engine overheat full rpm

[Andy king]

hi. had my cummins 6BTA rebuilt sounds great when running took out for trials when doing around 1500/2000 rmp all good temp wise but soon as you give her full load temp go up to 200 far ease back off then the temp settles back down,again run at lower rpm no problems could this be thermostat problem,or maybe air lock any help please. cheers Andy.

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[Rob Schepis]

Good progress..

[Andy king]

hi mate
done like you said we drained old coolant could only run her up on berth as weather pretty crap here right now,but took her up to 85 it then settled back down to 80 more coolant went in than before by 3 liters so was air lock. but heres the crunch thought i check thermostat someone had put it in the wrong way round so subject to a real sea trial i would say its all good now. i send few pics as well later but thanks for help mate.

[Rob Schepis]

Send pictures too, pictures are always helpful. Also – if you have anything external plumbed into your coolant loop such as a water heater with a coolant heat exchanger be sure they are not air bound

[Andy king]

thanks very much mate we are going to drain off tomorrow and re do i send message let you how it go. cheers

[Rob Schepis]

When you refill the coolant you should refill very slowly and this will help with eliminating any air trapping. Squeeze the coolant hoses to push out any trapped air. On your first run leave the expansion tank cap loose and bring her slowly up to operating temperature to open the thermostat, 1,000 to 1200 rpm’s should do it. If you watch the temp gauge you may see a quick jump of the gauge but it should stabilize. Then let her cool down and top off and this should have burped out any air and prevent any hotspots. Never hurts to do it a second time. These small hoses (spitters) going to the coolant expansion tank are vents, although the back of the tank is higher than the front, for air burping purposes keep the coolant level in the tank a good inch or so down.

[Andy king]

thanks for reply mate sounds like air to me then as i noted the coolant was put in quick no hoses was squeezed all the above was not done, so if i was to flush the engine and put coolant back correct this could sort it ??.

[Rob Schepis]

Naturally the first two things that come to mind are the seawater side and the coolant.

As to the seawater side – Not sure what your “rebuild” entailed – were all coolers replaced or at least pulled and bench serviced? Pump and impeller new or ?? Hoses all checked, especially connections on inlet side of pump and seacock or strainer – confirm she’s not “sucking air” or a collapsing/kinked inlet hose?

Coolant – were you mindful in not getting the coolant loop air bound?….. very slow fill, squeeze the hoses along the way, burp the engine at tstat opening temperature with the exp tank cap loose, etc ?

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