Yes, the 6.5 has overheating failures in other rigs and the #8 is the most common failure in pickups, vans also. Yes it has been “solved” but making specific adaptations to driver preferences exists and variations have proven to work for different drivers/ environments.
Other cylinder cracks, Cylinder head cracks and blown head gaskets occur as well and this engine is more common than gas engines of similar size and occurs in all platforms.
Hummers amplify the problem because of the angled radiator.
Most vehicles overheat sitting stillmor city traffic, but on the freeway get more than enough airflow to shed the hear just by the oncoming airflow from howay speed. Hummers overheat worse at higher speeds because of the radiator positioning & aerodynamics involved.
But many but not all of the pickups & vans still struggle with the heat
Every since the serpentine belt waterpump replaced the Vbelt waterpump which reversed direction of the waterpump- they amplified the heat issue.
Rejecting enough heat in a hummer is a balancing act because of desires for avoiding power loss when the fan is on along with the noise complaints.
How hard the person runs the truck and if they bump up power which creates more heat, more must be done to mitigate it. Member HummerH1 here has basically turned himself into a professional hummer driver logging 40 hours or more per week behind the wheel. But he runs a db2 ip kept mild, keeps boost below stock levels, keeps his speeds down, etc. So he adapohis driving from “normal” driving to a more mellow rolling speed and no longer has the second radiator in the bed of his hummer…. But If I drove his hummer like I drove mine here in Vegas area- it would overheat right away.
So how you treat it is the biggest part of the equation is my point.
Get the components of the 04 hummer into the cooling system. There is a specific AC Delco part number of the waterpump that works best. I don’t recall the number but have posted it here before. If we can’t find it we can ask the guys on TTS to dig it up, more active site there - way more pickups alive than hummers.
If you choose to run the dual stat housing, you need the brf. Etter is the single stat crossover WITH BYPASS BLOCK OFF. Because fitment is hard - and the desired thermostat crossover is gobbled up by other owners years ago- finding the factory one is highly unlikely. So look at the link in my signature. Its not a kit- it is a component that you can build a functional bypass thermostat system from.
Correcting your heater hose routing to what the 04 uses is the pattern to follow. It involves adding a port to the metal tube in the lower radiator hose or just buy a new one for the 04 to replace yours if you can weld.
The fan clutch & fan are the last part and different people choose different options. Remember these thermo viscous fan clutches last around 5 years before needing replacement.
Some do ok with the factory clutch & fan. Most by doing the “fan clutch mod” where you cause the engagement to occur at a lower temp.
Going to the 01-05 duramax pickup fan blade trimmed down slightly and running a better fan clutch is enough for most. Last I knew Kennedy’s fan clutch was still hailed as best but several over zelous hummer owners were a-holes to him for him not knowing what was needed on hummers and he almost won’t sell to anyone with a hummer now because of it. His customers are pickup owners for decades now. So you buy his fanclutch for the 6.5 in a late 90’s pickup. They usually trim their fan shroud not the fan- we have to trim the fan. Leroy sells the fans already trimmed if you don’t wanna diy.
One of the drawbacks to the thermal viscos fan clutch is they have a percentage lock up and it varies by unit. So an 80% - if the waterpump is spinning 2,000 rpm the fan max is 1,600 rpm, 90% is 1800 rpm fan speed.
The other part is how it works. Engine temp cool, radiator cool, wir going across radiator cool so the thermal viscos bimetal valve is open so fan stays off. By time engine is hot, radiator is hot, air through radiator hitting fan clutch bimetal gets hot then finally engages fan. This system works when heat increase gradually. Sudden heat loads like cruising to hard throttle - starting a mountain climb for instance- the engine heat runs away faster than the fan can act.
The military hmmwvs use a water temp sensor to engage a fan, so it’s faster reacting. Then the fan clutch they use is 100%. Either on or off. The temp switch they use is called a Cadillac valve. They choose a really high temp so they still have a high failure rate. Also the “customer” doesn’t complain about the fan noise and massive power loss as their complaint is laughed at by higher ranking individuals. So they just hear a louder roar and more often. Many auctioned off hmmwvs - the owners learn to buy a different Cadillac valve at a lower temperature, they accept the noise & power loss and have long lasting engines from it. Eric. Hummer H1 can probably tell those interested the number. His high mileage one in all the picks is a hmmwv in disguise.
. Oh yeah t the hmmwv clutch uses power steering fluid for the actual engagement media.
The hmmwv fan clutch system works so well in pickuos with their fancy vertical radiator- many do ok with the 4 bolt waterpump (not the balanced flow at all) and survive. Some doing extensive heat mitigation inside the engine during a rebuild or new engine disassembly for improvements before install as well.
Using an Electro-viscos fan clutch is another option. Very appealing because you use water temp to engage, can adjust temps to come on at, snd has a 100% lock up like the hmmwv clutch. And a couple wires to the fan clutch rather than a power steering hose. This system has proven highly successful in pickups, vans, and one RV I am aware of. An added advantage to those of us who really enjoy cold a/c. Because replacing your binary ac switch with a trinary and your fan can come on to make the ac colder like happens in modern vehicles (modern as in since the 80’s) Only Two hummer owners have tried it, both removed. To frequent fan used I beleive is the issue.
@Tad might have more input.
Remember that what works for Bob won’t work for Bill because Bob is low power and drives easy, and Bill drives faster and has a bit of hopped up hummer- he is trying to keep up with idiots like me who think Hummers should lap other drivers on the freeway and like sending rooster tails and the sand dunes.
