Universal Diesel 5411 overheats with recirc line open, never gets warm with recirc line pinched closed

Jun 20, 2021
18
Catalina 30 Arkansas River
B490718E-85A8-4766-AE98-01E19E5BBC31.jpeg


New to me boat that's been sitting for two years. I recently got the engine started. Engine temperature was fine for the first hour of run time, then it began to get overly warm. The Sherwood impeller had come apart. Upon replacement, I found several impeller vane pieces in the water pump ports, both the inlet and outlet. I didn't find any pieces in the thermostat or thermostat housing. I back flushed the engine from the thermostat housing through the water pump (impeller cover removed), with the full flow of a water hose, no noticeable resistance.
Now my engine will eventually overheat unless I pinch closed the recirculation hose, this forces the hot water to exit through the muffler instead of heated water recirculating endlessly. I've blown through the thermostat housing to muffler hose by mouth, no noticeable resistance. The thermostat is new and I've verified that it opens when warm and closes when cool. With the recirculation hose pinched closed, the engine never gets up to operating temperature (as if the thermostat isn't closing).

To recap- With the recirculation line open, the engine overheats. With the recirculation line closed, the engine never gets warm.

Thanks.

B490718E-85A8-4766-AE98-01E19E5BBC31.jpeg
 
Oct 22, 2014
16,148
CAL 35 Cruiser moored EVERETT WA
With the recirculation line open, the engine overheats. With the recirculating hose closed, the engine never gets warm.
Looking at your diagram. The critical point is the thermostat. Are you sure that the thermostat is working properly.

Thermostat in your system needs to be closed sending water down the recirculating hose til the water temp gets to 135 degrees. Then the thermostat needs to start opening sending some water out the exhaust and some water into the recirculating hose.

When water temps are above 150 all hot water goes out the exhaust.

I'd check the thermostat for proper function.
 
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Nov 22, 2011
981
Ericson 26-2 San Pedro, CA
Looking at your diagram. The critical point is the thermostat. Are you sure that the thermostat is working properly.

Thermostat in your system needs to be closed sending water down the recirculating hose til the water temp gets to 135 degrees. Then the thermostat needs to start opening sending some water out the exhaust and some water into the recirculating hose.

When water temps are above 150 all hot water goes out the exhaust.

I'd check the thermostat for proper function.
This was my thought as well, based on the way in which it malfunctions. However, he did say that he tested the thermostat. Nevertheless, I'd look at it a second time. Since pinching or not pinching that hose is essentially functioning after the manner of the thermostat and achieving the expected result, it almost seems as though it has to be the thermostat.
 
Oct 22, 2014
16,148
CAL 35 Cruiser moored EVERETT WA
Yes Alan, the action being taken to pinch the recirculating hose is functioning as the thermostat should be.
 
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Jun 20, 2021
18
Catalina 30 Arkansas River
It's a new 143F thermostat. I pulled it out when the engine temp was 180F. The thermostat was open until it cooled in the air, then it closed.

Also, no water comes out of the exhaust with the recirc hose open, none. With the recirc line pinched closed, lots of water comes out of the exhaust. How does pinching off the recirculate cause it to discharge a steady flow from the exhaust (preventing the engine from reaching operating temp)? The thermostat should prevent water from entering the exhaust when it's closed.

I need to look at the thermostat housing again to confirm but I think a closed thermostat should force all the water to recirculate and an open thermostat allows some water to enter the exhaust and some to recirculate (both) (it doesn't force the water to exhaust, by design).

Note- this all started when the impeller came apart. I suspect there is a piece of vane stuck somewhere causing the problem. But water can and will flow freely throughout the system when I force it to.
 
Last edited:
Dec 2, 2003
622
Hunter 260 winnipeg, Manitoba
Are you sure the thermostat is installed in the proper orientation? I believe an incorrectly oriented stat would behave as you describe. Spring and wax pellet housing should be oriented towards the engine.
 
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Dec 28, 2015
1,357
Laser, Hunter H30 Cherubini Tacoma
Try flushing the block with different hoses off. You might have pieces floating around in the circuit and getting stuck on things when the engine is running. This happened to me and I found a bunch of pieces in the hose that goes from the raw pump.
 
Jun 20, 2021
18
Catalina 30 Arkansas River
From the internet. He was having an Universal 5411 overheating issue, no mention of him trying to pinching off the recirc hose to force cooling:
Kerry, The problem is now resolved. The thermostat has 2 small holes in the flared seat. When installing the thermostat it must be seated so both holes are open on the seat. There is no indicator on the thermostat or the thermostat assembly to guide it. The thermostat just drops in place but there is only a small area in which the holes are open. The manual does not mention this and all the "experts" I consulted did not know this. This allows a small amount of water to pass through to the exhaust at all times. When the temperature rises to 143 degrees the thermostat opens and all the water passes through to the exhaust at the same time cutting off recirculation flow back to the throughhull input, thereby causing the water pump to pick up new cold water. This new cold water cools the engine, closes the thermostat and the process starts all over again. Thanks for your input. I hope you learned something about small universal diesels

Rodney

I've seen the two 1/8" holes in the thermostat flange. So I read, they let a constant small amount of cooling water enter the exhaust system to cool it. I didn't realize they needed to be oriented a certain way. And I don't know how their orientation prevents larger amounts of water from entering the exhaust when the thermostat opens. Interesting.
 
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Jun 20, 2021
18
Catalina 30 Arkansas River
Solved: I read on the internet that a $25 Mercury-Mercruiser 47594 Thermostat 143F would fit the Universal 5411 vs the $109 OEM Z2707, just drill the two 1/8" holes on the flange for exhaust cooling flow. It did fit, physically.
The OEM thermostat has a nipple on the bottom. When the thermostat opens, the nipple stops flow into the recirculation orifice, forcing flow into the muffler/exhaust orifice. The $25 thermostat doesn't, allowing endless recirculation of the coolant water.

https://www.catalinadirect.com/shop-...l-diesel-5411/

https://www.wholesalemarine.com/merc...ostat-143.html

Also, my OEM thermostat does need oriented correctly to allow flow through the 1/8"holes.
Thanks for the replies. I'm learning.
 
Nov 22, 2011
981
Ericson 26-2 San Pedro, CA
Solved: I read on the internet that a $25 Mercury-Mercruiser 47594 Thermostat 143F would fit the Universal 5411 vs the $109 OEM Z2707, just drill the two 1/8" holes on the flange for exhaust cooling flow. It did fit, physically.
The OEM thermostat has a nipple on the bottom. When the thermostat opens, the nipple stops flow into the recirculation orifice, forcing flow into the muffler/exhaust orifice. The $25 thermostat doesn't, allowing endless recirculation of the coolant water.

https://www.catalinadirect.com/shop-...l-diesel-5411/

https://www.wholesalemarine.com/merc...ostat-143.html

Also, my OEM thermostat does need oriented correctly to allow flow through the 1/8"holes.
Thanks for the replies. I'm learning.
Glad you no longer have a problem. But I'm still a bit unclear as to what failed on your original thermostat. You said it had been working fine and then stopped working after your impeller issue.
 
Jun 20, 2021
18
Catalina 30 Arkansas River
The original thermostat didn't fail. The engine began overheating due to impeller pieces stuck in the water pump inlet and outlet. I changed the thermostat while going through the coolant system looking for impeller pieces, just as general maintenance (causing the continuous recirculation issue). Thanks