Hi -
I have a '99 Chevy Silverado 1500 pickup w/4.3 liter V6 +A/C. I recently found coolant leaking into the passenger compartment. I pulled the plastic cowling covering the vents/compressor and found the leak dripping through a hole in a duct (support/attachment post was broken by a careless monkey, apparently). Started the engine, ran the AC for about five minutes until the coolant stopped dripping through the hole. Stopped engine for about five minutes, repeated process with no coolant apparent. Repeated process with heater on and, while significantly less coolant was exiting the hole, there was still a small bit dripping out. Note that no coolant was coming out through the actual floor air vents, and there was no apparent evidence of it having done so.

So, could this be some fluke, such as overflow from the coolant reservoir (which has become detached from its original position) being sucked into the intake manifold for the AC, or is this a heater core problem, or something else entirely?

There's a VERY high chance this is the heater core itself leaking. Sometimes coolant can follow down in where hoses connect underhood. Check hard there, bypass if necessary and pressure check just the core, look for traces and cracks in the inlet necks and then this simply must be blamed on the core itself

T
Tom Greenleaf - MetroWest Boston - USA
http://www.acsource.com/

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http://www.autoacsystems.com/tomgreenleaf/

Tom's advice is excellent. I need to add; however; that in 35 years i have never failed to find the heater core leaking when coolant is found on the floor board of the vehicle. unless there are other components (such as heater control valve) inside the vehicle cab.

Thanks for the quick answers! Couple more brief questions for ya:

I haven't replaced a heater core before, but have worked (successfully) on my own vehicles in replacing parts. On a 1-10 scale, how difficult is this repair, and how much time would it take on average to complete? What would an average (i.e., reasonable, non-dealer) cost be if I paid someone else to complete the replacement for me?

Thanks for your time!

according to mitchell time guide this heater core takes anywhere from .9 hrs on a diesel truck with air conditioning to 2hrs on a gas truck without ac. i have found this time guide to be right on for me as a professional. as a dyi'r with some mechanical experience i would say it will take you this same amount of time plus 1 to 2 hrs. it is not a difficult job other than sometimes the hoses get stuck on the heater core tubes. also i usually pinch off the heater hoses under the hood to eliminate the need to drain and refill the radiator(not to mention the cost of antifreeze theses days). if you don't have a repair manual go down to the zone and get one for the basics for replacement. be aware that these manuals want you to remove much more than is usually needed for the repair. use your eyes and go slow while watching everything you do to find the shortcuts. if you must remove the heater box from under the dash it becomes more complicated due to the mount bolts/screws. some are located under the dash and one or two will be located under the hood. if removeing the heater box under dash be careful not to cross any vacuum control hoses-or crush any when remounting the box. i'm not sure on this particular vehicle but some gm's had access to the core by removing only one section of the box which eliminated the need to disrupt the dash. If the whole box needs to be removed the difficulty would be in the 6 to 8 range. if the box does not have to be removed the difficulty will drop to the 2 to 3 range. also the dealer or independant shop will charge the flat rate labor (found in a labor manual which they use -possibly computer software) plus their cost on the core plus their usual percentage markup. i would estimate the cost to you to be in the range of $200.00 labor or less plus parts.

Hey rick/all

You old timers would remember these.
Remember the old mustangs that the heater hoses used to come thru the firewall and clamp on the heater core inside the car.
Only time that there would be leaks other that heater cores.
But like you,in my 40 years ,other that those,always was the heater core.

Just had to throw my 2 cents in....I was bored

Jim

OK, so having determined that this is NOT in fact a 2-hr. job (sorry, brbettge, but you might have looked up an earlier model year in the Mitchell guide, which puts this at 6 hours for a '99 - saw the listing myself, and am told reliably by several people that have changed the heater core on this model that the entire dash panel needs to be removed, due to the insanely stupid component arrangement) and needing to drive about 150 or so miles tomorrow, can anyone tell me if it'll cause problems with this particular vehicle if I just bypass the heater core and drive it that way for a while? I can't see that it would, but I always like to second-guess myself.

Only if your planning on defrosting the windows or needing to warm up...other than that there would be no problems in doing that for the time being.

Ditto with Dave. May I suggest you make a loop with the existing heater hoses at the firewall end? You'll need to make up a "U" shaped deal and I think one is 5/8th the other 3/4in ID hose. Hardware store stuff should do. Don't use PVC unless rated for the heat......

T
Tom Greenleaf - MetroWest Boston - USA
http://www.acsource.com/

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http://www.autoacsystems.com/tomgreenleaf/