Exhaust temperature: safe temp. range of water ejected over side?

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We have a 44 hp, 4 cylinder Kubota diesel on our Fisher Northeaster-30. What is the expected range of temperatures we should see when holding a thermometer in the water stream being ejected just outside the boat, in the exhaust stream, given cruising rpm and running hard rpm?
 
Actually its not that critical and will vary from engine to engine. If it is a heat exchanger system, which I assume it is, it will depend entirely on the efficiency of the heat exchanger. If it is only just sufficiently big and the raw water pump is the same, the water exiting the exhaust at "full chat" could be close to boiling. If you have a big pump and heat exchanger it could be barely warm. The fresh water system is regulated by the thermostat and will keep the engine to the right temperature by regulating the flow of fresh water in either case. The water flow rate of raw water remains constant and will therefore vary.
 
He didn't say he had steam in the first place....... But yes it can be very close to boiling and the engine still running at normal temp.
 
With raw water cooling the temperature of water flowing through the block will be at most 60-70°C. It will have some cold water added which has bypassed the block and gon straight to the exhaust (this is to cool the exhaust when the thermostat is cold. At full throttle you would expect very little cold to be added so range is from sea temp to 70°.

A fresh water cooled engine runs at 80-90° but the water flowing through the heat exchanger has to be quite a bit colder for heat transfer to take place. For the same reason the sea water volume is a lot greater for fresh water cooling. Expect a range from sea water temp to around 60°

If you get anything hotter than these, suspect a fault.
 
Steaming is almost always abundently present at a "hard run" of about 80% of max. rpm (cruising is usually at about 65% of max. rpm and produces just a little steam). If I can count on the posted max of 60C. for exhaust temperature, then I guess I'm near that at about 50C. when we're running hard. Otherwise, it's closer to 45C. at cruising rpm. The seawater is seldom above 19C. and is mostly at about 15C.

Perhaps my installing a raw water pump of about 20% increased capacity (A Sherwood G908) will give us a little more "head room" (our current Oberdorfer puts out about 3 gal./min at cruising speed (actually measured) while the new pump will increase this to about 4 gal./min.

We are a little bit 'over-propped' which reduces our max rpm by about 300 or 400 below specs for max but changing this is not in the cards.

The heat exchanger is a "four pass system" so it should be up to what's needed and there is little room for a larger one.

The freshwater temperature is at about 78C. for cruising rpm and can rise to about 85C. when run hard at 80% max rpm. We don't know if this is a reasonable rise but it seems to us that we're on the cusp with this. Kubota's, we are told by mechanics and Kubota, do not "like" to run hot.

With thanks to all for your interest, Loren and Sandy
 
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