As always comments, corrections and critiques always welcomed
Fabricating a Radiator Fan Shroud - My Version
INTRO:
Why am I doing this? Although I’ve never had any major issues with the stock cooling setup, I wanted to see if I could “improve” the efficiency of the air side of the cooling system. With the radiator out to install a new fan I decided to add a fan shroud at the same time. These are my thoughts on the subject from a non engineers perspective.
With not a lot of available room in the front compartment, Lotus had to fit a radiator that could meet the cooling needs of the engine. The radiator they used to fit in the allotted space is a two pass, four row with a surface area of approximately 160 in sq. and a front to back width of 3” fin to fin. This is a thick compact radiator and under most operating conditions, seems to be more than adequate. My concern with the stock setup was the amount of air being deflected back with the fan running with the car at a standstill due to the thickness of the radiator.. I’m thinking that a shroud will maximize the air flow through the radiator with the fan in operation by creating a higher differential pressure across the radiator (non engineer thinking here).
A fan shroud with a 10” diameter fan opening (78 in sq) will block approximately 50% of the stock radiator core surface area. Running primarily on open roads or track conditions, a shroud will most likely be detrimental to overall engine cooling. However, for hot climates with typical urban traffic conditions, a fan shroud should be considered. This is the condition where all of the fan output needs to go through the radiator core rather than be deflected back into the front compartment; I believe a fan shroud will do this. Conversely, once up to speed, it may take longer for bulk coolant temperature to come down to normal temperature due to the air blockage from the shroud. I’ve decided that due to my geographical location (Southern California) and mostly urban (slow speed stop and go) driving conditions, the benefits of a fan shroud will offset the disadvantages and I believe this setup will be of benefit to me
TOOLS & MATERIALS:
My primary goal in fabricating this fan shroud was to build one that is simple and functional using only hand and power equipment most handyman types or homeowners probably already own and not require the use of a welder or a sheet metal brake. The only other requirement was that the shroud installation had to be easily reversible in case the shroud doesn’t work out for you.
The only operations required are cutting, drilling and pop riveting the fan shroud material. For the material, I chose aluminum for ease of cutting and drilling. Most of the aluminum stock was purchased at either a surplus metal center, my local hardware store or McMaster Carr. This is the list of the materials I used:
Note 1: If required for your needs, McMaster-Carr also has angle aluminum in other various dimensions and thicknesses
- 1”x1”x1/16” or 1”x1/2”x 1/16”, 90 degree angled aluminum stock for the side braces
- 2”x2”x1/16” or 2”x1”x1/16” 90 degree angled aluminum stock for the top and bottom braces, either one depending on availability.
- Aluminum sheet for top shroud: I used 17 gauge sheet metal thickness or 0.06” thick aluminum sheet. Choice of thickness is up to the fabricator. In my opinion, anything
thinner than 0.06” may be a bit too flexible in use
- A selection of short aluminum pop rivets. I used a ⅛” diameter by 1/8” grip rivets.
About the only power tools absolutely essential simply to make life easier are a circular saw and an electric drill. A miter/chop saw is a “nice to have'' item but not essential. The last power tool that is only essential if the fabricator does not want to farm out the job of cutting out the 10” diameter circle to a machine shop is a palm/ trim router with a circle cutting jig. Hand tools needed are a hack saw (if not using a chop saw), tape measure/ruler, files (or Dremel tool), a carpenter's square and a pop rivet gun .
FABRICATION:
For all Europas, there have always been clearance issues between the right side headlight bucket and the corner of the radiator side tank. The clearance seems to vary from Europa to Europa where in extreme cases, the buckets have been bashed in to obtain clearance. This clearance will determine the available depth of the fan shroud (photo 1). In the case of my TCS, there is approximately a ½” gap between my unmolested headlight bucket and the radiator side tank corner.
I’ve presented two options on where the side braces can be installed, inside or outside the side tank cover (photo 2). For most Europas, there will probably not be enough of a gap to use the ½” brace outside the side tank. Mine had a ½” gap and used the ½” brace outside the side tank option; the shroud corner barely cleared the bucket with a 0.07” gap using a feeler gauge. I suspect most cars will have to use the 1” side brace with the inside the tank method.
The first step is to determine the clearance between your headlight bucket and the corner of the radiator side tank. The steps using this Go/NoGo method described below will give you an idea of the approximate height/depth of your shroud that will fit in the available space..
Note 2. At this time, removal of the fan and the headlight bucket will make the clearance measurement easier.
- Cut out two strips from plastic or other stiff material, the first one ½”x2” and the second 1”x2” to use as your clearance gauge..
- Slide the ½” wide strip along the outside edge of the side tank and see how far it will slide up before contacting the headlight bucket. If the top of the strip reaches the top of
the radiator top plate then the side brace will fit. If it doesn’t then the corner of the side brace will have to be ground off till it clears the bucket.
- Do the same with 1” strip inside the side tank edge. Due to the somewhat ovoid shape of the bucket, moving the brace inside will give a fraction more clearance to the
bucket so, there is a good probability that the 1” strip will give adequate clearance with minimal to no grinding necessary (photo 3).
- Decide whether to go inside or outside the side tank flange depending on found clearance. After constructing both versions, I found that going with the inside the tank version
will give a tad more leeway in shroud clearance and would recommend going with the inside the tank version.
The core area of a stock S2 and TC radiator measures out the same so this article applies to both. Because these radiators are handmade, there may be very minor differences in the dimensions from one radiator to another. Mine after a rebuild varied in height by a fraction of an inch from one end to the other. This definitely affected the fit of the braces to the top and bottom shroud plate.
The first piece that needs to be cut is the top shroud plate This piece needs to be measured and cut as accurately as possible since this is the reference piece from which the top, bottom and side braces will be measured and cut.
Note 3: All of the measurements listed were the dimensions taken from my radiator and are meant to be used as a reference only. Use the dimensions from your radiator since there may be slight differences. Remove the radiator for the measurements.
Whether the inside or outside the side tank flange was chosen, the only difference between the two shroud dimensions is the side to side width; 16-½” for outside the side tank and 15-¾” for inside the tank. The tallest points of the radiator will be where the fan mounting straps (if still installed).are soldered to the top and bottom closing plates and should be the point of measurement for a stock radiator and measures 11-⅛” (photo 4). If the straps are removed, the height will be 11”.
The aluminum sheet was cut using a circular saw with a 60 tooth non ferrous metal cutting blade. It worked beautifully making a very smooth finish on the edges using a straight guide to ensure the straightness of my cuts. For the four angled aluminum side braces, use the dimensions taken from the top shroud plate. I used a basic power miter saw also with a non ferrous metal cutting blade to cut the braces. The side braces then had the inside corners cut at a 45 degree angle to allow a tight flush fit on the top plate surface. After all of the pieces are cut, perform a trial fit of the pieces. Again, ideally all of the corners should abut each other when fitted to the top plate shroud to minimize unsightly gaps (photo 5). Unfortunately in my first version, the braces had small gaps on the corners. The fan shroud was still functional but the gaps will have to be addressed later.
Note 5: The pursuit and my focus on having tight gaps is due to my misplaced sense of aesthetics and having small gaps has no effect on the overall function of the shroud.
With the radiator on the workbench, this is the sequence I used to align and attach the pieces. First line up the top brace flush to the front edge and the ends of the top shroud, drill and rivet the top brace to the shroud. Do the same for the right side brace ensuring that it is square to the top brace. The top and right/inside brace will be visible so aesthetically this will show the best side and fit. Before the bottom brace can be attached a slot has to be measured and cut out to clear the tang on the bottom front of the stock radiator (Photo 6). I used a Dremel tool and cutoff disc. Fit and attach the bottom brace. If there are any gaps between the bottom brace and the radiator bottom plate the space can be shimmed later on to fill the gap. Both the left and right side braces need to be fit tight against the side tank flange. Any misalignment between the left brace and the top shroud plate will not be visible so it doesn’t matter. With all of the braces riveted, the braces should have a snug fit with the radiator.(Photo 7)
Note 6: I don't know what function this tang has except a place to allow the radiator manufacturer to hang their company tags. Cutting it off may be a better option.
The next step and the most daunting for me, was to cut out the hole in the shroud for the 10” fan. For this step, you have a choice of either electing to attempt to do this on your own or farm it out to a fabricator or machine shop to make the cut. Although it is possible to make the hole using a jig or scroll saw, my procedure uses a trim router. Using a trim router for the first time, it made a fast and clean cut for the fan opening and I highly recommend using one. Harbor Freight has a trim router for about $30.
Depending on the attachments included with your router, it’s possible that you already have the attachment necessary to cut a circle. My router came with a straight guide that could be converted to a circle cutting jig. (photo 8). If a circle cutting jig is not included, a workable one can be made from a bent piece of 1/2”x6”x1/16” piece of aluminum flat stock. Another aid which is essential to cutting the perfect circle is to use a wood base to support the shroud to prevent any movement or shifting of the top plate during the final part of the cut (photo 9). The pivot bolt for the circle cutting jig also has to rest in the hole of the wood base support. If this is the first time using a router to cut a circle as it was for me, I would highly recommend watching a few Youtube videos and then first practice on a scrap piece of plywood before making your actual cut. For the router bit, I used a ⅛” diameter fluted bit.
After the circle is cut out, mark out and drill the mounting holes for your cooling fan. Use your method of choice to mount the fan to the top shroud, I used Rivnuts installed backwards. This has the advantage of acting as centering dowel pins and supports the fan without allowing it to shift (Photo 10,11). If there are any gaps between the corners of the braces, seal them using aluminum tape, silicon, or epoxy, your choice.
The final step is to secure the fan shroud assembly to the radiator. I drilled two holes into the top and bottom brace and into the radiator support plates. I highly recommend using a drill stop to prevent drilling into the tubes. Pop rivets were used to secure the shroud assembly to the radiator. . During the final alignment, to eliminate the possibility of contact between the tubes and the side braces ensure that there is a gap between the side braces and the tubes in the core if using the inside the tank method.
The moment of truth is upon us. Install the radiator and shroud assembly into place. Install the headlight bucket into place. If you’re lucky there will be no clearance issues and the bucket sits flush in the opening.. It's not the end of the world if contact occurs before the bucket bottoms out. If the headlight clearance was determined correctly at the beginning of the fabrication, the amount of aluminum to be removed should be minor. Remove material from the shroud corner using a file or dremel tool until clearance is achieved. Cover the hole with epoxy, JB Weld or aluminum tape. The minor surgery will not be visible to the casual observer. With my two different shroud attempts on a stock radiator, I came up with a clearance of 0.07” (½” side brace outside the flange) and 0.02” (1” side brace inside the flange) by feeler gauge, no grinding necessary. .
Photos 12-15 show the not so pretty final result of my first attempt.
Photo 16 shows as stone guard replacement
Photo 17 shows another shroud on an custom aluminum Griffin radiator with the inside the side tank placement
Thoughts on further improving cooling
With the radiator already removed for the fan shroud installation, it might not be a bad idea to examine the rest of the air side of the cooling system. The front plenum where the radiator is located acts as a pressure chamber to force air flow past the radiator at speed. A low cost way to optimize engine cooling is to minimize any paths that bypass air flow around the radiator; I see three potential areas. The major culprit in my opinion is the cutout opening for the radiator into the wheel well. On my car the cutout does not match the radiator core perimeter along with having huge gaps that need to be filled. My original foam weather stripping had long since disintegrated and will have to be replaced with new foam. The second area to check is the open cell foam separating the spare tire/radiator compartment from the frunk. Renew if missing or deteriorated. The third minor area are the two openings (TCs) where the radiator hoses enter the compartment and the rubber plug for the master cylinder cover. Sealing the hoses around the opening with rubber sheets may help somewhat and make sure that the plug for the master cylinder cap is installed. On the S2s, the opening is much larger and will be more difficult to seal. The last area that may potentially restrict rather than bypass flow is the stock wire stone guard behind the radiator. Visually, the guard appears to block flow with the individual wires being relatively thick (0.06”) but unless tested with an air flow device, there is no way to be certain. With that being said, I still plan on substituting a nomex honeycomb radiator screen in place of the wire stone guard.
Conclusion
The shrouded radiator is installed but I have not road tested my changes yet to see how effective they are but plan on updating this writeup when I do. If you decide that the fan shroud is detrimental to keeping your Europa cool, removal is relatively simple. Unfortunately the radiator has to come out but only requires that the pop rivets be drilled out.
Photo 1 - Shows point of contact between headlight bucket and radiator side tank corner.
Photo 2 - Shows two radiators with either inside or outside side tank option
Photo 3 - Shows 1" plastic gauge against side tank flange up flush with the top of the radiator support plate indicating a small gap. Good indication of sufficient clearance without the need to modifying the corner of the shroud.
Photo 4 - Shows additional height that needs to be taken into account for the fan straps
Photo 5 - Shows back view of shroud with pieces assembled. If not measured and cut carefully, there will be minor gaps.
Photo 6 - Shows a slot required to be cut out of bottom brace to clear the tang. Consider cutting off the tang. It seems to serve no purpose except to attach radiator work tags
Photo 7 - Shows fully assembled shroud with all braces attached to top plate
Photo 8 - Shows palm router set up to cut out the circle into the top shroud plate.
Photo 9 - Shows wood support base used to cut out the circle. The shroud need to fit tight against the base support to keep from shifting as the cut is completed.
Photo 10, 11 - I used Rivnuts in the reverse fashion to mount the fan to the shroud. I watched a few Youtube videos to installing Rivnuts without the proper tool; I had mixed results. Not wanting the Rivnut to loosen up and come loose and start turning after it was installed, I broke down and purchased a Rivnut tool.
Photos 12-17 - Shows results of my first attempt. As shown, my top shroud plate was not measured/cut precisely enough indicated by all the braces not being flush with the top shroud. My subsequent attempts were a bit better.
