2004 Hyundai Santa Fe - White Smoke Coming from Exhaust

Maintenance/Repairs
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1

hello!

i have a 2004 hyundai santa fee with about 200,000 miles on it. the check engine light came on about one year ago (code P0421 - mechanic said it was no big deal so i’ve never done anything to fix this). about one month ago (june 14th) i was stuck in traffic for about 45 minutes and noticed a lot of white smoke coming from my exhaust. it stopped once i started moving at a steady pace and didn’t start happening again until a few weeks ago, again while i was stopped in traffic.

i just got the oil changed on july 14th and checked it today, everything looks good. i checked the engine coolant on monday and noticed it was low so i filled that up and it was low again this morning, after having barely driven it since filling it up. there are no leaks underneath the car when it’s parked and the smoke doesn’t come out when driving.

internet says it’s probably a blown gasket head but i just wanted to confirm that that’s most likely the case before i take it somewhere to get looked at. alternatively - how serious is it if i keep driving the car? i commute pretty far to and from work every day and i want to make sure it’s not going to blow up or something before i can get this looked at.

2

When the engine is cold, remove the radiator cap.

If the coolant is low, add coolant.

With the radiator cap off, start the engine and while the engine idles watch the coolant in the radiator.

If bubbles begin to form in the coolant as the engine idles, that’s an indication of a blown head gasket.
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Tester

3

There’s a good chance the white smoke and low coolant level point to a blown head gasket, especially since you can’t see any external leaks

And that can potentially damage a catalytic converter, thus P0421

If you replace the cat without resolving the coolant problem, it might not live long