Thank You "Elle"

Thanks a million "Elle". I checked my coolant. It was bone dry. I addded
anti-freeze/water mixture, took a spin around the block. The car is
running normal. I will check the owner's manual and purge the line as you
recommended.
Thanks again.
Krystyne

 

Neat. But, hey, bone dry? How did this happen?

Hopefully you mean just the reservoir was bone dry, and that this was due to
neglect.

Though I might sound like your mom, again remember to only open that
radiator cap with the engine stone cold. When warm at all, the radiator
cooling system is under pressure, and hot fluid will dangerously burst out
at anyone who takes off the cap. When cool, all is safe.

Follow the manual's instructions about purging carefully.

Make sure you use the right coolant, and mix it only with distilled (not
tap) water.

Last summer my 1991 Civic was revving like yours. The coolant levels
appeared fine. But in fact a few months before I had replaced the cooling
system thermostat and got some air into the system. I did not know how to do
a proper purge and so hadn't done one after this little repair. Folks here
helped me figure this out. I learned it would take a long time for the fan
to come on (something like 3/4 hour) during the purge procedure. It finally
did, and I added coolant per the purge instructions to get the level
correct.

 

Aha! So it seems that in spite of my experiment in disconnecting the TW
sensor, and in spite of Misterbeet's assertions, there IS evidence that a
low coolant level WILL cause a fluctuating idle! VERY cool! (So to speak.)

Now the question: WHY? jim beam, Misterbeets...?

 

Easy Tegger.

The coolant temp sensor will get wrong readings from having the air hit it
rather than coolant.


--
Stephen W. Hansen
ASE Certified Master Automobile Technician
ASE Undercar Specialist


http://www.troublecodes.net/technical/

 

check out the sensor in the manual - it's a tiny thermistor embedded in
a brass stalk that sticks about an inch into the coolant stream. and
the manual shows it's resistivity curve too - logarythmic. takes very
little change in temp to make a big change in resistivity and therefore
a big change in the signal it's sending the ecu.

 

I have a fatory manual, and that's exactly what I thought too, but
Misterbeets dissuaded me.

The ECU goes into closed loop ONLY when the coolant is reported as 90C, so
it would not take much of a drop to convince the ECU the engine is cooler
than fully-warm.

 

-------------------------

That's what I've been trying to say. . they are 'full immersion'
sensors. Hold them above a pot of boiling water . . nothing. Dunk them
in and they act completely different. When the water pump starts
pumping, one side of the cooing system goes LOW if there's air in there,
and idle is affected because sensor(s) is now above waterline. Same
thing when thermostat opens. Air shifts around.

That's why the manual should have said 'Keep the coolant in the
reservoir at the MAX' especially because MIN is impossible to see
without a clean engine compartment and a flashlight (some models).

'Curly'

 

If you tried to keep it at MAX you would be filling it every day if you
lived in a place where they have summer (like here in Dallas). Steady state
for these things is at the MIN line when cold and at the MAX line when hot
after driving. If you start at MAX or above, the expansion tank dumps the
excess when the overflow moves into the tank. After the system sucks the
overflow back in as it cools, the tank will be sitting exactly at the "MIN"
line every morning, no matter how much you added to it before you drove it.

If there is air in the system, some of it can burp out through the overflow,
in which case it will draw down to below MIN when as it cools.

Every car I have owned in the past 15 years works this way (including cars
for the teenagers, that comes out to 4 Hondas, 6 Nissans, a Ford, an
Oldsmobile, and a Mazda). Air in the system will not be introduced by the
expansion tank as long as you keep it at the MIN line.

I think the the directions in the user manual match the function of the
system - keep it at least at MIN and it works as designed.

 

===========================

I half-ways agree with what you're saying, but don't confuse pressurized
reservoirs with (some?) Honda reservoirs. I'm suggesting that people
(who don't know any better) remove the cap and look down into the
reservoir (because they can't actually see it from the side). They see
three ounces of coolant in the bottom and assume it's OK. My CR-v
'feeds' the reservoir from a snorkel hose that goes thru the top cap,
and if the rad sucks the reservoir dry, there's always a bit in the
bottom. Maybe there should have been a 'magic green eye' like they have
on the battery (or a sensor). . . Easy to see if the reservoir is _too_
empty. BTW, the service manual says it's normal for the water pump to
'weep' a bit of coolant, so we can't assume that a Honda never needs to
be 'topped up'.

'Curly'

 

I'm not. None of the cars I listed have a pressurized reservoir. The only
car I ever had that did was a Volkswagen. What a nightmare that was. When
the car was only 3 years old, the pressure caused the plastic reservoir to
crack open like an egg.

I'm not advocating that they never need to be topped up. Normal evaporation
in the expansion tank will eventually cause it to drop below MIN, even if
the system is perfect.

I hear you about seeing the marks on the tank. What are they thinking? I
have had some success by marking the MIN and MAX lines with a grease pencil
when the tank is out for cleaning at anti-freeze change time. Usually that,
in combination with a flashlight, is enough to be able to see the marks once
its back in there.

Nissan seems to have given this a little bit more thought. There is about
1/2 inch of daylight along the side of the radiator on my '02 Pathfinder and
the tank is mounted such that you can clearly see the marks on the expansion
tank as well as the level in the washer bottle on the other side if you look
across the front of the radiator.