Overheating

[Tim Dranttel]

A while back I had problems with the infamous alternator adjusting bolt on my Universal 25 diesel so I had a professional take the manifold off and rework the treads and fixed the problem. While I was waiting for the manifold to get replaced I figured it was a good time to replace all of the hoses. What a pain but I perservered and the job was complete. After the head was replaced I took the boat out for a spin. Now it overheats! The temp guage slowly goes from cold to 205 degrees in the space of 15 minutes at 1500 rpm. I've heard of air pockets so I bleed the system. Still overheats. I have the water heater valve fully closed to run water through the water heater. I've heard that this may cause an overheat but logic and other opinions I've heard say that this should not cause a problem. Did I mess something up or do I need to ask the mechanic to come back out and fix "his" problem? By the way it is a fresh water cooled Universal 25 diesel.Thanks for the inputTim

 

[Steve Smith]

Sounds like there is still air in the lines. You said you bled the system. Did you also open the bleed valve at the water heater? I had a similar problem until I bled air from that valve. Also, you might check that you have sea water cooling. Check the heat exchanger operation. Engine running, place your hand on the seawater heat exchanger inlet hose and on the outlet hose. There should be a noticeable change in temperature as the seawater picks up heat.

 

[Joe Luciano]

I have the same boat and engine. A year ago, I too changed my hoses, flushed my coolant and replaced it with new. Initially, I had the same problem with overheating and it indeed was air in the lines. The water heater is very difficult to get liquid full and remove all of the air. It takes a long time and lots of patience to finally get it all out. One of the diesel mechanics in my area told me about this before I made the attempt. I remember running the engine, bleeding from the tank, putting the radiator cap on to build some pressure in the system, then removing it, repeat. I would see bubbles in the coolant when removing the cap. Eventually, the air worked its way out of the system and circulation was re-established. When doing this, you have to really watch the temperature and shut the engine down if it rises too high. Let it cool off and try it again. It took several attempts before the air worked its way out, so have patience and you should be able to do it too! Good luck.