Cummins 6CTA overheating at WOT

G

GMAN1

Member
Sep 4, 2008
90
Fort Lauderdale, Fl
Boat Info
51 Sundancer
Engines
Cat 3196
Need help with 42 foot SeaRay with twin Cummins 6CTA's. Port engine runs perfect. Starboard engine runs over 210 degrees if throttles are 3/4 to fully open. The minute I slow down the temp backs down to 160 degrees. What am I missing?

I did the following:
Cleaned thru hull of any debris
Strainer
Pulled off raw water hoses and flushed with fresh water to remove any blockage (None)
Checked oil cooler for blockage - flushed good
New water temp sender
New impeller
After cooler and heat exchangers ultra sonically cleaned
New t stats

Again it runs perfect at idle all the way up to 3/4 throttle. It then slowly starts to creep up past 200 degrees once I get past the 3/4 mark to full throttle mark.
 
I heard about coolant from diferent brand mixe or react with diferent part of the system and could coat metal part and prevent good heat exange

if you find please let us know im very curious. also maybe a good question to ask on the boatdieasel forum
 
Just a general statement about diesels- overheating may also be due to engine overloading, not necessarily a cooling system problem. Have you ruled out a fouled or slightly damaged stbd. prop? Any smoke?
 
There is some smoke blowing out of the exhaust at high speeds. The prop could be damaged but I do not have any vibrations.
 
Forgot to ask- was the stbd engine able to turn up to your target rpms at WOT? (I'm assuming the port one does...?)

Failing to hit max rpms- and overheating due to overloading- can be due to growth/fouling on the prop. And, it doesn't take much- a few lousy barnacles can do it. I'd check the easy stuff like this first. Jump in the water (well, easy for me to say- water temp is 80 here, don't know where you are) or hire a diver to check it. My $.02
 
You have done everything that I would have considered in the way of troubleshooting and repair.
My stbd engine would approach ~200 degrees shortly after I bought the boat-the T-stats were the culprit. I wonder if one or both of the t-stats that went into the stbd engine are faulty, and are perhaps not opening as they should?
Have you confirmed the temperature with the engine mounted gauges? This is a stretch, but I made it a point to check the engine mounted gauges in my boat, in order to eliminate a gauge error at the helm. In my case, both the helm and engine mounted gauges showed the same reading.
 
Seems to me that if the t-stat were defective the engine would overheat at normal cruise rpms (and below)- not only when nearing WOT.
 
Sometimes, when coolant gets old and begins to silicate, deposits are left on the stem of the thermostat. Those deposits can prevent the thermostat from opening all the way when they will operate normally in other respects.

The description of this problem reads just like the engine is running out of cooling capacity, like with a dirty heat exchanger, or a fouled fuel or transmission oil cooler that are in the cooling circuit. For that reason, I am curious about the ultra sonic cleaning. No one uses such a method in our area. Where we are, the core is removed, acid cleaned and the tubes rodded out. Some of the crud is very hard to get loose and gone, so I wonder if the ultra sonic method described got the system clean.

Your location is a mystery, so we don't know if you are in fresh or salt water, but sometimes, an oyster shell will form in the sea cock or hose ahead of the strainer. you might try closing the sea cock and removing that hose to see what is inside.
 
Thanks guys for all the replies. I am located in South Florida (Fort Lauderdale area). I talked to Cummins today and they are baffled too. Both engines at WOT reach 2600 rpm's each engine. I have used a thermal laser gun to check temps all over engine and really nothing out of normal. I am leaning toward the prop. I took a dive in the water and checked them out. Has that sharkskin feel to them. I can clean up the best I can and check out if this fixes it.

To comment on ultrasonic cleaning of heat and after coolers - they are hotted dipped in a tank. They come out clean as a whistle. You lose all stickers and they need to be repainted. Most radiator shops do not do it because of EPA issues. The way to go.

I will keep everyone posted on progress.
 
I had a similar heating problem on a near new Cummins 6BTA 370. After considerable sea trial diagnostic testing by Cummins BC, we determined it was a faulty heat exchanger. This exchanger was a "U" shaped unit (double bypass heat exchanger?) which had the inlet and outlet near one end. This meant the water had to travel all the way down and back the length of the unit. Unfortunately, there was an internal leak "across" the unit, shortening the path for the water and reducing the effectiveness of the exchanger. It only caused a problem at wide open throttle. New exchanger solved the problem.
 
sbmar.com said:
GMAN,

You have two thermostats--One could easily be at fault...........

Tony
Click to expand...

My thought as well, restricted water flow is still the issue. These thermostats are about all thats left to check out.:huh:

If you go for the Thermostats, might as well change them to 180 degree models and get a happier engines in the bargain. Also, there is a right angle reduction hose under the coolant reservoir that is a PITA to get to and while you're there a new one with new clamps might be advisable.

Good luck.
 
Last edited:
Thanks for all the replies. I did fix the problem. It was the intake manifold temp sensor that mounts to the heater grid. It was faulty causing the block heater to constantly stay on. I swapped it to the other engine and that engine started to overheat at WOT. Put new one in and perfect now.
 
Hi, I know this is an old thread, but I'm having a very similar problem and I'm wondering if the problem is the same as you had. My confusion and question is related to the block heater aspect of the issue. I have the same engines, but I don't have block heaters. Would it be unlikely that I have the same issue with the sensor if I don't have heaters? Many thanks.
 
You must log in or register to reply here.

Forum statistics

Threads
113,267
Messages
1,429,703
Members
61,145
Latest member
Chris1
Back
Top