Greetings,
Here is the problem I am having. I own a 2002 V6 accord, 3.0L, 4-speed automatic, with ~259K miles, original engine. I have a problem that so far no one has been able to fix (I've taken the car to 3 shops). The problem started when I noticed that water from the radiator was being forced out from the right side where the reservoir is located during long distance drives and I had to put water (about 16 oz of a bottle water) in the radiator every other day. All this started back in August 2010. To make my long story short, in sequence in different weeks:1) had the radiator cap replaced and fans checked well - but water was still forced out; 2) had upper & lower radiator hoses replaced, all 3 heater hoses replaced, complete radiator system flush - coolant flush w/sealer & conditioner, & thermostat replaced - same problem, water was still forced out; 3) had radiator and engine pressure tested & nothing negative was found - same problem, water was still forced out; 4) radiator was tested for leaks & no leak found - same problem, water was still forced out; 5) radiator cap replaced again - same problem, water was still forced out; 6) radiator couldn't take it & busted, went ahead replaced the radiator with a brand new one, had engine pressure tested & nothing negative was found - same problem, water was still forced out. The water pump was replaced last year when I had the timing belt done. I am driving the car & still the same problem, water being forced out from the right side where the reservoir is located. I still put water in the radiator every other day. I don't know what else to do maybe I need to take it to another Honda service location. Any help on this is appreciated. Thank you.

 

How is the rubber hose from the radiator cap over to the reservoir? Any cracks or holes?

When the engine heats up, coolant moves over to the reservoir. When the engine cools down, it's supposed to suck back in. If there's a hole in that hose, it'll suck air instead. After a couple times, coolant might overflow from the reservoir while there's air-space inside the radiator.

 

You say leaking next to coolant reservoir. Can you tell us more specifically where it's loosing coolant. And..why can't you just put coolant in the reservoir ? If cap is fine and system is working, the radiator should pull coolant from reservoir. Is that the source of your leak? The reservoir?

 

Thanks JimBlake for replying. The hose between the radiator and reservoir is good. Yes the reservoir does get filled but when the radiator is low in coolant it sucks it back in. I noticed this a couple of weeks back when I saw the reservoir overfilled over the max and when I drove the car 40 miles and checked under the hood, the coolant in the reservoir had dropped down right at max. Later when the car cooled down, checked the radiator and it was low in coolant. Poured water (~16oz of water) in the radiator to fill it up.

Thanks Old Honda Dude for replying. As you're aware now radiator does pull the coolant from the reservoir. I check under the hood every morning and the target area where the coolant is splattered is always on the right side where the reservoir is located. Coolant being forced out in the reservoir because the reservoir gets filled.

Something is triggering the radiator to force out the coolant/water but cannot figure it out. Any other suggestions are appreciated. Thanks everyone.

 

New radiator cap & new radiator is puzzling. The fit between radiator & cap would have been one of the first things I'd suggest.

So maybe if I explain how everything is SUPPOSED to work, you can check it all out to see if something doesn't look right. The radiator cap has 3 different seals doing 3 different jobs.

Large rubber gasket in the cap needs to seal against the outer/upper rim of the radiator neck. When heating up it may or may not leak. But when cooling down that leak might suck air rather than sucking coolant from the reservoir.

Middle-size rubber gasket in the cap needs to seal against the inner/lower rim inside the radiator neck. That's the pressure relief seal. When pressure exceeds 1.1bar that spring-loaded disk lifts allowing coolant to escape into the hose & to the reservoir.

The smallest little disk inside the radiator cap is a vacuum-break seal that seals closed against itself when the pressure is high. When the radiator cools down it would draw a bit of vacuum which opens that disk - sucking coolant back in.

 

I suspect you have a small leak in one of the cylinder head gaskets allowing combustion gas to enter cooling system. This will force coolant out of the radiator when pressure exceeds vent pressure of the radiator cap.

I'm surprised that no garage suggested performing a system leak test to look for a head gasket leak. There is also a coolant chemical test to test for combustion products in the coolant. Either should be able to definitively say yes or no on head gasket problem.

Instances of misssing engine (wet plugs) would also be consistent w/ cylinder head gasket leak.

Sometimes coolant can enter the oil lube system causing yellow-brown foam in the valve cover area and/or rust on the oil dipstick.

good luck

 

The last two replies are exactly what I was going to write. Head Gasket. Remember... this diagnostic is without hands on vehicle.

 

Cracked head? When it warms up the crack opens an pressurizes the system. Crack may not leak when the engine is cool, may need to heat up to leak???

 

Thank you all for your replies. Today I will be taking the car for another diagnostics in another Honda service location. The previous locations, according to them, checked everything - the second shop performed coolant chemical test and system leak test and found no leak and the third shop performed a cylinder pressure test and found no problem. Of course this was done before my radiator busted. I have a feeling that there might have been a very tiny crack that might have been undetectable by the previous two shops. Since the radiator busted about two weeks ago and the current input I have received from the forum about the head gasket, I am beginning to believe that this diagnostic will detect it. Especially since in the last two days I had to fill up the radiator with 1 gallon of water. I do have two questions, can a defective thermostat cause the coolant to be forced out from the radiator? Can a defective water pump also cause this? Will keep you posted on the diagnostic results.

 

It is common for some makes ( Volkswagen ) to have problems with the impeller on the water pump to break. Never seen it on a Honda. It has probably happened but...anyway with the radiator cap off and warmed up ( catch can underneath ) you can see if coolant flows by watching coolant where cap would be. If it just keeps comming out without pause it is probably head gasket or head problem.