Diesel Engine Temperature

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serini

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I have just re-engined a 40ft sailing boat with a 40HP diesel (better not say which one, may break forum rules 'cos I am not a happy bunny). Many problems with new engine but main one is that it is running at nearly 90C. Located in home waters. My question is "if it is running close to the over heat alarm of 95 here in the UK will it not simply overheat all the time when I take it south?" The engine manufacturer seems baffled by my question - any ideas??
 
what does the engines stat open at? or, what have they quoted?

I have seen engines do this when they are sucking some air in thru the raw water system...
 
Thermostat quoted as 79C but do you see my point about sea water temp? Of course the sea water evaporating in the exhaust will cool down the exhaust, almost independantly of the sea water temperature itself. But in the heat exchanger the temperature difference between the (cool) seawater and the (hot) fresh water coolant must have an impact on how much heat the water can take away from the engine......and if hotter seawater takes away less heat then the engine temp. must go up.
 
hmmm interesting argument but look at this way a minute - if the engine is running at say 1500 rpm and is generating x heat energy which is being cooled by the heat exchanger with th eavailable external water..........why doesn't the engine temperature (cooling water) go up in temperature if you increase the revs to say 2200 and run at that?

my boat diesel runs at 70 degrees, 1000 or 3000 rpm, car diesel runs at 90 degrees.
 
you said New engine

Have you checked the impeller on the sea water pump as it is not unknown for them to be damaged by dry running at engine suppliers before they are sent out ,or by initial start up

2 alot of new design engines run at 90, however with the thermostst stamped 80 I would be a little concerned, other than a new engine will be very stiff and naturally warm up much quicker and may be run a tad hotter in its early life.
 
Thanks for post...increase revs then increase water flow so increase capacity of sea water to take away heat so stays sort of the same. Now keep revs same, magically put boat in Tropics, sea water temp goes up, engine temp surely must go up. Modern engine so runs hot for efficiency and all those greenhouse things, so now in the Tropics just overheats or.....am I missing something??
 
Thanks for post. Impeller checked (lots of times actually since seawater pump also leaked at first). Do you get my basic question though about if seawater is hotter (where I hope to go) then engine will overheat unless it runs cold in our (cold) waters??
 
No, I don't think you are!

FWIW, the sea water temperature in our river last weekend was 21 deg C and I have seen it at 27 deg C summer before last.

Ancient Kelvins like the J and K series run so that you can comfortably keep your hand on the block after a couple of hours at full power - engines have gradually got warmer, but 90 deg seems hot to me.

Boil the thermostat with your wife's sugar thermometer (ideally not when she is in the kitchen!) to check it.
 
Its not really helpfull but my 2gm20f at the start of the season runs at 70 ish in march, by july/august is always at 85 degrees, never goes above that even flat out.



steve
 
thanks - that just leaves engines all designed for one optimum operating temperature running at different temperatures in different ambient water temperatures..............or do the fit different sized pulleys to the water pumps depending on local water temperature?
 
Thanks for reply, This increase you see in home waters spring/summer is exactly what I am worried about. There must be an answer to this, I'm not the first person to have re-engined a boat hoping to go somewhere warm but last time I did this I rebuilt a Bukh and took it across the pond. Thing was you could always comfortably put your hand on the engine wherever it was and however hard it was running (so about 70C). I will check the thermostat but engine is new (50 hours) so lots of warranty issues. Increased flow does seem like an answer to me which means either different thermostat or different pump/impellor/cam. Thing is more water in exhaust then more back pressure then higher temperature 'cos engine has to work harder against the back pressure.....
 
Aye! PC just crashed so my last post may have got lost. Increased flow does it but......more seawater in exhaust increases back pressure, engine has to work harder so higher temperature......Only answer I can see is increased flow but do not put all the seawater in the exhaust.
 
I seem to remember from school science energy transfer doubles for each 3 degrees difference, so i understand your concern

next items to check

1 is the seawater plumbing the correct size

2 ditto filter mesh

3 is it an all new installation or was there a smaller engine there before

4 exhaust hose diameter

reused components injection elbows etc clear not clogged

5 remenants of seawater impeller blocking heat exchangers etc
 
[ QUOTE ]
Thermostat quoted as 79C but do you see my point about sea water temp? Of course the sea water evaporating in the exhaust will cool down the exhaust, almost independantly of the sea water temperature itself. But in the heat exchanger the temperature difference between the (cool) seawater and the (hot) fresh water coolant must have an impact on how much heat the water can take away from the engine......and if hotter seawater takes away less heat then the engine temp. must go up.

[/ QUOTE ]

I don't think this is quite the issue you think it is. The temperature probe is almost certainly monitoring water temperature in the cylinder head. The thermostat is downstream of it and will be regulating flow out of the head according to its operating characteristics (although I agree the actual operating temperature is up for debate). It is trying to maintain a steady temperature in the engine of say 90 degs. The heat exchanger will complete the loop with the engine - water released by the thermostat from the head will be cooled in the heat exchanger and recirculated back to the engine according to demand. Demand will be dictated by the thermostat. So, in short, the water in the engine should reach operating temperature quickly with the thermostat closed, the thermostat will then regulate flow to maintian temperature. This does not mean that the whole fresh water volume will be at or near the same temperature as the cylinder head.
 
Thanks Moonfire, I understand your point but please let me expand a little. I have NOT taken the 'stat out of this new engine so maybe it continuously regulates the coolant flow as you suggest but there are two things that make me think not (1) I rebuilt a Bukh and as part of that tested the 'stat by heating in water with a thermometer. What I saw on the Bukh 'stat was just that it opened, not progressively, just opened so it didn't look like it would continuously regulate, just allow the engine up to temp. as quick as possible. (2) This engine reaches 80C within about 3 minutes, then there is a slow rise from 80C to 90C (as read on gauge) so it looks like 'stat opens then with coolant flowing it reaches some sort of heat in equals heat out state. Maybe I am worrying about nothing but once I cross Biscay I will be sort of stuck with this problem also I am amazed that the engine manufacturer does not even understand the question let alone have an answer for me.
 
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