C5 Corvette Radiator Upgrade: Why Aluminum is Better Than Plastic

The 5th generation Corvette (produced between 1997 – 2004), better known as the C5, has been around more than long enough to prove itself to the automotive world. Luckily for enthusiasts, depreciation has these cars fall into the realm of being an affordable and easy way to build a road race car or track day toy.

Last year my wife and I flew out to Madison, Wis. to pick up my new-to-me 2003 Corvette Z06. I had to find the nicest, stock, low milage example in the color I wanted – all with the full intention of turning it into a track day car, and eventually into a full wheel-to-wheel racecar. During the 8-hour drive home I was already thoroughly thinking of all the upgrades I would be doing to get the car track-ready.

While the C5 Corvette is a highly capable car out of the box, it certainly isn’t without its shortcomings once you start hot lapping on a road course. The forums and Facebook groups are filled with valuable information (once you weed through the hard-headed opinions) on what works for these cars and what doesn’t. One of the biggest issues I kept seeing was that the factory radiator is barely adequate for spirited street use on a stock Corvette, let alone anything that has been given power adders or racing duty. How does a car radiator work? GM has actually came forward with a Special Coverage Adjustment in 2021 for 2015-2018 Z06 Corvettes that extends the warranty on the cooling system due to a “condition” that may cause overheating when driven on the track. That “condition” is that the factory radiator just isn’t up to the task of cooling while driven in a high-performance setting. While the C5 Corvette is far too old for GM to worry about extending any coverage on the factory components, you can clearly see that GM admits that they didn’t put the very best components in these cars. The brand for C5 Corvette radiator replacement I saw recommended time and time again was “DeWitt’s”. Not only are there a large number of racers recommending a DeWitt’s radiator, but the team at DeWitt’s have been active on their social media by posting very detailed responses to forum posts and helping the community out by providing their expertise.

As I build my car, I have been using the Spec Corvette race series rule book as my guide for when the car eventually makes it to wheel-to-wheel racing. Since anything related to cooling is open, I knew the DeWitt’s radiator would be legal to use in the race series.

Personally, I opted for the DeWitts® 1139097M '97-04 Corvette C5 Direct Fit® Radiator, which is the manual transmission version without built-in oil coolers. I did this because I am installing a large separate oil cooler in the nose of the car behind where the front license plate would usually mount. While not required, I also decided to go ahead and grab the Dewitt’s SP015 Electric Fan Kit, since it doubles the factory fan output to an impressive 3,200 CFM. The DeWitt’s radiator can accommodate either the factory fans or the DeWitt’s kit.

Inspecting the Dewitt’s unit and comparing it to the factory GM radiator clearly shows the advantages right away. Perfectly welded everywhere, the Dewitt’s core measures more than twice as thick as the original radiator (.950” thick vs 2.25” thick). Besides having the additional cooling capability, little things such as having a metal coolant drain valve instead of the factory plastic plug that strips out is sure nice to have.

While doing my exhaustive research before buying a C5 aluminum radiator, the only issue I found online about installing a DeWitt’s radiator was that the hose connection on the driver side could cause the upper radiator hose to rub on the later years ABS module and brake lines in front of the engine. Turns out that this was old information from years past, and DeWitt’s has redesigned the hose inlet to angle upward and provide more than enough clearance for the radiator hose. A fine example of where DeWitt’s listened to their customers and developed their product to be the best it can be.

A Couple Quick Installation Tips:

1. Make sure to transfer the rubber isolators from the old radiator.

2. The A/C condenser needs to be blown out with compressed air to clean out any debris. It is surprising how much stuff came out of mine. You don’t want to skip this step, as you don’t want any air getting blocked from reaching the radiator.

3. The C5 Corvette is a bottom feeder for the radiator inlet. The lower air dam must be complete and functional, with all three sections in good condition. If the air can’t get pushed up through the radiator, the radiator can’t cool the engine. Aftermarket ground effects & splitters may look neat but can reduce the amount of air reaching the radiator as well.

4. Regardless of mileage, the hoses and hose clamps should be inspected or replaced. These cars are approaching classic car status at 20+ years old, and it is cheap insurance to get new hoses. The thermostat should also be replaced at this time as well.

Make sure to blow out all the debris from the condenser before installing the radiator. All of the air for the radiator must first flow through the condenser, so a clean air path is necessary.

With everything installed, I filled the radiator up with VP Racing 2305 Stay Frosty Coolant, Race Ready Formula (1 Gallon) & (4 Gallons). I chose this coolant due to it being a water-based, glycol-free formula. Glycol does a great job keeping the coolant from freezing in the winter, but that is also what makes the coolant feel so slippery. Many tracks don’t like having glycol-based coolant spills since it is so slippery, that it might as well be oil on the racing surface. Having the extra cooling capability of the Race Ready Formula doesn’t hurt either. I just need to make sure to drain my coolant out before it freezes this winter. If you need a coolant with freeze protection, DeWitt’s 305 HP Coolant, or the VP Racing Fuels 2307 Coolant, both contain Propylene Glycol.

After finally getting the car fully buttoned up after several other projects, I went out to the Motorsport Park Hastings road course to see how well everything would perform. The day started out perfect in the upper 60’s, then by early afternoon the temp hit the mid 90’s.

Throughout the day I was watching my temps closely, and even when the outside air temp was 95 degrees, my coolant temp never raised above 205 degrees. Later, I was able to verify coolant temps in more detail as I was data logging with my HPTuners OBDII scanner. Clearly, the DeWitt’s radiator is doing its job.

Now it’s time to do some nut and bolt checks, corner weigh and re-align the car, then get back to the track several more times this summer to get in some much-needed seat time. I am also looking forward to running a few events this year, such as the Sandhills Open Road Challenge and a couple of SCCA & NASA Time Trial events. Although it is just one part of many, having the DeWitt’s radiator keep my engine cool will free me from worrying about hurting my engine while on the track, and allow me to focus on becoming a better driver.