Fan clutch replacement guidance and recommendations

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j_anderson

j_anderson

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Location
Fort Wayne, Indiana
1972 Dart with 318 and AC.

I am trying to track down an issue with excessive heat in the engine bay. It gets so hot in there you can't touch anything without being burned. Air cleaner, brake booster, hoses, all of it is extremely hot. The temp gauge runs right in the middle at city speeds but climbs quite a bit at sustained highway speeds. It never goes over or near the max reading on the gauge. After reading some older threads here I had a few things to check.

Radiator, Timing, AFR, fan clutch, fan shroud

Radiator - I had my OE re-cored at a local rad shop before I reassembled the car at the end of my restoration
Timing - good
AFR - Pulled a 4 of the spark plugs to make sure they looked fine and they do. I want to get an AFR gauge at some point to really see what my ratio is.
Fan clutch - I had my dad start the car up then shut it down. The fan continued to spin for 45 seconds to a minute before stopping. I read it should only spin 3-4 times then stop. Pretty sure this is at least part of the excessive under hood temp issue. Also, I'm noticing some slop in the shaft bearing. This is the original clutch. It has the coil on the face of it (assuming this means its a thermal unit?)
IMG_5043.JPG

Fan shroud - OE fan shroud is installed. Over the years it seems to have gotten deformed a bit. where it attaches on the sides, is tight against the radiator but in the center on the top and bottom there is 1/2" to 3/4" gap. This might be playing a little bit to the issue and I'll re-evaluate after fan clutch replacement

Shopping for a replacement clutch but I don't know what I need. I see regular, medium and heavy duty units. I measured the factory clutch height at 2-7/8" and I did notice 1-1/2"+ clearance to the radiator. so I think if I stick to a clutch that's 3" or less, I'll be fine.

Searching on google, I see some at $35-65 then some at $225 from vendors like classic. Does anyone have a recommendation or guidance?
Screenshot 2024-06-23 at 8.15.20 PM.png
 
Not real well versed in fan clutches, but if your heat problem is at highway speeds probably not the clutch. At those speeds and rpm it should disengage.
 
Are you sure you have the right radiator for that car? If you have the right radiator, has your engine been modified to produce more power that the radiator can handle? It sounds like the radiator is not getting enough air through it to me. Did you modify the grill?
 
ch1ll said:
Are you sure you have the right radiator for that car? If you have the right radiator, has your engine been modified to produce more power that the radiator can handle? It sounds like the radiator is not getting enough air through it to me. Did you modify the grill?
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I had my original radiator re-cored by a local shop. It's the 22" unit for V8 LA engines with AC. I have had the cylinders bored 30 over and have a mild cam installed but it's not a crazy hot rod engine by any means. The grille is a brand new factory reproduction by OER
 
j_anderson said:
I was reading this thread which made me think clutch
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That’s the idea of a fan clutch. To stop spinning at mid to high rpm’s or when you get into it, I believe. Air moving through your radiator at highway speeds should cool your coolant without a fan.
 
Did you have the block sonic checked before boring? Anything you can think of that would cause excessive friction in your engine? Does it perform the way you think it should? Hard to diagnose this without physically being there to witness it happening.

Anyway it does sound like your fan clutch is shot and needs replacement.
 
ch1ll said:
Did you have the block sonic checked before boring? Anything you can think of that would cause excessive friction in your engine? Does it perform the way you think it should? Hard to diagnose this without physically being there to witness it happening.

Anyway it does sound like your fan clutch is shot and needs replacement.
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The engine was thoroughly gone through when it was rebuilt but I am not sure if it was sonic checked. It was rebuilt back in the early 2000's, reassembled and stored in a crate in the corner of the garage until about a 18 months ago when I dropped it back into the car. After storage, drained the oil and opened the pan to look up into the cylinders. Pulled the intake off to view things from the top. All looked good. Before initial fire up, the engine was primed, rotated by hand and primed until oil was observed flowing to the top of the rockers.

Can't really think of anything that would cause excessive friction. The engine has 340 X heads on it, a 340 factory intake manifold and 340 exhaust manifolds.

I think I will start with the fan clutch but have a feeling there is more involved to the cause of the issue.
 
If there is noticib;le slop in the bearing, its going out. I'm not so sure about the spin test with thermal clutch.
Hayden /4-seasons is the main (only?) manufacture of new ones. I have vague memory that's its possible to repair them but not enough to remember where to look.

I just looked at the 2007 catalog - 1/4" movement at the tip of the fan blade is considered excessive.
Send me a PM if you can't find the catalog online. I'm sure its too big to attach.
Give me some time I should be able to find the interchange for the factroy units. I think its in a notebook or file folder.
 
All that said, the engine bays do get super hot - especially on long drives and in hot summer weather. Not being able to touch stuff is pretty normal. The radiator is dumping heat into the engine bay. The engine is dumping heat. The exhaust manifold s are dumping heat and will melt pretty much anything. manufactures spent quite a bit of effort in finding the coolest locations to place the coil (and later the ECU). Alternator is also dumping heat. One of the improvements in alternators was better heat transfer.

Clutch fan issue should show up most when the vehicle is not moving or moving slowly.
 
Here is what I posted before.
If need be I can look in my folder for clutch fan and radiator - I think thats where my notes are.
Mattax said:
Hayden 2947, Thermal drive.
View attachment 1716163536

View attachment 1716163537

edited my earlier post again.

Found this:
If my notes are correct, the Hayden catalog showed.
1968-73 340 => 2707 thermal, 17107 non-thermal, 2747 Heavy duty
1968-73 318 => 2706 thermal, 1706 non-therrmal, 2747 Heavy Duty
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Keep in mind my focus was 1967-69
 
Mattax said:
All that said, the engine bays do get super hot - especially on long drives and in hot summer weather. Not being able to touch stuff is pretty normal. The radiator is dumping heat into the engine bay. The engine is dumping heat. The exhaust manifold s are dumping heat and will melt pretty much anything. manufactures spent quite a bit of effort in finding the coolest locations to place the coil (and later the ECU). Alternator is also dumping heat. One of the improvements in alternators was better heat transfer.

Clutch fan issue should show up most when the vehicle is not moving or moving slowly.
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Yeah, I understand. My dad who's worked on these old cars since the 70's is very concerned about the heat. He says he's never worked on one where everything in the engine bay was that hot, under normal driving conditions. Mine does not seem normal.

I agree that the fan clutch is likely not the sole cause of the issue but I think it's playing a part.
This is from the info on the Hayden parts on RA.
Screenshot 2024-06-23 at 9.22.43 PM.png



but also mention this... which points more to the radiator...
Screenshot 2024-06-23 at 9.28.19 PM.png
 
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You may be able to rev up the engine in park after a good long drive & watch hose to see if it is collapsing.
 
Mike69cuda said:
You may be able to rev up the engine in park after a good long drive & watch hose to see if it is collapsing.
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Would that indicate blockage if it collapsed? If so, lift up the rear axle and put it on jackstands after a long drive to get it where you think is over temp. Maybe even take the tires off. Have someone look at the hose as you maintain 60 mph. Don’t do it too long as you won’t have any air coming through the radiator, matter of fact I wouldn’t try this till you have your fan clutch issues solved and do it carefully so your not riding a cruise Missile through the back wall of your garage.
 
Think about this;
1) A fan clutch allows the fan to turn off or slip, depending what kind it is. Thus it will not help an overheating engine even one bit.
2) saying the timing is good, is meaningless.
3) saying a factory gauge is whatever, is likewise, meaningless.
4) saying the underhood heat is excessive, is also meaningless.
5) saying you don't know if the lower hose is collapsing is not at all helpful.

Here's what you have to do.
Firstly; get an accurate temperature gauge, and,
Secondly; determine the efficiency of the system; If the coolant temp drops 30 degrees, from top to bottom at idle, then it is as good as it gets. If only 20*, then it is borderline, but you still cannot blame the rad for that. You have more diagnostic checks to perform.
 
ch1ll said:
Would that indicate blockage if it collapsed? If so, lift up the rear axle and put it on jackstands after a long drive to get it where you think is over temp. Maybe even take the tires off. Have someone look at the hose as you maintain 60 mph. Don’t do it too long as you won’t have any air coming through the radiator, matter of fact I wouldn’t try this till you have your fan clutch issues solved and do it carefully so your not riding a cruise Missile through the back wall of your garage.
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The hose collapsing probably means that it is not able to stand the pull of the water pump. That was the purpose of the spring inside hoses on some models.

I suppose that it could also be an indication of blockage in the radiator, but I would think that would show up at idle as well. Just a thought, I am not an expert.
 
Drain the coolant through a coffee filter and see if any casting sand comes out with it.
 
Generally speaking, running hot at speed is a water flow issue and running hot at slow speeds or at stops is an aif flow issue. You can throw the fan in the ditch runnin down the road at 50 plus MPH. I would be looking at the thermostat, water pump and the overall condition of the water jackets in the engine. Also as someone mentioned, the lower hose collapsing is another thing to look at. Squeeze the bottom hose when it's cold with no pressure. Does it squeeze really easily? That's the suction side of the pump and if the hose is all squishy, it's likely being sucked closed at highway speed. Make sure the thermostat is working properly. Remove it. Put it in a pan of water on the stove with a thermometer. Make sure it starts opening at or before the marked temp on it. It should be fully open by the marked temp. With the thermostat removed, this is a good time to back flush the system and see if there's a lot of crap in it. Remove the lower hose from the water pump and blast water in from the thermostat housing on the intake. The backwards flow can sometimes break junk up and it will come out the water pump inlet. If you see murky or brownish red crap, then you need to properly flush the whole system, including the radiator. Also, check the fan speed in relation to the crankshaft speed. Measure the crank pulley diameter. The water pump pulley diameter should optimally be a little smaller, allowing it to spin faster than the crank pulley. This will allow the pump to spin at an optimal speed to pump coolant out of the hot engine quickly. That's the whole ball of wax with the cooling system. To get the coolant OUT of the engine as quickly as possible and into the radiator so it does not have a chance to get too hot. This business some talk about of slowing the coolant down so it stays in the radiator is hooey. Get it OUT of the engine and into the radiator as quickly as possible.
 
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