02-18-2011 07:06 PM
Hi guys....As you may all know, high temp is by far the number one enemy of diesel engines. I have lots of friends with boats with different engine brands, MAN, Cummings, MTU, Volvo and other and they all run at a much lower temp (160-170F). My ONAN Generator at full load runs at 165F. I know that Caterpillar run hotter than other engines, but which should be the normal operating temp range? There are lots of different opinions on this issue. I think here our friend from Caterpillar have the chance to help us on this matter and tell us ....WHAT IS HOT.
02-20-2011 12:10 AM
Older CAT engines were right in line with the competetion, old school thinking was cooler was better, long before fuel consumption and emissions a concern. Typically lube oil temp runs about 15 degrees hotter than the jacket water temp, means most engines were running with a lube oil temp below 200 degrees F. At that temp the lube oil has a hard time cooking off moisture and some water soluble contaminents. Also, to "overcool" a given size engine requires extra cooling system capacity, meaning a larger cooler (more weight) and a larger cooling pump or pumps (more parasitic horsepower). Allowing the engine to operate at a higher "normal" operating temp allows a larger approach temperature and you can get more cooling efficiency.
Most current engines have a shutdown at 225 degrees F and alarm at 215 degrees F, and not just CAT, I recently was on a diesel electric system with 4 1.8 MW marine Cummins units, and we verified jacket water system protections at those same temperatures. A vessel with MTU units I visited several months ago appeared to run cooler, until we noticed the gauge was reading the inlet, not outlet temperature.
I think you'll find virtually all newer engines trying to meet current tier emissions levels will be running at higher jacket water temps. Frankly in all the engines I get around I don't see any negative impacts from operating at teh higher temps, and I think oil life is somewhat improved, although hard to fully quantify since there have been so many significant changes in lube oils and their additive packages in recent years.
So my two cents, I would consider a current production engine operating normally up to about 210 degrees F, as long as the lube oil temp to the engine (after the cooler) was within about 15 degrees of that. I would not operate any modern diesel engine below 180 degrees F for extended periods of time, otherwise I think you'll see reduced lube oil life, sludge and varnish buildup, and a reduction in fuel efficiency.