MACS Service Reports - 2016 - OCT3

Toyota

Toyota

Spectrapremum.com

often in heavy-duty trucks (the over-8500 GVW models
such as the Ford F-250 and F-350, plus the Chevy/GMC
and Ram (ex-Dodge Ram) 2500 and 3500 versions. Here's
why they are becoming a special problem for A/C-cooling system specialists.

These models, which usually are equipped with small
turbodiesels, have more complex cooling requirements.
One obvious special need is the air-to-air charge air cooler for the turbocharger. Another is the power steering
cooler; a third, fourth and fifth are the EGR, engine oil
and transmission oil coolers. In most cases there simply
isn't room for all. Although the vehicle engineering team
may determine that a diesel fuel heat changer is also
needed, it's usually for heating the fuel in winter rather
than warm weather cooling.
Obviously, packaging is a problem, which is why Toyota had combi-coolers for the Prius. Another approach
is to have a single engine coolant-system heat exchanger
at the engine, so the hot gas for the EGR system is run
through its heat exchanger with engine coolant. Ditto for
engine and/or perhaps transmission oil. Or there even
may be a transmission oil heat exchanger to quickly
warm transmission oil during engine warm-up, using
engine coolant, and have a separate heat exchanger for
Figure 5: 2003 Prius had a combination condenser and radiator, with
the forward section the condenser. This is an aftermarket unit.
transmission oil cooling in the front-end module, maybe
even (as with passenger cars) built into a radiator rank.
That all sounds like a packaging plus - just dump heat
from engine oil and EGR into the engine coolant and let
that one heat exchanger - the radiator - take care of multiple cooling tasks.
But there's a problem with that approach. It works
from a packaging standpoint to one extent - moving two
or more heat exchangers away from the front-end cooling module. But there's just so much heat the radiator
can handle, and the vehicle makers are using the most
efficient designs they can get. If they go too thick with a
radiator, say a three-tube design, they run into a frontend packaging problem - not so simple to just make
that front-end nose a little longer.
More likely available with a truck is some front-end
vertical space at the top or bottom (and here again, there
may be a problem with aerodynamics - yes even with a
Figure 6: 2004 Prius put the two radiators on a single frame - motor
truck). So the stack is a carefully engineered package,
electronics unit on bottom, engine cooling radiator on top.
and if there's a cooling problem, a possible answer is a
second radiator. Ram took
that approach on the new
models, putting a small second radiator in front (at the
top end) of the regular radiator, which has the transmission oil cooler, as part of the
active warm-up system we
described in the September/
October 2012 issues of MACS
Service Reports, on new technology. So long as the stacked
exchangers are separately
mounted, you can replace
them individually.
Figure 7: 2004 Prius also had a condenser and a sub-cool unit (labeled "super-cooling") built on a single frame.
The passenger car is hardly
"Modulator" is alternate term for receiver-dryer when integrated with condensing package. This is a common
immune
from these issues.
approach on late models of all makes.

October 2016

3

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