Last one standing

So having previously discussed all of the other radiator placement solutions for a T2b that was originally air-cooled, there's only one place left to go: below.

This is a first generation solution (circa 2005) from
Custom Off Road in Queensland, Australia. (Now Custom Vee Dub)
The radiator body is fed air by forward motion via the
louvers punched in the bottom plate. Electric puller fans above the
assembly come on when needed.

If you've ever examined this idea, you'll find there are a lot of mixed emotions out there about it.

• "A Radiator does not belong UNDER a car."
• "How is this any more efficient than the other ideas proposed?"
• "Aren't you concerned about bashing up your radiator and spilling all your coolant?"

But I've been chasing this bear around by the tail for the last few years. Lots of folks have put their radiator underneath and the success rate is no more mixed than radiators in the engine compartment.

Unlike the Vanagon conversion, however these underbelly conversions didn't get their start in the sand and surf California scene. SoCal is ground zero for all of the continuing air-cooled scene. If you want to stay stock, most of the innovators (ha!) in Type1 (Beetle, Ghia, Split-window Microbus) are there. But the folks in SoCal are crippled by their own emissions regulations. And the later the vehicle gets, the loopier the laws are. So there is precious little innovation coming out of SoCal these days for the late bus owner.

The source of the most of the really aggressively engineered ideas are coming from Australia and the UK. Engine conversions are not at all unheard of down under, and the appetite for the 'Caravan' in the UK is undimmed, to the point where the Brits are buying dry Buses from SoCal and shipping them to the damp island.

With all of this motivation, is it any wonder that they were the first movers?

The mesh at the front to keep from scooping up
road kill is a nice touch. But with your fans on
the bottom, you're sort of asking to get them
ripped off the radiator. Better protection is
necessary though at least these
are mounted as puller fans.

Unfortunately placing the radiator underneath has raised all kinds of differing opinions about what the best way is to provide airflow to such a beast. There are heated (no pun intended) debates about 'Bernoulli effect' and push fans vs. pull fans, and whether to put the ECU in control of the fans or whether to run the fans as their own subsystem, with the temperature sender acting directly on the fans and telling lies to the ECU.

But the one constant is that, to be sure to run cool, you'd better have a scoop, and you'd better have fans. This doesn't mean that the scoop has to scrape the ground. The T2b has a startlingly high stock ride height, officially 200mm/7.8inches. Yet that actually describes the bottom of the front suspension beam e.g., the lowest part of the vehicle. The T2b (and the T1 and T2a before it) are built in a 'ladder frame' construction. The bottom of the actual frame rails (the bottom of the frame of the vehicle) is 300mm / 11.81" almost a foot off of the ground! And that doesn't include the extra 100mm (about 4 inches) from the bottom of the frame rail to the actual floor of the platform. (There are some necessary occlusions, like the shifter rod tube and the clutch cable tube.) Indeed, there is actually gobs of space to use...if you use the right radiator.

The rule of thumb for sizing the radiator is that it needs at least the same BTU capacity as the vehicle that the engine originally came from. In some cases, people have used two radiators plumbed either in series or in parallel, and still experienced overheating. Why?

The use of parallel radiators has shown itself to be a problem of indeterminacy: for what ever reason, one radiator has less resistance to flow than the other. So all the flow goes there until the resistance equalizes. But all this means is that one radiator does most of the work, and the other one stays mostly cold, even if the other side of the coolant loop is so hot that it is cooking the engine in its own juices.

Series radiators do better, because all of the coolant is forced through both radiators. But compromises have to be made: if you plumb the output of radiator #1 to the input of radiator #2, you have to make sure the connection curves up higher than either radiator and that there is a radiator vent valve there to vent the air out. You can wind up with a blown head gasket for failure to get the baby 'burped' correctly.

So ideally, you'd want a single radiator of the total cooling capacity you require. Additional plumbing has the potential to be headache enough. Why make it harder? Stick to a single radiator that will fit the space, and meet or exceed the BTU capacity of the stock radiator.

The issue of a scoop is enough of its own issue to merit a separate installment on this blog, but one thing has become abundantly clear to me: tilting the radiator itself is not a wise design move, and tempts you to other follies like not ducting the radiator properly or to placing your fans on the bottom of your radiator where they can be sheared off. The following design practices are required to make a good radiator installation:

• Air that reaches the the radiator must do so under positive pressure. There are lots of different ways to achieve this, either by setting the radiator upright at the front of the vehicle (no matter how ugly it looks) or by ducting air to the radiator, but no matter what, it needs to be under positive pressure MOST of the time, e.g.when the vehicle is moving.
• Air that is leaving the radiator needs somewhere to EXIT. If you duct from the bottom up, once the heated air is in the cavity, it has to have somewhere to go. In an ideal world, that cavity would vent to an area of lower pressure, thus causing the heated air to move from high pressure (the duct) to low pressure (the cavity) before being exhausted out the area of flow. A Venturi effect.
• When you use a fan to make up for a lack of sufficient input air volume, PULL, don't PUSH the air through the radiator.
• Box in the assembly. You can't make any of these air pressure or air speed effects work in your favor (and you need all the help you can get, considering the compromised placement of the radiator) if you just screw the assembly to the bottom of your bus and call it done. You need these passages sealed. Remember rear radiator solutions? The air will find the passage of least resistance, right past your radiator. The same thing goes for your ducted installation: seal it up!

A special note: I've gone all 'Father knows best,' here.That's not because I do know what's best, I've only just observed others closely and seen what has worked and what hasn't. You may be able to use a massive enough radiator and enough fans to cause your T2b to lift-off from the ground! You might even have enough oomph with this unducted design to keep it from overheating. But the four principles above all but guarantee success. If your goal is to drive and ignore the engine temperature, designs based on these attributes can't help but work.