Overheating on the T & M

Glancing down at the temperature gauge one day last month, just after we'd ascended Tatenhill Lock on the Trent and Mersey, I saw this. Ah. That needle should have been approximately vertical, not hitting the endstop. (This is an edited version of my contemporaneous post, from 5th April 2009, but with pictures this time.)

We stopped and I lifted the deckboards covering the engine. There was some water vapour down there, but not nearly so much as when I gingerly opened the coolant filler cap a fraction. For some reason the engine had decided to get hot, and there wasn't enough coolant doing the rounds to do its job. So little, in fact, that there wasn't enough to pass through the calorifier, evidenced by the coolness of what should have been the (domestic) hot water. After a while I opened the filler cap some more, releasing more clouds of water vapour, and then removed it.


There was coolant down there, but the level was rather low. I boiled up some water and slowly added it from the kettle, and sounds of bubbling came from within. The engine was clearly very hot indeed. Another kettleful. And another. Now the level looked where it should be, so I replaced the filler cap and started the engine. All seemed well, so we continued. But why did the engine lose coolant? Was it a perished hose or rusted Jubilee clip? A blown gasket? When looking around when hot, I noticed that there was some bubbling around the thermostat housing. Perhaps the gasket there needs replacing. I'm not convinced that's the primary cause of the loss of coolant, as it looked more like a result of high pressure caused by overheating.

I hope the boatyard - Tattenhall Marina, where we were taking the boat (still some 75 miles and 72 locks distant) - has checked it over and rectified any fault. For the rest of the trip I topped up the coolant every day to a higher level than usual, and encountered no more overheating.