Diesel Engine Temperature

As a first step change the thermostat - they can mis-behave even when new and are cheap.
Second stage is to monitor the water temperture at various points around the circuit to confirm your fear. Best done with a thin flexible thermocouple which can be inserted into the flow via a flexible hose connection (fiddly as the circuit needs draining each time).
 
That's what the thermostat on my antique Volvo (probably older than your Bukh!) does. It opens almost instantly when put in a saucepan and cooked to operating temperature.
 
Hi serini,

Have been following this post with interest. I suspect your earlier Bukh thermostat may have been faulty. By coincidence, I have just removed the one from my Bukh 20 (for a different reason) but took the opportunity to test it. It most definitely opened progressively, (which I thought was the norm with all thermostats) and closed slowly when removed from the hot water.

I tried this several times and there was always a slowly increasing/decreasing aperature. When you think about it, it has to be this way in order to regulate the engine's water jacket temperature constantly.

Could it be that the housing into which your thermostat fits, has some dirt or deformity that is preventing the 'stat from opening fully? Or that the 'stat itself is faulty?

Re your concerns once you cross Biscay, don't be too worried! The world doesn't end there and spares are readily available for just about every modern make of engine. In the event that everything gets too hot, just remove the 'stat.

Might be worth trying that anyway, just to see if the engine runs cool.

Cheers Jerry
 
Given that the thermostat seems to be opening at 80, then temp rises slowly to 90 I agree that you may have a problem where seawater temp is higher. I think you need to try and establish which cooling circuit is the problem, that is do you have a full flow of fresh water round the engine and heat exchanger, with no air where there should be water, and similarly is the seawater side getting a full flow? I take it you have checked all the obvious things like kinked or obstructed hoses, and adequate hose sizes. I have seen hoses which look OK outside, but have collapsed internally where they have been kinked in the past. If all the flows look adequate you may be OK. The engine should be quite alright unless the freshwater actually boils, which it will not do until well past 100 celcius as the pressure cap ensures a higher boiling point. Water will boil at 100 celcius at atmospheric pressure, (14.697 PS1 absolute) Water at 20PSI absolute will boil at 109 degrees. This is well within the pressure contained by a 7PSI pressure cap. This is why you should never release the cap on a hot engine, as the superheated water will flash into steam and scald you seriously.
 
Believe it or not the stat does continually regulate the temperature.When driving your car, it doesn't matter if it is the depth of winter or a hot summer day, the engine temperature remains the same. The stat does not simply open at the running temperature and stay open,it modulates the flow of water accordingly. Try running an engine with no stat and you will soon see that the temperature fluctuates wildly depending on ambient conditions and how hard the enine is working. In warmer seas the stat should allow greater flow maintaining the working temperature. however I agree 90 is a tad high. Try changing the thermostat.
 
Have you added anti freeze / summer coolant to the fresh water side.

More efficient cooling with the additives.
 
more efficient cooling with the additives

Less efficient surely? The specific heat capacity of an ethylene glycol based water solution is less than the specific heat capacity of clean water. For example with a 50% solution the specific heat capacity is decreased by approx. 20%. (Figures plundered from the web).
 
I agree, thermostats [at least ones in car engines] continually open and close when the engine is running. I used to travel in a car with a very sensitive and accurate ether-filled temperature gauge. and you could see the small temperature fluctuations as the 'stat. did its thing. The thermostat is the first thing to check as they can be faulty from new.
 
Thanks for the advice folks. I have checked obvious like water flow, kinks etc. and manufacturer says my measured temp. (measured with a remote temp gun pointed at thermostat housing and backed up by temp. gauge on engine and heat lables from RS) at 90C is at the 'top end of range but within range' when I asked manufacturer about taking the boat to hot places (River Gambia actually) and wouldn't the engine run hotter there because the basic cooling water was hotter he couldn't give me a convincing reply. The basic answer I have got from you guys is that the thermostat should continuously regulate, ie is not just an 'open/shut' valve. OK here is the humdinger. This morning I phoned a diesel engine installer up here who was recommended to me yesterday. In answer to first question about 'will it not just run hotter 'cos seawater hotter' he just said 'of course' In answer to thermostat continuously regulating he said 'No, it would wear out if it continuously regulated, it just opens'. So, there you have it. Perhaps not as simple a question as I first thought! Now I am off to ask engine manufacturer for a spec on seawater temp. BTW same engineer has thrown up another observation for the basic engine temp being a bit high - back pressure - Thanks for all the replies.
 
further thoughts

does it run at 90 at idle no load ?

light load?

medium load?

if so the thermostat is working , but just high.

I take it if the engine is new, the prop has been changed to match the new engine output.
 
I did not know that.

If you read the blurb on the side of anti freeze / summer coolant it seems to suggest better cooling properties than plain water.

But then they would wouldn't they!
 
Thermostats should open at a preset temperature and stay open until the coolent they are immersed in falls below that temperature. They open fully over a fairly small temperature range and once fully open, they cannot open any more, so temparature could continue to rise. Putting one in that opens at a lower temerature will not stop the rise in temerature if the coolant flow on either freshwater or seawater side is too restricted. Modern engines do run hotter than some old ones, for efficiency reasons, but you still need to ensure that they do not boil. The margin between running temp and boiling, has been reduced by modern engine design. I think that your thermostat is fully open well before 90 degrees, and that warmer seawater will cause the temperature to go higher still. The way to check is with the thermostat in a pan of water on the stove. Heat slowly and stir the water to maintain even temparature. Note the temp. when the stat begins to open, and when it is fully open. If the latter is below 90 degrees the engine temp is certainly going to go up in warmer seas. Car engines have the advantage of a powerful cooling airflow, boat engines don't, so it is all up to the heat exchanger.
 
Won't a new engine run hotter because the machined tollerances? After a few hundred hours it will wear out a bit and not be so tight - had that issue with my MGB ...

IMO the engine will run hotter with hotter raw water - that is what happened with us in Croatia on a flot .. and thats how the engineer explained the overheating - it was a volvo with heat exchanger - we sorted it out for the one trip by opening all the hatches around the engine (including removal of the steps!) and getting some air around it - the extra cooling power sorted us out for that day!

If you have just re-engined, have you increased the comparitive volume & power of the engine compaired to what you did have? It could be that a bit of air circulation could help?

If the thermostat is opening then it doesn't matter how much you boil it - it will open to a specified apiture then stop - try just removing the thermostat and running without it - will take longer for the engine to come up to temperature, but you should get a larger flow of water through to the heat exchanger...
You have checked the water pump haven't you?
 
Did you use the original gauges when you replaced the engine. There are different types, US resistance and Euro resistance, you may have a conflict. Also even if same resistance there may be a mismatch. Also gauges work on resistance so could be a corroded terminal on the wiring loom. Check temperature with a digital thermomiter to ensure your gauge is reading correctly.
 
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