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Fan / Clutch Upgrade

Will L. said:
The fanclutch is an incredibly important part. Imo I would return the unkown spec fanclutch and get the ones that are proven.

Does your fanclutch attach to the waterpump with 4 studs and nuts or with a single large nut?
Click to expand...
It has 4 studs. I really didn't know what to get. If you know something better I'm all ears.
 
So the waterpump you have was an engineering mistake by gm that was later fixed. Currently 70% of the coolant flows on the driver’s side and only 30% through the passenger side. Hence all the #8 cylinder and passanger side heads cracking. There are still some places that sell “rear head cooling loop kits” AVOID THEM. If free, throw it in the trash. They cause different issues covered elsewhere in the forum.

GM tried a high output pump that was still unbalanced but it still creates issues. So replacing the waterpump with the updated one has a bigger effect than a fanclutch and fan. The balanced flow waterpump is identified by the single large nut. Only AC Delco or GEP for the waterpump.

Then get the Kennedy fanclutch (or if you want to do the Electronic controlled one AK Diesel driver.

The hydraulic lockup fanclutch that SC Trailrider has is a killer set up pulled from hmmwvs. They have a 4 bolt waterpump but it is vbelt driven instead of serpentine belt. This means opposite rotation which was the design error of your water pump.

Having the 100% speed lockup of the Hmmwv fanclutch along with balanced flow spin on pump would be the ultimate set up, but no one has made that work yet. I am on the list of people trying to make it work currently. Maybe meet up with Chris and check his out before pulling the trigger on anything.

Leroy is working on another all electric full lockup fanclutch for the spin on pump. Not sure where status is on it, but worth a call to find out.

There is a TON of info here about the cooling system. Invest some time in researching it so you only have to deal with it once.
 
Last edited:
Jaryd said:
Go to Rock Auto and go to the 2000 year model 6.5. That’s the balanced flow water pump that Will is talking about.

Don’t forget to use the forums 5% off code for Rock Auto if you decide to get it.
Click to expand...

FellowTraveler said:
From what I've gathered all 1999 6.5td's built MAY + have the newer balanced flow pumps mine did.
Click to expand...

And with that, I am wondering before ordering, if the restricted bypass hose fitting that Leroy sells would help the 2000 year engines ?
 
MrMarty51 said:
And with that, I am wondering before ordering, if the restricted bypass hose fitting that Leroy sells would help the 2000 year engines ?
Click to expand...

Yeah Leroys BRF does help our trucks even though we have the 2000. I don’t have one in mine yet but I’m going to put one in one of these days. Hopefully before summer gets here.
 
Will L. said:
The hydraulic lockup fanclutch that SC Trailrider has is a killer set up pulled from hmmwvs. They have a 4 bolt waterpump but it is vbelt driven instead of serpentine belt. This means opposite rotation which was the design error of your water pump.

Having the 100% speed lockup of the Hmmwv fanclutch along with balanced flow spin on pump would be the ultimate set up, but no one has made that work yet. I am on the list of people trying to make it work currently. Maybe meet up with Chris and check his out before pulling the trigger on anything.
Click to expand...

Some have already done the 100% hydraulic lockup fan off the military Hummers and even posted it on here. The biggest issue is the Serp belt accessories are spaced differently on pickups SUV's requiring custom work to the water pump/fan pulley. Finding a 12v vs a 24v solenoid to unlock the clutch from PS pressure is easy. I thought there was a kit offered now?
 
hoodiegadoo said:
Yea I’m going to try that fan clutch and see how it does. And put a new turbo on the upgrade list. It’s a 6% grade for 3 miles straight up. It’s all highway so you’d think there would be plenty of time for the fan clutch delay to kick on and cool things down, no? I don’t push my truck that hard up the hill so no WOT. Maybe 3/4 or less and just slow down in 4th gear.
Click to expand...

I actually run hotter at lower throttle than WOT simply because it doesn't downshift with lighter throttle. Even with the KD fan clutch the GMx "Asthma Attack Turbo" would have me hit 210 on a light grade towing: due to the heavy throttle in OD, 4th. Not enough RPM for the water pump and fan for the load. Case in point - manually shift it to 3rd and wind it up. This will give you more RPM to move coolant and the fan clutch will lock up faster with more RPM. Sadly this puts the GMx turbo out of it's RPM range so YMMV.

Just 3 miles? If you can do that at 60 MPH that's 3 min. I bet you can't at 60...

Regardless it can take 2 Min for the fan to lock up alone. That's 1/3 or more of the way up. Add to it the other delays of actually heating up the fan's obsolete thermal spring as I outlined and the time to get the fan on is a serious concern. Hell I even have trouble with an electronic viscus fan clutch being too slow to get locked in combined with an ECM bug from Dodge engineers freezing their asses off in a snowbank of Michigan resulting in the AC blowing it's charge out the relief valve at 450+ PSIg. Under some conditions like engine cold the ECM bug doesn't kick out the AC compressor when pressure gets to extreme pressure of blow the system up. Thermal spring or Electronic valve the Viscus clutch takes it's time to lockup. The 2 Min time to "do something" pass/fail test is at 2000 RPM for electronic clutches.

Bottom line is the long delays in getting the fan to actually lock up are a serious concern because the ECT runs away until the fan does come on. The lower temp T-stat and KD fan clutch simply move the ECT spike lower.

On/Off fan clutches are controlled by a temp switch and have zero delay. Click-Slam-Screech-Roar...

Again the GMx turbo when towing really keeps heat in the engine due to high backpressure on the exhaust side. You will be surprised at how much less the fan needs to run with a better turbo.
 
If you have the dual thermostat housing, absolutely get the fitting from Leroy. Hummers have worse heating issues because of the angled radiator deign, and EVERYONE of those guys that has put them in have bragged it up.

It was John at Unique diesel that makes the kit to do the hmmwv fanclutch on c/k pickups. afaik he only did the 4 stud ones so far, but said he could make the spin on style but has not had customers ask yet. I would go that way except I can just use all the hmmwv parts readily available in my hummer except I need 12v instead of 24v solenoid.
 
Will L. said:
So the waterpump you have was an engineering mistake by gm that was later fixed. Currently 70% of the coolant flows on the driver’s side and only 30% through the passenger side. Hence all the #8 cylinder and passanger side heads cracking. There are still some places that sell “rear head cooling loop kits” AVOID THEM. If free, throw it in the trash. They cause different issues covered elsewhere in the forum.

GM tried a high output pump that was still unbalanced but it still creates issues. So replacing the waterpump with the updated one has a bigger effect than a fanclutch and fan. The balanced flow waterpump is identified by the single large nut. Only AC Delco or GEP for the waterpump.

Then get the Kennedy fanclutch (or if you want to do the Electronic controlled one AK Diesel driver.

The hydraulic lockup fanclutch that SC Trailrider has is a killer set up pulled from hmmwvs. They have a 4 bolt waterpump but it is vbelt driven instead of serpentine belt. This means opposite rotation which was the design error of your water pump.

Having the 100% speed lockup of the Hmmwv fanclutch along with balanced flow spin on pump would be the ultimate set up, but no one has made that work yet. I am on the list of people trying to make it work currently. Maybe meet up with Chris and check his out before pulling the trigger on anything.

Leroy is working on another all electric full lockup fanclutch for the spin on pump. Not sure where status is on it, but worth a call to find out.

There is a TON of info here about the cooling system. Invest some time in researching it so you only have to deal with it once.
Click to expand...
Great! Now it looks like I am going to be buying a water pump. And another clutch.
 
ak diesel driver said:
Mine does not take 2 minutes to lock up. Might be that the PCM is taken out of the equation as it's trying to give the minimum amount needed to keep it cool for MPG
Click to expand...

FWIW: 2 minutes to lock up is a worst case delay before you fail the clutch taken from a Trailblazer Electro Viscus fan clutch testing procedure. More or less bring the engine up to 2000 RPM and tell the fan via a scanner to lock up and then unlock. The fan has 2 minutes to lock up and then 2 minutes to unlock to pass the test. Clearly the Obsolete Thermal spring can take longer just because you have to heat the spring up and, again, worst case. (Tests are different for the thermal spring clutch.) Think of 'morning sickness' where your fan is locked up on a cold start and how long it takes before it unlocks and the roar stops. The times given are mainly to generally illustrate the real delays the cooling system has to finally get the fan locked in during WOT ECT thermal runaways. The RPM is also important in affecting 'time to respond' due to moving the silicon working fluid faster with higher RPM. Thus the known known 2000 RPM test point and time.
 
If you look in my electric fan clutch thread on page 9 I posted that it took 8 seconds to come on. I bet 2 minutes is the discard time limit.
Probably affected by temperatures too.
 
ak diesel driver said:
If you look in my electric fan clutch thread on page 9 I posted that it took 8 seconds to come on. I bet 2 minutes is the discard time limit.
Probably affected by temperatures too.
Click to expand...

Exactly, anything that doesn't respond in 2 min is clearly toast. I am dealing with my 2003 Dodge EV clutch and it doesn't respond in 8 seconds. It may be closer to the end than the beginning of it's life.

Possum said:
The more I find out about this truck the more I'm thinking I shouldn't have bought it.
Click to expand...
Check out my Comeapart thread... :greedy: These trucks are just cheaper to work on.
 
Possum said:
The more I find out about this truck the more I'm thinking I shouldn't have bought it.
Click to expand...

Well, you could possible do what the previous owner(s) did- just manage with what you have as long as you can. but getting it "perfect" means reliability is even greater. Maybe wait till it is time for a new water pump then do it all?
 
@Possum I have some parts here, I'm not sure at the moment just what all is here, I will look this weekend and I may have something you can have cheap, I know I have a 9blade fan I'm not using and a good clutch, let me check this weekend, if you haven't ordered anything yet hold off till I check what I have...
 
I really appreciate all the insight. (Even though this isn’t my thread [emoji23]) I’m starting to figure this engine out I think. So I’ve got a 97 c3500 with the 4 stud metal 9 blade fan and dual tstats. My best shot at keeping this thing cool is the ac delco 252717 water pump with the Kennedy fan clutch and 180 tstats? I just had someone put head gaskets in while I was out of town for a bit with the military and they put on new heads as well. So I’m trying to keep those in good shape. Thanks again guys for all the help.
 
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