Originally Posted by Rbrucek
Thanks everyone I'm going to clean the heat exchanger now
I'm sure this has been raised before on other 4-108 overheating posts but I'll mention it again. The cylindrical core
stacks used on many engines are enclosed in a bronze/ brass tube with a hole through it at each end to allow the flow of coolant through and over the tube bundle. Raw water goes through the small tubes longitudinally. If the coolant flow is able to just travel down the outside of the bronze
tube the heat transfer is greatly diminished and you get a slow coolant temp increase and eventually an overheat. To direct the coolant flow there was a flange inside the heat exchanger housing to stop the coolant from taking the shortcut outside rather than through the more restrictive tube stack. Perkins used several different methods to direct this flow including simply aligning the hole to the tubes with the circulating pump
inlet or , on the perkins Prima , the inclusion of a plastic sealing ring around the core
outer tube that had to be pushed into a casting sealing face in the housing.
The trick is to get a good flow of coolant through and around the tubes, not straight past em.
Hope this might help if you're having the slow overheat.