Here is a quote from another part of the board..............
I have been asked a number of times about whether you should use coolant supplement pellets with DexCool in the Northstar engine or 4.1/4.5/4.9 engine?
Simple answer: USE THE COOLANT SUPPLEMENT PELLETS REGARDLESS OF
WHICH TYPE OF COOLANT YOU ARE USING.
The coolant supplement/sealer works to seal any microscopic porosity or incipient leak in the coolant system. Internal coolant intrusion is not good for any engine and the coolant supplement is cheap insurance against any internal coolant intrusion.
The supplement should be added each time the coolant is changed. I think the confusion exists because factory installation of the coolant supplement was stopped in the late 90's as it was felt
the supplement was no longer required and added cost and made the coolant system look "dirty". This happened about the same time the DexCool was introduced so people assumed the two happenings were related. This is not true. There is nothing in DexCool that negates the need for coolant supplement , especially in an older engine.
Personally, I use the supplement in every car, snowmobile, tractor,etc. I own and I strongly recommend to everyone to use it as it is very cheap insurance.
The standard green coolant and DexCool are both ethylene-glycol based products. The green coolant has a silicate based corrosion inhibitor and DexCool has an organic acid based corrosion
inhibitor. The silicates in the green coolant get depleted over time and the corrosion protection diminishes dramatically. That is why it needs frequent replacement. The DexCool lasts virtually
forever due to the different chemistry in the corrosion inhibitor. The ethylene-glycol is what give you the boiling and freeze protection. It never wears out but the corrosion inhibitors are equally important, especially in an aluminum engine. Corrosion protection in an aluminum engine is vitally important. Aluminum exhibits a phenomenon called hot transport deposition corrosion...microscopic bits of aluminum break away from the hottest areas (exhaust port) into the coolant and precipitate out in the cold areas of the cooling system (radiator). Cracks result
in the hot areas as stress risers develop. Cracked heads, coolant leaks into exhaust ports and failed head gaskets are common signs of a poorly maintained cooling system where the corrosion
inhibitors have failed. The cold rolled core of the head gasket will corrode from the edges where it contacts the coolant if the inhibitors have failed.
Poorly maintained cooling systems on aluminum engines are common unfortunately because the coolant stays nice and green even after the silicates have depleted and corrosion sets in because the alum corrosion does not "color" the coolant. An iron engine will tell you the corrosion protection is gone because you see red rust in the coolant. Also, the alum engines deplete the corrosion inhibitors more quickly than an iron engine.
DexCool is not designed for 18 wheelers or trucks. Big commercial diesel engines need nitrates in the coolant to prevent cavitation and erosion of the wet cylinder liners. I do not
think any big diesel engine manufacturer recommends DexCool. Any trucker experimenting with DexCool could have saved himself the bother and engine damage by reading his owners manual.
Conversely, because it does not work in a big diesel is no reason to not use it in a gasoline passenger car engine.
If the engine was completely drained and flushed and switched to DexCool that is fine. Continue to use the DexCool but I would still recommend periodic drains and refills. Since the engine was
"plated" internally with silicates from the green coolant the DexCool lifetime advantage is not as effective and it need periodic replacement as it becomes contaminated with silicates
from inside the engine thus depleting its corrosion protection over time. In either case...USE THE COOLANT SUPPLEMENT.
The green silicate coolant has two undesirable side effects that bear mentioning:
One is that the silicates are very abrasive and shorten water pump seal life by abrading the surface of the seal. Also the silicates can build up on the seal surface and "unseat" the seal
causing seepage. The seal is fine but the silicate contamination does cause a leak. The coolant supplement pellets tend to prevent the latter situation by cleaning the surface of the water pump
seal and preventing the silicate build up. The little fibers in the supplement literally "scrub" the surface preventing the silicate buildup. It doesn't seem to prevent erosion of the seal
by the abrasive silicates unfortunately. The second situation is more pronounced in occasional use cars that might also get a higher than the recommended 50/50 concentration of coolant (more coolant than water). The silicates can "congeal" in low flow areas like the heater core forming this
green "jello" that plugs the heater core. The lower the flow, the greater the coolant concentration and the longer the down times the greater the tendency to form the green jello. Usually it can
be flushed out with a strong water flow from a garden hose but it is a pain.
Both of these problems prompted the use of DexCool from the factory as well as the long term corrosion protection compared to the green coolant.
Switching the system over to DexCool will not necessarily give lifetime corrosion protection as previously explained but it will eliminate the two problems above which are worthwhile in themselves.
Neither the green coolant nor DexCool should ever be added straight to the cooling system. ALWAYS PREMIX 50/50 COOLANT/DISTILLED WATER. Premixing is important because you do not want to run a greater than 50/50 mix of coolant. The cooling system will loose capacity due to the lower heat transfer capability of the coolant and lower flow due to the added
viscosity of the coolant. The added silicates in the green coolant are not desirable as mentioned least the dreaded green jello form. The acid DexCool must be premixed as it is very
undesirable to introduce the acidic coolant directly or have a greater than 50/50 concentration.
My personal recommendation is to avoid flushing the system as it ends up introducing plain water and/or flush chemicals which are very harmful (minerals and caustic, respectively) Just drain the
radiator periodically and refill with 50/50 premix. do this once a year and the system is protected as a fresh charge of corrosion inhibitors is always being introduced and the coolant is always
being replenished. Since no Allantes ever came with DexCool it is safe to say that draining and refilling with either coolant would be recommended as DexCool in any Allante will be only partially
effective over the long run due to the inherent silicate contamination.
Several more things come to mind regarding the overall coolant issue. You will see at truck stops a "heavy duty" or "long life" silicated green coolant. NOT RECOMMENDED. Too much silicate
concentration for a gasoline engine. Highly likely to gel and/or cause water pump seal problems. Just as DexCool is not designed for heavy duty diesel use the "heavy duty" silicated coolant is
not designed for passenger cars.
I recommend Texaco DexCool coolant. Texaco developed the stuff in conjunction with GM and is the OEM supplier. Others market a "DexCool compatible" long life coolant but I would recommend the Texaco product. I also recommend Prestone.