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C3500HD Tow pig

Mine must have a 195F thermostat, gets up to 205 but doesn't really try to go over that since the new fan clutch. Even though the HD's have better airflow across the radiator it still needs the cooling system upgrades.

Am considering using a stand alone oil cooler as a secondary radiator. Plumb the port at the rear of each head, run them to a filter, then the aux radiator, then back to either the thermostat housing where the heater core runs or into the water pump. That's if after turbo and usual cooling upgrades it still gets up over 205F when towing heavy.
 
That's not a good way to do it off the blocked off crossover passages on the back of the heads. Your routing is the same as the failed "flow increaser" Y hose sets (I won't mention Vendor names, but we all know the Blue silicone hose set with the fancy stainless steel machined Y connector that was supposed to prevent the #8 & #7 cylinder cracking on the 6.5 in HumVees by "improving" flow from the back of the head to the radiator) that did the same thing without the cooler.

Instead, consider using the heater core Send and Return hoses, either just tee-ing in for partial flow through the cooler, or diverter valves for full flow through the cooler only and none to the heater core(s) and remember to flip the valves the other way every winter so you have cab/rear heat, and back every summer for maximum auxiliary cooling..
 
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Husker6.5 said:
That's not a good way to do it off the blocked off crossover passages on the back of the heads. Your routing is the same as the failed "flow increaser" Y hose sets (I won't mention Vendor names, but we all know the Blue silicone hose set with the fancy stainless steel machined Y connector that was supposed to prevent the #8 & #7 cylinder cracking on the 6.5 in HumVees by "improving" flow from the back of the head to the radiator) that did the same thing without the cooler.

Instead, consider using the heater core Send and Return hoses, either just tee-ing in for partial flow through the cooler, or diverter valves for full flow through the cooler only and none to the heater core(s) and remember to flip the valves the other way every winter so you have cab/rear heat, and back every summer for maximum auxiliary cooling..
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Didn't know that previous setup caused issues
 
Yes. Most commonly #8. So common rumors took hold in hummer community of “at risk blocks” and “#8 fail” until some nut (me) explained there were the same blocks and heads going in vans, trucks, rvs that didn’t fail the same way, so it wasn’t a hummer conspiracy and a ton of their info is skewed. For anyone that believes it though, I have the magic GM 99 post fix block and heads you can buy from me for higher than optimizer price of course! Haha.

“The rear head cooling kits” lowers the number on the gauge, but the middle cylinders in the heads got WAY hotter, leading to Way more often Cracked heads, warped heads, #7 & #8 did a little better but the middle cylinders started failing. If the flow wasn’t altered a ton then the same cylinders failed but in different area on the cylinder wall. Trading one issue for another and often in the harsher climates like southwest failed sooner and more catastrophically. Usually block and both heads are not rebuildable. More than just hummer suppliers- Heath used to make and sell them until he was sent proof from a couple of us that is was worse, from there he contacted a GM engineer he knew and he verified it. From there he quit selling them. Gm spent millions redesigning crossovers, water pumps, etc - yes they tried many versions of the easy alterations like a “T” and a couple heater hoses. They even tried electric water pump on the rear in conjunction with and in place of the main water pump. Reverse flow was too much thermal shock forour crazy hot heads.
 
red said:
Didn't know that previous setup caused issues
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Oh yes. In fact, it was found once (unlucky) users had used the Y flow bypass from the rear of the heads for a length of time, that it actually increased the coolant temperature at the rear of the heads and hastened head/cylinder failure due to the coolant flow characteristics of the 6.5. When they first came out, I too thought that the idea made perfect sense since racing SBC manifolds like those of Edelbrock used four-corner "X" coolant flow, but a SBC coolant flow path and relative coolant flow/pressures are much different than that of the 6.5.

IIRC, the problem with the Y hose configuration off the two blocked off coolant crossover ports on the back of the heads boiled down to (pun intended) essentially the coolant pressure at the point the Y hose rejoined the coolant flow ahead of the front crossover was greater than the pressure at the rear of the heads, so the coolant "stagnated" at the back of the heads and the rear of the heads and cyls #7&8 actually ran hotter than without the Y hose assembly. When the vendor who developed and sold his Y hose assembly as a "cure" to overheating discovered that it actually did the opposite, he immediately pulled it from his 6.5 parts webstore. @WarWagon and @Will L. are both familiar with the Y hose saga, as I'm sure several other "Old Timers" on here like @Turbine Doc are, as this was about 12 or 13 years ago that this occured.
 
I see that @Will L. already expounded further on the subject, and kept it under two pages! Thanks, Will! Also, he went where I didn't want to go, and named the vendor/developer. Didn't Kennedy also offer a variant of the Y hose, too? I thought it was him, not Bill, that developed and manufactured it. Hey, I could be wrong, wouldn't be the first time and won't be the last!
 
Interesting, missed it when all that was happening. Well T ing off from the heater would work well enough since the filter could be plumbed in before the T, providing filtering capability year round. Then divert to a second cooler in warm months if the temps won't stay down after the upgrades are done.

Yes a filter would reduce some flow to the heater core. Whether enough to be an issue come winter time if traveling to a colder area...... In Texas not an issue haha
 
red said:
Interesting, missed it when all that was happening. Well T ing off from the heater would work well enough since the filter could be plumbed in before the T, providing filtering capability year round. Then divert to a second cooler in warm months if the temps won't stay down after the upgrades are done.

Yes a filter would reduce some flow to the heater core. Whether enough to be an issue come winter time if traveling to a colder area...... In Texas not an issue haha
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Go take a road trip and drive it up to see @ak diesel driver this December!
 
Amazing the difference humidity and altitude play when it comes to feeling the temperature. 15F in northern Utah feels like 40-45F down by the gulf coast in my experience living in Houston, Texas and Destin, Florida. Once you pass 110F-115F though it doesn't matter, it's just damn hot hahaha.

Finally replacing that coolant fitting/hose between the heater and the thermostat housing with a barb and a silicone hose. For now will leave it that way an add the filter bypass later. Engine oil/filter change along with the Fumoto drain valve getting done once they arrive, about to roll to 160,000 miles.


On the financial upside, I'm working in the oilfield again so won't be living on as tight of a budget for awhile haha. Figure the money from the first few months will go towards paying off everything along with a few upgrades for the truck and toy hauler, after that it will be focused towards house construction.



List:
-Cooling system, want it to not exceed 205F anymore period.
-Larger remote oil cooler for engine oil.
-Gauges for EGT, Fuel pressure, boost or maybe not. Air pressure x3 gauges for eventual upgrades.
-Air ride hitch. Being that both trailers are gooseneck and places I've towed/will continue to tow (offroad) going to stick with that. Plan is the 'cody cushion' for the truck.
-Finish the bed.
-Trans oil cooler, probably go with the one that bolts to the PTO outlet and adds 1 quart of capacity.
-Turbo swap. Considering I stay at lower rpm's (1700-2300) the hx35/40 hybrid is looking like the best option.
-4" exhaust
-Tune



Last 4 things are of lower priority for the truck but to get it exactly how I want it:
-Limited slip in the rear axle (no selectable locker for the 37 spline dana 80) and regear.
-Swap the Dana 60 from the old k30 into the HD. Has 4.10's which is just about perfect with my tire size. Either limited slip or selectable front locker.
-Install the NP205 from the k30 with the PTO divorced from the trans.
-Gear vendors (maybe)
 
Yeah. 90° with a 75° Dew Point at Ft. Polk, LA is unbearable heat/humidity (but then again, Ft. Polk itself is unbearable 😁). Yet, I found that 115-117° (and even the day the wet bulb thermometer in the shade at the TOC read 135°!) at the NTC, Ft. Irwin, CA (on the other side of the mountain range on the west side of Death Valley) to be quite bearable and not really all that bad at 5% Relative Humidity. The only difference between 115° and 135° that I could tell was on 115° days I drank 3 gallons of water and the day it was 135° I drank 5 gallons of water!
 
Well AC decided its going to be a priority. Compressor clutch pulley decided to lock up which forced a replacement of the AC compressor. Figure since that's new might as well get the system working on my week off from work and ordered new hoses, condenser, electric fan for the condenser, orifice tube, and receiver/dryer. Install all that stuff either Tuesday or Wednesday next week most likely then get the system vacuumed/charged up.

Ordered a Cody Cushion air ride gooseneck hitch which will be in later that week.
 
MrMarty51 said:
Be careful there young feller, or, You’ll have that old beast like brand new. 👍😹😹😹
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Lol well who knows its future with me. Will admit its towing capabilities are perfect for me, the chassis strength and brakes are excellent for my uses. Being a 6.5 upgrades are available and cheap compared to other engines.

The 3 main issues i have with the truck are top speed, 2wd, and regular cab.

Top speed gets addressed after turbo and tuning since refuse to sacrifice the current towing capabilities in that exchange. How it currently handles itself at 60mph towing heavy, do the same later at 70mph (maybe 75mph).

2wd to 4x4 is almost a bolt in on the HD because of the solid front axle. Have the np205 and dana 60 front axle sitting here. New engine crossmember is the hardest part to do the swap at stock height.

Cab size, well thats either body lift or stretch the frame. I'd go body lift and 8-9ft bed (no chassis mods).


Or just buy a second truck and have this as a backup. The brakes while towing heavy though, its impressive knowing that this truck can safely/comfortably bring about 26k pounds to a stop without trailer brakes in an emergency situation. Hard to compete with that and its usually cheap maintenance costs.
 
AC rebuild is delayed a few days but the parts arrived. Have everything but oil/freon ready to be installed.

Little 12 volt air compressor is here along with the new air ride hitch, Cody Cushion. Might be enough adjustment in the toy hauler hitch to deal with the extra height, but not the flatbed for certain. Going to notch the crossmembers and move the gooseneck hitch lower into the bed frame.

20200902_133057.jpg20200902_133105.jpg
 
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