2003 GMC Sonoma - Oil and coolant

Smell of oil, after driving. Have to fill radiator with 6 oz of antifreeze daily. Do I have a leak? Don’t see any fluids on the ground.


based on the extremely limited information you’ve given, it could be a breached head gasket

  • 1 on the bad head gasket! That is my vote, too!

The 4.3 6 cyl is well known for intake manifold gasket leaks letting coolant into the oil. I had to have the intake manifold gasket replaced within 6 months of purchasing my 2000 Blazer in 2003.

Ed B.


Thanks to all replies. James Abbott

When you check your oil, does it look like normal oil or a chocolate milkshake? Is the level correct or too high?

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Normal colored oil, and below recommended level. The oil guage sometimes drops to low levels when in idle.

Might consider adding enough oil to put it at the full level.

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If the coolant is going into the oil, the oil level on the dipstick will rise, so check there.

Your truck may use an oil cooler. That’s sometimes where oil and coolant leak or mix.

If you have an automatic transmission it is very important to check the transmission fluid level, b/c coolant can go into the transmission via the transmission fluid cooler and that will cause all sorts of expensive problems. There’s no corresponding path for a manual transmission, so if you have a manual that’s not a worry.

Generally small coolant leaks not leaving a puddle on the ground are either leaking onto something hot that causes them to evaporate. In that case you can often see rust/lime stains on the external engine surfaces; or the leak is into the cylinders b/c of head gasket failure. One quick way to check for that is to have someone follow you in another car as you accelerate up a freeway on-ramp. If there’s any white smoke coming out your tailpipe, good chance you got a head gasket leak.