Yachting and Boating World forums: Perkins 4108 Question

After a long renovation, I started my Perkins 4108 last week for first time in 3 years. Initially I ran it with no cooling water just to check everything. I've run it today with a hose stuffed down pump inlet - I should mention boat is out of the water on a cradle. I've changed filter and oil and fitted a new fuel (lift) pump and fuel filter plus thermostat. As a matter of interest as it comes up as a discussion point periodically, previous owner always used easy start. I reconnected thermostart and with half throttle plus thermostart it starts after 2 or 3 revolutions, not bad for a 28 year old diesel and no sign of it having become addicted to easy start. Number 2 injector was weeping around the base so needs some work, but other than that all seemed very sound (touch wood)

Three questions;
1. what is the unit on top of heat exchanger (it's direct cooled) towards front of engine? About 2 inch diameter and 2 inch deep and screwed into thread in heat exchanger. Could it be some kind of pressure relief valve?
2. New thermostat is set at 74degrees C. Seems very low for an engine thermostat. Is it correct unit?
3. Could anyone with a similar set up tell me what running temp of engine they expect? After about 20 mins running, temp gauge was about 85 - 90 degrees C. At 1500rpm water pump also wanted more water as hose could not keep up with demand, lots of air bubbles showing in clear inlet hose - this surprised me. With sufficient water I would expect running temp to be slightly lower.

Thanks for any comments.

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