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Regular Contributor

Re: 3512 DITA Low coolant pressure

Coolant pressure, particulary if your systems / switch trip point is more than a few psi, should be taken at the discharge of the water pump and before the engine oil cooler. This is where the pressure is at a maximum and is consistent regardless of thermostat operating position. Measuring the pressure at the location you describe is outlet pressure and with inlet controlled thermostats from this point the coolant is flowing directly to the expansion tank and back to pump inlet when thermostats are closed and as such will be low pressure. The pressure at this point will increase as the thermostats open and flow is now subjected to the resistance offered by the heat exchanger circuit but will still be less than pump discharge pressure.

New member

Re: 3512 DITA Low coolant pressure

Hey thanks for the reply, the machine has in fact been on another of our ships before being installed on this one and it's certainly been, er, adapted to fit the ships in its time.The coolant pressure is taken off from the housing immediately below the regulator housing, the one where the head outlets return to via the exhaust manifolds. Not sure if this is the original or a yard special. The problem only seems to have manifested since the refit, as I say the engine was sitting alone and unloved for a year. It does not overheat when run unloaded, we're considering putting it online manually in order to see if there is sufficient circulation and cooling even with the lower pressure. A colleague of mine from another ship, who I just bumped in to quite randomly, suggested the engine has had a history of gassing up. Guess I'll look for more places to bleed the beastie ^_^
Regular Contributor

Re: 3512 DITA Low coolant pressure

Has his problem only started recently after the refit ? These engines are inlet controlled thermostats but the operating position of them (open, closed or somewhere in between) should have no bearing on the jacket water pump discharge pressure.

Does the engine overheat? Assume your sensor and test point are in the correct location?

New member

3512 DITA Low coolant pressure

Hi all, I'm tasked with a headscratcher and I'm hoping to find some help here - please!

 

I work on a UK merchant ship and one of our diesel generators is a CAT 3512 DITA, driving a 1MW alternator. It's old but only has around 6000 hours run time. I've been maintainer for this set before and it's mostly been reliable. None of the guys in my outfit are CAT trained or experienced, it's literally this one engine that's here as something of a corporate afterthought.

 

I've joined the vessel after a lengthy lay-up and refit, and the CAT does not want to play after nearly 12 months out of service. I've solved all of the problems except one - the cooling water pressure is way down, approx 4psi when I'm expecting something more like 12. This is right on the alarm point and stops our PMS from having automatic control of the set.

 

It does seem to circulate, when I start the engine off-load the temperature increases evenly throughout. I've gotten it up to approx 140 degrees, well below the operating temp or trip. We have it pumbed in to a seawater cooler and the coolant exits the engine hot, goes back in stone cold. There's a steady discharge if the pump outlet bleed is opened.

 

After a thorough but fruitless bleeding of air, I took the engine driven coolant pump off for a look-see. The bosses and I all agreed that it looked serviceable. Next, the bossman wanted me to look at the temp regulators. These were looking tired, and were very stiff but I managed to work them and they now move - I didn't withdraw them for testing, for fear of damage as getting spares is a major evolution in this outfit.

 

I've bled it everywhere I can think to do so, and all I get is water. The expansion tank pressure cap is U/S and doesn't seal, but since the tank is vented anyway I can't see that making a difference. Everything else is tight and leak-free.

 

One of my colleagues is suggesting replacing the regulator cores as a matter of course, and I wondered what you folks might think about that. Otherwise, I am at a loss of what to suggest as a next step! Any and all suggestions appreciated, thanks in advance.