330 6BTa – cooling problem

test gadget

Here is a scetch of my home made test gadget

Problem solved!

Thanks to all who provided input – I have the problem solved. It was an undiagnosed airlock in the closed cooling circuit after all, which was presumably created by me, when filling up with new coolant after bench servicing the gearbox cooler, heat exchanger and after cooler.

It does cheese me off though that when Cummins was called it, to do a a-z health check on the engine, they picked up the overheating problem and put in a new thermostat, but failed to pick up or purge the airlock before replacing the thermostat!

For the benefit of others, this is what I have done.

Firstly I made up a 40mm piece with a 1/4″ socket to which I connected a pressure gauge. This I installed in-line just after the sea-water exit from the heat exchanger. This way, I was able to eliminate a possible sea water restriction in the exhaust mixer.

I then ran the boat with the radiator cap off the expansion (header) tank, slowly increasing speed, allowing the engine to heat up slowly. Once it went above 70 deg C bubbles started escaping from the coolant.

Once the thermostat opened the remaining bubbles escaped.

I then closed the radiator cap and opened the bleed nipple until a steady stream of un-aerated coolant escaped, closed up and voila – to the amazement of the technician, the problem was resolved.

I ran the boat with WOT on one engine only, and could not force the temperature to go above 83deg C after this purge !!!
Once again, Thanks everybody!

Reply 2

The boat is a 34ft Blackwatch (Similar hull to a Bertrams 31) It is about 12 years old and the engines have done 1800 hours but has been standing on the hard most of the time over the last 3 years, Therefore all the preventative maintenance done on all the coolers, raw water pump, injector and injector pump.

From new, this SB engine had a tendency to run a few degrees warmer than the port, but never “hot”
I do have a water heater on board and will check if it gets hot (I never use this – it might not even have fresh water in it at the moment)

The thermostat and almost all the coolant was replaced by Cummins a few days ago so maybe I do have an airlock somewhere….. When they return tomorrow, I will ask them to specifically check this. thanks for the feedback thus far.

330 6BTa – cooling problem – follow up

Thanks for your reply

I did post my questions……

In answer to yours:
1. I am using the original Cummins supplied VDO sender and switches as per the attachment
2. To the best of my knowledge there was no airlock after filling with coolant.
3. When the problem was first encountered, Cummins technicians installed a new Genuine Cummins thermostat 5292738 and new gasket and I presume that they have properly vented the coolant system when they re-filled it.
4. I have no idea why the alarm comes on at 196 deg F Note that I have verified that with a IR thermometer aimed at a spot right adjacent to the sender at the time. At the same time, the heat exchanger was still much colder at the inlet just below the vent valve (below 160 deg F) and the the actual body of the heat exchanger even colder just over 130 deg F.
5. At what temperature should the alarm come on, and once on, at what temperature should it switch off again?
6. Note that I do not believe this is simply an alarm issue – I have actually measured temperatures of 206 deg F adjacent to the sender before I slowed down to allow the engine to cool off

I now want to test the functioning if the coolant circulation pump itself – advice on how to do this or where to measure the pressure would be highly appreciated