Radiator Fan Always Engaged...

7milesout · December 3, 2018

Guys,

Sorry about my lack of formality. I searched the forums a bit, and didn't see what I need. The topic is regarding my dad's truck. He's a senior, senior citizen (yes, I put that in there twice!), and his instrument cluster is clusterized. So, I went and got his truck and brought it home to fix / repair his cluster. He lives about 145 miles from me. I brought it to my house to be able to use my tools. Turns out, it was a 10 minute job to pull the cluster, just needed a 5/32" socket (I think was the size). And the cluster is on its way to be rebuilt as I type.

Anywho - Upon driving his truck, there are a few other things I'd like to fix while I have it. So, let me provide the details of his truck. It's as basic as it gets, which is good in a lot of respects.

2003 GMC Sierra; 4.8L, Standard Cab, 2WD, automatic. 82,000 miles. Clean, stock, no mods.

The problem that annoys me, is his radiator fan stays on 100% of the time. Start up, shut down, down the interstate, cold weather. It doesn't matter. That fan is roaring. I've hand spun the fan with the engine stopped and the clutch feels fine. It spins easily, but with that fluid type resistance. And, when the engine is running, if I accelerate briskly, the engine rpm will jump right up, and the fan comes running along behind it … catching up. Which is to say, the fan is damped by the fluid so it doesn't accelerate as quick as the engine sometimes (the dampening effect), but it does catch up without much delay. The damping can be heard meaning that say I hit the throttle and it goes from 1,500 rpm to 2,500 rpm and hold it at 2,500 rpm. The fan more progressively ramps its speed up to match the rpm of the engine. So the fan clutch is doing it's thing. But the fan clutch never lets go.

Here's my theory … bare with me. This is not my truck, and this is not something I'm an expert about. My theory is that whatever signal is received by the ECM to would trigger the fan clutch to disengage, that signal is stuck telling the ECM that the coolant is VERY HOT. And therefore the fan is always sucking max air across the radiator. So, seems like it would be the coolant temp sensor. Shoot, I've got a BT connector at home and an app on my phone, I guess I could try hooking up to it. The app displays the coolant temp. If it's the coolant temp sensor, I would suspect the coolant temp to be hot from a cold start. I'll check that out. I don't know if having the cluster out is going to screw up the readings from the OBD-II or not. But the fan was roaring before I took the cluster out.

I hope this is not on the forums a thousand times. This is my first time in these forums, so I apologize if this subject has been discussed to death. His truck runs good, but you cannot hear the engine or exhaust due to the roar of the fan.

THANKS!

7milesout

diyer2 · December 3, 2018

Cooling fan controller?

https://www.rockauto.com/en/moreinfo.php?pk=4664736&cc=1415416&jsn=414

Fan clutch?

https://www.rockauto.com/en/moreinfo.php?pk=1028578&cc=1415416&jsn=426&jsn=426

A guess on my part.

Not expensive IMO to replace.

txab · December 3, 2018

You have a centrifugal fan clutch. No electronics involved. Operates on temp. of air crossing it. If you think it's bad replace it

https://www.wikihow.com/Test-a-Fan-Clutch

7milesout · December 3, 2018

As you suspect, I'm aware it's centrifugal, not electric. It seems like it is working fine. Unlocked when not cranked. But I'm not familiar with this type of fan. I don't know if the fan clutch is TOTALLY controlled by air across it, or if there is some level of electrical control. Sounds like there is NO electric control by your post (thanks).

If it IS controlled only by air temp, then yes, it must be bad. Looks like I have some learning to do as to exactly how a centrifugal fan works (what's new!). Thanks.

7milesout

diyer2 · December 3, 2018

On second thought I agree with txab.

Same fan as my old truck.

txab · December 3, 2018

There is no electronic control of an OEM fan on an '03.

ETA: LInk to plenty of reading

https://www.google.com/search?q=testing+centrifugal+fan+clutch&ie=utf-8&oe=utf-8&client=firefox-b-1

sefiroxx · December 3, 2018

Combination of air temp and resistance (can only spin so fast before blades are spun off). If spinning too fast, then at risk of full failure. . Replace

SILVER SLED · December 3, 2018

MY money is on the fan clutch.

7milesout · December 4, 2018

Fan clutch will be replaced as soon as I can get to it. I don't know this truck, is it difficult to do this? I wouldn't think so. I would imagine the fan shroud would have to be removed.

I cruised it down to my house. Because the level at which I refueled it down in my area could have varied somewhat, my interstate cruise plus just a skosh around town gave anywhere from 19.375 mpg and 20.4 mph. Sounds reasonable to me. I put it on 70 mph and cruised, no A/C, no drama, just steady cruising. Probably would have done an mpg better if it were not pushing the fan so hard.

My dad's truck looks like txab's … without the extended cab. Same color, same wheels, same 2WD.

sefiroxx · December 4, 2018

Remove shroud. Rent tool from free rental shop that allows you to hold the pulley/pump while removing the bolt that holds the fan on.

txab · December 4, 2018

Plenty of youtube videos out there too

7milesout · December 5, 2018

I've got a mechanic locally who will do this for barely more than the cost of the tool. And he does darn good work. Very thorough, very fair. I've not found any place I can rent that tool locally. And I think I'm going to get him to replace the Intermediate Steering Shaft and bearing while under the hood. That steering knocking / bumping sound and feel is annoying.

I could do these repairs, but it's a difficult thing to get around to doing, with 2 boys wrestling and killing my weekends with that … and for the fact that it's cold outside and this guy has a nice warm professional garage. And is seriously fair. He's done so much work for me, and will keep on getting my business. It's great to find stand up people like this guy.

Anywho - txab - What does your cab badge / emblem say? SLT? My dad's came off in a car wash (both sides). I'll replace them if I can find them at a reasonable cost.

Thanks.

04z71crew · December 5, 2018

Like others have stated the truck being a 2003 will come stock with a fan clutch. The repair is not very difficult at all. >>>Remove the air intake tube coming from your air filter to throttle body>>>Remove fan shroud>>>Use a large crescent wrench and a good size hammer and it will break the nut loose>>>Spin fan off>>> remove bolts and put your stock blade on your new clutch.

Based on my personal experience aftermarket flan clutches will stick and stay on at all times, I switched mine out for an original Ac Delco purchased on Amazon. Has been very quiet since.