At 07:16 PM 9/12/99 -0400, Rick Brown wrote:
>....
>I believe Ive also heard about a dip stick oil heater - looks like a dip
stick with an electrical cord attached - just stick it in the dip hole and
plug it in.
>
>If anyone finds one of these let me know where as I would like to order
one for my winter driving.
Don't bother. My brother worked for Everco Industries for a while, the
company that makes these things, and I have garnered quite a bit of
information here. The dipstick heater is of course as small as a dipstick
and only engages the oil for about two inches of depth (assuming it's at
the full mark). As this contact area is so small the thing is quite
limited in heat transfer capability, so they are designed with fairly low
heat output to avoid boiling the oil in a local spot. In extremely cold
weather they only heat the oil in a spot just a few inches across, not
doing anything useful for starting the car, as the oil doesn't circulate by
convection when it's very viscous.
In milder weather oil heated this way will circulate by convection, and the
oil and sump will get warm to the touch, but even this does not transfer
heat noticeably up into the block and water jacket area, as the sheet metal
sump will still be cold in the area above the oil level, and heat transfer
through the air inside the engine is pretty inefficient. If you just want
the oil to be warm when you start the enine, that's fine, but if you
actually want the engine to start in very cold conditions it won't help
much. A flat plate heater on the bottom of the sump will heat the oil much
better, but still probably won't help starting much unless it supplies lots
of heat (poor efficiency at heating the upper engine).
The very best cold start heater is one that goes directly into the water
jacket in place of an engine block core plug. These are much higher in
heat output and you could use two for extreme cold conditions. As the
coolant warms up it circulates freely in the engine by convection, heating
the block and the head, and in turn the intake manifold and carburetor(s)
to some extent. If you apply enough heat in this manner it will actually
open the thermostat and circulate coolant through the radiator by
convection. The radiator will then dissippate any excess heat and prevent
overheating of the coolant. With warm coolant in the engine block you also
get nearly instant warm air from the heater when you start it up. If you
leave the heater valve open for convection it may even defrost the
windscreen in mild freeze conditions.
Success of this installation depends on having sufficient space in the
water jacket just inside of the core plug, so it is best to select a core
plug that is located midway between two cylinder liners, like in the center
of a four cylinder engine block. Companies selling these engine heaters
usually have them listed by car model and engine type, but may not have a
lising for older cars. In that case you need to supply the actual size
(diameter) of the core plug to get the part that fits correctly. The
heater is sealed to the block with a rubber o-ring, and is secured in place
with a t-bar inside which is held with a single screw in the center of the
new core plug.
Another type of engine heater has a small external fluid tank which is
plumbed in series with a heater hose. These will not work at all unless
the heater valve is open, and even then the operation is hit or miss,
because there has to be a physical height difference at the hose
connections to create thermal convection. This works best if one
connection is high on the engine or heater box, and the other connection is
somewhat lower on the water pump or lower radiator connector. This type of
heater will circulate coolant through the engine by convection, although
somewhat inefficiently, with a result similar to the core plug heater. It
is also somewhat more expensive and takes up substantial space in the
engine compartment, but it can be installed on nearly any engine that has
an external heater hose connector. This heater would work better in an MG
if one hose connection was attached to the cylinder head at the heater
valve location, possibly with a tee in the heater hose and the heater valve
left open. The other hose connection should then be made to a tee in the
lower radiator hose, creating a substantial height difference for good
thermal convection through the engine block, and also bypassing the heater
core.
And lastly I will mention the heater element that installs in the lower
radiator hose. This is similar to the core plug heater but is installed
through a hole cut in the side of a straight moulded radiator hose, or
sometimes in a short metal connector pipe installed in the hose. This type
of heater doesn't work well either, as the engine thermostat is closed when
cold and coolant will not circulate through the radiator. As such, the
thermal convection has to occur all in the one lower radiator hose with
coolant flowing both ways up and down in the same hose. Small bore and
corregated radiator hoses common to our small displacement LBC engines are
very bad in this respect, as the two-way convection current must travel
from the heater element all the way up through the water pump to the engine
block water jacket and then return through the same small passage.
Attempts to force enough heat into the system to be effective by this
method can lead to local boiling of the engine coolant.
Now what didn't I cover?
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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