The Stovebolt Site Forums The Shop Area Engine Shop Overheating problem - have a shroud example?

Hi,

I have a 1940 1/2 ton with a mid-50s 235 with shortened water pump shaft (I think). I'm about to flush the cooling, check the temp valve, examine crank pulley diameter, etc. but does anyone have an example picture of a shroud that might fit a '40 with a non-stock fan placement.

thanks,

Doug

You'll probably have to fabricate a shroud to fit your specific application.
Some things to consider:
(1) use the pulley approx. 6"-7" diameter for the 55-62 (235) pump. The 54 and earlier pulley is too small and turns too fast causing cavitation.
(2) use a 55-62 (235) fan blade. There is more pitch to the blades and pulls more air thru the radiator.
(3) use a 180 degree thermostat.

We used to make shrouds when we still used old trucks as trucks back in the 50's. We took a piece of 14 gauge the size of the radiator and mounted it with the radiator bolts. Then cut a round hole a little larger than the fan and then made a hoop out of 1 " flat and welded it around the hole. Not the prettiest in the world, but it kept our old GMCs cool in the Texas heat.

Thanks for the all the great suggestions - I'll let you know how it tuns out.

Another question: From other posts, It sounds like running lean is another potential cause for overheating. When I disconnect the fuel line right by the carburetor and crank the engine, there is only a trickle of gas. Should it be shooting out like a faucet?

- Doug

I have used aluminum cookie sheets, fiber glass, ABS plastic, and of-course templates of cardboard and duct tape to make shrouds.

Doubt if you will find one off the shelf, however they are easy to make. Come to the middle of the blades, get as close to the od of the fan as posible (without hitting)

Strips cut from an old bicycle inner tube make a great gasket for metal sheets that don't quite seal up, prevents chafing squeaks & rattles. Pop-rivets with a small washer holds it pretty well.
This is also a good time to examine the radiator/bulkhead area for air leaks - all air must go through the radiator core, so plug all extra access, wiring pass-throughs, lights not used, bolt holes etc. The hood must seal to the radiator support top when closed.

Thanks guys for the good thoughts. I think I'll go the 14 gauge route with inner tube gaskets and rivets or welding. Sealing up ALL the holes may be a bit tricky. The fan on the 235 sits really low - the very bottom of the blades swing below the radiator so the rim of the shroud fan whole will not even be able to go entirely around the fan... (see image)

http://picasaweb.google.com/lh/photo/oMzSpp2lMxrxUGUVPaJhzw?feat=directlink

A 235 in a '40 sounds like a pretty common occurrence so I'm guessing that even a partial shroud will make some improvement. I see there are short shaft water pumps and water pump offset adapters (which I believe requires moving the radiator forward?)

Shrouding what I have is the most preferred option. Does anybody have any strong feelings about the other potential options?

Warmly yours,

Doug

Doug, It looks like you have the exact setup I have in my 46. I'm not using a shroud and don't have a problem with overheating as long as I'm moving. When I'm just sitting the temp gage will go up into the red zone but I've never had it boil over.

I have made some modifications to my raditor also. My radiator guy welded up the stock overflow outlet that comes off the top-center of the raditor and put on a modern neck so I can use a pressure type cap. The new overflow hose comes off the neck just like a modern vehicle. One thing to remember if you go this route is to use a 7lb MAX cap. The seams in the raditor won't handle any more than that. I'm running a 7lb now but I think I'm going to change over to a 5lb just to be on the safe side.

This set up will let you run a little hotter than having a atmosphere over flow.

Keep up informed on how you doing with your shroud. I have thought about adding one to my truck but I just haven't done it yet. I'll be interested to see how you do yours.

George

You have a lot of radiator with no air flow from the looks of the picture. A shroud should help a lot. Also keep a 50/50 coolant mix. It is not the heat that hurts them but the boiling. 50/50 raises your boiling point a lot.

From the picture I note a couple things that need to be addressed. First of all, the pump is centered low on the radiator, the "short pump" pulley is not going to give you the proper pump rotation speed and the fan isn't helping your over-heating situation.

Having been faced with the same issues with my AD truck I used an adaptor plate and an "early" 216-235 waterpump to raise the fan up to draw air through the top of the radiator. I tried a pricy "short pump" and it gave me fan/radiator clearance but did nothing to improve cooling. The adaptor plate, which is available from one of the members of this forum as well as on Ebay, moves the pump up where it draws air through the top of the radiator which is where the hot water enters. The "early" pump has the correct pulley size (in both fan belt widths) and was available at a local NAPA. In addition, moving the pump up lets you run a 15" 6 blade fan (Summit FLX-1615P@$25.95)if you want. The center fan mounting hole has to be opened up to mount on the early pump snout. This is easily accomplished by scribing the correct hole diameter and working it with a rat-tail file. By moving the pump/fan up you also gain extra fan clearance from the generator/alternator/harmonic balancer pulleys.

Even if you did fabricate a shroud the low fan position and incorrect pulley size will not cure your overheating issues. Using the adaptor plate ($40.00) is the most common fix. I have a number of pictures in my Webshots albums that illustrate the installation process which is accomplished with hand tools with the engine in the truck with front sheet metal installed. My truck with A/C operates at thermostat temperature even with extended periods of idling, even with ambient air temps between 90-100 degrees F. In addition, if you use the 7 lb cap and fill the radiator only to the top of the core you will leave enough expansion space so you don't have to concern yourself with boiling over. I hope this helps you solve your cooling issues.

Dave

Hey Doug,
I'm thinking the overheating is from another source. I run a 235 in my '40 and never had much of a problem with overheating even with the short-shaft pump. I would suspect something in the radiator system - plugged radiator, bad pump, collapsed hoses. Or, a problem with timing. If it has recently been rebuilt perhaps the crank and cam are not phased correctly. Just a thought. Hope you find it.

Doug,

Since I make my living working with cooling systems for 105 and 125F ambient conditions, I can tell you one thing. a fan sitting in space like that does a really good job of making an air donut due to recirculation. you can check this out with cans of aerosol smoke (or a holloween fog machine) The air is brought through the fan, goes around the blades and comes back through the fan - not really making much of an effort to pull through the radiator. Therefor you will get almost the same cooling if you took the fan in the picture and nailed it to a wall. (I ran the Durango for 2 months without a fan - relying solely on highway air flow.) It provides marginal air flow at idle, however is not helping at all above 15-20 mph.

14 gauge is 0.078. that is extremely thick for a fan shroud. It is also the thickness of material that RangeRover uses on their frames. you need nothing thicker than 20 gauge in either aluminum or steel.

the reason why George has cooling when he is moving is because there is airflow when the truck is moving and not when its is idling.

There are many rules of thumb when it comes to radiator cooling systems:
Rule #1 - Fan diameter to radiator face diameter ratio. The Fan diameter should be no less than 85% of the width of the radiator. The bigger the better without overhanging more than 5%
Rule #2 - Fan spacing from radiator should be no less than 1/2 the diameter of the fan hub away.
Rule #3 - Use a box shroud as a minimum, Lip or venturi shroud preferred.
Rule #4 - Fan tip clearance at absolute minimum to prevent recirculation
Rule #5 - Airspeed through the radiator should be between 8 and 15 ft/sec. (it should be able to hold a half empty cereal box on the radiator face just due to air flow)
Rule #6 - Fan speed is dependent on fan profile, number of blades and diameter to get the desired air flow.
Rule #7 - Recirculation is bad.
Rule #8 - The fan is no longer helping above 25mph.

Just as a general comment, automotive systems are not designed to cool 100% of the heat that the engine is capable of producing. This is because they are sized on the average duty cycle for a road going vehicle which is 10% power at idle for 10% of the time, 90% power for acceleration at 5% of the time, etc (each manufacturer has their own duty cycle profile). The other end of the spectrum is Logging equipment and garbage compactors that expect 50% fouling of the radiator at 100% load 100% of the time. The Military falls just short of that, however has the uphill grade requirement (must cool fully loaded at top speed while traveling uphill at X% grade at 125+F ambient)

Assuming that your engine is in good tune (ignition timing and fueling can seriously increase the amount of heat generated at idle when there is no fan air flow), the radiator is not fouled - a simple box fan shroud with a 1" lip around the fan opening will do wonders. If your running a 18" fan, the hole should be between 19" and 19.5" max (assuming soft isomounts allowing between 3/8" and 5/8" movement in each direction)

The box should end at 1/3 of the fan profile, with the lip extending to the 2/3 mark. Simple adhesive backed foam works well to seal gaps between the shroud and the radiator.


Hope this helps.

Scott

Hey Scott,

Thank you for the very detailed points - it is really helpful! I agree about the 14 gauge. I went to get some and was surprised by its thickness (and its a bit thick for home shop working. I have so far reverse flushed the engine and radiator, checked the thermostat (actually installed one - there was none in there), and gotten as far as a cardboard shroud prototype.

The truck still overheats in a short short 1 mile stop and go (city) distance (with 60 degree weather), so I am starting to thing airflow, timing, and fuel issues may all be at play.

In your opinion, is the low fan position and the subsequent partial only shroud condition an alarming cause for concern or do you think it might me workable? (it definitely reduces the percentage of radiator area covered by the fan.)

see picture here:
http://picasaweb.google.com/lh/photo/oMzSpp2lMxrxUGUVPaJhzw?feat=directlink

Thanks again,
- Doug

I have never done this but you might consider having the radiator flow tested. It might be gunked up even after flushing. The lower position of the fan would not be enough to cause significant problems, especially at 60 degree temp. Mine idled all day at that temp without boiling over. Granted the shroud is a better way to go but does not come into play at these temps. I think something else is getting in your way first. Do you see the water swirling in the radiator when the thermostat opens up?

Thanks Dennis - That's interesting I should check that out. I have not looked in the radiator when the thermostat opens. I do know that when I pour water in, it takes a while to "percolate" down into the radiator - I'll have to stop after a half gallon while the water seeps in then I can continue. What does would swirling indicate? Is that because the water has few places to pass to the lower radiator?

- Doug

I have a 57 235 in my 37 and when I first put it togather I used the short pump with the 216 pulley but there was no room for the fan so I put a electric fan in front of the radiator and it did not over heat,it was not a original radiator but a custom made 4 row with the original tanks. It did not have a working temp gauge at that time but some times I would hear gurgling in the radiator when shutting it off after it was driven hard and got me thinking about one with a correct sized pulley,the shortened water pump broke and went into the radiator so I installed the adapter and used a 54 water pump and got a stock fan on it and while I was doing that found a NOS temp gauge and it does not go over 180 and this is with a non pressurized system. I also found a original shroud of a big truck and installed it but I dont think I really needed it but it was available so I got it.

The factory shroud off the big trucks may be a good start already has the 18" diameter center for the 216/235 fans. I have sold three this year for around 40-60 a pop on EBay here are a couple pictures and the last description from the one I recently sold.
This is an original fan shroud for Chevrolet trucks. It bolts to to the 6-radiator attachment bolts. These carry part #3705063 and are suitable for all models of truck except the 5000 series COE. These make a significant cooling difference in a stock motored street/show truck of about 10 deg. Best thing is they are factory so period and points correct.
http://good-times.webshots.com/photo/2705488650102454676sLCmCA
http://good-times.webshots.com/photo/2673348600102454676qtmVHy

The shroud probably wont work with the fan being too low with the 55 to 62 motor,he needs to get the adapter and put on the earlier water pump or go with a electric fan. I am glad I went the adapter route with my 37 as the engine compartment looks more correct with the fan in the right spot.

the lack of a thermostat may say something about a pre-existing prob
what about airflow through the rad? can you see daylight through it? if not, it may need washed

Lots of daylight is visible, looks pretty clean. I do know that when I pour water in, it takes a while to "percolate" down into the radiator - I'll have to stop after a half gallon while the water "seeps in" then I can continue.

Is this the way its supposed to be? (I'm thinking of having my radiator checked out)

- doug

rads can 'seep', but indicative of a problem would be determined by how long the seep is; seconds? minutes?

you should be able to fill the system at about 3 gallons per minute with a perfectly clean

It sounds like I would have the radiator checked by a local shop if it is only "trickling" in.

No thermostat would cause the coolant to flow too quickly, make sure you have a thermostat. Is the pump actually pumping?

Stop and go traffic = no air flow if your fan isnt moving air.

Have you tried at least a piece of cardboard in front of the radiator to check airflow? A good system will hold a half empty box of cheerios in place (or a 3/8" thick magazine). A bad system wont hold up a piece of cardboard. If it cant hold a piece of paper, there is no appreciable air flow.

Scott,

Thanks for the down and dirty garage test. (the cereal box test is my favorite). I did the test quickly...

Cardboard yes, magazine and cereal box no. I will concentrate first and foremost on getting more air moving through the radiator.

Thanks,

Doug

Good advice Scott, gonna add that to my reference files however I do have a few questions running across my mind when I try to picture this.
1. Easiest one first; Where can you get canned smoke? I can probably find that myself by Googling it but I’m to busy asking questions.

2. What is a “Lip or Venturi shroud”? I can picture a box shroud and I assume the venturi looks like the factory shrouds which transition from a square or rectangle into the round shape surrounding the blade right, but what is a Lip shroud?

3. “no less than 1/2 the diameter of the fan hub away” that would be a pretty large distance for an auto or truck, wouldn’t it? The fan hub diameter on my 6 blade fan is about 3 1/2” and I would have to move the radiator forward a bunch to satisfy that.

4. By a 1” lip I assume you mean that the opening should be flared with a 1” leg on the lip? I take it that this is to help kill the tip losses where the high and low pressure tends to spill out with an open un-shrouded blade?

5. My 6 blade fan profile is 1 3/4”. I’ll round the decimals out here to the closest fraction because we are working with sheet metal. In this case your saying that the back of the box (assuming you are using a box shroud) should be about 9/16” behind the front of the blade leading edge, with the lip extending back another 1” thus ending it at 1 9/16” behind the leading edge of the blade. This only leaves 3/16” of the blade profile behind the lip on this particular blade. This violates the rule ending the lip 2/3 at of the blade profile, which would be at station 1 5/32”. Where would you make your adjustment, by moving the shroud to comply with the back of the box, at the end of the lip or the 1” length of the lip???

And I would think even 20ga would be way heavy, I would think something like 24 or 26ga. would be more in the ballpark for a shroud of this size.

Pain in the ars aren’t I!
Denny Graham
Sandwich, IL

A simple test to determine if a radiator is clogged up can be done with nothing more than the palm of your hand. After the engine has been run until your temps are up....SHUT IT DOWN and with the palm of your hand (or better yet an infrared thermometer) run it over the surface of the radiator core searching for spotty COOLER areas which will indicate areas that are clogged. Naturally, the top of the radiator should be evenly hot with even, cooler temps as you progress lower towards the return hose at the bottom. The clogged areas will be obvious. The core should be progressively cooler as you move down with no "cold" spots. Having a clean radiator is going to give you the proper potential for circulation. Once you get the radiator working efficiently, I'd make it a point to run a 12" heavy wire up inside the block at the block drain hole just in front of the oil pressure sender port. This passage, which opens up to the water jacket is often clogged solid with crud. You may even need to use an awl and hammer to break through the hardened crud. Running a hose into the open thermostat housing will commonly flush out a quantity of sludge that is restricting normal water circulation. On an engine that is torn down, even after being hot tanked, this passage can/will remain plugged. Removing the freeze-plug adjacent to this little port will also let you break up the hardened sludge that is causing hot spots in your block.

However, the only true way to correct your overheating woes is to use the adaptor plate and early pump to correct the misplacement of the fan and the incorrect fan rotation speed. Applying "band-aids" and "hoping" is just a waste of time and energy. The 216/235 does not need a shroud....if the fan is positioned to draw air across the top 1/3 of the radiator and the pump rotational speed is correct, as I mentioned in my earlier post. Taking the initiative to make the correct fix is going to solve the problem......the band-aids are just going to prolong the issue and detract from the fun you'll experience driving your truck without keeping an eagle-eye on the temp gauge.

Dave



However,

I've never had a problem with over heating in the three summers that I've had my stock '50 truck on the road. One of the first things on the list was a good clean cooling system. Block and head well flushed actually they were chemically dipped in a hot tank, had the radiators gone over by a competent local radiator shop. A new pump, (not rebuilt) new hoses with the wire supports on place, new 180°stat. In fact, she’s a beauty when it comes to staying cool. I’ve sat in heavy dead stopped traffic in the hottest Midwest weather and the needle just came up a tad.
But that doesn't mean that I'm not interested in getting the maximum cooling that the stock system is capable of. The vast majority of the new vehicles wear a cooling shroud and it only makes sense that a shroud would give you much better cooling at low speeds. These were stock on the big haulers back in the day and I don’t doubt that they were installed on a lot of the Advance Design light duty trucks after delivery where the vehicle was restricted to low speed travel, such as heavy city stop and go use.
It’s just common sense that air flowing across 100% of the core is a better deal than the 67% that gets pulled across by an 18” fan blade.
A good clean well maintained cooling system is essential to keeping the needle at the 180° mark but it sure wouldn’t hurt to have a little extra when you’re stuck in traffic in downtown Metropolis on a 110° summer afternoon.
Denny Graham
Sandwich, IL

Denny,

1.) Not sure where the test guys got the canned smoke. It came in an aerosol can. It was actually fine talcum powder with a CO2 propellant. I think McMaster would be a good start. We used a walmart fog machine (holloween thing) while in the shop because it lasted much longer than the cans did.

2.) A lip is a single ring around the round opening in the shroud. A box shroud is simply a plate with 4 bent sides going towards the radiator and a hole in it for the fan. A venturi is the rounded edge (found on most Class 4-Class 8 trucks) as well as high dollar mobile equipment. (the low end stuff gets brake-press formed box shrouds).

3.) with a 3.5" hub (should be counted to the point where the blades start their profile) you would be a minimum of 1.75" away. For bigger fans, I had hubs from 6" on small diesels to 2' on large diesels. Air likes to move in as straight a path as possible. It generally wont turn more than 90 degrees without turning vanes to help it, so assume a perfect 90 degree cone covering the hub with the point at the radiator. The height of the cone would be 1/2 the diameter of the hub. You can run it closer, however it leaves a dead air spot in the middle where the hub is.

4.)yes.

5.)it is a rule of thumb, and it usually is where the box portion of the shroud is. The lip simply reduces tip losses. The rule is more for a box shroud (back of box you mentioned) - puller, 1/3", for a pusher 2/3 in. I did a test once with the launch of the 644e / 944e Lull's where we had 6 different fan spacer combinations and 4 shroud lip lengths. This rule requirement diminishes as the tip clearance is minimized and as the lip length gets longer. However for fans under 24", 1" is a simple lip length to keep. I wouldnt go less than 1/2" on an 18" diameter fan.

20 gauge aluminum works well, can be bent on the edge of the workbench with a rubber mallet and can be riveted easily.


Dave for what its worth. spinning a fan faster robs much more power than spinning a properly designed fan slower. It also makes more noise. Going back to the comment that fan speed is a function of fan blade design. Having discussed fan profiles with the folks at Multi-Wing and GT fans for years, to determine a fan speed, I need to know the radiator pressure drop and fan stall points.

Hi All,

Well the cooling initiative goes on...
Based on Scott's and others suggestion that a shroud may contribute to better cooling, for about $15 and a few hours I made a quick shroud ("lip") out of sheet aluminum. With my low fan placement I made the most complete shroud I could. Result: On a beautiful 50 degree fall day I still overheat in a mile or two. :-(

Dave and Jeff: It's not that I didn't believe you when you said I needed to move the fan up...its just that I was a little intimidated by the process of drilling & taping the block to accommodate the adapter plate. I'm not really set up for that kind of thing. I have another concern - the current fan clearance between the timing wheel and the radiator is really tight (1/8" from the flywheel, 1/4" from the radiator. Picture here if you are interested: http://picasaweb.google.com/lh/photo/ZcxPoQ0W5ARoJwaTW4yKQw?feat=directlink ). I assume the adapter plate adds about 1/4" to the length of the fan shaft assembly. Have any thoughts on what to do about this?

I think my next step will be to get the radiator checked out. However, when I drain it, it seems to accept water at almost 3 gal. per minute or so - which seems acceptable. I'll look for cool patches first.

I should also check out the timing as Dennis suggested since I believe the engine had some work done on it before I purchased it. I haven't played with a cars timing on 30 years but I still have my old timing light.

Dennis: You have a similar "low fan" in your 235/1940 - What type of fan do you have and do you have similar clearances to those that I have (see picture)?

Thanks to all for this great discussion.

Doug

if anyone is interested, here are some pictures of my shroud:
http://picasaweb.google.com/lh/photo/XtDbCoRYzPCAW2eNSqUQ8A?feat=directlink
http://picasaweb.google.com/lh/photo/s5NcxJKvJ8kxppsMrploiA?feat=directlink
http://picasaweb.google.com/lh/photo/1emxXOtsOfxrCXiYBgNkjg?feat=directlink

If you put the adapter on its best with the motor out or the front sheetmetal off,I dont think the adapter puts the water pump closer to the fan since the 37 to 54 water pump have a plate on the rear of it and its removed and the adapter takes its place.

The shroud looks good, tip clearance is a bit more than I would have done, however it should improve air flow. There are three things in a cooling system. Air Flow, Coolant Flow, Surface Area.

your shroud will have helped the air flow.

Having the radiator checked will verify the surface area. If you find a blockage, may correct coolant flow. If not, you have something amiss with the water pump or engine itself.

The fact that the engine is overheating within 1-2 miles has me concerned. Running a vehicle without a water pump turning would allow you to do that before the coolant temp increased enough to boil. (My Sister-in-law's personal best is 6 miles down the road before the engine overheated due to a broken a belt).

Are you sure the water pump you have is good? Is the thermostat working properly?

you can buy 'canned' smoke from just about any ac/heating supply house. typically in the form of a small stick of dynamite, fuse and all

i have a 1960 235 bored .080 over in my 2 ton. i did the water pump relocation plate
a new 216 water pump and the stock rad. it
runs nice and cool even at idle in the summer. i think i read short shaft water pump i bet you could move the pump and fan up where it belongs and you wont need an unsightly shroud. philip

The primary reason for running the adaptor plate is so that you can gain fan/radiator clearance when running a later model 235. The notorious "short pump", incorrect pulley diameter, clogged radiator and that particular flex-fan are going to keep you grasping at straws until you decide to FIX the problem. The plate and early pump combo will move your fan back away from the radiator. In addition you will get the correct sized pulley that comes fixed on the early pump so you're creating proper flow. Using the adaptor plate/early pump will also let you use a decent fan (did I say ditch the ss blade?)

Drilling/tapping the block isn't rocket science. It can be done with a battery powered drill and a couple decent bits following the instruction sheets I have in my webshots album. You use existing bolt holes in the block to bolt on the adaptor plate which centers the area to be drilled. The block drills like butter and if you can screw a top on a jar you can cut some threads. Even if you have to buy a new drill bit and a tap (less than $10.00) and follow the instructions you could have done the job in less time than you've spent on this thread.

And btw.....there are some of us who actually have our trucks on the road every day and have gone through many of the same trials and tribulations you're facing. In addition, some of us are Old Farts......been building and modifying vehicles since Moby [censored] was a minnow. We understand that theory and conjecture have their place, but often simple serve as distractions when seeking an answer to a real-life issue. You would be better served to improve your skills at sorting out the tried and true suggestions from the canned smoke. When you reach that point you'll be able to correct your problem and be able to focus on enjoying your ride. The choice is now yours.

Dave

If you dont want to drill the block Patricks sells a shortened pump with the correct size pulley but when I last checked I think was around 90 dollars,if you do that your fan still wont be in the correct location.

I just installed a new 180 deg. thermostat and I'm not sure about the water pump. I see I can test it by having it pump at least 27.67" up (for one pound pressure). Is that what you'd do?

Doug