Radiator overflowing

[exranger06]

92 Honda Accord-
Lately I've been losing a little coolant. I've had to add at least 8 ounces to the radiator this week. Car is NOT overheating or driving strange in any way. This morning I noticed there was coolant all around the radiator cap and the overflow reservoir was still at the cold level. So all the excess coolant that would normally go into the overflow just got burped out of the cap. I just replaced the radiator cap a few weeks ago but maybe I got a defective one? The only other thing I can think of is maybe I have an obstruction in the hose going to the overlflow.

 

[JZiggy]

Check if the plastic top of the radiator has a crack anywhere. If you watch it while the car is running and is still hot after driving you may see bubbles and steam if there is a crack. I had this very thing happen to my old 94 Accord.

 

[eljefino]

^ That, or a burr or something. A pressure tester that you screw on in place of the cap and pump up would be your friend.

 

[tomcat27]

check the cap - maybe the gasket or spring is bad?

 

[Chris142]

Look at the cap closely. Often the valve falls off and into the Radiator.

 

[440Magnum]

Originally Posted By: Chris142
Look at the cap closely. Often the valve falls off and into the Radiator.


And I've also seen brand new radiator caps without the upper gasket installed. There should be a rubber gasket on the "plunger" part of the rad cap, but there should ALSO be one under the twist-top part of the cap that seals against the radiator neck. Non-overflow systems from bygone years didn't need or have that gasket, but its necessary for overflow systems.

 

[LeakySeals]

When is the last time you changed your coolant?
Are you using the factory recommended coolant?
Are you mixing coolant types?
Have you ever replaced the thermostat? (they can fail closed as well as open)

 

[exranger06]

Originally Posted By: LeakySeals
When is the last time you changed your coolant?

Last year when I installed a new radiator. So, less than 10k miles ago.
Originally Posted By: LeakySeals
Are you using the factory recommended coolant?

The manual doesn't specify any particular type of coolant. I use Napa brand regular green. (Although antifreeze type wouldn't cause this type of problem anyway)
Originally Posted By: LeakySeals
Are you mixing coolant types?

No.
Originally Posted By: LeakySeals
Have you ever replaced the thermostat? (they can fail closed as well as open)

If it was stuck closed, it would overheat. Like I said, it's not overheating.

 

[exranger06]

Originally Posted By: 440Magnum
Originally Posted By: Chris142
Look at the cap closely. Often the valve falls off and into the Radiator.


And I've also seen brand new radiator caps without the upper gasket installed. There should be a rubber gasket on the "plunger" part of the rad cap, but there should ALSO be one under the twist-top part of the cap that seals against the radiator neck. Non-overflow systems from bygone years didn't need or have that gasket, but its necessary for overflow systems.


I just checked the cap. It has both seals.

 

[LeakySeals]

Originally Posted By: exranger06

Originally Posted By: LeakySeals
Have you ever replaced the thermostat? (they can fail closed as well as open)

If it was stuck closed, it would overheat. Like I said, it's not overheating.


When I had that problem it was a stuck thermostat, bad cap, and not mixing 50/50 distilled.

 

[exranger06]

Originally Posted By: LeakySeals
Originally Posted By: exranger06

Originally Posted By: LeakySeals
Have you ever replaced the thermostat? (they can fail closed as well as open)

If it was stuck closed, it would overheat. Like I said, it's not overheating.


When I had that problem it was a stuck thermostat, bad cap, and not mixing 50/50 distilled.

Explain how an engine wouldn't overheat with a thermostat stuck closed, when it prevents any coolant from flowing through the radiator.

If the engine doesn't overheat, the thermostat simply cannot be stuck closed.

 

[mechtech2]

Since two caps have had the same problem, it is probably the neck or tank that is bad.
Like you mentioned, maybe the hose or it's connection.

 

[exranger06]

Just to update: I bought a cooling system pressure tester. I started to pump the system up and I immediately noticed a leak at the thermostat housing. System pressure is 16 lbs, I didn't even pump it to 9 lbs before I noticed the leak. I took off the upper rad hose and inspected it. It was fine; apparently the clamp had loosened. I'm also guessing the coolant below the rad cap had just dribbled down the hose from the thermostat housing. I reinstalled the hose, topped off coolant, and re-tested. It held 16 lbs for over 5 minutes. I tested both radiator caps. The old one failed miserably, but the new one is good. I haven't had any more problems since.

I love getting new tools to play with, especially when they prove to be very helpful and useful.