95 Accord runs hot on freeway

I have a 95 Accord which starts to run hot after about 15 to 20
minutes of driving on the freeway. It runs at normal temperature on
surface streets. I know for sure that the fans are working properly.

I’ve taken it to 2 mechanics and one says it’s the main fan motor and
possibly the thermostat. The other mechanic thinks the radiator needs
to be replaced due to a clog, and if not that, then it is most likely
the head gasket leaking. I’m really confused here. Any help would be
greatly appreciated.

 

take it for a run on the freeway. when it's hot, open the hood and look
in the coolant expansion bottle. if you see bubbles, it's head gasket.
if not, you can get it tested to be sure. if it's not head, go for
thermostat and radiator, in that order. but before all that, make sure
coolant level is ok - both in the radiator and the expansion bottle.

 

Jim beam's advice is solid. I'd add that I suspect the radiator more than
the thermostat because the heat builds up, but that assumes it isn't the
head gasket.

My own head gasket test is more sensitive but has the disadvantage that the
leak may not be as obvious when cold. I test with a cold engine by removing
the radiator cap and starting the engine. I pinch off the overflow tube and
put the palm of my hand over the radiator opening for a few seconds.
Steadily rising pressure or (worse) pulsations indicate a head gasket
failure.

If either jim's test or mine indicate trouble, shops can do chemical tests
for hydrocarbons in the coolant to confirm the problem.

Mike

 

If it runs fine on city street but not on the highway, it's most likely a
clogged rad.

A test: Next time it starts to overheat, turn the car's interior heater on
full-hot, along with the fan on full-blast. Does this make the needle go
down? If so, the rad isn't cooling properly.

One thing to check is the fins at the bottom of the rad. If they corrode
and turn to dust, the rad will be unable to shed heat efficiently.

 

Thank you for the great and very helpful replies. I am going to try
the things recommended here. Also, the mechanic that thinks it’s the
radiator, says that since the radiator is plastic, it needs to be
replaced. It cannot be flushed. Is this correct?

Since I have never had to do so, what would be the best place to start
to find a shop that can do the chemical test for hydrocarbons in the
coolant

 

Today I checked every recommendation posted.

First I tried the cold method to check for possibility of bad head
gasket. I pinched the reservoir hose, and placed my palm on the
radiator opening. I did not feel any pulsating.

Second, after a long drive on the freeway, when I stopped, I checked
the reservoir, and there were no bubbles.

Third, while driving on the freeway back home, when the car started to
heat up, I turned on the heater full blast, and the temp cooled down
right away.

 

Then your rad is internally blocked (or the fins have fallen off).

 

First put a new Honda thermostat in it.Not some aftermarket TS,a real Honda
TS.

 

It's not his thermostat. I'm sure of that.

 

[snipped]

Could be it is not opening all the way causing the temp to run hot. Using
the heater as a mini radiator helps to lower the temp. Of course that would
also work if the radiator was partially blocked.

 

at that age,it's certainly suspect.
Besides,just how much heat can the heater core dissipate,if it cools down
his motor? Maybe he's got a worn water pump too.

 

Heater core flow is completely independent of the thermostat.

Inlet flow is from the head's outlet end, and outlet flow is downstream of
the thermostat. In other words, the same circulation feeds the heater core
that occurs in the head/block due to the thermostat bypass when the
thermostat is closed.

 

There's certainly no harm (and lots of good!) in replacing the thermostat
while the cooling system is in dry-dock, but the thermostat is not the OP's
particular problem here. See my other post.

The heater core is an amazingly efficient heat-dump device. You wouldn't
think so due to its size, but it is. It can very easily compensate for a
rad that can't shed as much heat as it was designed to.

 

Jim Yanik wrote:

pump can't wear in a way that reduces flow - there's no parts that touch.

 

But it can't compensate for a thermostat that's stuck shut!

 

That's my view. The thermostat is a good target because it's inexpensive and
probably due for replacement while the coolant is drained, but the symptoms
are pretty classic for a plugged radiator. The plastic tanks in the radiator
are also plotting to crack, I'm sure.

Remember, 'pinkfloyd' - OEM only on the thermostat and be sure the system is
properly purged of air when the system is refilled with Honda premix (never
add tap water).

When you replace the radiator and thermostat, you can Set the Controls for
the Heart of the Sun and still stay cool. ;-)

Mike

 

is the impeller plastic or metal?
IMO,plastic can degrade,even immersed in the coolant.

 

metal. you're right, it can corrode, but rarely does. i wouldn't call
degradation wear, but yes, that's possible.

 

ISTR reading somewhere about a water pump impeller that had worn away.It
didn't say whether the impeller was plastic or metal.

also,I believe an old thermostat could open only part way,and pass -some-
coolant,but not enough,explaining why the heater core could dump enough
heat to keep the motor cool. I really do not believe a heater core can dump
enough heat -by itself- to keep a motor cool. Otherwise,there would be no
need for such a large radiator at the front.

 

Jim Yanik wrote:

it depends. it's all a matter of the energy that can be transferred per
degree of air temp difference. if the energy coming out of the coolant
is less than that which can be dumped through the heater matrix, then it
definitely can. you'd need to know the numbers to be sure.