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Master Coalroller
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Discussion Starter #1 (Edited)
There has been a lot to say for the cooling history of the Chev. In the beginning the 6.2 which morphed into the 6.5 was a reliable engine with mechanical fuel injection and things mostly worked well. In standard NA form the Chev runs a 76 GPH water pump, a viscous fan and a single thermostat housing. Generally the engine with this cooling system ran ok.

Once turboing came about, everything changed. The heat plume created by the extra fuel and boost mixture couldn't cycle quickly enough, and the sonic effects from the ignition under high fuel loads transmitted through the water jackets caused water cavitation on the bore walls of the water jacket. Large boiling bubbles like a pot on the stove would surround the larger portion of the upper cylinder wall and resulted in extreme problems for the upper cylinder and further upwards into the head.

There was a cooling upgrade released to cope with the problem. This consisted of a twin thermostat housing, a larger more responsive viscous fan and a larger impeller flow water pump flowing 130GPH. This didn't really solve the problem, as the problem is a design inefficiency. The Chev wasn't designed for turbo application. However there is ways to improve and effectively use this engine.

Begin with the coolant. Add heavy duty redline water wetter. This will reduce the surface tension of the coolant and effectively stop the cavitation effect on the cylinder walls in the water jacket. Nothing more to say here.

Fit the high volume water pump. Make sure it is correct for your belt fitment. There is clockwise and anticlockwise belt drives. The pump should have HO cast in the housing.

If you can run the twin thermostat housing do so, however it only works with the Stanadyne electronically controlled injector pumps as the housing fouls the mechanical injector pump accelerator linkage. Most Australian converted options are mechanical injection so not much joy there. The N/A original style thermostat housing only flows 96GPH so pay attention to the next two paragraphs, as it will address this flow problem.

Run a heater hose using a "T" from the heater supply line, fit an inline heater tap, and plumb it to the top radiator hose or tank. Run a push pull heater/bonnet type cable into the cab and open the tap whenever your temperature runs above 90C or if you anticipate running into some hard work.

Most V8 engines run identical heads. So on the Chev the coolant passage at the front is replicated at the rear with a plate covering it. Port a barb into this plate and run a coolant relief system back to the heater supply hose, fashioned using "T" joins. One for each head. The coolant will flow from the rear of the head where it's usually trapped when the heat plume from the upper cylinder walls reaches super heating temperatures and is at it's most potent. This balances the heat in the head. I use heater hose for this, soon I will run exterior copper lines instead.

When reconditioning heads, or fitting heads use a stud kit. Not withstanding the usual benefits of stud kits, there is a rear coolant passage from the block to the head that has a poorly designed badly performing gasket seal which is prone to leaking. Stud kit will solve this. I also run standard Rislone treatment constantly as the gel surface coating treats the areas prone to problems and is compatible with coolant, and not just a flush.

Correct assembly of the timing case is complicated and essential to the cooling system. Don't let hacks near your timing case. Like the TD 42 there's a number of layers for the coolant to pass through and it is perilously prone to leaking and corrosion.

Use coppermax on everything except head gaskets, as this engine was designed with poor sealing tolerances, it is commonly used by all in the USA and the military.

If I remember more ill post up here cheers :cool:
 

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Master Coalroller
nissan
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3,242 Posts
Discussion Starter #2 (Edited)
Once all that is digested you should be able to attain temp between 90C - 110C which is exactly what you want to get a good burn, cylinder temperatures of 550C and higher. >110C to 120C is where you need to start downshifting and lifting the accelerator pedal and stabilise the coolant.
Gauge reporting temps of 80C for around town idling and 90-110C on the highway or working hard is what's needed from these engines to get good energy efficiency, and therefore fuel economy.
It's a fallacy, that needs to be realised by all old school indirect injection diesel owners, trying to keep the gauge temp at 72C all the time. These 2H, 1HZ, TD42 and 6.2/6.5 Chev engines are revvy short stroke workhorses and need to be running hot and spanked to perform at correct service levels.
Edit: run the hottest thermostat possible high 80s
 

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Master Coalroller
nissan
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3,242 Posts
Discussion Starter #3 (Edited)
This is the rear of the LH head where the ported heater hose mod begins. The standard heater supply goes from the crossover back to the cab, both heads have these rear hoses feeding back and tee'd into the heater supply where the coolant then can still remain under the control of the thermostat. It's brilliantly quick to warm up the cab when you select the heater in winter lol.
This mod I have done also to TD42s by tapping 3/8 into the rear of head and using a brass elbow barb via a heater hose tee'd into the STD heater supply.
 

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Master Coalroller
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3,242 Posts
Discussion Starter #4 (Edited)
The redline bottle is sitting on the bypass line directly to the upper radiator hose, with the inline tap manually controlled by the driver. The bypass begins via a T in the STD heater supply line (unseen in pic). This means you manually provide relief when under high heat stress conditions where the HO water pump is restricted by the thermostat housing. Importantly when closed the entire system is still controlled by the thermostat for startup, warmup and normal driving/ workload.
This mod can also be done to the TD42
 

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Hi there, I was wondering if you would have the time to do a simple drawing of your setup showing water flow thru the bypasses etc I have found your info really interesting but I'm trying to visualise it all with no luck
 

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Master Coalroller
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Discussion Starter #6
Looks complicated but trust me, the hottest coolant will force its way through any passage of lesser restriction.
Primary benefit: Balancing your heads this way there’s a pathway for the hottest coolant to do just that, rear ported coolant will reach the exit to the radiator quicker when it’s superheated to a higher temp, exiting to the heater feed which is still under the control of the thermostat. The superheated coolant trapped at the back will exit back through the heater feed to the thermostat housing.
Secondary benefit: In extreme conditions you have the capacity to override the restrictive thermostat housing with a bit of foresight by pulling a cable in the cab, opening the bypass to directly exiting superheated coolant to the top radiator hose.
 

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