"Phil's Podium" posted by Roader is really talking about the flow direction inside the engine. It doesn't say anything about upwards or downwards in the radiator.

 

Jim, you're right, it doesn't explicitly say anything about bottom-to-top flow. It does, though, imply that direction of flow:The top hose on my F engine goes right to the head so I've always assumed it has a reverse flow cooling system, especially since the thermostat isn't on the head coolant flange. When checking for thermostat opening, I feel the lower hose. It gets hot first closest to the thermostat and the heat eventually moves through the hose towards the bottom radiator inlet. I think that indicates a bottom-to-top flow but of course I could be wrong.

I haven't a clue if the OP's K engine's coolant runs top-to-bottom or vice versa. I've never even seen a K engine. It would surprise me if Honda reverted to top-down coolant flow but, I've been surprised before. It would seem that closely regulating the temperature of the cylinder head would be necessary to meet emissions requirements but it could well be that Honda has some way of doing that with top-down coolant flow.

 

The coolant flow on your '96 F series engine is also from the top radiator hose, through the radiator and out the lower radiator hose.

 

Honda traditionally puts the thermostat at the suction side of the waterpump. And coolant is circulating through the engine (& heater) all the time, even from a cold start. That circulating coolant is always flowing through the thermostat housing, and the sensing-end of the thermostat sits in that flow. When that coolant (coming from the engine) gets hot, then the thermostat opens to suck some cooler water from the lower radiator hose.

 

I think a lot of this makes sense to me, thanks guys!

So it does look like the t-stat is mounted on the engine on the lower rad hose. The wax part that reacts to the heat to open is on engine side immersed in engine coolant. This seals the lower part of the engine when cold so when I do the drain at the rad I should only get everything in the lower rad hose up until the t-stat, everything in the rad and everything in the upper rad hose and above in the head. The only coolant left is in the block up to the start of the upper rad hose.

1. When I refill the rad it should fill up the lower rad hose but leave an air pocket.
2. Since the upper rad hose is even with the head, it fills up both upper rad hose and head until it reaches top of filler neck.
3. When the car is started, since upper rad hose contains the same coolant that's inside of the head and by contact the engine, it heats up quickly.
4. Whatever is in the lower rad hose whether it's air or coolant doesn't heat up as quickly due to the t-stat blocking contact with engine coolant.
5. No coolant is circulating out of the engine, this is so the engine can heat up ASAP to get the cat working fast for emissions reasons.
6. When t-stat opens because the engine coolant is hot enough, the coolant is sucked into the engine from the lower rad hose pulling air into the engine where it bubbles up to the highest point which is either top of cylinders or head.
7. The rad coolant will drop as a result. We top it off and as the coolant continues to fill the engine, since the system isn't pressurized the air moves up and eventually exits the head through the "water outlet", if the car is parked on an incline or if the head is just lower than the upper rad hose slightly, the air moves up the upper rad hose and leaves the filler neck. Air bled and done.

Some engines have a drain bolt mounted towards the front of the car on the head or a little lower, I assume this is so you can drain more coolant here but nothing lower than the bolt. If you do drain it here when you fill the rad you will fill what you removed from the engine since the coolant you put in the rad maxes the radiator level, flows through upper rad hose and evens the engine coolant height with the upper rad hose height.

 

Thermostat isn't a perfect seal. When you drain it, coolant drains slowly through the thermostat so you get much of the coolant out of the engine.

F-series engine has a drain bolt on the back of the block, sorta near the oil filter. I don't remember the K-series having that. The thermostat housing comes apart with a spring clip. That makes the K-series easier to drain & fill.

 

Whew. So I "think" I finished the change and bleeding today. Can any one tell me if my result had some problems in it?

1. Total amount of fluid that came out was 1.125 gal.
2. I bled according to directions. Parked on inclined driveway with wood under front wheels to angle higher than the driveway.
3. I hooked up spill free funnel, filled with coolant, started it up and idled.
4. I idled 25 minutes for it to reach the temp it usually maxes out at when I'm driving on the highway, right below center of temp gauge. It's very cold outside. Fan blows hot air so there's no air in heater core right off the bat.
5. I idled another 20 minutes waiting for cooling fan to come on. Didn't come on. Temp remains unchanged. Lower hose was still ice cold, upper hose getting hotter. It's pretty cold outside so I thought maybe I was out of luck.
6. Idled another 20 minutes. Lower hose became hot, upper hose became unbearably hot. Did thermostat open? I think yes, but the cooling fan didn't come on.
7. Every so often I would squeeze upper rad hose and get bubbles coming out.
8. Got tired of idling so I decided to rev it in park to about 1000rpm and finally cooling fan came on after 20 seconds of throttle and shut off after 5 seconds. Is the a/c fan supposed to kick in at the same time? Bubbles came up continuously for about twenty seconds afterwards. The upper hose and lower hose are both steaming hot now and the coolant in funnel is giving off steam from the cold air outside.
9. Revved it again at 2000rpm, cooling fan came on again, some more bubbles. Coolant is giving off more steam, everything is all nice and hot now.
10. I repeated this four times total. On the fourth time the cooling fan came on, no bubbles came up so I stopped. Squeezing upper rad hose gives no bubbles.

Does this sound good? I heard when thermostat opens there's supposed to be a lot of bubbles, the coolant level should drop and the fan should kick in but this didn't happen to me. The level barely dropped, bubbles came up and the cooling fan kicked in only after I revved it, the lower hose became hot before the cooling fan kicked in. I assume the thermostat is physical so it will always open based on coolant temp but the fan is separate?

Temps never went past normal max temp (below halfway mark). I noticed the radiator level kept dropping when I was cleaning everything up so I kept topping it off before I finally put the car to rest. I have the cap on all the way so tomorrow I assume it will have pulled some from the reservoir over night so I can just top everything off. I'm tempted to try the bleeding again tomorrow because I feel like it might have went wrong since the level in the funnel didn't drop.

Is there any way I can examing the radiator cap to tell if it's bad? The rubber seal looks good, the center of the cap has this little cylinder that if you pull on it, it actually comes down. I think that's supposed to be like that since that's the vacuum part that draws from reservoir back in. Is it supposed to be springy? Is it supposed to just drop?

 

A system full of coolant will not drop the level when the thermostat opens.

If you idle is stable and the temperature gauge is reading normal, then any remaining air bubbles will work their way out through the radiator cap. It does sound like you got most if not all of the air out.

The fans will turn on when the coolant reaches a certain temperature. There is a temperature switch on the cooling system that turns on the fans. The thermostat is mechanical and does not control the fans, or vice versa.

It was probably cold enough outside to help the radiator cool the coolant to below the set temperature to turn the fans on.

Keep an eye on the temperature gauge in your car, but it sounds like you are all set.

 

Makes sense. If there's no air then there's no where for coolant to go. But what does that in itself mean? If drained it and filled it, why was there no air in system? Or maybe it's because I kept squeezing the hoses instead of letting the air build up at the upper hose and come out all at once?

How? If there are air bubbles and they reach the filler neck while the cap is closed, where do they go? Can they push through the cap like the fluid?

This kind of makes sense to me. The themostat can open by itself since it's mechanical but I thought the wax would make it so it opens at the same temp as the fans turn on. If there's a difference between the temps then it would make sense but I thought there wasn't. Also the fact that the thermostat opened but it looks like the temp sensor is in the same place. So both must be touching the same coolant. Why didn't it open and turn the fan on at same time?

 

The radiator cap has a relief valve that allows liquid over to the overflow bottle. Then when cooling off, it sucks it back in. During that process, air bubbles go to the bottle & liquid is sucked back in.

Thermostat opens at a lower temperature than the fan switch. The fan is supposed to come on after the thermostat opens fully & coolant gets hotter yet. I'm not surprised you had difficulty getting the fan to run when it's cold outside. That's a sign your cooling system is working well.