Dex-Cool...Good, Bad, or Ugly - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 02-12-2003, 12:44 PM   #1
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Default Dex-Cool...Good, Bad, or Ugly

Hi All,

I was wondering if any you had any input or bad experience with Dex-Cool coolent? I have been looking at another automotive forum site dedicated to the GM minivans like Ventures, and Montanas, and came across some interesting info regarding Dex-cool. Appearently these vehicles with the 3400 V6 also have intake manifold failure issues like the H-Bodies. The problem with the 3400 is the gasket material seems to degrade prematurely and this may be accelerated by Dex-cool. Dex-cool seems to have some additives in it that increase it'* life but damages gasket material, and it also seems that GM has swithed to Prestone long life in the newer cars. Here is some info from Prestone.

"Thanks very much for your inquiry. The Prestone Extended Life Antifreeze has recently (2001) been requested by GM to be factory filled in their vehicles. This is our patented formulation that meets GM Dex-Cool requirements and is approved
for use. Our product is not aggressive towards gasket material and is safe to use"
[email protected]

Is this true?

The car owners on that site are pretty steamed with GM and are trying to start a class action lawsuit about the intake failures in their cars. We have a Montana but we have not had any intake problems yet. We are having transmisison problems with it though, and that also seems to be a common problem with these cars.
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Old 02-12-2003, 12:58 PM   #2
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The Dex-Cool has nothing to do with these failures. It has to do with GM using a thermostat that really needs to be 1 step lower than stock installed. They do this get you in for service and will never admit to doing this. Ford, Toyota and Nissan also do this to some extent.

The added heat is the breakdown culprit. I always recommend (as others here do) a step down to the next available temp setting on all GM vehicles, unless you are in a low temp (IE, the Great White North...) then you'll want to change out in the spring and fall.

My wife has a GP with the 3100 and it will be getting a lower temp unit in the spring. Just to be safe.....
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Old 02-12-2003, 03:37 PM   #3
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There'* also some info on Dec-cool up in Techinfo.
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Old 02-12-2003, 08:28 PM   #4
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Old 02-14-2003, 11:23 PM   #5
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most of the gasket problems on the 3100 and the 3400 is not the dex cool. its the cheap material that they are made of, they are plastic frame with a rubber inlay to seal. the rubber inlay is great, but the frame falls apart after many heat cycles. i have taken intakes off of the newer 3100 and 3400 motors and the plastic frame just falls apart at the corners.
another reason they went to the plastic frame for the intake gasket is to incorp. the pushrod guides in them
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Old 02-15-2003, 01:14 AM   #6
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That'* one of the reasons we push the 180 thermostat and tranny cooler so much. I can tell you, though, JSeaberts seals were all intact on his 93 SSE when we pulled them at 180,000 miles. None of the plastic seals failed, it was the rear head gasket at #6, and the upper intake at #3.

Cool those suckers down, and this won't EVER be a problem. I'll be inspecting mine tomorrow during the SC Nosedrive rebuild.
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Old 02-16-2003, 09:37 AM   #7
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i dont think i have ever seen the plastic frame gaskets on the series 1 engines.
i thought they were all fiber material. i have only seen this problem with and 3400 and the 3100. that have the plactic frame gaskets with the silicon rubber inlays in them.
the only thing other than that , i have seen a build up of a sludge material in the coolant overflow.
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Old 02-16-2003, 01:00 PM   #8
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Quote:
Originally Posted by jeffrey10x2
i dont think i have ever seen the plastic frame gaskets on the series 1 engines.
i thought they were all fiber material. i have only seen this problem with and 3400 and the 3100. that have the plactic frame gaskets with the silicon rubber inlays in them.
the only thing other than that , i have seen a build up of a sludge material in the coolant overflow.
The only "plastic frame" gaskets on a Series I are the Lower Intakes. The rest are "fiber" gaskets or "rubber" gaskets on a 3800 NA engine. I think in addition to this, the TB Base Gasket is "Fiber" on the SC 3800 too.
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Old 02-16-2003, 03:04 PM   #9
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Gotcha Rat!

3800 SC Series1 TB base gasket is plastic frame 'racetrack' silicon, too.
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Old 02-16-2003, 04:04 PM   #10
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the one on my 92 Tb was plastic, but the one on the 95 i got was fiber paper with a silicon bead printed on it
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