'94 Sundance overcooling at highway speeds

Hi,

I have a 1994 Sundance with 2.5L engine that will not warm up when
driving at highway speeds. In city driving it will get 3/4 the way up
the temp guage, but at highway speeds it stays right on cold. Also, in
city driving, if I really rev the engine high, it will also drop the
temp. down to cold and then slowly climbs back up.

I have replaced the Temp. Sender, Temp. Sensor and the thermostat. I
replaced the thermostat twice, first time with one from Canadian Tire
which I was told can cause problems, so I bought an OE thermostat and
nothing has changed.

I have the manual for this car and the troubleshooting for
"overcooling" only mentions the thermostat and the temp sender...

anyone have any ideas what might be going on?

Thanks,
Kevin

 

Your heater core is stopped up causing the no heat and the temp fluctuation.
Try and back flush the heater core to see if that helps.

Glenn Beasley
Chrysler Tech

 

Please clarify: Do you have any evidence the engine is "overcooling" aside
from the gauge readings? Does your heater grow cold at highway speeds? Do
you get a Code 17 when you check for flash codes?

 

Okay, sorry... yes, other than the guage reading cold, the heater will
only blow lukewarm air on the highway... when I check for any stored
codes, I only get 5-5 (end of codes) so the computer doesnt know of any
problems. I was having a problem with the heater core not giving me
any heat, but I clamped on a hose to the inlet and outlet (alternating)
and blew anything out that would come out... when I was done, the water
coming out was coming out at the same rate as if I had the hose end in
my hand... When I am driving in the city, there is lots of hot hot air
coming out of the vents...

I hope this info helps...

thanks for the help so far!

 

Check head gasket. Very common causing those symptoms.

 

Im not sure I understand... what would the head gasket have to do with
cooling the engine too much? I am not losing any coolant and the
engine is running good right now... I do not know exactly what is
involved in checking the head gasket, but if it means taking the engine
apart, that seems a bit drastic... are there any other suggestions?

 

And is your coolant level up? Maybe you have air in the system. If you
changed the thermostat and temp sensor and such, you have lost some coolant.
Did you let the ngine warm up with the cap OFF! to let air escape? And top
up as necessary.

 

I should have mentioned I had that problem with a jeep before. Would not
heat up at all. And the jeep was brand new. Turned out to be a small pinhole
leak in the rad, which would not build the heat and pressure to warm up
engine, let alone me when it was -30 in Saskatchewan. A rad cap that is old
can cause this also.

 

Yes, coolant is full and I used the bleeder screw to eliminate all air
pockets in the system... as previously stated, I am not losing any
coolant. The coolant gets hot as it should under city driving
conditions, it is only at highway speeds that it will not heat up...

 

Is your cooling fan stuck on? Maybe a burned out relay?

Try pulling the power connection to the cooling fan or fans
then doing highway driving and see what the temp does. At
highway speeds the fans shouldn't be powered because
there should be enough road draft through the radiator to
cool it, also your not burning a lot of fuel at highway speeds and
so the engine isn't generating that much heat then.

Ted

 

And what is the outside temperature? And what is your coolant protected to,
Temperature Wise? If your coolant is too diluted and your on the highway at
subzero climate then yes your going to be running cooler. And around town it
will show warm.

 

None of the above is correct.

 

Shoot, there is more information I already knew that I should have
posted, which would have saved this... The fan actually only comes on
when the temperature gets about 3/4 the way up the temp. guage. For a
while I thought it was broken or a signal was getting to it somehow,
but it did eventually come on. About the car not burning as much fuel
at highway speed... that does make sense! I never really thought of
that. The only thing is, could the car REALLY be designed that way? I
mean, from what I understand, the thermostat should NOT open until the
engine is very warm, and until it does open, the coolant should just
keep circulating inside the engine (and through the heater core) until
its gets quite warm, when the thermostat should open. So to test this
operation, I tried driving with the heater set to cold (just to make
sure) and the fan to OFF. It still will not allow the temp. gauge to
get above the cold level. Is there really enough cold air at 110km/h
(65mph?) to cool the engine completely, offsetting all the explosions
happening at 2000-3000 RPM? I am no scientist, but that seems odd to
think that could be possible... its not like it is -40 outside
afterall... Actually, the temperature only have to drop to about -5 to
-10 celcius (25-15 fahrenheit) for this problem to occur. If the
temperature is above zero, the temp. guage will read warm and I can get
more heat..

Is there ANY possible was that some lines could be hooked up wrong that
would allow the engine to bypass the thermostat and let some coolant
get through to the radiator? I tried tracing all lines and it really
seems impossible, but I am at a loss here! There has to be something
wrong... surely Chrysler couldn't have designed such a poor
cooling/heating system...