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anyone use the "Rear Head Cooling System Kit"...........

@21102k3500 Electric fans are rated at max of 5000 CFM freestanding. That is no radiator stack, closed hood, or engine in the way. I personalty measured a fan of a Trailblazer SS with wind speed readings on the radiator and averaged the MPH to obtain 10,000 CFM from this EV clutch fan in place: hood closed with full restrictions. The scream of the belt starting to slip was impressive around 5000 RPM. The same 21" TBSS fan put under the hood of my 1993 6.5 TD was NOT enough to keep it cool pulling a trailer in Lake Havasu, AZ. It didn't have enough "pitch" on the blades. Windows down, heater on high, No AC, SUCKS in 121 degree weather! The steel fan and Duramax fan have a lot more pitch and will pull way more than 10,000 CFM that, frankly, you can't get electric fans to pull. Pulling Lake Havasu with a Duramax fan and Kennedy Diesel low temp fan clutch allowed me to climb the grades with the AC on below 210 ECT.

This is why some fan catalogs note the 6.2/6.5/6.5TD as not recommended for electric fans due to not enough CFM.

Electric fans in front of the clutch fan are a restriction due to the windmill effect. Unless the blades are stopped and locked with a parking brake: running or free spinning the electric fan is reducing airflow.

The factory 6 blade POS fan and 20+ year old clutch one may be comparing electric fans too is no contest. The factory OEM fan clutch expired at 5 years old (they loose 200 RPM per year) and the 6 blade fan was a HO 6.5TD mistake from GM they corrected in later years. Many 6.5 engines went to china as scrap metal with the garbage 6 blade fart fan still attached.

Electric fans only help at idle for AC period and maybe. You would get better results with a 1100 RPM high idle and locked up fan clutch. The delay for the clutch to come on with a cold engine is another advantage of electric fans, again for AC only.

The only better than a Duramax fan setup with a low temp fan clutch would be a direct drive on/off fan clutch like Hummers have. This is mainly to overcome the delay in getting the thermal spring obsolete clutch to lock up after you go WOT and stay there watching ECT rise till the fan comes on.
 
WarWagon said:
@21102k3500 ...

The only better than a Duramax fan setup with a low temp fan clutch would be a direct drive on/off fan clutch like Hummers have. This is mainly to overcome the delay in getting the thermal spring obsolete clutch to lock up after you go WOT and stay there watching ECT rise till the fan comes on.
Click to expand...

2 items:
1. Hmmwvs not Hummers. Just don't want someone buying the crappy hummer parts thinking they are upgrading.
2. Along with hmmwv instant lockup by ect temp instead of thermal spring, is the fact that it is 100% waterpump speed. The highest lockups (thermal fanclutch) I ever seen were 90%. Most are 75-80% when new.
At 2,000 rpm that lost 200-400 rpm is huge. Rigs geared like mine that travel at 2800 rpm that is 560 rpm lost.
 
I could go measure my pulleys - but do you know off hand what speed our pump/fans spin at? Are the a 1:1 of engine speed or different?
 
Industry norms are over driven fan water pump: 1.29:1 LB7, 1.35:1 5.9 Cummins, and off the map out of the norm 1.48:1 on LLY. No info on 6.2/6.5's out there but eyeball pulley size says it's overdriven. I wonder if a LLY pulley would fit a 6.5TD? Maximum overdrive WP/fan pulley for a 6.5 would get results for AC performance for sure.
 
Will L. said:
On the thread heading of rear head cooling kit- avoid it like the plague. Missy hit the high points. Some of the testing we did with/for GM involved several versions of this- all were detrimental. Some gave lower gauge readings but created eddy currents and pockets of no flow inside the block- most specifically around cylinders 7&8. Also loss of flow through the front of the heads which increased cracking issues between the valves.
Click to expand...

Will,
How long ago was this posted? I've had the balance flow kit on mine for years and didn't know there were negatives. I did know that the new water pump setup was supposed to be better, but I didn't see any harm leaving Heath's kit on until I got the extra time and money to take it off to replace the pump.
 
Your saying the balance flow kit...lets be clear.
Not talking the balanced flow spin on waterpump as bad.

The 2 rear head coolant block off plates That get modified and tie together with hoses, sometimes with a tee and go back to the heater hoses or surge tank. That is the bad item.

Back when I worked at the unical outfit where we did the oil and fuel testing, we had the fleet of the 6.5s. When their engineers were out one time going over stuff we talked about the overheating issues, and thats what got us into doing their coolant flow testing issues. They showed me the files on all the testing they did trying a bunch of different things to help with the passanger side overheating issues.

They tried routing with the rear blockoff plates about 60 different ways, tying front to rear, rear to rear, secondary pumps just to the rear, you name it -they did it.

We (before GM engineers got involved) were trying the same setup heath used that tied the 2 together and into the return heater hose. (Seems to be the most common "solution" everybody comes up with). GM's research on it showed the passanger head cracking much easier if the flow coming out of the head is low volume, and if it is high enough volume it would cause overheating on the cylinder walls of #6 and #8 where the are close to each other. Infact, several coolant flow alterations caused this result, but they had not determined why that change occurred.

Later when we cut the side of the block out and made a window with some mr5000, and colored water, we found why. The change in current flow created an eddy current between the 2 cylinder walls where the bolt casting was done short on the rear cylinder. So the eddy current kept about 1 quart of water trapped their in a continuous cycle and all the other water just flew right passed. We even did a separate test with a long needle we jb welded through the plastic window into the area and had all the water clear, then injected red dye into the water of that eddy current. It didnt mix with the rest of the water until we shut the engine off.

GM put out info to techs in dealerships to watch for people adding to the rear head blockoffs - that it voided warranty. This is why.

How it "helped". By taking some of the hotter coolant out of the loop that feeds to where your ect temp sensor is, more cool water feeds that cirtuit. So your temp sensor does infact stay slightly cooler, or can cool back down slightly quicker after been heated up above normal. The problem is, the 2 nightmare locations, #8 wall and the heads between the valves get WORSE, not better. But since you dont have temp probes there to monitor the difference, you don't know. But Gm put them there in their testing, as did we.
As soon as we did our testing confirming what GM theorized, we went on 12 hour shifts, for 2 weeks straight to keep up our normal work and get all ot them removed from our fleet.
 
How long ago was this information? In this thread Missy posted it back in August 2011, long before I was a member here. She has much of the information correct, but didn't apparently know all of the blocks that were affected. She mentions 97-99, but 93 and up have had the same cracking #8 issues. Only the optimizer corrected the casting design. My '95 hummer block cracked there and iirc the block was cast in 94 for example.
Hummers experienced it worse because or cooling stack is much worse that pickups. Adding the turbo to the previous all n/a 6.5 hummers amplified it by the uppipes wraping the rear of the head and turbo above the area increasing ambient heat in the area.

As for Heath selling the rear head cooling kits (I prefer that description, it separates itself from the water pump description): He, like many others, sold them thinking he was helping customers out. When he later learned of the damage it caused and learn the correct "fix", he quit selling them.

Some suppliers like for example Dave, owner of "Blue Hummer" gave away plugging kits for free to all of his customers that just ask for one after he learned the truth.
Leroy could have made kits and sold them for profit here, hummer forum, and the web- I notice he doesn't. Honor above money? Idk- speculation on my part.

Heath just stopped selling them, and will say to remove it and install HIS waterpump kit instead. He will not tell you of the damaged casued. Many things Heath does is great. He has always tried to be at the fore front of the 6.5 world. But he will only push towards his sells. His new camshaft is the best thing ever invented because of the advance & delay in flow 1 head from the other to help the turbo mounted on passanger side. But asked about issues to a centermount turbo he said it will make no effect. Sorry -you can't have it both ways- it either has an effect or it doesn't. But he just wants the sell. His pride and accomplishment in the hummer hood scoop he designed was amazing, until air flow testing was provided to show it was detrimental. Only then did he mention the other company selling his design modified his original design for aesthetic reasons. Now his hood scoop is no longer promoted, his percentage of the sales also happened to stop when promotion of it did before the testing was out. Many have said it before about him- if he sells, it it is the greatest thing ever. If he doesn't it's a piece of junk.
I don't like his business practice of this. But I will give him credit that once he learns something is damaging, he quits selling it. My guess is he wants to truly help his customer base, but just can't admit errors on his part even if it was an honest mistake. Probably a bit of narcissism -not meant as a put down, just is what it is. My ex-best friend for almost 40 years is a major narcissist, so I'm very used to recognizing and dealing with it. I just wish he would put honesty and admit error in front of profit.
 
I am sure I have my original block-off plates somewhere. I don't throw anything away like that. I guess I need to hunt them up. Got your PM, too. Thanks! I'm going to try to give you a call this weekend if I can.
 
well, I looked everywhere I could think of this morning, and couldn't find them, assuming I did the work at home. Found them, still sitting on the work bench, in dad's shop - I guess I did the work down there, instead of at home.

Thanks for the tip on Dave with Blue Hummer. He still has the plates available at a reasonable price and I plan to get the gaskets from him, since the dealer doesn't have them available, unless I buy a pack of 10.

To your other point, where you offered the explanation yesterday, yes, I'm referring to Heath's balance flow system, not the water pump. My kit has the water hoses that come from the rear of the heads, as you described, coming into the small reservoir, then out into one hose, where it dumps into the factory crossover.
 
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