Analysis of Thermal Propagation
Some of you may have seen my recent thread: d89: Now with Predator-vision!
After running the block heater for >8 hours, I whipped out my new thermal imager to examine the quality of the prewarming. This was performed at night (no solar/IR heating) and the ambient temperature was 22F.
Built-in defrost is a fringe benefit. This is a shot of the base of the windshield on the driver's side. We can observe a temp rise there of about 15F. This roughly aligns with my observation of the defrost feature losing the bulk of it's effectiveness around 15F ambient.
Opening the hood, this is what I saw.
This is the front, passenger side of the engine. Alternator is at lower left, and the heater tube is above the crosshair. Right away, we notice that the 120F of the engine block minus the 22F ambient doesn't align with the previously measured peak rise of 84F. This may be explained by the location of my fan controller's sensor (the object teed into the heater line above the crosshair). Starting from cold, with no pressure in the system, the heater will boil off some coolant until the pressure rises. This coolant vapor will, no doubt, accumulate at the highest point of the system it can travel to. Vapors are poor thermal conductors, so we experienced a false low reading.
I confirmed this by keying on the truck. Indicated temperature on the controller was 71F.
This is the block heater itself. The temperature recorded is of the nut/cord connection.
Looking at the side of the block next to the heater, we can see an expectable gradient right at the level of the heater.
Another shot. This is the hottest area I could find on the engine.
This is the front of the engine block, by the water pump and above the gearcase.
The heat is contained mostly within the engine block itself. We saw in an earlier picture the alternator did not absorb much heat. This picture shows the vacuum pump.
It should be obvious what this is. Temperature of the pump and the fuel line (targeted) were about the same, as one might assume by the similar color.
Another thing that affects cold-weather startability is oil viscosity. I'm not going to do a bunch of math right now to compare the viscosity of my oil at 22F compared to the prewarm temperature, but the more heat the oil absorbs, the thinner it will be, the easier the engine will start, and the higher the quality of initial lubrication will be. This is very important for maximizing the engine's lifespan, as wear rates are extremely high immediately after startup.
Sniping around my axle and steering linkage, I got these two decent shots:
Not tremendously impressive, but the transfer of heat into the sump is going to be very inefficient. The mass of oil is similar to the mass of the coolant (though they have different specific heats, also not going to do that math right now), both are separated with a layer of air which has terrible thermal conductivity, and essentially the only direct path of heat transfer will be conduction through the block and the oil pan itself. We can't really do much about that, except to eliminate as much BTU waste as possible and conserve prewarming heat within the engine.
I discovered a substantial loss of heat through the radiator. While the thermostat is closed, the jiggle pin is in the down position with the engine off. This allows convection currents to carry warm coolant into the radiator and the coolant to lose a lot of heat. The upper radiator hose was 96F, the top of the inlet tank was 93F, the top of the outlet tank was 56F. I did not measure the bottom. The natural assumption is that one could enjoy a massive increase in heater effectiveness by installing a valve in this line, leaving it closed except when working on the cooling system. However, this may be unwise as the jiggle pin is also the escape path for coolant vapor created by running the block heater. With that valved off, vapors would build up behind the thermostat, potentially enough to cause an overheat when the engine is warmed to operating temp. Perhaps a normally closed solenoid valve, wired to keyed power is the answer? I may pinch the line off and FLIR the engine again to see if it would be worth the hassle.
Coming up, imagery of the engine at operating temp, and prewarming with dual block heaters.