Overheating - Please read, this is not another fan switch and blade swap question.

This is not really overheating, right?

You're not seeing excessive temperatures are you?--normal operating temps, not overheating?

The air bleed provides a path to let air out while refilling the system after drainage. It should be full of fluid and not leaking air.

Does the reserve tank fill up and run out the overflow tube? When cold the reserve tank only needs to be at the lower level to operate properly. The reserve cap must not be blocked but should be free flow to let air in and fluid overflow as required. If the reserve cap / overflow tube is blocked the system will not work properly. Do you have a dirt dobber nest in the overflow tube?

It's normal for the volume of the coolant to expand and contract as the temperature rises and falls. If you fill up the engine and radiators with coolant when cold then some will need to overflow to the reserve tank when it heats up. This produces a lower-than-ambient pressure (vacuum) in the system when it cools down again that should pull fluid from the reserve until the pressure is balanced.

You don't want to clamp the reserve line or the system will not function properly.

If the reserve tank is not overflowing then you don't have a problem. Fluid level in tank should rise and fall.

If the reserve tank is overflowing then you have an air leak (cracked hose, loose clamp, etc) that is pulling air back into the system instead of the fluid from reserve tank. But if you have the reserve tank clamped off then it can't pull fluid and it will pull air from whatever path has least resistance.

 

Your thermostat is opening a little bit late. Per the Honda service manual, it should beging to open at 176F-183F, becomming fully open at 203F with 8mm lift. I don't quite think this is the issue though.

I think you've got a leak in the system somewhere, whether it be a gasket or a hose. The reason being is your sporadic fan. When your fan starts working intermittently, this is usually because there is air trapped around the fan switch and it isn't reading the temperature properly. Hell, perhaps this is where your leak is coming from.

 

Pressure test the radiator cap (If it were me, I'd just replace it). completely seal the cooling system and pressure test. The only way it will pull the coolant back out of the res is if there are no leaks. The contraction of the cooling fluid in a sealed system is what creates the vacuum to draw the fluid back out of the resevoir........the only thing between the expansion res and the rads is the hose and the cap....If you're pressurizing the expansion res and you're not getting it back, then I'd start there..no sealed system....pressurized expansion tank...no return when cooled, system isn't sealed.




.

 

If there is air in the cooling system it will not pull coolant back in. Air compresses unlike fluids.

 

ding, ding, ding...we have a winner. Now, do us all a favor and tell us where it's coming from.




.

 

Local Honda dealer cant explain it either, what a waste of money.

I am convinced the system is getting fresh air in. There was still pressure in the system when i opened the cap yesterday morning. It bubbled in to the reserve tank and gave a quick fsssst when i unscrewed the cap. Where on this bike is there pressurized fresh air?

 

Did you replace the t-stat or just check it?

It occurred to me that you can't be holding pressure over night and have a normal atmospheric leak. Cooling systems don't inhale air under normal conditions, they blow out. The pressure builds from expansion due to heat. In this case the system is ejecting its coolant (cold radiator on the left) due to internal pressure that acts like normal expansion but it's not. I know what your combustion leak detector said but it sure sounds like your system is being pressurized.

 

Carlisle, PA

 

The only way to get air in the system, assuming no leaks and properly bled, is through the siphon tube.

When the system cools, it looks to siphon coolant back from the overflow reservoir. If that tube has any leak at all, it will suck air, instead of coolant.

I hate to beat a dead horse, but if you still haven't checked that hose out, I renounce the ties of our VFR blood, and my dominion over you as my progeny. As your maker, I release you.

:crazy:

 

Even at a distance i believe our collective brain trust and thousands of years of combined experience should be able to solve this mystery !

 

Yes but diagnostics through forum posts is like working blindfolded while wearing a pare of arctic mittens.

 

I'm only like 2 hours away, ish.

 

This may sound un-orthodox, so take it how you want, but it did work for me a few times on a car. It is a bit tricky though

The same device for pressure testing cooling system can be used to measure pressure in it. The tricky part is that it will not release pressure like radiator cap would do, so you can not run the bike for long with it.
However, I think you can hook it up, and start the cold bike for 30-40 seconds, and if you see the pressure go up quickly (like over 10 psi), you have a gasket leak.
Under normal operation, 30-40 seconds of running a cold bike does not produce enough heat to warm up the cooling system, expand the coolant and open the radiator cap.
On the other side, if you do have a head gasket leak, blow by will pressurize cooling system quite quickly.

You did test for exhaust gases chemically, but I had so-so success with those testers, so I do not trust them always.

Just thinking out loud, another idea might be a busted radiator filler neck, where a plastic "ring" that mates to the cap has a crack, and leaks coolant, effectively rendering cap as not there, since system will not hold the pressure with the cap. Depending on the type of coolant pressure tester you used, if it had a thicker seal/adapter, you may not expose this crack.

 

Ah, one more idea. A few years back, a buddy of mine was changing a water pump on his GM truck. Since he was cheap and did not want to flush coolant at the same time, he stuffed main hose with plastic grocery bags. Needless to say he did not take all of them out. Car has been overheating when driven ever since
Did you try to flush out individual parts of cooling system? Like remove all hoses and put a garden hose to radiators, pump, coolant block intakes ........

 

This is something I would seriously consider. What you are experiencing is not normal in the sense of "normal" cooling systems problems and failures. You have to start turning over every rock no matter how far fetched or insignificant it my seem. You have to determine if every part of your cooling system is functioning properly.