Coolant Leak--Head Gasket?

I recently experienced an interesting (and expensive-to-fix) coolant leak in my '99 Saab 9-5. Not that I’m paranoid, but I’m wondering if these symptoms are indicative of a leading head gasket.

Filling the reservoir while the car was cold and driving 2 miles resulted in a lot of burning of the leading coolant under the hood (source impossible to discover). Upon returning home, the leakiing was gone, but the “low coolant” message came on again. Upon opening the reservoir while the car was at operating temperature, coolant rushed into the reservoir from the radiator, to the point that I couldn’t add any! I discovered that if I left the cap of the reservoir loose, the engine operated fine (although I still had to add coolant every 40-50 miles).

I thought the reservoir was to take excess expansion and then send it back to the radiator upon cooling and contraction. This is bizarre to me! My mechanic said the excess pressure was due to the blown head gasket.



The coolant can be tested for traces of combustion gasses, and the cylinders can be tested for compression leak-down. Don’t guess about a possible leaking head gasket. Be sure, one way or the other.

If you can smell burning coolant under the hood it’s probably not from a bad head gasket. All coolant consumed by a leaking head gasket goes out the tailpipe as steam. You can’t smell it under the hood.

Is there any visible coolant leak or puddle under the car when you park it?

How much coolant are you adding every 40-50 miles?

You’re trying to compare apples to oranges. You cannot compare hot coolant volume to cold coolant volume. The comparison really has no meaning.

With the engine COLD, as in hasn’t been run for hours, preferably overnight, open the radiator and fill it. Put the cap on and tighten it completely. Then fill the reservoir to the COLD mark and no higher.

Drive the car a day or two, then when the engine is COLD, as in not run overnight, check the levels again. If they’re different start looking for a reason for the coolant loss.