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2004 Silverado Crew Cab Solid Axle Swap (LLY with ZF 6 speed)

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I suspect a lot of your issue with the fan not locking up is that your radiator/intercooler were probably full of dirt. These are viscous fan clutches and rely on air flow through the fins in order to give the temp "actuator" thingy on the front of the fan clutch the correct temp signal to know to turn on the fan. If the fins are full of dirt the airflow isn't enough to tell the fan to come on and it will never work properly. You just replaced both of those so they should be clean and have good airflow so the correct fan clutch should work like factory and also cool it down like factory. I always wash out my radiator as best as I can at the car wash every time I wash my vehicle, wash it through the grille til clean water comes out the bottom side. A lot of the time especially with diesels and all the coolers they stack on top of each other it is not enough and you end up having to pull the cooling package and wash it out separately every few years. My wife's gasser 2008 yukon xl denali currently has a dirty radiator but it runs electric fans so I only have issues when towing or pulling really big, long mountain passes. I pulled the fans and washed it out a few years ago but it's dirty again and I just need to pull the radiator and wash it out really good. This was the number one issue I saw working on medium duty semis that run viscous fan clutches. Yours probably gets worse with all the off road use it sees.
 
I've never had this issue with the Silverado honestly. I definitely have the issue with my diesel pusher RV (acts like a big vaccuum cleaner on dirt roads). The radiator was replaced a year or two ago and the intercooler was fine at that time. All of these issues are with the fan clutch, not a radiator issue. I still have the OEM fan clutch I just bought in it and it's still doing the same thing even with the new intercooler.
 
The later dirtymax units used a computer controlled fan clutch. I suppose one could swap that in but it would require a bunch of changes to the harness and ecm to do it. Probably not worth the effort/cost to gain the control.
 
ZooMad75 said:
The later dirtymax units used a computer controlled fan clutch. I suppose one could swap that in but it would require a bunch of changes to the harness and ecm to do it. Probably not worth the effort/cost to gain the control.
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I believe there are aftermarket stand alone controllers out there, I would not be looking to do a full FICM swap.
 
Last night I took the truck on a shakedown run out to Saguaro Lake. I threw the old NAPA fan clutch that previously was locking up way too early on before we left.

The weird thing is, it didn't lock up either... Temps got up to 221, it locked up after I stopped at a light once, but once again it unlocked at about 205-210. I could hear it partially locking so it was working somewhat better, but it only fully locked a couple times.

I did have a thought, I just went through some pictures and I put that Mishimoto radiator in back in December 2021 (not quite a year ago like I thought). The Hayden fan went on before I did that and worked after, but stopped locking up around April.

I did have my inner fenders out yesterday, so that may be letting the air escape too quickly and not heat soak the fan clutch properly, but I'm not sure. I'll have to do some more testing.
 
So I've been doing some searching online and I'm beginning to wonder if there is even an issue. Some sites say that it's normal for a duramax fan clutch to not lock up until 225-230, so maybe I'm just being paranoid...

Like most vehicles, the Silverado dash gauge just points to the middle (210) and maybe just a bit past that when I'm hitting 225. Before I had the Edge Monitor in there I wouldn't have even thought about temps and I recall seeing temps over the 3/4 line (235F) when I used to haul around the blazer with the cabover on it. The check engine light doesn't come on until 245-250 and I've never seen that.
 
It's weird how warm manufactures are letting engines get these days before they get concerned about cooling.
 
My LLY was running 225-230 pulling through the rockies a couple years ago coming home from BB20. Never heard the cooling fan lockup. Only time I ever hear it is first cold start of the day for about a minute or two.
 
It's so wild trying to find out if this is an issue or not, half the posts will say it's normal, the other half will say I have a bad water pump or thermostats. We're even reading that the Mishimoto DMAX radiator is junk and doesn't cool as well as the stock one (and is prone to cracking)...

I'm going to do some more testing today with a laser thermometer and with the fender liners in.
 
A lot of mentions of the Hayden #2886 kodiak clutch on diesel forums. Is that the one Stephen mentioned?
 
I like the mishimoto radiators. I did one in an '08 powerstroke, those ones do have cracking issues but it's due to a shitty Ford design that allows the front end to flex too much.
 
Fastereddie said:
A lot of mentions of the Hayden #2886 kodiak clutch on diesel forums. Is that the one Stephen mentioned?
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Yes, I believe that is the one he suggested. He put it on his wife's truck but ended up taking it off because it was always locked up and too noisy. I ended up getting the Hayden 2843 clutch.
 
Truckman4life said:
I like the mishimoto radiators. I did one in an '08 powerstroke, those ones do have cracking issues but it's due to a shitty Ford design that allows the front end to flex too much.
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The person that commented about the Mishimoto radiator said that they love Mishimoto radiators, but for some reason the one they made for the dmax sucks. :dunno:
 
OK, more testing and now I'm pretty sure I know what the problem is.

I took my laser thermometer out, heated up the truck to 210+, stopped and popped the hood (cooled down to 205) and checked. I was getting ~200 down by the temp sender so that agreed with the gauge, but on top of the thermostat housing was only 195ish, hot side tank right by the radiator hose was ~169, cold side tank by the hose was ~129...

The fan clutch isn't locking up because there's no heat. I just replaced the thermostats with AC Delco Original Equipment thermostats back in September 2019, so apparently they suck (I replaced the water pump at the same time, hopefully it's OK).

I just ordered the Mishimoto thermostat kit, they come on about 5° cooler (174 and 180 vs 180 and 185). It will be here tomorrow and I'll see if that fixes it.
 
I also did some testing with the EGT probes. I have 2 probe kits from Edge going into my cts3 monitor. If I swap the adapter from drivers to passenger, it still shows that the drivers side is high even though the adapter for the drivers side is plugged into the passenger side now.

This is the second time I've had erroneous EGT readings from my Edge monitor. The first time was because the cable going from the OBD2 port to the Edge was bad (it probably got kicked too many times), this was actually giving me the occasional canbus CEL. That's when I upgraded from the Edge CTS2 to the CTS3. I still had the EGT probe from the CTS2 and apparently it was damaged or something, because it's reading high now.
 
I should have guessed it wouldn't be so easy...

I guess I'll order a water pump and see if maybe that fixes it or if I'm just chasing my own f*cking tail.

Fan clutch still doesn't lock up, truck runs slightly cooler (probably due to the thermostats opening earlier) but the temps are still off, 150 outlet temps on the rad, 170 inlet.
 
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