Volvo tmd 40 139 hp 6 cylinder turbo diese l984 overheating

This motor drives a 46 ft 18t

This motor drives a 46 ft 18tonne Yacht
At 1000 rpm all o.k.
At 1200 rpm temp rises to 100c
At 1400 rpm over heating starts
We have cleaned Heat Exchanger and oil cooler tubes.
The heat exchager rubber end cap may be faulty. could this be a water by pass problem?
Could the thermosat in the heat exchager bea problem?
Could this thermostat be removed without detriment to the engine performance?
Are there any other possible solutions?

"The only thing that could hap

"The only thing that could happen if the end caps were bad is getting raw water in the expansion tank or visa versa, which is not good but would not be the cause of your problem. The thermostat my be the problem, but do not remove it without replacing it with a new one. Your engine must maintain the proper temp for economy, performance and so that the exhaust is not to cool as this will cause scaling and corrosion.
I assume that you have checked the raw water pump and impeller and the coolant (fresh water side) pump, sea strainer and through hull."

"Since Your raw water/exhaust

"Since Your raw water/exhaust temp does not give alarm it is most probaly a 'internal circulation' problem. Did it happend sudden or gradually. If sudden, check the thermostats. I think to remeber there should be two and with different temp setting. If so, be sure to replace them with right specifications.
If it has happened gradually, and there is no smell of exhaust in the fresh water cooling expansion tank, You should try to clean the freshwater side. If the expansion tank has traces of oil/exhaust, the head gasket is probably gone."

"James
Replace the pressure c

"James
Replace the pressure cap on the tank. If the fluid is not under 7-15 lbs of pressure the fluid will not move, even though the pump is turning."

"Had a similar problem with a

"Had a similar problem with a
TMD40-A. After cleaning out all of the coolers and piping to no avail it was resolved to the cast iron turbo exhaust elbow being a clogged ball of rust internally. The raw water was being obstructed there. Replacing the exhaust elbow fixed the problem. The new one has a stainless steel internal diffuser.

Ray
M.V. ShelyAnn
http://bcmarina.com"

"same problem. also took off t

"same problem. also took off the exhaust elbow , cleaned it out and presto, no more problem."