The Official FC Radiator Thread.

[vex]

I did a quick and dirty search about radiators on here and didn't come up with anything, so I figure I'd start this one. The stock radiators now are approaching if not exceeding 20 years of duty (unless replaced). It would be wise to replace them with something that doesn't have a plastic top and bottom. For this cause I've started a list of possible replacements that can be installed with minimal effort into the stock location on the FC.

For starters let’s look at the actual size of the stock radiator (S4): I measured an over all length of 22.5 in and an overall height of 20.25 in. This is of course just a rough estimate because I didn't think it necessary to remove parts of the intake to get an accurate measurement (as even the universal radiators have specific dimensions). The overall thickness of the radiator is about 2.25 in. This includes the end tanks but not the brackets.

The overall length of the core is 21.5 in while the height of the core is roughly 17 in. The estimated thickness of the core is about 1.5 in (may actually be larger, but measurement was just eyeballed to give me an idea).

As for the number of passes or flow type of stock I believe (correct me if I'm wrong anyone) is a single pass. This means the coolant is just dumped into the radiator and at some point works itself down to the lower portion of the radiator as it cools. This is one of the least efficient means of cooling for a few reasons:

1. The movement of the coolant is not controlled resulting in higher average temperatures across the radiator
2. The coolant increases in temperature much more rapidly than other flow designs.
3. Coolant does not have adequate time to cool to a lower temperature. Thus resulting in a higher engine temperature.

With these things in mind we can now look at a few different options. Lets first look at the specifically engineered OE replacements.

Direct OEM Replacements

KOYO

Koyo produces three different radiators for the FC. All are aluminum construction and are a direct fit for the year they are produced. Koyo produces one (1) radiator for the early FC (1986-1988) and two (2) radiators for the late model FC (1989-1991). The main differences are as follows:

The radiator produced for the early FC is (as far as I can tell) a single pass radiator. So although you have an increase in cooling efficiency, you still have the down fall of it being a single pass. Koyo claims a reduction in stock cooling temperatures of about 20-30%. This may be an affordable option for those who have not heavily modified their cars and are just looking for a slight increase in cooling performance. This is a direct replacement with OEM (just remember to keep the brackets to mount the radiator).

The second radiator produced by Koyo for the FC is for the S5. Similar to the previous radiator discussed it too is a single pass radiator style. On the other hand, the final radiator produced by Koyo for the S5 is an "N-Pass" flow pattern which increases the ability of the radiator to cool the engine significantly. The "N-pass" is basically a 3 pass flow pattern allowing the coolant to remain in the radiator and cool to a lower temperature before returning to the engine. This radiator comes highly recommended by those who have installed it. But may be overkill depending on your level of modification.

All the Koyo radiators retail for anywhere between 300-400 dollars.

CorkSport

Along these same lines Corksport produces their own similar radiator for the FC (both S4 and S5) at a slightly lower cost. The radiator is single pass aluminum construction. Which leads me to assume a similar efficiency to that of the single pass Koyo's (about 20-30%). Expect to pay around 300 plus shipping for one.

Fluidyne

Fluidyne offers similar radiators for the FC as the Koyo, however they are slightly more expensive--starting at 400 and only increasing from there depending on where you order yours from. Effeciency is similar to the Corksport and Koyo.

AWR/Ron Davis

AWR/Ron Davis offer two different radiators for the FC. One being a single pass and one being a Dual-Pass cross flow. These radiators are usually built for racing and as such their price reflect that. I can not find the stats on the single pass beyond the fact that there are no pre-drilled mounting holes on the mounting tab to allow you to mount the radiator specifically where you'd like it to be. Looking at the radiator it seems to me to be a down flow design, however I may be mistaken on that.

There is also the AWR/Ron Davis cross flow radiator. It is signifcantly more effecient than the Single pass radiators and offers increased cooling benefits as the coolant has to travel accross the radiator multiple times before being returned to the engine (I believe it's a cross flow two pass radiator). Construction is also different than the radiators mentioned above. The core is fully tig welded while the ones above are brazed. However with all these benefits they carry a hefty price tag. Ranging from mid 400 to upper 500 depending on where you purchase them. The dimensions of that radiator are as follows:with an overall length of 28 in and a height of 19 in. The core is 18.25 in. in height and 24 in. in length while the core is 2.25 in. thick.

CSF

CSF offers a few different radiators for each individual year. For S4 they sell radiator No. 864. It is an all metal replacement for the OE radiator. Beyond the same dimensions as stock with metal end tanks little else is declared from their site (no price tag either). Dimensions:
Core Size 16-3/4 x 22-1/8 x 1-5/16
Tank Size Inlet 22-1/6 x 1-9/16
Outlet 22-1/6 x 1-9/16
Hose Fittings Top 1-1/2 Right
Bottom 1-1/2 Right
No of Rows 2


CSF also offers another radiator for S5's but with the same stock dimensions. Radiator No. 2006. Dimensions are as follows:

Core Size 16-5/16 x 22-7/16 x 1-5/16
Tank Size Inlet 22-1/16 x 1-9/16
Outlet 22-1/16 x 1-9/16
Hose Fittings Top 1-1/2 Right
Bottom 1-1/2 Right
No of Rows 2

Universal Radiators

Universal type radiators... what can I say about these? They are remarkably cheaper for the amount of radiator you get. This isn't necessarily reflected in the workmanship of the product but the cost savings come to you by the ability of the company to mass produce the radiator to specific dimensions and sell to a wider range of applications. Since there are so many universal radiators available it would be impossible for me to list them all and keep them all updated. For this cause I will list a few radiators from different companies. Note that depending on your situation you may need to either alter the universal radiator, pick a smaller one, or even modify the radiator supports to accept the sizes I recommend.

Keep in mind that no matter what radiator you decide to go with you need to be aware of how much heat your engine is generating. Do not select a small or medium 4-pass 3-core Cross flow radiator and expect tremendous cooling capacity to cool your insanely large turbo and heavily ported engine. It just doesn't work like that. You will always get more cooling capacity from more surface area. Period. The larger the radiator the better (there is a point of diminishing returns, but just as a rule of thumb that will work). My personal recommendations is a two or three core radiator should be standard (for the most part, they are. It's quite difficult to find a single core radiator, and why would you even want one? I don't know). Single pass will be fine for stock to slightly modified and any pass (2,3, 4, x pass) will be fine for slightly modified to extremely modified. This is of course, a rule of thumb and you will need to figure out your own cooling needs before putting on any radiator. Alright, enough. On with it already:

AFCO

I believe Ted said it best: These radiators offer the same level of cooling as Ron Davis but at a fraction of the cost

Originally Posted by Ted

[A]n AFCO Racing 80125N is about the same thing...for under $300.

The only catch is that keeping the stock battery (tray) is next to impossible. It's a 26" width rad, so things get tight up front, but it does fit between the engine frame rails; [t]here are several options to mount this unit, but be prepared to do some minor cutting.

Some specs...
The rad has the hose fittings on the proper sides...The top hose is 1.5" - same as stock. The bottom hose is 1.75" - stock is 1.5"; we use auto parts stores generic hose that's around 11" long but uses a 1.5" on one side and 1.75" on the other - perfect. It is a double-pass design for better efficiency. It's a 3" thick core. It uses a "domestic" type rad cap on the rad - need to buy separately. The rad cap filler neck does have a 1/8" NPT fittings for bypass use. This filler neck makes it easy to bleed air out of the system. If you want to add any of the stock FC stuff - lower thermoswitch, coolant level, heater hose - you need to add / fab them yourself.

Which brings up a very good point. Many of the universal radiators do not have the appropriate holes or bungs for the different sensors. Be aware that if you wish to retain those sensors you'll need to drill, tap, and/or weld in the appropriate fittings to mount the sensor. One may also need to modify the mounting location to make sure there's enough space and a proper alignment for good airflow.

See post number 14 for more radiators