Lan, I can't often say this but I think you may be wrong on this one.
My brother had this problem on his truck and the dealer did a complete
system flush under warranty. It seems to have corrected the problem too
(they think the system was not bled properly at the factory).
As in the past, the MACS 2001 Convention and Trade Show in Orlando
provided some very interesting and helpful air conditioning
information. However, the sleeper presentation at this show was not
about refrigerant, but—of all things—engine coolant! (Sleeper
does not refer to making you sleepy; it was anything but boring.)
Marketing departments of major consumer goods manufacturers are known
for their attempt to conceal even a shred of negative publicity about
their products. You can't blame them; you do the same in your
business. That's why it was refreshing to witness a candid GM/Texaco
presentation about DEX-COOL coolant and its related field service
problems. I give the big guys credit for even bringing up the subject
because, well, let's face it, there are not a lot of kind words being
spoken about this coolant at automotive service shops today.
(Especially at radiator shops.)
GM's Jay Dankovich and Equilon Enterprises' (Texaco) Stede Granger
directed a 2-year study of thousands of DEX-COOL cooled vehicles.
Armed with the results, they really didn't have anything bad to say
about the coolant. In fact, they strongly defended the product's
reputation. What they revealed to the audience is that specific
models of GM vehicles have specific cooling system contamination
problems. And essentially, that DEX-COOL is not the culprit!
Their presentation started with a 14-minute video that is now being
circulated to technicians at GM dealers nationwide. In the video,
GM's trainers succinctly described the problems that have been found and
the corresponding corrective actions to be taken by technicians.
Suggestion. This video is a "must see" for all technicians
considering themselves antifreeze/coolant experts. Without this
information, your cooling system service knowledge of late model GM
vehicles is severely limited. Seriously!
Fortunately, you can buy the video for only $10 (plus S&H). Call MSX
International of Auburn Hills, Michigan at 800-393-4831. Ask for the
DEX-COOL Video: "Understanding Radiator Cap and Cooling System
Contamination." Part number: RADCAPK. Immediately following this
article is a report on this training video by John Brunner, recently
retired GM field service representative.
What was said at the presentation? Besides the video, Jay and Stede
included their personal observations about the study. At the end,
they fielded several questions from the audience. Here's a recap of
their entire presentation.
1. Keep the cooling system filled. In fact, fill the reservoir bottle
to "Hot" level when the system is cold. Problems arise when a
system's coolant level is not maintained. (Fleet vehicles receiving
regular maintenance, and with reservoirs kept slightly above normal, do
not show signs of contamination. This even applies to the specific
"problem" vehicles.)
2. The coolant problems found in this survey were caused by system
contamination, and not due to the breakdown of DEX-COOL.
3. Check and keep the pressure cap clean and functioning. A
contaminated and/or malfunctioning cap causes low coolant levels, which
in turn causes overheating and a greater loss of coolant: the notorious
vicious cycle. No matter what the vehicle, if the cooling system acts
suspiciously, test the pressure cap.
4. On the ST vehicle models mentioned in the GM DEX-COOL video, you
"must" replace all suspect radiator caps, especially those with a
Drop-Center design, with a Stant Model 10230 or 11230 (Spring-Center
type). (Just DO it.)
5. Make sure that the coolant is at a 50-50 mix. Often, the flush
water was not being removed from the engine block. Consequently, when
a 50-50 mix is added to the system the resultant mixture could approach
30-70. Like any fluid that has been diluted beyond its recommended
levels, the lowered level of inhibitors will not be able to protect the
coolant system effectively. Low levels of inhibitors can cause
pitting on aluminum surfaces and general corrosion of cooling system
metals.
6. A safe method of achieving a true 50-50 mix is to first determine the
actual capacity of the system (use the owner's manual). Then add 50%
of "that" amount of undiluted DEX-COOL (or any coolant), and top it off
with water.
7. Mixing a "green" coolant with DEX-COOL reduces the batch's change
interval to 2 years or 30,000 miles, but will otherwise cause no damage
to the engine. In order to change back to DEX-COOL however, the cooling
system must first be thoroughly drained and flushed.
8. Bacteria cannot live in a hot, Ethylene Glycol environment and is
therefore not a threat to DEX-COOL.
9. While there have been intake gasket failures on CK Series, V8 powered
vehicles for various reasons, DEX-COOL has never been found as a cause.
10. Use a refractometer to check the condition of DEX-COOL. Its
inhibitor package is strong enough that if the batch still provides
proper freeze protection, it is probably still providing proper
corrosion protection as well.
11. DEX-COOL can handle the minerals in hard water better than silicated
conventional chemistry coolants. Drinkable water is suitable for top
off.
12. In ST Blazer applications where the radiator cap is mounted at an
angle to the ground, the vehicle is more susceptible to radiator cap
contamination and its related problems. The Stant 10230 is a wise
choice for these vehicles.
http://www.imcool.com/articles/antifreeze-coolant/dexcool-macs2001.htm
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
There are two classes of pedestrians in these days of reckless motor
traffic - the quick and the dead.
~ Lord Dewar 1933 ~
Climbing into a hot car is like buckling on a pistol. It is the great
equalizer. ~ Henry G. Felsen 1964 ~
>> Stay informed about: Sluge in coolant tank 
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