Hi I need to building a 4 ohm 1500 watt "cantenna paint can style" dummy
load for audio and guitar amp work. I have forgotten what type of oil to use
for heat transfer.
Id like something easy to get (like peanut or something with a high
flashpoint).
Don't want to loose the house.
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Assuming a resistance wire load made from thick galvanised fencing wire
( freq is low ;no RF) carrying up to sqrt 1500/4 equals approx 20
amperes , I would just use a large paint can filled with motor oil.

The 2 dummy load connections can be best made with heavy duty insulated
panel sockets with screwed head to be fitted in the can's lid. The stiff
resistance element can be fitted unsupported and kept free from the can

I also use motor oil for RF dummy loads with metal oxyde resistors and
over the years the resistance hasn't changed.

To prevent the oil filled (paint)can 'weeping' oil it is important that
the can's vertical and bottom seals are tight by applying solder inside.
Depending on the type and duration of testing ,the heat capacity of the
dummy load can be increased by placing the lower part of the can in
(flowing) cold water.
The can's lid should have a small vent hole (1-2 mm)

Frank GM0CSZ / KN6WH

To prevent the oil filled (paint)can 'weeping' oil it is important that
the can's vertical and bottom seals are tight by applying solder inside.
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That hasn't been my experience, but if one must solder, for sure don't
use a lined can. And then after soldering, clean and apply a
protective coating on the outside to cover all areas where heat has
discolored the metal... because these areas will be far more prone to
rust.
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It is hardly possible that rust develops when the can is filled with
(any) oil.
Another way to prevent oil weeping from the can is to cover the seams
internally with 2 component-expoxy adhesive.I had a motor oil filled
dummy load in operation for 15 years without problems , resistance
measured remained constant (50.3 Ohms) over that period.
That dummy load was made with 20 ea 1000 Ohms ,2Watt carbon film
resistors. With so many resistors in parallel the inductance of the
device is sufficiently low for use up to VHF frequencies.

Frank GM0CSZ / KN6WH