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Discussion Starter · #1 · (Edited)
Hello friends,

Is the radiator supposed to be filled to the very top?

I have a 2010 Odyssey EX-L, of which the radiator does not stay filled to the top. There are no apparent leaks, and the reservoir is filled to the proper level, however upon filling the radiator to the top, there will be a smell of coolant when driving and the fluid level will lower. The level doesn't drop excessively, only enough to drop just under the top of the radiator. The reservoir level doesn't appear to change, and the engine doesn't get too hot.

I had recently replaced the old radiator as it was leaking, however this old one would stay filled to the top despite the leak.

Upon changing the radiator I also replaced the thermostat with an aftermarket one. I've been sporadically getting a code for the engine temperature being too cold, but I think that's due to the thermostat being an aftermarket one. Anyone else run into this issue?

Any advice would be appreciated, I'm slowly losing my mind trying to figure this one out.

Edit #1: Just checked the coolant overflow tank (which is what I mean by "reservoir"), the engine is slightly warm, almost cool. The overflow tank is almost at the "full" mark and the radiator still appears low. I adjusted the overflow tank hose, which looked like it wasn't at the bottom of the tank.

Overflow tank cap isn't super tight (threads a bit worn), which might be the issue. Radiator cap might also be the issue, I'm looking into changing it.
 

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Your explanation, a little confusing. Did you just now replace your radiator, because the OEM was leaking?
So, you have a brand new radiator now?

If the radiator was old. A common source of a leak, is the "plastic radiator reservoir" which sits on top of the
radiator. Gets old, and plastic cracks. If you can, remove any covering on top of radiator. Examine the "seam"
between the reservoir and radiator. Look for dried green crust and mist (if engine is hot).

When you say, radiator not filling to the top? Do you mean, the "plastic" overflow container? Or the
"actual radiator reservoir" located on top of the radiator (has the fins).

Also, check your thermostat. Not sure if that would have any effect. But you mentioned you are getting a code.
(inserted backward)?

Since you smell the antifreeze. Should be easy fix. Be sure hose clamps are all snug/tight.

Good luck. :)
 

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1st, you changed the radiator cap also?

If you smell while driving I suspect your heater core or somewhere towards that system.

Sent from my moto g(7) power using Tapatalk
 

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Discussion Starter · #4 · (Edited)
Your explanation, a little confusing. Did you just now replace your radiator, because the OEM was leaking?
So, you have a brand new radiator now?

If the radiator was old. A common source of a leak, is the "plastic radiator reservoir" which sits on top of the
radiator. Gets old, and plastic cracks. If you can, remove any covering on top of radiator. Examine the "seam"
between the reservoir and radiator. Look for dried green crust and mist (if engine is hot).

When you say, radiator not filling to the top? Do you mean, the "plastic" overflow container? Or the
"actual radiator reservoir" located on top of the radiator (has the fins).

Also, check your thermostat. Not sure if that would have any effect. But you mentioned you are getting a code.
(inserted backward)?
Radiator was replaced in the summer as the OEM was leaking. The leak was within the metal fins itself, rather than the upper plastic part. By "reservoir", I'm referring to the overflow container - The old radiator would stay filled up to the upper plastic part with no issue, the new one does not and I'm not sure if it's supposed to.
The strange part is the leak almost sealed itself with dry coolant, it still leaked slowly though.

As for the thermostat, I'm certain it was installed correctly. All hoses are secured as well.
 

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Discussion Starter · #5 ·
1st, you changed the radiator cap also?

If you smell while driving I suspect your heater core or somewhere towards that system.
Radiator cap is a few years old, I actually just now considered that a possibility. I don't think it's the heater core, as the smell comes up only after attempting to fill the radiator to the very top.
 

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Definitely get a new radiator cap.
 

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++ for radiator cap. They s/b replaced every several years. I had one that was leaking and I thought it was the radiator, so I bought a rad + cap, then replaced the cap and it solved the problem. And I'd recommend a OEM cap.
 

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Overflow tank cap isn't super tight (threads a bit worn), which might be the issue.
The cap on the overflow tank is designed to fit somewhat loosely to allow air to enter and leave as the coolant level in the tank rises and falls. Otherwise, the tank would collapse or burst.

As others have said, replace the radiator cap. One of its jobs is to regulate coolant migration to and from the overflow tank so that the radiator always stays full.
 

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Pretty simple test to verify no leaks in your cooling system. Run down to your local part store and check out their cooling system pressure tester kit. Most parts stores will loan these kits for free with a security deposit of course. If there is a leak(s) in the system you will know within minutes.
 

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Stockholm asked a question that has not yet been answered:

"Is the radiator supposed to be filled to the very top? "

The answer might depend on Stockholm's definition of "very top". Very top of the radiator body? Very top of the internal fins? Very top of the filler neck?

The answer, per Honda, is this:

"The coolant level should be up to the base of the filler neck. Add coolant if it is low."

One could assume that any more than that might cause the fluid to rise more than can be handled by the overflow tube and seep out, perhaps around the cap itself. It's possible that it's not being seen because the heat of the engine/radiator is drying it very quickly. The fluid seeps out of the top, emits the odor as it burns off, with just enough making down low enough to appear as a leak.

Think about a pot of water that boils over on the stove. There will be water around the burner but the outside of the pot may be completely dry because of the heat.

In addition, I've had pin-holes in radiator hoses that sprayed directly onto the engine. I'd smell the fluid while driving and I'd need to keep adding fluid, but nothing would ever be wet. Everything would dry before there was enough to drip. Only when I'd open the hood with the system under pressure would I (hopefully) see the mist or stream shooting out.
 

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OP: Has 2 questions.

1. antifreeze level in the radiator reservoir. Above poster answered that question. Done.
Replacing, radiator cap, might solve the issue of low "reservoir" in the radiator.

2. smells antifreeze. Where is the leak? Is the 2nd question.

Seems to be easy fix. Lots of good advice.
 

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Discussion Starter · #12 ·
Thank you for all your advice friends, it is appreciated.
I'm now almost certain it is the radiator cap - the current one, despite saying "Japan Spec" is some cheapo offbrand and appears to be the source of the leak. I will be sure to replace it asap.
 
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