C5 Corvette - DIY Oil Cooler & Accusump Install - PT 1

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When it comes to things you worry about on a car you track... blowing up a significant part of the drivetrain is a serious concern for most. The engine blowing up is definitely one of the biggest concerns in that regard, and for sure one my largest concern with my C5 corvette.

Bearing that in mind, while some folk build their cars for maximum power, I've chosen to focus on reliability and handling. One of the main areas you can take a C5 corvette and increase reliaibility is through ensuring the oiling is good and the engine temperatures don't get too high.

Available solutions are out there, but not all applied to me or worked well together.

For oil starvation protection, on certain models of C5 corvette you can get the improved racing baffles. These keep oil by your oil pickup and help ensure during heavy cornering you don't get oil starvation. They've been tested, and known to work. Unfortuantely for me however, these require the later model C5 corvettes with the two piece oil pan. I've got a single piece oil pan, into which I cannot install the baffles. This leaves the accusump option for myself. For those unfamiliar, the accusump is a pressurized cylinder that your oil pump will fill with oil. When your oil pressure drops, or worse goes away, the pressurized cylinder of oil (your accusump) will force oil into your engine, saving you from oil starvation. Added bonus as well, when you start your car an accusump wth an ignition relay will pre-oil your engine. Extra increased engine life!

For engine cooling, there's a few options out there, but nearly all of them revolve around oil cooling. Some have the oil cooler built into the radiator, which some say works well, but others say is prone to issues since it just passes the oil heat into the coolant and thus right back into the matter. The remaining option is an external oil cooler, which if positioned correctly will not introduce any heat back into the engine.

Given that I've had high oil temperatures and want to be able to get out on warmer track days (warmest I've done was 115F), It would seem to me both from my experience and from researching, that an oil cooler is the way to fly.

That all seems simple enough. Get an oil cooler, get an accusump, presto done!

Well, therein lies the problem. There is very little documentaiton on how to make the two work together. There are DIY kits for oil coolers, but none of them seem to be setup to play well together. After reviewing and analyzing what others have done for months... I came to the conclusion I'd need to DIY this for myself.

General Concept + Parts List

Link to lucid chart diagram

Note about the diagram: This is conceptual only at this time and may change during actual implementation. I see a lot of people attaching their 12v valve direct to the accusump. This would reduce the amount of fittings needed and points of failure in the system.

Above is the diagram I came up with of the general routing. The plan seems simple enough. Run a block adapter on the engine, that goes out to the oil cooler. Go from the oil cooler to a one way check valve and a t-fitting. At the tfitting, downstream of the one way check valve are the accusump and the return to the block adapter. This will ensure that if oil starvation occurs that the accusump will only be pumping oil into the engine, not through the oil cooler.

Oil Cooler Parts list:

Accusump Parts List:

  • 2 qt accusump
  • Accusump 12v switched (ignition) EPV (electric pressure control valve) Valve
  • 10an t-fitting (male on all sides)
  • 3x 1/2 NPT to 10an connectors
  • 1x 10an female to 10an female connector (check valve to t fitting

Initial plans have me placing the oil cooler behind the license plate mount up front. I'm not utilizing it anyways, so it's a fin location to mount my oil cooler and it has access to some pretty good air flow. The next largest item to figure out placement of is the accusump. I'm currently thinking placing the accusump where the windhsield washer fluid resrvoir was makes the most sense. I'm not utilizing that anyways and the 2qt accusump seems to be about the same size as the fluid reservoir.

The block adapter I went with does not feature a thermostat. Some people say this is ideal to keep your engine from running too cool, or to keep it from taking too long to heat up. In my case... I don't really dool with cool temperatures much and I can be patient with my startups on the Corvette. Also, this in theory should make changing the oil much easier since I can drain the oil cooler just as i would drain the oil for an oil change. Add in that all I need to do to drain the accusump is turn on the ignition... this should make for hopefully reasonable oil changes!

One detail worth noting that isn't discussed enough is the selection of your 12v valve, and ideally selecting an Electric Pressure Control Valve. In my case, I went with a 20-25PSI EPV, and I would recommend similar for you. That means any time the engine drops below 20-25psi, the valve will open allowing the stored up oil pressure to push oil back through the system. Without it, the accusump is constantly pressing extra oil back into the engine any time the pressure drops. The idea here though is to store that oil pressure until a nescessary event such as oil not reaching the pickup during heavy cornering or starting the engine when it has no pressure to begin with. While some companies recommend choosing your PSI to be just under your hot idle oil pressure, I went with 20-25 as that is safely below my idle (and the lowest available) and will ensure I get oil protection against oil starvation.


While I awaited parts to show up so as I could complete the job, I started tackling small bits of the project a bit size chunk at a time. First up was whether the accusump would even fit where I intended for it to go. Low and behold, it appears to fit there without issue!

An Accusump test fit where the windshield washer fluid reservoir would normally go on a C5 Corvette.

Some questions do remain however, such as if I should back the area etween the accusump and wheel well with sheet metal to help protect from debris, along with the best way to cap off and trick the sensors that were previously on the winsdshield fluid reservoir. Overall though, the location has plenty of space, the side I need to run the electronic pressure controlled valve has space and I should be able to rout nearly all of the 10an line through that generally area.

How the install played out

The further I got with the install, the more details surrounding the accusump became prohibitive. While the accusump fits into the space where the overflow reservoir went, I'll be damned if I could figure out how to make a bracket work there.

So, in a "moment of genius" I decided I would just install everyting, but cap off the Accusump side of the T-fitting to allow for later install of the accusump. Here's what the parts for the T fitting and one way valve and wound up looking like:

As I'm sure you can tell... this is ridiculous. It's over 8" or so of connectors. Worse, they're all rigid, making the task of snaking them through to the block adapter nigh impossible.

For this reason, I decided to delay the accusump install for now and pick the project back up again at another time. I definitely want it, and I have the parts already, but this part of the project is tabled temporarily.

Having delayed the accusump, next up was getting the oil cooler placed somewhere reasonable. Given my welding equipment is not currently in my garage, I went wit hthe simple solution of angle aluminum bolted together to make it all work. I then used rivnuts in the front crash bar to hold the bracket, and it all went together fairly smoothly.

Some folks looking to mimic what I've done here have been asking for dimensions of my oil cooler, so the image above should capture it. External dimensions including the AN fittings is 12.91" wide, 6.5" tall, 1.97" thick. It is a 19 row oil cooler.

One thing I wanted to do different with my oil cooler install, was figure out how to install it "right side up". As you'll see in the diagram way above, my inlet/outlet for the oil cooler are on the top. This is so oil enters the coolers, and when the engine shuts off the oil does not drain back into the block potentially overfilling the block. Welp, guess what? Top mounted inlet/outlet interfere with the foam block that helps reinforce the bumper from warping at high speeds. It also is likely to contact the bumper itself, and introduces all sorts of headaches in general. DOH. So, I had to flip it over just like everybody else. It's been fine and without issues.

The above pictures are first of the oil cooler orientated correctly with the foam put in place, and then below it is the final state of the oil cooler install with the lines and everything in place. Note that the only difference between the two is I was fooling with relocating the one way valve location, which I also give up on doing as it did not free up significant enough space.

With the oil cooler in place. The lines were to cut to the right length and routed through a gap next to the radiator brace, through some brake lines, barely over the steering rack, and then through the space between the block and the engine mounts to keep it all away from the exhaust headers. Yep, that's a run on sentence, and the task really was that much of a headache as you tried to yoga your hands into spaces not meant to be accessed and push hoses through spaces not meant to have hoses. It was a nuisance, but in the end it came together.

With all that in place, then came connecting the block adapter for the oil lines. This also proved to be a headache as access was poor. After fighting with a variety of ideas, it became obvious there was only one way to really proceed. I had to drop the cats/mid-pipe section of my exhaust to make room. This added about an hour total to the project, but I probably burned just as much time hemming and hawwing over if I really needed to. If you do this project yourself, just do it in advance. Your knuckles will thank you and it will make the job reasonable.

The technique I wound up using involved removing the cats/mid-pipe, attaching the block adapter without the hoses attached to it, and then threading the hoses on. Access was also poor for threading the hoses on, but I was able to just cut a crescent wrench down allowing me reasonable ease of access.

Initial Testing

With everything all bolted up finally and snugged down, it seemed appropriate to test it all before I put the bumper back on. I fired the car up, and after a very brief "low oil pressure warning of 1 second, oil pressure quickly built right back up to 40 lbs at idle. So to all the naysayers citing low oil pressure with an oil cooler... you're bananas I got tons and I'm on an OEM oil pump.

Letting the car warm up for 15 minutes the oil cooler barely hit 100 degrees with the car had hit 185. The oil cooler seemed to be clearly doing it's job. I did stop a few times to check the oil level, and I found I had to put about 2.25qts of oil into the car to bring the oil back up to the level I like to have it, which is 1qt overfilled to help prevent starvation at the track when cornering.

At no point did I leak oil. I attribute this to using a very small dab of thread sealant on the threads of every AN fitting. Some people will chastize this, an AN fitting doesn't need this, and infact getting anything between the mating surfaces in an AN fitting can cause an issue. This is correct, if you are using aerospace grade AN fittings. We aren't, and there are imperfections in there and our environments aren't perfectly sterile. It's not unheard of for a fitting to weep, and with a dab of thread sealant, everything worked flawlessly for myself.

The next day, I decided to take a bumperless journey around the backroads of the area I'm in. I got a lot of funny looks as I drove around, but after about 20 or so miles of slow suburban puttering I was able to get the oil temperature up to 175 degrees. It is worth noting that the coolant temp hit operating temperature long before hand, so I feel this is a demonstration that the oil cooler was doing it's job.

The following day I tidied the bumper up, reinforcing a few bits of the lower air dams while I was in the area, and then secured it all together. The oil cooler wound up quite "stealth" with my configuration. Given the black mesh and the black oil cooler behind it in a backspaced area... no light really got in there to give away that the oil cooler was there.

I took the car on my usual shake down route. It's a 12 mile highway jaunt up the coast, 8 miles back on a slow coastal road, and then another 4 miles of highway back. Temperatures outside were a cool 58 degrees with a moderately cold onshore wind of about 14 mph.

Operating emperature wise on this final shake down run the car never got up to full operating temperature. The car averaged 167 degrees but peaked at 176 degrees, with both oil and coolant temperature being within 4 degrees of each other at any time. I believe this is likely because the block adapter is not thermostatic, and is just always on. This slows down the time the car takes to get up to temperature, which is obviously not idealy. However, it's one less piece to fail and thus track folks generally recommnd against it. Given I rarely street drive, it should be okay. One possible solution is to put a normal license plate cover on when driving to and from the track, and only expose the oil cooler when nescessary. The effort may not be worth it though since the car is plenty happy at 176 degrees, and warmer day time temperatures may affect this as well.

Legitimate Track Testing 

Since writing this article I've had about a dozen track days at various tracks. Prior to these events I was regularly seeing 274 degrees as a peak temperature during my quicker laps, and this was on 45-55 degree coldy windy days. This is also a "low speed" track with top speeds around 108mph or so, with lots of tight technical turns and elevation.

With the oil cooler my oil temps never exceeded 234 degrees, and this was on hotter 65-75 degree days with minimal wind. I also noticed coming off the track and going for a short cool down my oil temperatures would quickly drop another 15-20 degrees, where as before oil temps would not drop nearly as quick.

Unfortuantely, my oil temps did pick up yet again once I added a splitter, but this time the all time peak was 282 degrees after pushing the car through many back to basck sessions in 110+ degree temperatures. At the same time I discovered a small leak in my coolant expansion tank, whish was preventing that system from sealing entirely, which in turn meant my coolant had peaked quite notably as was not cooling as effectively as it should.

Overall, I would say this setup WORKS, and had I not had it I would have been in for quite some problems when the expnasion tank stopped pressurizing and when I switched to the front splitter, which is known to cause issues with the OEM lean back style radiator.

More information to come as I work towards adding in the Accusump.

I skipped the accusump originally as I was unable to cleanly mount it, and I had many other projects in mind. At this point, I am now debating placing the accusump behind the drives side wheel well as many folks reccomend. We'll see though, since I currently have the wheel well vents opened up to allow air to exit my wheel wells.

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