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Discussion Starter #1
I know! Worn out subject! But this is kind of a sticky wicket. I have a '26T coupe with a 350 SBC. Started out as a stock Goodwrench engine. Has a fairly new aluminum radiator configured for a 6" chopped '32 shell. The core is 16" square. I have one just like it in my 500 HP 383 '27 T roadster with a 15" electric fan. Never goes over 180. The Goodwrench 350 in the coupe would run at about 180, but would start to climb to about 210 when waiting in a fast food line or something, but would cool right back down once it got going. It has a nice aluminum shroud, but the bottom of the shroud is not there, so only about 270 degrees. Could not fit it in. The front crossmember is there and acts like the bottom of the shroud. It has a mechanical 14.5" 6 blade fan. The fan is right against the pulley, no spacer, no clutch, and the fan is about 1" from the radiator. Running a 180 thermostat. The center of the fan is about 2" lower than the center of the radiator. so about 1-1/2" of fan is below the core. The shroud transitions down for this. I'll try to post a pic. The timing is set at 14 initial with 20 degrees of manifold vacuum advance, so idles at 34 btdc. Also 20 degrees of mechanical advance. So, 14 initial + 20 mechanical =34 total. 34 total + 20 vacuum = 54 cruise total. I know this is not ideal, but I am working on that.
That is the background. Now for the problem. I rebuilt and upgraded the Goodwrench motor. Basically raised the compression to 10:1, Promaxx aluminum heads, and Straub cam that is pretty much the roller version of the old L-79 cam. Same carb, distributor, water pump, thermostat, pulleys, fan, hoses (lower hose has a spring inside), etc. Makes probably 350 HP. I kind of expected this new engine to run a little cooler than before, but this rebuilt engine wants to run at about 185 around town and highway. Just a few degrees warmer than before. But the other day I stopped in an Arby's drive-thru and had to wait on about six or seven cars. The temp climbed to 230 before I got out of there. Ran it down the highway a couple of miles and it cooled right back down. It took 15 or 20 minutes, maybe more, to get that hot. I live in a low traffic area (the Boonies), so I can and do drive it all the time without any problems. It is actually my daily driver. The car has almost 25K miles on it. It has been that way from the start. The problem is I don't know what to do to fix it. I know that the radiator is of sufficient size because it has no problems running down the road. It has to be airflow through the radiator at idle. This happens whether the side panels and hood are on or not. So I don't think it is a matter of getting rid of the air coming through the radiator. It's not possible to put a bigger fan on it. There is only 1/4" clearance between the fan and the lower radiator hose. I don't think the idle timing of 34 degrees is doing it, but that will soon be fixed (new properly curved distributor).
I can't think of anything else to do to it. I guess I'm hoping for a magic cure. Anybody got any ideas? I'm afraid I've built myself into a corner.
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Just guessing , ( or thinking out loud) I believe its the shape/ design of your fan shroud . There's no shape/ space to create a venturi effect ??? An other thing that comes to mind , when I installed my brodix aluminum heads , they were very specific about enlarging the coolant passages in the head gaskets ....
 

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Discussion Starter #3 (Edited)
I believe its the shape/ design of your fan shroud . There's no shape/ space to create a venturi effect ???
I'm not quite sure what you are getting at here. The shroud is about 2" deep. The shape is pretty much dictated by the size of the core and the diameter of the fan. The blades of the fan are half in, half out. I don't think there is much I could do with the shape. Now the bottom of the shroud missing could be a contributing factor. I have never tried the rag in front of the radiator trick on this one. I need to do that.
when I installed my brodix aluminum heads , they were very specific about enlarging the coolant passages in the head gaskets
I have had ProComp, Dart, ProMaxx, and Profiler aluminum heads. None of them required enlarging gasket water passage holes. I have never had Brodix heads. I am interested in which holes they had you enlarge. I have never done it before. Never needed to. But it sounds like something that might help. I am sitting here looking at a used set of 1003 Felpros. You can clearly see the impressions the head and block made in the gasket. There are several areas where the gasket covers a lot of hole. I don't understand why it would be necessary to open them up in this situation, now though. I always figured the engineers restricted those holes for some good reason. But hey, I am willing to try almost anything.
Edit: I have never run it without the shroud. Maybe I should try that. The fan is close enough to the radiator that it might work. Lots of old cars didn't have shrouds. I would have to remove the radiator to remove the shroud. It's a major PITA. And would have to do it twice if it didn't work.
Don't ya just love HOTRODDING? Trying to make a modern car out of a really old one can strain engineering skills.
 

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Tie the centrifugal weights down, Test the temp at idle. The 34 degrees is way to much at idle on a street engine. At the initial of 14 degrees it should stay cooler at idle.
 

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Discussion Starter #5
Tie the centrifugal weights down, Test the temp at idle. The 34 degrees is way to much at idle on a street engine. At the initial of 14 degrees it should stay cooler at idle.
I agree. 34 is probably too much idle timing, but tying the mechanical weights down would not affect the idle timing as there is zero mechanical advance at idle. But if I disconnect and plug the vacuum advance, that would leave me with 14 at idle. I haven't tried that yet, but I will. That would at least tell me if a properly curved distributor would fix the problem. I think probably 24-26 advance at idle with vacuum advance hooked up is where it should be.
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I wish I new how to send a link , but alas.....If you google Gaskets-Brodix , there is a photo of which holes to enlarge . If there were a hoop maybe 1 1/2" wide that surrounded the fan attached to the existing shroud it might improve the fans effectiveness . I have an old friend who operated an HVAC company , he was a bit of a fan / air flo guru. The only example I can think of is go out & look at the shroud around y our a/c condenser fan ...something about the " funnel" shape makes the fan " pull" better. You can control the efficiency & sound of the fan by how much of the fan tip is in or out of the funnel/ bell . 1/2 way is usually good .
Retarded timing is normally what makes an engine run hot , not advanced , if any change is made , I'd limit the vac advance to 10 -15° , as long as it doesn't clatter & burn a piston !
 

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1949 Ford Coupe RESURRECTION
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2old2fast is correct about the "funnel effect" for want of a better description. It makes a difference, especially at low RPM/airflow. I have a quick question though. Since the fan is engine-driven what happens if you sit there in neutral and raise the RPM? When you are sitting in line waiting for your Hamburger and your fries and your chocolate malt do you just stay at idle?

I can't tell for sure from your pictures but from your description if the sides top and bottom around the radiator are not covered and if there's not much wind the air will tend to recirculate back to the front of the radiator again. Just something to think about.

I didn't see you say anything about what the ambient temperature is when your having the problem.
 

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What's the pulley ratio between crank and water pump?
Maybe you need to speed the fan up at idle.

Reducing timing at idle is likely to only make things worse...retarded timing builds heat.

I have never modified a head gasket for any head either, and have read info in several places to not open the upper row of small holes, the ones that cover the big core holes in the block deck or it will flush too much water up the intake side of the head at the expaense of the hotter exhaust side of the head.

I have modified various SBC blocks for the improved cooling hole in the deck, on the exhaust side between the two center cylinders, per the Fel-Pro instructions.

On high performance builds, especially with 400 blocks, I pipe tap and plug those big upper core holes in the deck with solid pipe plugs that then cut the heads cut off flush and the entire deck then milled cut flat in an effort to stiffen the deck.....then the small coolant path holes to match the head gasket are drilled through the plugs. Never had one of those engines overheat because of those small gasket holes....GM engineered the gasket hole sizes to be a flow director and controller. Most all companies do that, the big holes in the block are just to get the sand out, not for water flow path sizing.

Here is the Brodix info, only mod like that I've ever done is in Brodix location #2, ...but it was the block drilled to match a cooling hole Fel-Pro added to the gasket(GM added it sometime in the late 70's to all SBC blocks also).
If you ask me, the Brodix mod looks more like a 4000+ rpm race type mod more than anything, when there is plenty of water flow going on.....it is also called out as a replacement for traditional steam hole location drilling in the heads....which is a 400 only thing, not on 350" or smaller bore blocks.
So I can't so how it would apply to your GoodWrench 350.


With it cooling fine on the road, it sounds like you are just not pulling enough air through the core at idle

You could experiment, turn the idle up to 1100 rpm in gear and sit for a while after a drive, see if it still creeps up on temp.
 

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In my experience vacuum advance wants to be about 7 or 8 degrees. Maybe some body could explain why you would need/want more.

I have found to have a smaller pulley on the water pump and a larger one on the crank increases pump speed as well as fixed fan at idle.
 

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what you describe is definitely an air flow problem.
make sure any air cannot flow around the radiator instead of thru it. the picture helps but it looks like maybe the shroud
opening is to big ? 1/2" from the blade is the most there should be. also the fan is at it`s best half in like you have stated.
as someone else mentioned, be sure the air is also leaving the engine bay instead of circling back.
you may need a different fan ( more aggressive ) or as stated a smaller pulley for your set up.
 

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Discussion Starter #11
I hadn't thought about changing WP/crank ratios. The lower pulley is the 6.75" pulley. Same size as the HB. The WP pulley is about the same. So 1:1. I would have to get a smaller WP pulley to speed it up. I'm not sure if there is a smaller diameter WP pulley available, is there? Most people want to slow the pump. My 383 has a 5.5" crank pulley with a 6.75" WP pulley w/ same radiator with centered 15" electric fan. Stays 180. I can run down the road with no fan on most of the time.
I'm starting to think that the misalignment of center of fan to center of radiator core is the culprit here. Fan center is 2" lower than core center. About 1-1/2" of fan is below the core. When building the car I thought this would not be an issue. Apparently I was wrong. I think the small size of the core, 16"x16", and the small 14-1/2" fan make that placement more critical than I figured on. I'm guessing I'm losing 10-15% fan efficiency or so there. Maybe just enough. The only way to remedy the misalignment is to lower the radiator. That would be no problem if it wasn't sitting1/8" above the front crossmember. Of course the front crossmember has the leaf spring mount and the panhard bar mount welded to it along with front shock mounts. So in order to fix this the sparks are going to have to fly for some really major surgery. I'm not a fan.
 

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I don't believe the fan being off center has anything to do with it. It looks like from your picture that tips of the fan to that sharp edge of your shroud is it least an inch maybe more. A LOT of air is slung out by centrifugal aerodynamics from the tips of any blade fan, and a lot of it never even gets out of the shroud without the vacuuming effect of having a "funnel effect" caused by having a "sleeve" to minimize that effect. Spend 60 bucks and get this---(keep the pan to reheat your French fries..hahaha)

 

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Discussion Starter #14
I don't believe the fan being off center has anything to do with it. It looks like from your picture that tips of the fan to that sharp edge of your shroud is it least an inch maybe more. A LOT of air is slung out by centrifugal aerodynamics from the tips of any blade fan, and a lot of it never even gets out of the shroud without the vacuuming effect of having a "funnel effect" caused by having a "sleeve" to minimize that effect. Spend 60 bucks and get this---(keep the pan to reheat your French fries..hahaha)

For some reason the pic's are making the gap look bigger. It is 3/4". That shroud you show would need a lot of modifying to work in this car. I am capable of making my own. The sleeve you speak of is interesting, but this shroud is only 2" from the radiator to 1/2 in 1/2 out, so a sleeve of any width is pretty tough to get in there without being too close to the radiator or swallowing the fan. Would a sleeve of 1/2"-3/4" create this effect?
 

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I'll mention this even though its probably not the problem , you could get a combustion gas test strip on the outside chance there's a leak problem . Other than that , a strip of aluminum & some self tapping screws might be worth the time to experiment . I really don't feel the diameter of the fan is the problem . IMO 3/4" could be all the difference needed . worth a shot. The aluminum ( expensive) duct tape would hold a test ring long enough to see if it works . you could always strap it for more security ..
 

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Discussion Starter #16
with a 16" radiator you should be running a 15" or 16" diameter fan for maximum air flow.
I agree. I had a 15" fan in it. I hit a deer. Had to replace the radiator. New radiator (same part number!) had the lower hose outlet moved inboard slightly. I had to shorten my fan from 15" to 14.5" to miss it. I hated doing it but it was the only solution. This was several thousand miles ago and didn't seem to have any effect one way or the other.
 

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I think you might have missed the concept. As you can see this sleeve is adjustable to various diameters and the little angle brackets are secured to the shroud and to the sleeve such that this sleeve is entirely outside and away from the radiator.
 

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You need to close the bottom of the shroud, it has to be air tight from the bottom of the radiator to the fan. That goes for all the way around the radiator so air trying to get to the fan face is forced to go through the core, it doesn’t take much leakage before there is more air leaking around the core than through it. The core presents an obstruction to air flow so the fan will pull it from the source of least resistance. Remember that air is compressible which means it changes density with pressure and temperatures to a very large extent so you cannot think of it as a liquid in terms of how it can flow.

The sharp edge of the shroud is probably not helping a lot either. A rolled edge will improve the exit flow. Later model GM fans use a hoop around and connected to the blades, as with winglets on modern aircraft wings this hoop catches the flow slipping lengthwise in the fan blade forcing the flow to exit the back face of the fan rather than building pressure and creating turbulence inside the shroud. Mig 15 classic case of this, they used very large fences to redirect the air flow across the wing instead of along it.

Bogie
 

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Discussion Starter #19
You need to close the bottom of the shroud, it has to be air tight from the bottom of the radiator to the fan. That goes for all the way around the radiator so air trying to get to the fan face is forced to go through the core, it doesn’t take much leakage before there is more air leaking around the core than through it. The core presents an obstruction to air flow so the fan will pull it from the source of least resistance. Remember that air is compressible which means it changes density with pressure and temperatures to a very large extent so you cannot think of it as a liquid in terms of how it can flow.

The sharp edge of the shroud is probably not helping a lot either. A rolled edge will improve the exit flow. Later model GM fans use a hoop around and connected to the blades, as with winglets on modern aircraft wings this hoop catches the flow slipping lengthwise in the fan blade forcing the flow to exit the back face of the fan rather than building pressure and creating turbulence inside the shroud. Mig 15 classic case of this, they used very large fences to redirect the air flow across the wing instead of along it.

Bogie
Yes, I have agonized over the bottom of that shroud since I built the car 5 years ago. I built the shroud the full 360 degrees, but couldn't install it with the bottom on. Its really tight in that area. I have it on the lift tonight and have spent an hour sitting under it trying to figure out how to close the bottom off. I don't have a good solution yet. As far as an inner sleeve in the shroud around the fan, that shouldn't be too hard to pull off with a narrow sleeve except of course at the bottom. I'll have to come up with something.
Thanks guys. I have a few things to work on, now.
 

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I run 50" to 75% of the fan blades hidden inside the shroud depending on how much leaning over the shroud I will be doing.

Pretty easy to test this. Grab a piece of aluminum, cut it down to say 2" or so tack it into a circle and tape/screw or tack it to the flat part of the shroud, then watch your temps during a test drive.
 
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