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Best coolant for 1996 GM 6.5L

M

mhixson

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Mount Vernon, WA
I have a '96 Hummer with the GM 6.5 TD. Coolant has turned a reddish/rust color so I'm going to do a flush. What coolant is the latest and greatest for this engine? And to do the flush do I need to use any flushing liquid or just distilled water?
Thanks for any advice.
 
Good old original green coolant. do not use dexcool. the green is getting harder to find, last time I checked Oriliey auto still carries it in there house brand.
 
I'll go with: It depends.

Glycol based is good providing it gets proper maintenance and flush / change at recommended intervals. Not everybody is anal about the maintenance part. Letting this stuff run too long can lead to rust in the coolant, pitting in passageways from boiling at hot spots, along with galvanic corrosion which eats metals (Yes, I actually had a block deteriorate and leak from previous owners' neglect of the coolant. Only explanation was that the pH got out of balance and caused galvanic corrosion).

I switched away from glycol a long time ago and prefer waterless in vehicles I care about. The two downsides to waterless are that it has a slightly lower heat exchange coefficient (as compared to water / glycol) and leaks are expensive. The stuff does have a shelf life to it and Evans will test a sample for whether it is good for continued life (last conversation I had with Evans was about 10 years ago and this service was free at that time). Upsides to waterless is low / no risk of stray electron currents to cause galvanic corrosion and the coolant will continue doing its job well into the engine's temperature redline (put another way, if the cooling stack is messed-up, the coolant is not the weak link). Oh, and some engines are more sensitive to the coolant's pH where waterless scores another win against glycol / water.

While the slightly lower heat exchange coefficient of waterless may concern some, will offer real world experience with it. Will caveat that a solid cooling stack is key (and the 6.5 TIDI arguably is a royal mess when it comes to the cooling stack, and I am tracking that the Hummer does not have a great cooling stack either).
- I have the stuff in two different 7.3 TDI Ferds, have pulled 8K# travel trailers up 6% - 9% grades and the ECT needle did not budge.
- The 6.5 TIDI Burb was a bit more problematic as I had to limit throttle application to ~1,100*F EGT and manually control the automatic transmission (to keep the RPM's avove 2K) in order to keep ECT and TFT temperatures under control while pulling the 8K# trailer up 6% grades. Even with the waterless coolant, do not have any confidence that I could have done better with glycol / water.
- Zero issues with it in my 5.6L gasser.

Waterless coolant is flamabale in the right conditions. So is glycol, and some of Ferd's ambulance packages with glycol had a recall due a few ambu-b-b-q's ;)
 
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