MACS Service Reports - 2015 - JAN4

bor, and unless the customer is really willing to go for the
full-price alternative, it's likely that any improvement you
get from the effort will be perceived by most customers as
worth the lower investment.
Just as an aside: this vehicle has a heater coolant valve, so
make sure it isn't the problem; a subject we'll talk about later
in this report.

ota's mid-engine small sporty car with an extremely complex front-to-rear cooling system layout, worse in some
respects than any Nissans. In fact, many shops would just
make sure there were no leaks, drain and fill the reservoir
and radiator, thermocycle the system (warm-up, let air
bubble out of fill neck, then top up and let system cool
down and top up again -- repeat twice). Not the greatest practice, but it beat the alternative. If you had a leak
and had to repair and then refill, you could follow any of
the on-line recommendations of enthusiasts, or use the
factory procedure, which you'll find in your aftermarket
service information system. But there aren't many MR2s
on the road, so we'll continue to focus on the more conventional cars, as few are problem free. The main issue
is that all cooling systems have become more complex,
"catching up with Nissan," with a couple of dozen hose
connections. The complexity gets worse with hybrids
and plug-ins, which often require coolant flow loops for
power electronics, battery chargers (for plug-in hybrids)
and in some cases for the battery packs (see Figure 8,
Chevy Volt ). And for specialty vehicles with high-output electrical systems, coolant-cooled alternators also are
part of the picture.
The best defense, therefore, is to be pro-active when the
car is in for any other service. You should be checking
for seeping connections, looking for any indication that a

THE AIR POCKET

gmtechinfo.com

The high mounting of the heater core on many cars
means that they can be prone to trapping a lot of air. Probably the most notorious are Nissan products, and there
are more complaints about trying to jack up the front end
of a Nissan vehicle so that the air pocket works its way
up to the front and out. "I had it up so high the rear bumper was touching the shop floor, and the air bubbles still
wouldn't come out" is a line we've heard more than once.
Some Japanese cars have installed air bleeds on hoses at
the top of the firewall on a few cars we've seen, but the
complaints persist. The company has issued a variety of
service recommendations over the years.
Nissan hardly is the only one with air entrapment issues, but it has used coolant flow patterns that are among
the most complex in the industry.
Nissan is also not the only one with air bleeding issues.
The "worst ever" probably was the 2002-2005 MR-2, Toy-

Figure 8: Chevy Volt is one of the hybrids with several coolant flow circuits. Shown is the one that is combined with the A/C circuit to heat the battery pack
in extreme cold or cool it in hot summer weather. Flow control valve has one inlet port (from battery pack) to three outlets (one to battery radiator, surge
tank and electric pump; a second to the battery chiller in the circuit that includes the A/C heat exchanger; a third that bypasses both of the others). For
heating the battery pack, the valve goes straight up, and coolant flows from battery pack into pump, through heater (electric, turned on) and then into battery pack. For cooling, valve is flat down (horizontal position), so coolant flows from battery pack to and through battery radiator and surge tank and into
pump, through electric heater (turned off) and into battery pack. For extra cooling, valve is in mid-position (45 degrees), so coolant flows from battery pack
through chiller (where it's cooled by A/C) and then into pump (electric heater is turned off).

January 2015

MACS Service Reports

http://www.gmtechinfo.com

Table of Contents for the Digital Edition of MACS Service Reports - 2015