Radiator Fan Not Coming On - Overheating

THANKS FOR THIS IDEA AND OTHERS! I talked to the mechanics and they
felt bad it wasn't fixed and said they would try anything I came up
with to see what it could be, since they are stumped. I'll pass on
these ideas and let you know.

John

 

Well, I did some extensive tests on my 94 vx on the weekend about the
overheating. This is what happens on overheating -
-radiator full and reserve at max line
-start the car
-idle for 25 mintues
-at first only top hose is hot and then after a few minutes bottom
hose from radiator is also hot
-temp gauge is stable at mid-point
-fan comes on goes off after about 30 seconds
-fan comes on again a few minutes later and then turns off after about
30 seconds
-reserve tank begins to fill and keeps filling until radiator fluid
is spraying out from under the reserve tanks cap
-temp gauge rises
-fan comes on again
-temp gauge goes back down
-reserve tank fluid receeds
-fan goes off
-reserv tank starts to fill again and overflows
-temp gauge rises
-fan comes on
-...and on and on it goes

John McConnell
Vermont

 

Well, I did some extensive tests on my 94 vx on the weekend about the
overheating. This is what happens on overheating -
-radiator full and reserve at max line
-start the car
-idle for 25 mintues
-at first only top hose is hot and then after a few minutes bottom
hose from radiator is also hot
-temp gauge is stable at mid-point
-fan comes on goes off after about 30 seconds
-fan comes on again a few minutes later and then turns off after about
30 seconds
-reserve tank begins to fill and keeps filling until radiator fluid
is spraying out from under the reserve tanks cap
-temp gauge rises
-fan comes on again
-temp gauge goes back down
-reserve tank fluid receeds
-fan goes off
-reserv tank starts to fill again and overflows
-temp gauge rises
-fan comes on
-...and on and on it goes

John McConnell
Vermont

 

That really sounds like a bad radiator cap. Most garages will have a
pressure tester to check if the cap will hold the specified pressure. Have
you tried testing it or simply replacing it (they are relatively
inexpensive)?

 

That really sounds like a bad radiator cap. Most garages will have a
pressure tester to check if the cap will hold the specified pressure. Have
you tried testing it or simply replacing it (they are relatively
inexpensive)?

 

To me that sounds more like a bad fan thermoswitch. If the engine is
overheated, the fan should not turn off.

 

To me that sounds more like a bad fan thermoswitch. If the engine is
overheated, the fan should not turn off.

 

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

John, I explained on the 12th that it's probably your rad cap... Coolant
will boil if not pressurized. When it boils, your thermostat and temp
sensors won't work correctly (just like certain types of industrial
thermometers have the words EMERSION ONLY printed on them) Steam won't
trip a sensor / thermostat the same way a bath in boiling hot water
will.

A rad cap is so cheap to try.......... An internet search will surely
find you a explanation of why they presurize cooling systems. Here's a
hint: A pot of water boils at a lower temperature in Denver, than it
does in Panama.

'Curly'

 

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

John, I explained on the 12th that it's probably your rad cap... Coolant
will boil if not pressurized. When it boils, your thermostat and temp
sensors won't work correctly (just like certain types of industrial
thermometers have the words EMERSION ONLY printed on them) Steam won't
trip a sensor / thermostat the same way a bath in boiling hot water
will.

A rad cap is so cheap to try.......... An internet search will surely
find you a explanation of why they presurize cooling systems. Here's a
hint: A pot of water boils at a lower temperature in Denver, than it
does in Panama.

'Curly'

 

He says the temp gauge goes back down when the fans come on, so as far as
the car is concerned, its not overheated.

 

He says the temp gauge goes back down when the fans come on, so as far as
the car is concerned, its not overheated.

 

Excellent description! Many people have suggested a bad radiator cap,
but if I read your post right, the coolant is not leaking out from under
the radiator cap but from the reserve tank cap/fitting. Typically
radiator caps are made to open up above a certain pressure, that is the
safety release. The reserve tank cap should not open up. Remove the cap
and look for damage both at the neck of the reserve tank and at the cap
itself. Perhaps there is a gasket that is torn or has moved out of
position. I believe the reserve tank cap part number is 19110-P08-000,
perhaps you could go to the dealer and ask to compare your cap to a new
one. Should be less than $10 to buy a new one should it be needed.

 

Excellent description! Many people have suggested a bad radiator cap,
but if I read your post right, the coolant is not leaking out from under
the radiator cap but from the reserve tank cap/fitting. Typically
radiator caps are made to open up above a certain pressure, that is the
safety release. The reserve tank cap should not open up. Remove the cap
and look for damage both at the neck of the reserve tank and at the cap
itself. Perhaps there is a gasket that is torn or has moved out of
position. I believe the reserve tank cap part number is 19110-P08-000,
perhaps you could go to the dealer and ask to compare your cap to a new
one. Should be less than $10 to buy a new one should it be needed.

 

===========================
Randolph,

I'm sure the reserve tank isn't (ever) pressurized on the Honda we're
discussing. The plastic lid is designed to not be air-tight, so it's
always at atmospheric pressure.

When the cooland boils, (because the rad cap isn't building pressure)
the overflow get forced thru the little hose and once the reservoir
fills, it blows out around the plastic cap.

When the coolant cools, the rad cap is supposed to allow the stuff in
the reservoir to be sucked back into the engine. Sometimes, on larger
engines they put coil springs inside the rad hoses, to prevent them
'sucking flat', which would prevent any coolant sucking back into the
rad after a hot run.


'Curly'

 

===========================
Randolph,

I'm sure the reserve tank isn't (ever) pressurized on the Honda we're
discussing. The plastic lid is designed to not be air-tight, so it's
always at atmospheric pressure.

When the cooland boils, (because the rad cap isn't building pressure)
the overflow get forced thru the little hose and once the reservoir
fills, it blows out around the plastic cap.

When the coolant cools, the rad cap is supposed to allow the stuff in
the reservoir to be sucked back into the engine. Sometimes, on larger
engines they put coil springs inside the rad hoses, to prevent them
'sucking flat', which would prevent any coolant sucking back into the
rad after a hot run.


'Curly'

 

Sorry I didn't mention this, but I did buy a new radiator cap.
Actually, I was so excited it would work I left work early and bought
it after I saw your post Curly - no go. And, for those who haven't
followed the saga, a garage has already replaced the head gasket and
the thermostat.

Thanks for everybody's help.
John

 

Sorry I didn't mention this, but I did buy a new radiator cap.
Actually, I was so excited it would work I left work early and bought
it after I saw your post Curly - no go. And, for those who haven't
followed the saga, a garage has already replaced the head gasket and
the thermostat.

Thanks for everybody's help.
John

 

Open radiator cap when engine is cold. Else, put a rag over the cap and then
open it slowly.
Idle the engine until hot. Check for air bubbles coming out of the radiator.
If there are continuous bubbles, either the head gasket is bad or there is a
crack in the engine/head.

Another check you could do is to check the thermo switch that control the
cooling fan. Remove it from the car. Suspense it in a pot of water, make sure
that the contacts don't touch the water. Heat up the water. Measure the
temperature when the switch short the 2 contacts. Replace it if it works at
temperature much higher than spec.

In 1st case, the gas force the cap to open. The coolant flows into the
reservoir then. In 2nd case, the faulty thermo switch turn on the fan too late
to prevent overheating. Even though it cycles, it could be cycling the cooling
fan at temperature near boiling point of that pressurized cooling system.

Do the 1st check 1st, since it's easy. The 2nd check requires a meat
thermometer with at least 220 F range, and a meter to check the contacts.

 

I stand corrected. On my grandmother's old Renault the reservoir was
pressurized like the rest of the system, and the reservoir was made from
glass. Working around a large glass bottle under the hood makes you pay
attention to where you throw your tools!

 

I stand corrected. On my grandmother's old Renault the reservoir was
pressurized like the rest of the system, and the reservoir was made from
glass. Working around a large glass bottle under the hood makes you pay
attention to where you throw your tools!