99Honda CRV overheating

My 99 Honda CRV is overheating...especially when I'm on the interstate or going at high speeds. When I come to a stop, the temp returns to normal. We just replaced the A/C fan and condensor as that was not working so now we have air...but the wierd thing is the air works at stops or slow speeds, again, going 65 or more, the air seems to slow or stop working

We are at a lost as we thought when we found the A/C fan pretty much melted to the condensor that we had found the problem...we do get air now, but again, not consistantly

Is it our thermostat? And yes, we have enough coolant in the coolant dept. And yes, we do turn on the heat (we have to) to keep the gage from going all the way to HOT!

Any suggestions would be appreciated!

 

going at high speeds. When I come to a stop, the temp returns to normal.
We just replaced the A/C fan and condensor as that was not working so now we
have air...but the wierd thing is the air works at stops or slow speeds,
again, going 65 or more, the air seems to slow or stop working.

melted to the condensor that we had found the problem...we do get air now,
but again, not consistantly.

dept. And yes, we do turn on the heat (we have to) to keep the gage from
going all the way to HOT!!

It wouldn't hurt to replace the thermostat, but one would think that the car
would overheat at low speeds as well. (unless the thing is not opening up
all the way - usually the bad mode of failure is that it is stuck closed).

Are you sure your fans stay on? Perhaps short the thermoswitch that controls
them both (just for diagnostics purposes) and see if the car still overheats
with the fans going all the time. If it goes away, replace the switch.
In think on a crv the fans are controlled directly by this switch and do not
go through relays. You could also put a small light bulb or volt meter on
the fan's connector to see if the supply voltage to the fans drops or dies
when it overheats (again, diagnostics only).

Remco

 

You have already received some good advice, but here a few thoughts to
consider. Are you sure you're really overheating? Could your temp guage
or sending unit have a problem and be giving you a bad reading?
How high is the ouside temp when this is occuring and did it start all of
a sudden, or did it start over heating a little and get worse? Has anyone
ever heard of a Honda water pump impeller slipping on the shaft?
Mazda's have this problem, sometimes. Good luck.

 

Your radiator is clogged internally , or the external fins are corroded and
are falling off.

When it overheats, does turning the heater and its fan on full-blast lower
the temperature? If so, then there's your confirmation.

 

The simple thing to try first is replacing the thermostat, it's only a
few bucks. IF that doesn't fix it, then look to the rad.

 

The thermostat has nothing to do with this problem.

Remove the rad cap and peer inside with a flashlight. See opaque murk
instead of a clear green? White deposits around the tubes? Feel the rad. Is
it the same temperature all over, or is the bottom cooler than the top?

Have a look at the fins in the bottom middle third of the rad. Are they
crumbly, falling out, and missing?

This is the classic symptom of a rad that is not exhausting heat.

 

"I did not know that" <<in best Johnny Carson voice>>

Goes to show ya, one learns something new every day. Thanks, John.
Remco

 

Why are you so sure? I'm curious. The symptoms of overheating at high
speed (=high engine use) but cooling off at a stop with the cabin heater
going are precisely the symptoms experienced with a stuck thermostat.
"A/C fan melted to the condensor" and "air working at low speeds" tell
you it's the rad?

 

The radiator is the engine's heat exchanger. The faster the car is going
through the air, the better the heat transfer. When you stop the car, heat
transfer declines to near nothing since there's little air flow, and that's
why you need a cooling fan.

Heat transfer requires that water be circulated through the rad. If there
is no circulation (or impaired circulation), heat cannot be moved to the
rad core, and thus cannot be dumped into the atmosphere.

Since the engine generates much more heat under load than it does at idle,
more heat must be dumped, or the car will overheat. When the load is
removed, heat generation is similarly reduced. If the rad is exhausting
only a small amount of heat, it will readily keep up with an unloaded
engine, but not with a loaded one. If the rad is completely blocked, the
car will overheat at any load level.

It *is* possible that the problem here is caused by a stuck thermostat, but
a stuck thermostat is normally caused by either crappy aftermarket, or by
rust, scale, calcium, and silt in the system--the same things that plug
radiators. A clogged rad is far more likely in this case, so my reply
concentrated on this most likely scenario.

The ONE exception to this is a corroded exterior. The aluminum and brass
fins in the core are the devices that actually carry exhausted heat to the
atmosphere. If they are not there, the rad will not functin very well at
all, and will exhibit the symptoms of being plugged. You can have a cooling
system in top-notch condition, but if the rad has no fins, it will still
overheat.

Fin corrosion happens mostly to North-eastern cars. Cars in other regions
may experience gravel, sand, twigs, insects, and other debris wedged into
the lower third of the rad. This will have the exact same effect as the
other two conditions I list above. But the amount of debris has to be at a
hellacious level for this to occur.

 

I am quite curious what the problem ends up being now, because he
mentioned that his AC fan slows down when he overheats - those things
are just DC motors, aren't they?
When this happens, maybe his cooling fans slow down as well, not
properly cooling the car?

I couldn't think of a good failure mode on why it would do this but
maybe his supply voltage does something weird at higher speed.
Maybe his supply voltage is too high at high speeds and the motor won't
turn properly (do they have some sort of overvoltage protection in
them, maybe)? Or maybe the belt slips at high speeds and the supply
voltage eventually drops appreciably?

Perhaps check the voltage on the battery as well, just to make sure to
exclude it. You could just drive around, measuring the voltage on your
sigarette lighter plug - it should stay around 14.5 V without any
excursions at higher speeds.

Remco

 

Everything you say it true; however, I myself experienced this very same
problem just recently, and it was my thermostat that had stuck
closed--yes, I think it was a crappy aftermarket, which is alas what I
have in there now due to the emergency need to change it. Hence, my
recommendation that the thermostat be changed first--it's a lot easier
to try. Now, I've also had a clogged rad, so I know from personal
experience that this is also possible and is definitely worth examining.

 

Worth checking for excessively retarded spark.

 

He's overheating *at speed*, when the fans are superfluous. He's fine when
the car's not moving.

The fans are needed when the car is *not* moving, as then there is no air
moving through the rad/condenser, and thus little heat transfer.

 

As I said, it *could* be the thermostat, but in this case I do not think
so.

Now all we need is an update from the OP to confirm, and we know how
infrequently updates are ever offered...

 

We can always hope. I'm curious to see the resolution, myself.

 

I see now that I misunderstood his original post: was under the
impression that his fans slowed down.

Never mind what I said -- had a momentary fling with stupidity just now

 

First you can test the thermostat with hot water, thermostat fine if it open
in hot water and close in cold water. Other than the thermostat is the
radiator get clogged. My 1991 Accord has same problem, after the radiator
changed, it works fine.

 

Where did you get that from? Thermostats get lazy too, you know.

You CAN test it in hot water, but you need a candy thermometer. A 90C OEM
thermostat will start opening at 76-80C (169-176F) and be full open at 90C.
Lift height for my thermostat is 8mm (5/16").

Thermostats can refuse to open completely on account of gunk in the system,
or on account of age. They can also stick *open* for both reasons.