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Antifreeze odor inside car

I have an '05 Lexus SC430 with 53,000 miles on it. For the past couple of years, I have noticed an intermittent antifreeze smell (sweet odor) when driving. It never lasts for long and is apparently coming out of the vents. I can not figure out any common denominator to cause this, other than the radiator was replaced in Nov. 2014. My long-time mechanic has ridden with me a few times and I am unable to recreate for him to diagnose. Your thoughts?

Pinhole leak in the heater hoses would be my first suspicion. They enter into the passenger cabin up behind the glovebox, so if they leak you smell it pretty quick and sometimes have damp carpet under the dash.

You state the radiator was replaced in 2014. But was the radiator pressure cap replaced at the same time?

If not, the pressure cap may be weak enough to open and release coolant vapors which are then drawn into ventilation system below the windshield.

Try replacing the radiator cap. And if that doesn’t work, then have the cooling system placed under pressure both when the engine is cold and hot.


I’d guess a pinhole leak in the heater core, but all the above suggestions are possibilities.
There is a UV sensitive dye you can add to the cooling system that’ll light up under the blacklight (you can buy the kit) that will glow where the leak is. Trouble is, you’ll have to figure out how to see the heater core. Unless, of course, the inside of your windshield glows from the dye when you do the test. That’d be a dead giveaway.

Do you get a film on your inside windows that’s hard to clean? If so, the leak is probably in your heater core.

Keep in mind that coolant fumes aren’t good for your lungs, so I hope you can resolve this soon.

Are you loosing any coolant? Do you need to add coolant from time to time to keep it up to the full lever on the reservoir? If so, how much and how frequently?

I would agree it probably something minor and other than a heater core leak…if it was the core…you would smell it all the time…and u would also get condensate on the inside of the windshield as well.

Go with the minor suspects first in this instance

If you have a leak under the hood, the fan will suck in some of those fumes. So check all connections on your cooling system.


Has your mechanic performed a coolant pressure test?

Has he visually looked for evidence of coolant leaks . . . or dried coolant residue?

I experienced a very, very occasional whiff of coolant in my 2002 Mitsubishi Eclipse usually after a 55-60mph highway drive of 8 miles and stopped waiting to make a left hand turn. When it was serviced a very small dried coolant stain was written up. There was never a measurable loss of coolant I suspected the Mickey Mouse spring type OEM clamp at the engine side of the upper radiator hose. I decided to replace the OEM clamp with a worm drive clamp. When I wiped the engine side fitting with a shop rag I found a casting mark/ridge on the bottom. I filed it smooth and clamped the hose. No more whiffs of coolant.