Hi Dan

Make sure you also check the thermostat. (Not sure about the Perkins,
but it's usually in the casting just above the water pump.)

A previous owner could have installed the wrong part or it could be
corroded and malfunctioning. Test it by noting the temperature markings
on the flange, then put it and a thermometer in a pot with enough water
to cover it, turn on the heat and watch. Take the temperature as soon as
it begins to open and again as soon as it's wide open. If your
observations and the markings are in the same range, and the part is
correct for your engine, the problem lies elsewhere. Hopefully, however,
you'll find you need a new thermostat - cheap - and will have solved yet
another problem in your ongoing saga.

Cheers, Garrett

In case anyone wonders why I often quote data from a Corvette, this was the
only engine where I was able to fully instrument it including many non
standard things.  I calibrated all the gauges so I know they gave valid results.
The data I collected corroborated things that I saw on board customers  boats.

It was the only time I was able to have a mobile  lab to do experiments with.
The console looked like an airplanes with a lot of additonal  instumentation.

cheers

Arild