Mundgyver said:
I would think that once you shut down, that your are now not generating heat. The only reason we see a heat rise under the hood is we have no air flow over things nor do we have fuel flow to cool the VP. Some have refered to heat soak after shut down and are taking temp reading with a laser temp gun. One problem with these guns. They do work and I am not knocking them, as they will give you a good idea what is going on to some degree. But when we use one of these guns, we need to be aware of something called "emisitivity". I think I got spelled right. This is the property of the material that we are measuring. The surface of steel will give off a set heat reading to the gun. Now we move to what looks like steel, but may be aluminum or painted steel. Its emisitivity will be different than the steel that was just looked at in our prior example. Our readings will be off by some number, what exactly I do not know. This is why a direct contact probe would be my weapon of choice for taking heat reading in an around the engine compartment. My knowledge on this come from the industry I currently work in.
Back to our truck and the VP. I don't think heat soak is a big worry. Once we shut down, we are not generating heat and the only thing that can happen, is everything gets cooler. If we provide an assist for this, then we up the comfort factor, but I am not real worried about it. Just providing the VP with a little more volume of flow and maintaining pressure and input fuel temp at or below ambient temp works for me. I am at 150,000 + now and I don't think I will have a problem with the VP. I have probably just jinxed my self into a new VP with this thinking
Food for thought guys.
FIRST, on the "emisitivity" bit.
As far as I know, that refers to the reflectivity of the surface being measured by an infrared gun, and is easily demonstrated on surfaces where there is a shiny area next to a darker one on the same item. In that case, you WILL usually get differing readings from the gun, even tho' the surfaces are the same temperature.
Moral? Take the readings on the DARKEST areas you are attempting to measure if at all possible, and always try to get readings straight on - rather than at an angle - to the object being measured for best repeatable accuracy.
BUT, most of the surfaces we are dealing with here are NOT particularly reflective, and "emisitivity" not likely to be a big issue...
NOW, as to heat soak not being a big issue in regards to the VP-44, keep in mind that what we are attempting here, is REDUCTION of heat applied to the VP-44 - whether that comes from heated fuel, or underhood heat makes NO difference - heat is heat!
And believe me, once the cooling air from the fan and vehicle movement is stopped, underhood heat can easily quickly rise 30-50 degrees and higher. That heat comes both from the radiator, and also the engine and related components, like the VERY hot turbo and exhaust system. Plus, these Cummins are VERY large chunks of iron, and tend to hold/radiate heat FAR longer than smaller engines!
In the case of the VP-44, it sits within an inch or so of the engine block itself - which typically is at 180 degrees or more. The radiant heat that close definitely WILL heat the VP-44 - and the internal electronics this thread is mostly concerned with!
So yeah, heat soak IS a big issue - and as good as increased fuel flow and fuel line coolers are, they do NOTHING to address the issue of heat soak - and THAT is the reason for my interest and efforts with the outside cooling duct to the VP-44 - and so far, it seems to be working as hoped!
(EDIT)
When I get final readings on our RV trip next week with the current setup, I can easily move my underhood temperature sensor over to the VP-44 case, and gather readings there to confirm gun readings and get over-the-road readings as well...
Attention: TDR Forum Junkies 
). 
That is amazing 
