New Fan and Thremal Clutch Advice

[kelz702]

Hello all!
I have a 72 c20 350/350. I'm having a bit of an over heating issue. Temp fluctuates in traffic but stays cool on the freeway. I'm looking to stabilize the temp by adding a 7 blade fan and thermal fan clutch. I've done a lot of searching but can find anything definitive.
One obvious problem is how far the fan sits in the shroud due to the long water pump. I was hoping somone could tell me if I would be able to bring the fan closer to the motor by adding a fan clutch with a shorter shaft. And if so, how to go about searching for one. Another problem is the clearance on the outside of the fan shroud. The alternator is set pretty close to the opening.
Please let me know if there is any other information you need to to help me with this situation.
Thanks in advance!
Kelz

[kelz702]

A couple more pictures. Not sure what they are sideways. I'll try to fix that

[kelz702]

..

[Toms67]

I see what you mean about the fan being too far in The shroud. The air is probably cavitating. I wonder if you were to run it with the shroud off Just for the heck of it. If it isn't too much trouble. Just to see what happens? I know my 67 doesn't have a shroud. But I had a six in it.

[kelz702]

Originally Posted by Toms67

I see what you mean about the fan being too far in The shroud. The air is probably cavitating. I wonder if you were to run it with the shroud off Just for the heck of it. If it isn't too much trouble. Just to see what happens? I know my 67 doesn't have a shroud. But I had a six in it.

I would try but it's a pain to get that shroud on and off. Hopefully next time it comes off It will be for a permanent fix. LOL

[67 chevelle]

You can get the fan an inch or inch and a half closer to motor by removing the spacer [if that is a spacer] between it and the fan pulley , just get shorter bolts

[kelz702]

Originally Posted by 67 chevelle

You can get the fan an inch or inch and a half closer to motor by removing the spacer [if that is a spacer] between it and the fan pulley , just get shorter bolts

That was my first thought. If I remember correctly, when I had it off a few years ago, it was attached to the fan. If I use it, I'll have to remove the flex fan from the spacer, cut an inch and a half off and put it back together. That might work but it will be a last case scenario. I would really like to upgrade to a fan clutch.

[Stocker]

Living in Vegas, you're gonna need all the advantage you can get. That long water pump may make it difficult -- maybe impossible -- to get a fan to sit properly in the shroud. But it doesn't have to be perfectly centered.... close will work. FWIW, my clutch fan mounting surface is 1 1/2" to the water pump pulley. Can't tell how far your fan sits from the pulley -- maybe 2"? -- so you might gain a little going to a clutch fan.

I think at least part of your overheating problem is caused by my sworn enemy, a flex fan. The only time my K20 ever ran hot was when my fan clutch failed and I temporarily ran a flex fan. Some people get by with them but IMHO they just don't cool very well. And there's that little issue of them sometimes exploding....

I would ditch it and get a good heavy duty (not a standard) fan clutch with at least a 6-blade fan. My OEM fan is 7-blade which I prefer, but they are probably harder to find. There are threads here about how to identify the different types of fan clutches. When I have a little more time I'll look it up for you. Right now I'm in the middle of installing a radiator, had to take a coffee break.

[weq92f]

No shroud here with straight fan right up against rad. So far so good.

[kelz702]

Originally Posted by Stocker

Living in Vegas, you're gonna need all the advantage you can get. That long water pump may make it difficult -- maybe impossible -- to get a fan to sit properly in the shroud. But it doesn't have to be perfectly centered.... close will work. FWIW, my clutch fan mounting surface is 1 1/2" to the water pump pulley. Can't tell how far your fan sits from the pulley -- maybe 2"? -- so you might gain a little going to a clutch fan.

I think at least part of your overheating problem is caused by my sworn enemy, a flex fan. The only time my K20 ever ran hot was when my fan clutch failed and I temporarily ran a flex fan. Some people get by with them but IMHO they just don't cool very well. And there's that little issue of them sometimes exploding....

I would ditch it and get a good heavy duty (not a standard) fan clutch with at least a 6-blade fan. My OEM fan is 7-blade which I prefer, but they are probably harder to find. There are threads here about how to identify the different types of fan clutches. When I have a little more time I'll look it up for you. Right now I'm in the middle of installing a radiator, had to take a coffee break.

Yes, a properly working cooling system is imperative to living a desert where the summers reach 115°.
My mounting surface is 2" from the pulley. I will take anything I can gain. Do you have the part number for the clutch you're using? As far as the 7 blade fan goes, I'm confident I'll be able to locate one in town. I'll just have to do a little searching.
The long water pump was a huge mistake and has cause all kinds of headaches. Unfortunately, I'm stuck with it now.
The rest of the cooling system is new. I replace the the radiator last summer with a new 4row brass and the thermostat is new. It might be something else but I'm pretty sure this flex fan is the problem

[Stocker]

The one I bought is NAPA p/n 271303, fan clutch #2747. Made by Four Seasons in Lewisville, Texas.

If you're interested in more info about fan clutches, I found this site helpful: http://www.haydenauto.com/featured%2...s/content.aspx

[sKnNyPpY]

I have a long water pump (72 4x4 350 in a 71 2wd GMC) and had a disintegrating flex fan and spacer and cobbled together fan shroud that I replaced with a clutch and solid 6 blade fan from Advance auto and an A/C shroud (not as deep) from USA 1 Industries. I had to trim about an inch and a half off the lower half of the shroud to get it all in but cooling is MUCH improved and I don't have to worry about a flex fan blade blowing through the hood or engine bay. DO IT! Your shroud looks great, it might need to be trimmed to get everything back in with it already in the truck. I had to trim the shroud, assemble the fan and clutch, insert it into the shroud and drop it in place, mount fan, then attach shroud.

[kelz702]

Originally Posted by Stocker

The one I bought is NAPA p/n 271303, fan clutch #2747. Made by Four Seasons in Lewisville, Texas.

If you're interested in more info about fan clutches, I found this site helpful: http://www.haydenauto.com/featured%2...s/content.aspx

I came across that lastnight while I was reading. I've been reading about fans and clutches for days now. LoL. I'm going on vacation for a week so I'll have plenty of time to track down parts. Thanks to everyone for the replies. If anyone else has any info that they think might help, please don't hesitate to reply.

[paul blair]

Is the fan on backwards?

[kelz702]

Originally Posted by sKnNyPpY

I have a long water pump (72 4x4 350 in a 71 2wd GMC) and had a disintegrating flex fan and spacer and cobbled together fan shroud that I replaced with a clutch and solid 6 blade fan from Advance auto and an A/C shroud (not as deep) from USA 1 Industries. I had to trim about an inch and a half off the lower half of the shroud to get it all in but cooling is MUCH improved and I don't have to worry about a flex fan blade blowing through the hood or engine bay. DO IT! Your shroud looks great, it might need to be trimmed to get everything back in with it already in the truck. I had to trim the shroud, assemble the fan and clutch, insert it into the shroud and drop it in place, mount fan, then attach shroud.

If I'm unable to locate a 7 blade fan, I'll be getting that 6 blade fan and clutch from Advanced Auto. Im able to get it all in there without cutting the shroud. It's just a major pain.

[kelz702]

Originally Posted by paul blair

Is the fan on backwards?

LoL, I just ran out to check. It's not on backwards. It's pulling air threw through radiator to the motor. I wish it would have been that easy...

[tdangle]

I like running a thermal clutch with fan also, with a fixed fan or flex fan the fan is really noisy. With the thermal clutch fan setup, it is like my truck had an additional gear to shift into on the hwy. the fan (my clutch fan was frozen) made it sound like I was driving 100 MPH at 50.

[kelz702]

Update:
I ended up buying a Short Shaft Fan Clutch https://m.summitracing.com/parts/hda-2947/overview/ and 6 blade fan from Summit. The fan clutch brought the fan about an inch and a half closer to the motor. It's still not sitting where I'd like it but it will have to do. The temp gauge reads cooler for the most part. Occasionally the needle spikes but not as often. I was still concerned so I ran to Home Depot and picked up a inferred temp gun. Right below the thermostat housing reads 180°, sides of radiator reads 180° and the spot in the intake where the sending unit is reads 180°-190°. I'm pretty sure in in the clear. Thanks everyone for the advice.

[kelz702]

Sorry for the pics. I don't know why they post upside down and sideways

[Stocker]

Looks great, and thank you for the update! I never knew they made a short-shaft clutch. The blades appear to be well within the 'neck' (for lack of a better term) of the shroud, right where they need to be. Good fan and a good heavy-duty Hayden clutch unit -- you should be ready for those long hot Vegas summers!