John Lieberman <johnlee@softdisk.com> asked:
>A couple of weeks before leaving for Nationals last year, I took my
>'96 Chebby S-10 (4.3L Vortec V-6) in to the local Xpress Lube for a
>routine oil change. While going through the normal check, they found
>gobs of red "mud" in my radiator. It looked like somebody had dumped
>a shovel full of good ol' Louisiana red dirt into the cooling system.
>They scraped out everything they could get to and then did three
>complete flushes of the cooling system before they were satisfied
>enough to fill it back up with DexCool antifreeze and water for my
>trip.
Pretty typical DexCool reaction with various cooling system metal bits, I'm
afraid. Some folks think it comes from mixing conventional coolant with
OAT, but OAT does it all by itself, actually.
>BUT, the question remains, where in the hell is this red mud coming
>from and how in the world can I keep it from recurring?!?
It's parts of the inside of your engine, actually. Rust, primarily.
>According to GM, the cooling system shouldn't need ANY maintenance for
>5 years or 100,000 miles as long as you add only a DexCool
>antifreeze/water mix when needed. But, my truck is only four years
>old, has only 78,000 miles on the clock, and this is the SECOND bout
>I've had with this red mud.
Here's one for you: the ASTM (American Society for Testing & Materials)
standard water pump erosion/corrosion test uses a GM3800 water pump and
front cover because the whole thing is/was cast aluminum: pump housing,
front cover, and pump impeller. When GM released that OAT coolant
(DEXCOOL) in '95, the auto company I worked for at that time tested it
using the ASTM standard test. And we couldn't get it to pass. We tried it
again, made some calls to GM asking how they'd managed to get it passed,
etc., and they just said they had no problem. Soooo... we went to the
nearby Buick store and bought a new '95-spec GM3800 water pump... and the
impeller was now cast iron instead of cast aluminum. The cast iron
impeller would in fact pass the test...
I had a particular engine design that I just couldn't GET the water pump to
cavitate on conventional coolant, even injecting air into the inlet, but
it'd cavitate in a heartbeat on OAT (DEXCOOL).
>Your input would be GREATLY appreciated.
GM says you gotta use DEXCOOL or the warranty is void. I say I don't trust
the stuff very much, and I'd personally use conventional coolant as soon as
that warranty expired, after a thorough flush.
I'd also check to see if you have a partial-pressure cap or a full-pressure
one. A partial pressure cap, when you look at it right-side up, has the
little vacuum relief valve poppet just hang there open. A full-pressure
cap has a spring that keeps the vacuum relief valve poppet closed except
when it's actually relieving vacuum (which it does as the system cools back
down). Partial pressure caps can allow more air into the cooling system,
which increases the chance of rust formation (oxidation).
Jim Crider
autojim@delphi.com (No, this isn't Delphi the parts supplier. Their domain
is delphiauto.com)
All opinions expressed here are mine and mine alone, and don't go dragging
anyone I work for or with into it.
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