Coolant disappearing from reservoir

[mmlloo]

Another potential issue I recently discovered- the coolant seems to be leaking or disappearing from the reservior somehow.

I first noticed it before the 1st oil change at around 4500 miles- the coolant was at min level. I took it to the dealer and they pressure tested it overnight. Nothing. So they filled it back to max level. I visually verified it. Now at 2500 miles later, the coolant level is about 1/3 below max.

I guess I will wait for another 1k miles to see if it goes down to min again. In the mean time, what could be the problem? a cracked head gasket? Can the coolant evaporate from reservoir into the air? I never had a new car with that problem before. Obviously, if it's leaking somewhere, the leak must be extremely small because the dealer allegedly pressure tested it overnight. Maybe they did it over 15 min and considered it over night. I also checked engine and transmission oils, and there was no sign of coolant in them- no emulsification, that is.

[engkyq]

What is the coolant level in the radiator when cold?

[mmlloo]

Originally posted by engkyq
What is the coolant level in the radiator when cold?

1/3 down from max in the reservoir. I think that's what you meant to ask. I don't know what the level is in the radiator itself.

[engkyq]

I would verify that the coolant level in the radiator is up to the bottom of the pressure cap. Was the pressure cap tested? Here is a good link explaining how the level in the resorvoir tank changes. http://auto.howstuffworks.com/cooling-system7.htm

[William Wiles]

Initially the level may go down some as the radiator may not be completely full. Once full the level should not go down. It will change some between hot and cold so make all references at the same temp. Leaks may only show up when hot or cold so a pressure test may not show the leak. Inspect all places the fluid could leak for stains from the leak. Keep a close eye on the oil for signs. Sludge around oil cap and dipstick are sure signs of moisture in the oil.....

[6spdtl]

Easy to figure out. Next time the car is cold, fill to the minimum level in the expansion tank. Check it the next day cold, it should at the same level. If it is significantly lower or the expansion tank is empty, there might be a leak somewhere.

[shellebelle]

There's lots of things it could be, I went through this earlier this year with my '95 Civic. Though, a new car such as yours shouldn't be having this problem.

I'd do what 6spdtl suggested and fill the radiator and overflow tank, with the engine running so any air bubbles in the system are pushed out and you know it's full. Obviously, if there's a big bubble in the system your tank is going to go down quite a bit. I'd drive it around to get the engine good and hot, and to open up any cracks that there are. Then I'd check the levels. If the level goes down you know there's a leak. My bad head gasket didn't act up until 45 minutes down the road and until then was fine.

Possible culprits-bad raditator cap, loose radiator hoses, blown head gasket, bad radiator, cracked reserve tank or cap, or a general crack somewhere in the system.

FWIW We had an old Toyota van that had a coolant leak that ONLY showed up when the engine was rip-roaring hot (which it was every time we tried to take a road trip!). You may consider getting the engine nice and toasty and taking it directly to the dealer for a pressure test.

[engkyq]

Do not loosen the radiator cap on a hot engine as the radiator will be under pressure and coolant will be forced out.

[mmlloo]

If there is a leak, it seems to be a very slow leak because I think it went down by 1/3 of reservior between max and min mark over 2k miles. Filling it to max mark and check it the next day wouldn't work because there is not enough change in coolant level for me to see. I will wait for another 1k mile to see if the level goes down further.

[svezarov]

Hi mmlloo,

I am having the same problem with my Odyssey 2005 touring 25000 miles. Coolant is dissapearing very slowly from the expansion container. I don't see any leaks or smell it. What was the resolution on your problem eventually.
Thanks,
Tony

[mmlloo]

There has been no solution so far. The ody has gotten 2 overnight pressure tests and ultraviolet dye testing, and of course they couldn't find anything because it's such a slow leak. The tech told me that since the dye is in the cooling system, they can check for leak whenever I bring the ody in for service. So that's what I have been doing for the past year or so. Since last April, the coolant has gone down to right below half min/max level.

A friend who used to be an auto mechanic told me that it might be "vapor" leak that the coolant vapor is leaking through the reservior or other places, and that might be why it's slow and undetectable. The van is due for an oil change in a month or so, and I will bring that up to the tech at the dealer.

Please let me know if you have heard of any solutions.

[bbylon5]

And yes, the fluid in the overflow tank can and does evaporate slowly since it is after all at least 50% water. This loss will of course be accelerated in the summer and slow in the winter..
(and before someone quote's the fact that coolant doesn't evaporate thats true only if its 100% coolant. The stuff we get from Honda is premixed coolant/water)

As mentioned, if the rad was a little low it will take a while for it to purge all the air and replace with coolant from the expansion tank. Once this is complete the fluid lever will stabilize.

Just check it once a week in the morning before you drive it. You will probably find your level is just fine and you have no leaks.

[rcy]

Not quite sure reading your posts, but you should check the coolant level when the vehicle is stone cold (like sitting overnight). Depending on how hot the coolant gets, it can expand at different rates, so the hot level isn't always the same. I'd do what someone already suggested. When it's stone cold, add or draw out an amount so that the cold level is right on the MIN mark. From then on, always check cold, and it will be easy to see if it's fallen.

The other thing I'd suggest is a UOA to make sure coolant isn't entering the oil. If you confirm coolant in the oil via a UOA, and you're under warranty, I would think the onus would then be on Honda to figure out how coolant is getting in the oil.

[wild willy]

Bad radiator Cap

Leak in Radiator


Head Gasket


Hose

Hose clamp


Air Bubble

Could be lots of things......roll the dice and hand it over to the 6th graders at honda

[mflores]

Is it ok for the coolant level to be slightly above the MAX mark when stone cold? The service manual says it should be just slightly above the MIN mark.