Dear Experts,

On my old Fords, the thermostat was
on top of the engine. When the engine
was hot, the thermostat opened, the
coolant when through the top hose
into the radiator. After dropping
through the radiator, the coolant
entered the return hose at the bottom,
and re-entered the engine.


Now I have a 1996 Honda Accord
2.2 VTEC engine

I noticed that even though the engine was hot,
the top hose was cool. The only warmth that
the hose had was near the engine.
Elsewhere, the hose was cool.
Which seemed really odd.


I took a look at this Youtube video about
changing the thermostat.


Turns out that the thermostat is not directly
behind the upper hose to the radiator.

Instead, the thermostat is directly behind the lower
hose to the radiator.

See the pictures of the engine compartment.


So, my question is, which way does the
coolant flow through the radiator?

From top to bottom? Or,
From bottom to top?

Thanks a lot!

 

The coolant flows from water pump thru a pipe under the intake to the thermostat, thru the lower hose, into the radiator then out the top hose into the head, to the block and finally back to the pump...

 

The coolant flow '96 F series engine is from the top radiator hose, through the radiator and out the lower radiator hose. The upper radiator hose is warm/hot first, as the heated coolant from the engine is going to the radiator. Thus, the lower radiator hose is not warm/hot like the upper hose until the thermostat opens.

Here is some info. related to coolant flow on various Hondas:

https://honda-tech.com/forums/attach...low-dec-19.pdf

Honda Cooling Systems - Honda Tuning Magazine

 

FYI
The above is for the Honda K-series engines. This is why the 'front' of the engine and the intake/exhaust manifolds are all turned opposite of the F/H series engines.

 

Haha, I am wrong, but here's what threw me off.


The thermostat #4 on the f23 looks like its installed backward relative to the right to left flow direction (but not the engine). Typically the pellet and spring on the thermostat are up stream of the flow, apparently not true on the f23. Also I should have looked more closely at the water pump #1, the suction for the impellers is clearly connected to the left end of the pipe #11, so pipe flow direction is from right to left in the picture. So to be clear, flow is out of the head #9, to the top of the radiator (not shown), out the bottom, to #6, thru the thermostat #4, thru the pipe #11, into the water pump, #1 then into the block (not shown).

 

Thanks for your responses.

After driving 1/2 hour in the cold winter, I
stopped in a parking lot,
let the engine run,
and felt how hot the hoses were.

The hotter coolant is in the
Upper radiator hose.

The Lower radiator hose is cooler

So, the coolant does flow from the upper hose,
through the radiator, and
returns through the lower hose

I still find the placement of the thermostat rather odd.

 

Initially it does, but in operation it offers a more linear coolant temp throughout the engine.
With an old SBC/SBF engine warms up and the thermostat opens. Not until coolant that is too cool reaches the thermostat does it begin to close. Location of the thermostat on those engines means that the thermostat(which is supposed to be controlling running temps) is the last component to actually be affected by the temp change. Which is kind of silly to have the control unit the last device in line, this would create quite a differential in temperature throughout the engine which can create hot and cold spots.
Hondas routing has it so that the thermostat is actively controlling and ahead of the temperature changes inside the engine. It's a much more proactive system that maintains a more constant temperature throughout the engine. This improves longevity and sealing as the engine as a whole is warmed up and cooled down as a unit. In my older SBF/SBC/Olds powered toys it can be a bit nerve racking to watch teh temps sway from 180-220ºF during normal operation depending on load.
It's a latency thang yo.
Hondas way keeps the average overall temp consistent with little fluctuations in temp change. If you see the temp on a Honda start to move up beyond it's normal rock steady position, you can determine that there is an issue with the cooling system and still have a large margin of error before failure occurs. With the older engine systems you may not think there is something wrong until the temp gauge starts cresting past 220 before you realize there is an issue and it may be too late to react then.