Cummins 4bt overheating after conversion keel cool to heat exchanger

Tonight I tried a new loaner aftermarket temperature gauge, directly off the sensor, to compare with my gauge. But, the sensor has two leads and this gauge only had pos, neg and S - I assume for sensor. It seemed to work as it gradually rose but must not have been calibrated, or I did not have to connected correctly, as it started around 150F, and finished at 260F or so, whereas my gauge started at below 100F and topped at 210F - when I shut the engine off. I did not connect both gauges to the sensor at the same time, just one at a time and switched the wires to compare.

So, still not sure if my gauge works properly, but I believe it is more accurate than these false high readings- as it certainly wasn't 160F to start - engine was cool, say 75F.

One note though, as it was warming up, we got much more consistent bursts of warm seawater exiting and my temp gauge seemed to go up a bit, then stay there or cool a bit as the seawater took heat away, then seawater would go cold, temps would rise a few degrees, and the seawater warm again, temps drop a bit, and so on. This cycle went on a few times till it got around 200 - 210 so I shut it off.

As Baeckmo has mentioned I should have much more seawater flow (ie 20 gpm) I will likely break down and buy the proper gear driven Cummins / Sherwood m71 seawater pump. This electric setup was really just to sea trial and sea how the new boat performed. I am happy with the 23 kts hit so far, and the handling, so I can now justify making a bit more investment...buying the proper pump and doing more sea trials before continuing finish work this winter.

I don't understand though, if I was at 190F - 200F for more than 5 min or so, why was the thermostat not open more often / longer so it could circulate more hot coolant to the heat exchanger, more frequently?? seems to me the seawater flow would have been able to take away more heat, as I had cycles of perhaps 30 seconds or 1 minute of cold water exiting before say 30 seconds or a minute of hot water..

Anyway, I will likely get the proper pump and sea if that fixes things, or just rules out one more, expensive....thing..

 

Quick update - still have a bit of work to do trying a larger expansion tank, than the very small one pictured with pressure cap on it.
But, looks like the main culprit was air / lack or coolant in the system, which prevented hot coolant from getting to the heat exchanger intermittently. had boat out twice today and on 1st run we kept it under 1500rpm for about 30 min with temps staying good. but, when I opened it up more, temps started to climb. I shut it off and when I notice the reservoir and tank were cold, I opened it and added coolant. \then started it up and it immediately sent hot coolant to exchanger and temps dropped. After that ran mostly below 2000 rpms for another half hour and temps stayed good.
On 2nd run worked well and didn't overheat at all, but didn't run too hard.

I now have an overflow tank as well and have it at about the same level as the pressure cap. If I run it hard I notice coolant coming up out of the small vent line from the water cooled manifold which I have running to the over flow tank. On stock Cummins 4bts I believe it goes to the expansion tank, so hence the thought of using a larger one and routing this hose their.

will also get stock gear` driven pump as I think my electric pump is near it's max when I run med -hard - puts out alot of hot seawater.

 

Depending on the pressure cap , you can purchase the style that with a slosh bottle will refill the expansion tank with the captured overflow.

This is how its done on modern cars and trucks as getting ALL the air out allows a 25% smaller radiator , a huge cost saving.

Many boat cooling FW side is only 5 psi or so , locating a pressure cap to refill from the slobber tank might be a hassle.

When all the experimenting is over use DISTILLED water to mix with the anti freeze.

 

Hi Fred. Thanks for the additional help. I know it would have been mich easier to buy the stock Cummins expansion tank but I didn't go that route. Here is a pic of my current setup. It was only for testing and will be more permanent and better laid out later... I do have a plastic slobber tank connected but if I put it lower the manifold vent hose will fill it and starve the engine of antifreeze. Maybe if I reversed it to feed bottom of slobber bottle it would backfill as well???

 

water pump on engine

i would remove the water pump and check the impeller, and give the engine a flush

 

With the downward connections shown in the pics, there is a risk of air accumulating in the hexc. Use the (now upward pointing) drain to create a leak-off to the expansion vessel. A 2 mm dia hole in the plug would be appropriate. Beware to use the right ("inner") plug.

 

Would it be better to turn it back right side up and just try to keep loops lower than the pressure vessel?

Turlte-. I am getting new/ proper sea water pump anyway, so I don't need to check the impeller on the electric one. It works fine for its normal use.

 

With a keel cooler, you would have a pump and this pump would circulate the freshwater through the motor and back to the keel cooler.
It sounds like the pump that you have installed is hooked to the seawater side.
But is there a circulating pump on the freshwater side for the engine.
Probably but??
On some jet inboards, raw water cooled, the raw water off the pump was just routed through the engine without a circ pump.

So for a freshwater system to work you need a sea water pump and an engine circ pump

 

Hi Barry. Thought I replied already but yes I have an in engine, belt driven stock circulating pump for coolant and a seawater pump for seawater circuit. Currently using electric pump for seawater but stock gear driven Cummins / Sherwood seawater pump will be here soon!

I think largest issues now solved as I have installed larger coolant expansion tank - see pics

 

Bravo!

 

quick update - Have used the boat numerous time since installing the larger expansion tank and it stays around 180 degrees - working great.
also installed the proper gear driven cummins/ sherwood sea water pump. and measured temp of seawater at exit while running hard - can't remember exactly but it was around 110F so think all is well.

Thanks for the help!

 

Thank you for updating!

 

Permit me to revive this thread, if only to ask the following question:

How does the size (volume) of the header tank influence the closed-cooling circiut ?

Just by adding extra thermal inertia to the cooling circuit, thereby keeping engine temp. within limits ? Or is there more to it ?

Hats off to Baeckmo who was quick to spot the way-below-rated sea-water pump-flow initially employed for this app.

 

This whole thread is an exercise in futility!
Cummins has already figured all this stuff out, all that needs to be done is bolt the OEM parts back on and drive away.
Not to say that improvements cannot be made, but the baseline (original configuration) merits close scrutiny, and the OP does not appear to be taking it into consideration.

 

Cummins probably just purchases whatever is installed from a 3ed party.

A good look at how it was done should work to purchase similarparts at 1/5 the Cummins pricing.