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Slow coolant loss

Lately when I shut down the Accord hot, I can smell an ambient coolant aroma around the car.

I’ve noticed that it has been slowly losing coolant based on my observations at the radiator filling neck.

But I haven’t noticed any coolant dripping on the ground where the car sits overnight, or in Target’s parking lot, or at work, etc.

Where could it be going?

It was recently in with my mechanic having some PM done and he didn’t find any obvious leaks.

Are they going to have to induce pressure in to the cooling system to find the leak?


probably. Start with the radiator cap. It can get a little weak and allow coolant to vent as you’re driving. It would probably be a small enough leak that you wouldn’t see clouds of steam. Once you shut off the car, the system quickly depressurizes due to the leak, and since it’s at the top of the radiator, you wouldn’t see coolant drips on the ground in the morning.

The other possibility, which I think is somewhat unlikely based on your smelling the coolant, is that you have a leaking head gasket and the coolant is hiding in the oil. Easy to check. Pull the dipstick. If the oil looks like chocolate milk, that’s your problem.

Last night when we were slow at work I pulled the radiator cap to check and my hands were unusually greasy after messing with it. I’ll replace the cap and worst case scenario i’m out $10 if it doesn’t solve the problem. Oil looks good I check it often. Thanks man.

That pretty much seals it. You have a leak around the cap. It’s either the cap, or the filler neck (under the cap) is cracked. Might want to shine a flashlight on it and look very carefully for hairline cracks, which are hard to see because the top tank is usually black plastic. But I’m guessing it’s the cap.

A few thoughts from my experience.

A bad radiator cap, the cheapest fix.

A small leak in the radiator near the top. In my case (2000 Blazer), there was a crack in the plastic side holding tank. I noticed the smell when the truck was hot and there was a drop in the radiator level.

A leaking intake manifold gasket (popular GM problem). Oil will get into the coolant and displace the oil on the main bearings. I noticed a gradual drop in the level in the coolant overflow tank. When the oil was changed the mechanic saw a few drops of coolant as the last of the oil drained out of the pan.

Head gasket? I don’t have any experience with this, but probably worth getting checked.

There was no coolant dripping on the ground in any of these cases. Each time the leak was repaired before any major damage occurred.

Good luck,

Ed B.


So I replaced my radiator cap and the radiator is still losing approx 1/2 pint of coolant every 900 miles, and I can still smell the coolant with the engine running (from outside the car, but not inside).

Oil looks fine. Can we rule out BHG (or LHG) and Intake manifold gasket? The car will be up in the air Tuesday morning for diagnostics but i’d like to know what i’m up against at least.

@ Shadow and Ed B. thanks

When the intake manifold gasket was leaking on my 2000 Blazer, it was losing a similar amount of antifreeze. No drips, just the smell of the antifreeze.

Has the oil been drained and checked for coolant? My mechanic noticed a few drops of coolant as the last of the oil drained out. He was looking for it, otherwise he might have missed it.

You might want to remove the fan shroud from the top of the radiator. That’s how I found the crack in the side tank of the Blazer’s radiator.

Let us know how things work out.

Ed B.

The oil was changed a few weeks ago. I mentioned the issue to them and they topped off the radiator but did not bring to my attention any leaking coolant / contaminated oil.

@ Ed B and Shadowfax,

It ended up being the radiator leaking around the filling neck. As of late it started to pool up in the plastic crevices at the top of the thing. $360 later it’s being replaced today. Thanks again!