Losing Coolant After Shutdown

Hello all, I have a 2005 Silverado 4.3L with 74,000 miles. I have noticed a puddle of coolant in the driveway but can't locate the leak. It seems to only leak after driving it on very hot days or putting a little stress (towing) on the engine. This has happened maybe 5 times now where I find the puddle, but the leaking has stopped. I top off the coolant resevoir with some dexcool and then can't duplicate the leak to locate it. Like I said, this has happened maybe 5 times over the past year or so.

Also, today while driving, the vent was blowing extremely HOT air. So hot that it was uncomfortable to hold my hand close to the vent for more than 5 seconds. No change when I turned on the A/C. This went on for the entire 20 mile drive. The dash temp gauge read normal for the entire drive. I shut the truck down for 10 minutes while in the store. When I started it for the drive home, the 2 passenger side vents continued to blow the same hot air while the driver side was nice and cool. I made one more stop on the way home and shut the truck down for 10 minutes again. After this stop and for the remainder of the drive home, everything was normal. All vents blowing cool air and A/C blowing nice and cold. The outside air temp was about 80 degrees F.

Are these two issues related? Is my thermostat going bad. Could it have something to do with a bad water pump?

Thanks for any input.

-Brett

I have an 03 with a 4.3 that now has 76,000 miles. From about 20,000 miles a had a slight leak not enough to see a puddle but enough to smell it and lose a little coolant occasionally.

I had it at the dealer 3 times under warranty (before 36K) and all three times they pulled a couple of intake manifold bolts out from the front left side of the engine and coated them with sealant and said there you go.

It never seemed to completely fix the problem. Once out of warranty the dealer wouldn't touch it without charging even though I argued it was preexisting so I took it to a regular repair shop and they found the t-stat housing was just seeping enough to run down and make the two intake bolts look wet.

So $20 dollars later they had replaced the t-stat housing gasket and since I have not lost or smelled any coolant. Been about 35,000 since I had that done.

Not saying this is your problem but look that t-stat housing over real good on the front center of the intake.

are you putting the coolant clear to the top in radiator? if so theres a marker line at the top behind radiator cap and if your over filling it it may push out to over fill jug and maybe a hole in it or the rubber line running to over fill jug? but i agree to the guy that i'd start with new thermo. also you may have a small leak comming from water pump or hose. do you smell coolant when you shut it down?

I'm filling the resevoir to the fill line. I've never had any odor of coolant, just find the big puddle when I go outside a few hours later or the next day. It looks like a large amount of coolant is leaking for about 30-60 minutes after shutdown, probably 1/2 a quart. But then I'll go months with no sign of leaking at all.

I'm filling the resevoir to the fill line. I've never had any odor of coolant, just find the big puddle when I go outside a few hours later or the next day. It looks like a large amount of coolant is leaking for about 30-60 minutes after shutdown, probably 1/2 a quart. But then I'll go months with no sign of leaking at all.

Hoe many miles on it?
Has intake gasket been replaced?

You need to jack it up and put on stands and craw under it and spot where it is running out.
Get engine hot and check for leakage.
Look at back of engine and lower center and front end also under water pump amd rad.
Also under ac housing drain hole.
On top of engine inspect intake gasket area and heater hoses.
Make sure you check engine oil for coolant in it.

They make a leak test dye for coolant system and pressure testers to help aid in finding leaks.

Let us know what you see under there or on top of engine.

On the hot ac check all vacuum lines and hoses.

Borrow a cooling system pressure tester from your local parts store and pressurize your system, then go underneath and look for the leak. You'll have to remove any skid plates first to see where the leak originates. H
hope this helps!

Thanks for all of the input fellas!

The coolant leak was a worn out rusted clamp on the lower radiator hose.

The passenger side heat issue is attributed to the temperature control actuator on that side. The problem started after reconnecting the battery following some ignition work. I disconnected the battery for about 30 minutes and again reconnected it. Problem went away and hopefully won't return. I guess it's a fairly common issue.

I went ahead and replaced the water pump while I was at it. The bearings in the old one were getting pretty rough.

All is well again with the ole Silverado.

Awesome glad things worked out for you and your ride!