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My Recommended Mnx & Mod List for 1994 and 1995 6.5TDs

Good Article....What If I don't want to upgrade the water pump at this time....What Am I looking for, as far as a used Fan and fan clutch?

Like what years engine size (diesel 6.6?) and types of vehicle would I pull this off of at the junk yard?

I think I'm going to get a new 195Thermo as mine typically runs at 185....and I was reading I might get better mileage per gallon.
 
The cooling section needs a little more info. I have already ruined a good 6.5 from running it hot enough to scuff and crack a piston due to a fan clutch that would not stay locked up while towing. The 88-99 body style has a serious airflow problem through the radiator due to aerodynamics. This makes a working fan critical.

First it needs to be plainly stated that a fan clutch is garbage after 5 years old. They loose 200 RPM per year due to wear and viscus fluid breakdown. Their holding power at full lockup is also reduced by age. Any sign of leakage esp around the spring is good cause to replace the unit as it no longer has enough fluid to maintain full lockup. Yes, they will act like they lock up just fine, but, unless you measure the fan RPM and water pump RPM at high engine speed you don't know how much it is slipping and good luck getting the fan clutch hot enough for full lockup in the driveway/shop.

Perhaps it is time to request a special calibration thread on fan clutch. Myself I have not seen the disadvantage of the HO balance flow issue, rather the system delay to get that damn fan up to speed is more of a concern as temperatures simply run away till the fan locks in. To keep the engine from running over the 210 mark you have to shift the cooling system temperatures down. This means a lower temp thermostat and a lower temp fan clutch. Modifying a clutch is described in your article is the only way to use a thread on clutch. (Some have had very good success at doing this mod.) Hayden clutches come on slightly lower than factory clutch set points. Kennedy Diesel sells a 4 bolt water pump low calibration clutch that used with a low temp t-stat works very well to keep you below 210 no matter the load.

When you hit a hill the fan clutch is unlocked and the thermostat is partially closed from the low throttle conditions before the hill. When you have to mash the throttle to the floor it takes time for the thermostat to open. The engine temperature is rising fast from the WOT condition. The radiator then heats up and the cooling system is now saturated and starts to heat up with the engine. Airflow over the radiator starts to warm up the fan clutch thermal spring that opens the fluid valve in the fan clutch. But wait! There is an additional delay as fluid has to move to finally lock up the fan clutch. There is a gotcha: the fan takes longer to kick in at lower RPM. So if you sneak up on a light hill and go heavy throttle but not WOT: You don't downshift and your temperature spike is higher before the fan comes on. Low water pump RPM, slower airflow from low fan RPM's, and slower fluid transfer in the fan clutch contribute to this. (Recall the fan is always turning 10-20% of water pump RPM when fully unlocked.)

You are at the mercy of this system delay and will go from 180 degrees to 210 before the fan kicks in to stop the temperature rise. This range is shown with a Kennedy low temp clutch, low temp single thermostat, 20" 9 blade fan, new radiator, new clean R12 condenser, and 4 bolt HO water pump. Noted while towing a 28' trailer hitting a sudden 10% grade and yes slowing down at max power... Outdoor temps ranged from below 32 degrees to over 100 degrees - wrecked the truck before our summers 120 degree weather hit. 1/3 turn on the IP and 14 PSI boost that can add quicker engine heating over stock: a DS4 could heat you up faster.

Starting your temperature hotter with 190 t-stats and a higher temp clutch allow the temps to shoot over the 210 mark because temperature is not the factor - the delay to get the fan locked in is the cause of the temperature spike. Proof that the spring thermal fan clutch is not only obsolete but the wrong tool for the job with the especially narrow temperature range this 6.x engine needs to be efficient and not crack itself to death.

The only practical way to avoid this delay and not overshoot the temperature is to lock the fan in by ECT by using the Hummer hydrostatic lockup clutch. (A system not yet adapted for use in a pickup by anyone.) Otherwise you are lowering the system temperature to avoid the 210 max point from sudden load.

Anything less than sudden WOT due to a hill gives you more time and makes the delay in the system less critical. Less throttle while things are heating up reduces the max temperature spike. Your average daily driver that never has extended sudden WOT runs can live with higher system temperatures. (Fan clutch and t-stats)
 
Was able to open the original link, but not the second. I assume the original link also linked to the updated info. Lots of good stuff there, thanks buddy.
 
WarWagon said:
Starting your temperature hotter with 190 t-stats and a higher temp clutch allow the temps to shoot over the 210 mark because temperature is not the factor - the delay to get the fan locked in is the cause of the temperature spike. Proof that the spring thermal fan clutch is not only obsolete but the wrong tool for the job with the especially narrow temperature range this 6.x engine needs to be efficient and not crack itself to death.

The only practical way to avoid this delay and not overshoot the temperature is to lock the fan in by ECT by using the Hummer hydrostatic lockup clutch. (A system not yet adapted for use in a pickup by anyone.) Otherwise you are lowering the system temperature to avoid the 210 max point from sudden load.

Anything less than sudden WOT due to a hill gives you more time and makes the delay in the system less critical. Less throttle while things are heating up reduces the max temperature spike. Your average daily driver that never has extended sudden WOT runs can live with higher system temperatures. (Fan clutch and t-stats)
Click to expand...

Some interesting info here!

When you talk about the Hummer fan clutch, which Hummer model are you talking about, military or civilian? Do you know what would be involved with making this fan clutch work? Is this economically feasible?

Don
 
Nice write! Im starting to get to the mods that require more fabrication. Not as easy as all the others. I really need to buy a GMTD Scan tool/program..
 
I keep coming back to the file for info, today Im interested in the 2000 water pump and fan clutch with dmax fan. Got any part #s for them?
 
2000 L65 Water Pump: GM# 88894035 (ACDelco #251-603)
2000 L65 Fan Clutch: GM#15029405 (ACDelco #15-4691)
Not sure what year of Duramax fan you're supposed to use, but...
2001 LB7 Fan: GM#15010202 (ACDelco #15-80690)
 
You'll find the Delco water pumps are quite pricey, and I am not sure if anyone has any trouble with Bosch or other brands, or if they are any different in design. Its nice getting OEM Delco, but for some reason its twice the price of others.
 
What kind of price you talking on each? & where?. I have a call into my supplier he gave me a price but he is going to double check it.
 
dazed said:
Somebody posted this pump.....I think its an upgrade from stock... but its cheap
http://www.expedition-imports.com/p...rpump-251-590---GM-88894036---65-Diesels.html
Click to expand...

That is the high output pump from 97-99, but the one for 2000 has redesigned passages to balance the water flow to each head.

At the dealer, I checked out the price for the ACDelco pump and it was $340 for the Government Military price, like if I were to by it for the military, retail it was over $400. On Rockauto it is about $270. Bosch is like $100. Another company called DNJ Rock Products says New for $141. But who knows which ones are built to the OEM spec if not getting the Delco.
 
I see 3 left on amazon for 222$ (ACDelco #251-603)
Thats with free shipping
 
I have a good feeling I may be able to at least match Rock Auto on a GM piece. Whats Rock Auto selling GM or ??
Will let ya'll know tomorrow sometime.
 
Ya'll can get the water pump on Amazon cheaper than my cost is.
As a matter of fact I bought one myself.
 
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