the return hose to the heat exchanger is getting warm. This may take up to 10 minutes for the engine to warm. If the coolant to the HEX remains cool, it's possibly an air problem (pray it's not an internal blockage). As an alternate, also see @senang 's comment.

I'm not familiar with your engine and the elevation of hoses so hopefully someone will jump in here on how to best purge air from an Universal Diesel engine M20 5416.

Good luck and let us know how it works out.
 
Feb 26, 2009
518
Oday 30 Anchor Yacht Club, Bristol PA
pictures of your installation would help those trying to help you, it may be a design flaw in your exhaust system but hopefully not!
I had a 5416 in my oday 30 pretty reliable Little engine the water pump for the coolant was bad had really noisy bearings it's actually a Kubota motor and I found a replacement on an eBay supplier of tractor parts. You want to be sure you don't have a bad coolant pump also be very sure that your raw water pump is up to the task if it's the oberdorfer it's easy to rebuild.
We also had a bad anti-siphon Loop elbow, of course you want to make sure your heat exchanger is clear and doesn't have debris like parts of old impellers clogging the passages.
 
Jun 1, 2019
19
Oday 30 Saugatuck
Check that the thermostat is functioning correctly. Take it out and put it in a pan of water on the galley. Use a thermometer to check opening temperature.
I thought about that as well but the thermostat wasn't the reason I was having issues in the first place. I may give it a shot if I can't troubleshoot other options listed, thanks for the reply.
 
Jun 1, 2019
19
Oday 30 Saugatuck
Hi,

Troubleshooting overheating can be complicated because there are two separate water systems and both must work correctly.

First go through the raw water (sea water circuit). Make sure the raw water pump is working correctly - it is sucking up sea water and sending to to the heat exchanger and then out of the exhaust. If you see good water exiting with the exhaust then this is probably working correctly.

Next check the engine coolant system. This should have an automotive type antifreeze coolant. You need to make sure the water pump and thermostat (if present) are working. Since you have a water heater this gets a little more complicated. Trace the coolant hoses. They should go from the water pump to the water heater then to the heat exchanger and then to the coolant tank. When the engine is running the hoses should be HOT and you should be able to feel coolant moving through the hose. Squeeze the hose and see if you can heel coolant moving through. With a water heater it is EASY to get air in the system and an air lock that prevents water from flowing. You may need to remove the hose and 'burp' the line a few times.

Good luck,
Barry
Good stuff, I will give that a try next, thanks for your help
 
Jun 1, 2019
19
Oday 30 Saugatuck
Antifreeze cooling systems can be a bugger if you get air bubbles in them when changing the coolant.

Ensure that both your overflow tank (normal level) and your coolant reservoir (full to the neck) are at the correct levels. Run your engine at the dock (cheaper than a tow) and VERY CAREFULLY check your idling engine to see if the return hose to the heat exchanger is getting warm. This may take up to 10 minutes for the engine to warm. If the coolant to the HEX remains cool, it's possibly an air problem (pray it's not an internal blockage). As an alternate, also see @senang 's comment.

I'm not familiar with your engine and the elevation of hoses so hopefully someone will jump in here on how to best purge air from an Universal Diesel engine M20 5416.

Good luck and let us know how it works out.
Will do. I think I am on the hunt for some air in the hoses. Thanks for the reply
 
Oct 22, 2014
15,834
CAL 35 Cruiser moored EVERETT WA
If you see good water exiting with the exhaust then this is probably working correctly.
Additionally, the volume of water should increase as the RPM increases.

What temp shows when the engine is over heating?
It happens that stuff gets caught in the coolant or raw water lines. I would flush the system and remove the heat exchanger for cleaning. You can take it to a radiator shop which for about $70 will boil it out. Clean any debris from the unit. Pressure test and paint it. Good as new. You may find that goo or parts of an impeller fin have clogged the hoses.

One last thought. You have 2 pumps on the system. The Raw Water pump when you change the impeller, and an engine coolant pump. These engine coolant pumps have seals that occasionally fail. You will notice a fine mist or a drip of coolant coming from the pump. It is a sign that the [pump needs service.
 

RoyS

.
Jun 3, 2012
1,162
Hunter 33 Steamboat Wharf, Hull, MA
Probably an air bubble under the thermostat. Your engine should have a bleed device somewhere high up in the cooling system to expel the bubble. When you are changing antifreeze you must open this bleed device to even completely drain the old coolant. Then when filling with new coolant you must open to bleed air out. Close when coolant runs out. I added one of these to my Yanmar for bleeding. Cost about $5.00 at an autoparts store.

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Jul 5, 2011
598
Oday 28 Madison, CT
An easy thing to check is to pull the hose off the raw water pump to HE and check that it has no old impeller pieces partially blocking it anywhere and then at the heat exchanger where the hose attaches pull the end cap off and see if there are pieces there. A few of these can easily add 20+ degrees in operating temp.
 
Jun 1, 2019
19
Oday 30 Saugatuck
Hello All, just a quick update: I was able to locate the bleed valve on top of the engine for the coolant line. Ran the engine, air came out, closed it off. No more issues. Ran for 3 hours on Saturday and never got above 160 degrees. The kids got sea sick, but that a different thread post.
 

RoyS

.
Jun 3, 2012
1,162
Hunter 33 Steamboat Wharf, Hull, MA
Remember to open that bleed device when you next drain your coolant. If you drain your coolant without opening the bleed only a small amount will actually drain out. The rest will be held in the block by the sealed bleed device. Test this for amusement by draining the coolant with the bleed still closed until it stops. Then open the bleed and watch as the rest of your old coolant pours out.
 
Jul 5, 2011
598
Oday 28 Madison, CT
Might be useful for folks to know where this bleed device is exactly, say on the Universal's. Any photo or schematic available?
 
Feb 26, 2004
21,899
Catalina 34 224 Maple Bay, BC, Canada
Last edited:
Feb 26, 2004
21,899
Catalina 34 224 Maple Bay, BC, Canada
Thanks, Stu. probably safe to say if the engine is running 180 temp. or so at 90% throttle, probably not much air trapped right?
Yes. In fact, if there still is a reasonably big air bubble in the system, you will overheat in the slip at idle - it's almost immediate.
 
Jul 5, 2011
598
Oday 28 Madison, CT
Yes. In fact, if there still is a reasonably big air bubble in the system, you will overheat in the slip at idle - it's almost immediate.
Wow, that is impressive did not know that. Really small ones probably work themselves out also I am rough guessing....