Cummins 4bt overheating after conversion keel cool to heat exchanger

[Northeaster]

Hi folks. Sorry to be longwinded....This used engine was keelcooled with dry stack. I added a heat exchanger off of V8 chev I believe. I likely have one of the hose connected wrong as when keel cooled it had an expansion tank and now just has the little one pictured above heat exchanger.

First sea trial on new boat build and engine overheated went to about 220F and I shut it down. Seawater coming out of heatexhanger was cool. Back at dock I added antifreeze (as I had just connected new hoses and filled as full as it would take at the time, cold) and tried running at dock. This time stayed around 160F. Tried on ocean under load and overheated again. Back at dock added more antifreeze as small expansion tank went low when running. When shut down air bubbles came up so thought maybe airlocked. It seemed promising, as after adding about a gallon of antifreeze, and running at about 200 or 210F I got a surge of warm / hot water out seawater exit - figured thermostat opened.... and temp dropped to about 160 and stayed there at dock...not under load though. Out again on ocean and quickly overheated with seawater still cool when overheating - there was no surge of warm water in seawater exit... When not overheating seawater was warmer. I suspected maybe a sticky thermostat.... or still airlocked if that is possible.....

Currently only running a temporary electric water pump to circulate the seawater, but it does put out about 3-4 gallons per minute.. And, I would think if it were not capable of removing enough heat from heat exchanger I would find that the flow of water was warm/ hot all the time, just not enough volume. As mentioned, it is cold when the temp gauge goes high, so to me it seems like the engine / thermostat/water pump is not circulating enough hot antifreeze to the heat exchanger to have the seawater take on it's heat....but I am fairly new at marine engines.
Please have a look at hoses / setup for obvious errors.

One thing I noticed. While running at dock with pressure cap off the small expansion tank. There was hot antifreeze coming intermittently from the small hose connecting it just below pressure cap to the water cooled exhaust manifold. It has been 3 years since dismantling hoses from engine to paint so I may not even have them going to proper places. To me it seams like that small hose would go from below pressure cap to an overflow tank of some sort.... but if I have it wrong where does the small hose from the manifold go? It is on a double fitting with a somewhat larger hose. It looks like its correct based on net pictures I have seen, but the stock engines have large expansion tanks..... my setup from a gas engine doesn't....will this work on a diesel or do I need a larger expansion tank?

I also noticed tonight that the small expansion tank was not level (seen clearly in both pics), due to a fairly stiff new hose connecting it to front top of engine, near temp sensor - it was on an incline rising toward the belt / front end of engine, so I used some wire to bring it down to level. Engine was cold, but this caused small tank antifreeze to run into block so I again added more antifreeze...

Leads me to another question - As there does not appear to be an overflow tank, like on cars, how do you know if you have enough / too much antifreeze in system, if adding either when hot or cold? Can you put too much, if so what happens?

PS sea trial otherwise went well, lots of power, hit 22 kts before overheating and no leaks in new aluminum boat after a week in the water....

 

[kapnD]

The expansion tank overflow is going back to the top of the exhaust manifold, likely putting air into the system as the coolant heats and expands, as well as short circuiting the thermostat.
The fitting off the manifold is supposed to clear an air pocket at a high point to avoid uneven heating/boiling of the manifold.
I think you will need a larger expansion tank, and an overflow bottle to get this sorted.
Also fill the coolant SLOWLY to avoid air pockets, and run it for a few minutes without the cap to let it burp any air still trapped.
Shoot the cooling system with an IR thermometer to locate hot spots.
Check the thermostat operation, and make sure it is installed correctly, it will go in upside down with less than satisfactory performance!

 

[Northeaster]

Hi KapD - thanks for the reply and help!
The engine was used for years in another boat before I bought it, and was only taken out as the guy bought a bigger CAT engine for more power. Although the thermostat could be in wrong, I believe it should be in correctly as it was working ok before.

Should I take the thermostat out and check in boiling water, replace, or try running engine with no thermostat temporarily just to rule out the thermostat?

Or, do you think that trapped air, and/or the lack of a larger expansion tank could cause this with a healthy working thermostat and water pump?

I have a hard time understanding that the thermostat could be functioning properly as in years past with cars, you would see if the car heater had heat, if you suspected a bad thermostat... in my mind, the heat exchanger is like the car heater - if it is not getting heat, to pass on to the seawater, then I would think that thermostat is not opening correctly..... I don't know if too small of a tank or trapper air would cause this on their own..... but hope to learn!!

 

[FAST FRED]

The usual method for keel cooling uses no heat exchanger.

The circ water that would go to a radiator , (pushed by the stock internal engine water pump ), is fed to the external keel cooler and then directed back into the engine.

No seawater pump, no heat exchanger , although there can be a header tank to keep the coolant full regardless of water temp expansion.

Why so complex on your system?

 

[Northeaster]

Hi Fred. This engine was keel cooled in a larger fishing boat with a dry stack. I built a smaller boat and for various reasons didn't want a dry stack (small center console). So I bought a used heat exchanger off a chev gas powered engine and routed plumbing through heat exchanger. I am running an electric pump for seawater for now and have seawater going through gear cooler and then heat exchanger. But as pictured my used gas style heat exchanger came with the very small expansion tank or whatever it is with the pressure cap vs. A large expansion tank which seems common in images and videos of stock Cummins engines.

 

[FAST FRED]

If you do have a keel cooler , havinfg a sea water circuit just to service the exhaust id easy.

The engine circ pump easily runs 20-30GPM thru a radiator or keel cooler , it doesnt care.

Does the boat have a keel cooler? Or are you attempting to cool thru a heat exchanger , that is serviced by a tiny electric pump?

 

[Northeaster]

It does not currently have a keel cooler but is an aluminum hull so could be easily done, but not in the next few weeks.

The latter but it is not a tiny electric pump feeding the heat exchanger. It puts out about 4 -5 gallons per minute.
I just added an overflow container and routed both the overflow hose below pressure cap and the vent line from manifold to it. Ran at dock for 15 min or so and stayed around 160F. Circulation and thermostat seemed to be working as you would get a burst of warm seawater at exit (not currently hooked to exhaust). Then Temps started climbing to 200F and the seawater at exit stayed cold. To me this means my circulation and/or thermostat are intermittent. I don't believe the electric pump is at blame. It is pumping lots of cold North Atlantic seawater through the heat exchanger but I feel the hot antifreeze is not being pushed / passed through the heat exchanger regularly so that heat exchanger and seawater can do oits job of removing heat regularly.

When it was overheating very hot antifreeze was expanding / overflowing to the new overflow tank but was not going through the heat exchanger, as the seawater stayed very cold- unlike earlier when it was warming up a lot, effectively removing heat from the antifreeze and engine.

Please correct me if you see faults in my logic or have other ideas. Appreciate the help.

 

[FAST FRED]

When you get it running (remove the engines thermostat for a test) be sure to use a lazer thermometer to be sure the sea water exiting the heat exchanger is under 140F, to not plug with salt.

 

[baeckmo]

The sea water pump of a 4BT (130 hp/2500 rpm) should give 20 gpm (75 l/min), so your electrical pump is inadequate. The fact (?) that the sea water is leaving the system at low temperature today indicates that the engine coolant is not circulating correctly.

Is the exhaust manifold watercooled on your engine, and does it have a turbo and intercooler?

First check that the thermostat is correct; this device has a shunt function. When engine temp is low, the heat exchanger loop is blocked and the fluid is recirculated directly from thermostat housing to the circulation pump inlet. When temp is high, there is a small disc on the thermostat that will close the recirculation channel; all fresh water goes to the heat exchanger.

DO NOT RUN THE ENGINE WITHOUT A THERMOSTAT SINCE THIS WILL LEAVE THE RECIRCULATION DUCT OPEN AND THE ENGINE WILL OVERHEAT!

 

[kapnD]

Northeaster, you should post your query, with the pics, to boatdiesel.com. forums.
An awesome website where real experts (no offense to anyone here, you are getting good advice) will answer your questions.
I still think your manifold bleed line is incorrectly plumbed, and the reservoir is too small, as is the raw water pump and possibly the heat exchanger.
Have you verified that the heat exchanger is clean and functioning correctly?
Between inadequate raw water supply and possibly blowing air into the coolant loop, it is bound to continue to overheat.
An IR thermometer would be a big help in troubleshooting your motor.

 

[Northeaster]

My manifold and turbo are fresh water / antifreeze cooled - it is a factory marine engine, but was ordered as keel cooled, not heat exchanger cooled when purchased years ago.

Right now I just have a dry elbow- bare - no other pipes, muffler, etc for sea trail. And I am just dumping the seawater overboard with a hose. I have a wet elbow mostly finished -so will try and finish and connect it to wet hose, etc in next few days.

I tried last night without thermostat (Baeckmo - I had not read your post last night and did not know it would overheat with no thermostat at the time - I thought it would perhaps run too cool, as is common with cars ). Anyway, it seemed ok - went farther before temps started climbing too high and seawater was more consistently warm.
Then temps rose, seawater was then cool so shut off. Noticed overflow tank was full and later as cooled it went back into engine.

A friend pointed out that my rear large hose from heat exchanger to engine had a very high loop (as is stiff hose) and it is actually higher than pressure cap. He thought thus would have persistent airlock / airspace and I tend to agree. I will change plumbing today to make sure this point is below cap and has no air loop. I think trapped air would explain why it stops circulating (now that I have ruled out thermostat) and why the antifreeze would all be pushed int overflow tank as hot air expands.

The stock cummins heat exchanger has the rear large hose connection on the bottom (not the top as this mercrusier/ chev one does) so in factory setup, there is nor high rear hose. I may turn the heat exchanger upside down, so this hose connection is on the bottom. That would put the front one on bottom as well, but I can put a couple of 90 degree elbows ( or pre-shaped 180 degree hose) to bring this back up above and go to the small reservoir tank and fill / pressure cap. I don't see a downside to this as the front side will still fill and have no pas its below the cap.
Or, I could use an elbow or softer hose to keep the rear loop lower than the cap, but I like the first approach, unless anyone sees a big issue with it.

If this approach does not fix issue, I will consider joining boatdeiselm but I am happy as well with the advice given here - THANKS FOR ALL!

 

[Lepke]

Anti freeze above 50:50 will usually overheat. Straight anti freeze doesn't transfer heat as well as water.

 

[Northeaster]

Sorry. Yes. Have it mixed about 50 / 50. Thanks

 

[FAST FRED]

If freezing is not a problem 35% AF the rest water is fine for corrosion control..

AF has only 5/8 the heat transfer ability of water.

 

[Northeaster]

Thanks. Likely somewhat below 50 / 50 now anyway as have added more water.

I have now changed the thermostat to a new one and rerouted heat exchanger plumbing to mimimize high spots for air to be trapper.

Refilled with coolant. Ran at dock for about 15 min and temps slowly climbed to about 170F at a bit more than idle. Then the temp spiked to 190, 200, 210F within 30 seconds or so. I really feel that it is not circulating as the antifreeze in small reservoir that the fill / pressure cap is on was cold. There was not warm or hot antifreeze circulated to it. There was hot coolant coming intermittently from the manifold vent line to the overflow bottle.
I can't believe that the whole block or all of the coolant is going from 160F to 210F in a minute or less...so is it not circulating and the high reading is only for a small body of coolant near the sensor?

I don't have a temp gun here so may rig up another temp gauge tomorrow. Gauge could be faulty but temp climbs slowly before the spike so I feel it's likely accurate.

Stumped. Help please.