Paul
Dodge Dakota
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6/04/2015
14:24:13
|  RE: 2002 4.7 overheating
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Message:
I own a 2002 4.7 Dodge Dakota with 140K miles that had
over-heating issues. I bought it Dec 2013 and I believe I
finally figured it out in May 2014. About every 500 miles it
would happen. Additionally, I had a misfire on cylinder 3 (and
sometime include 1 and 5) that confounded me and was
totally unrelated. It started with a tiny puddle of anti-freeze
under the truck coming from the water pump. Since the
truck had no maintenance records, I would do lots of work or
have lots of work done to replace lots of items (plugs, coil
packs, injectors, transmission fluid, transfer case,
differentials oil, ball joints, brake lines, etc.). So when I saw
the leak, I had it replaced, pressure check, and a flush. 500
miles later though, overheat. Took it in, determined to be
stuck thermostat. Replaced. 500 miles later, overheat again.
Determined to be a faulty thermostat. Replaced and had a
new fan clutch installed. During a regular oil change, they
offered a fuel system cleaning that includes the slow-drip to
burn off carbon, etc., that I had done. So at this point, all the
work mentioned about has been done. Still have that
occasional #3 misfire, but pretty rare. Then less than a week
since the fuel system service, it overheats again and I make
an appointment. The morning of the appointment, I start the
truck and it’s running rough and smoke is billowing out the
exhaust. After it warms up, it runs fine and I take it it for the
overheat issue (again) and describe what happened. Original
diagnosis indicates air trapped in the radiator and it may be
clogged. Then they did a core test and said it detected
exhaust fumes. Based on overheat, mis-fires, rough start,
smokey exhaust, core test, diagnosis is blown head gasket.
Runs fine after warm up, but will the cylinder head fill up with
anti-freeze overnight and crack the head if I try to start it?!?
They don’t do that kind of work, so they’re not in it for the
money. I research engines. Jasper 4.7 - $6K installed. Ok,
what about just head gaskets (get both sides done) - $2.5K if
that’s all there is. So I have the truck towed to a place
recommended to me that can do the work, and check the
machine shop where the heads will be done - great
reputation so I’m comfortable going this route at $2.5K. The
place I towed the truck to do the work first conducts their
own tests. Two days worth of testing. They find nothing
wrong. Absolutely nothing wrong. They could have made
money off of me, so I’m grateful they were honest folks.
Anyway, I do some more research. As for the rough idle and
smoke from the exhaust that morning, a mechanic told me
that a tiny piece of crud from the fuel system cleaning could
have left an injector open enough for some fuel to trickle into
the the cylinder head and cause it…. said it wasn’t
uncommon. Anyway, the engine is notorious for trapping
air… has a bleeder valve on the upper radiator hose. There
are no leaks, so how is air getting in (assuming that’s the
problem)? Well, the radiator cap is dual purpose; spring
valve to let pressure out, and a diaphragm valve to let
coolant in when the engine cools down. I replace the cap,
which is not on the radiator but between two sections of
hose; on one side is the engine, the other side is the radiator.
Guess what I found out in this process (which I should have
discovered earlier). When pressing down on the radiator cap
to twist into place, the hoses give a little. I and the other
mechanics who worked on it probably thought we had the
cap securely in place by pressing and turning. But when I
placed one hand underneath for support and really pressed
down hard while turning, I was able to turn the cap more with
a distinct ‘snap’ into place. I think the whole time when the
cap was being put back on, everyone subconsciously did not
press down hard enough because it feels like you might pull
the hoses off. It takes a good amount of pressure to press
that cap down enough to turn it completely, and you really
can’t do it right without supporting the hose from
underneath. So in the end, I believe that was the problem all
along - the cap wasn’t secured completely, and during cool-
down the vacuum was drawing in air through the neck and
not from the coolant reservoir because there wasn’t enough
vacuum sustained vacuum to pull down the cap’s diaphragm
valve. Following this discovery, I also had the PCM flashed
from ‘C’ to ‘D’ at a Dodge dealership ($150). I don’t have all
the specs, but one of the fixes in the D version is correcting
false indications. I don’t know if that was related to the
misfires, but I don’t get them anymore and it runs better
overall. I think everyone who thinks they ‘fixed’ the problem
and have reoccurring heating issues should get a new
radiator cap, support the hose from underneath, and really
press down hard when turning it. The two sets of nubs on
the cap should line up parallel to the hose (another clue I
failed to recognize initially).
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