Jake wrote:
Hi,
If I got this right, your overheating occurs in overdrive, then it cools
down in drive? That sounds to me like a lack of coolant flow at the
lower rpm of overdrive is a "first thing to look at" problem, followed
by poor air flow.
Possibilities for poor coolant flow:
Partially clogged radiator. If you have been using coolant mixed with
regular tap water instead of distilled, it's possible you're starting to
develop some scale in your radiator that allows enough flow for "low
demand" cooling, but not enough for "high demand" situations. At five
years, you're close to halfway thru the average life of most radiators,
even when properly cared for, according to several sources. New
radiators aren't that expensive compared to the damage you may be
avoiding. Two online sources I've used are
www.radiator.com and
www.radiatorbarn.com. Both have higher capacity radiators than stock for
some apps. Take a look to see what they have for your car. My preference
is Radiator Barn for fit and quality. They are a little higher priced,
but the three trips to the warehouse to get a unit that fit last time I
used the other guys ate up any price differential!
Slipping drive belt, IF your water pump's driven by an adjustable belt.
I don't know how yours works on the 2000.
Grumpy thermostat: it's open, but not flowing enough coolant. While my
experience w/ t-stats says they USUALLY work or they don't, I HAVE had
some that didn't quite get all the way open when they needed to be or
acted very slowly. This is especially a problem if the car's been
seriously overheated and the t-stat wasn't replaced after that incident.
The t-stat could be damaged. Most folks recommend using Subie OEM
stats--some aftermarket units don't seem to flow as well. If you don't
go OEM, I've had good luck with Stant Superstats (also sold under the
NAPA brand as Superstats.)
Possibly wrong temp thermostat. In today's engines, it's not so likely
you'll have one that's too high a temp, since so many are running in the
190-195 deg F (88-90 deg C) range, but there ARE still apps that call
for a 180 (82 deg C), so if someone put a hotter one in, there COULD be
some flow problems.
Possibilities for poor air flow:
Fan clutch dying, IF you have a fan clutch. The fluid in fan clutches
does degrade over time, and the fan ends up turning slower and slower by
the year. You COULD have a clutch that still turns fast enough at higher
engine rpms but drops off when the engine slows. Just replaced one like
that last week!
Bad thermoswitch for an electric fan, or even a dead fan motor (check
fuses first.)
Radiator clogged w/ bugs or debris. Get out the garden hose or air hose
if you've got a compressor and clean it out. Doesn't have to be perfect,
but get as much crud out of the fins as you can without going crazy.
And one oddball possibility:
Wrong coolant mix. Most mfrs recommend 50-50 to 70-30 mixes. Pure water
cools best, and the cooling ability (not boiling point--actual heat
rejection capacity) drops as you raise the anti-freeze percentage.
Contrary to some people's opinion, a 100% anti-freeze level can cause
overheating! You can get testers at the auto parts store to test the
mixture level.
Lots of things to look at, no? Hope you find the problem easily!
Rick
