People have tried fitting radiators in just about every possible location when converting originally air cooled VW models to water cooled. Some of them locations can undoubtedly work OK, but which very few people would be happy with, such as in front of the front panel (i.e. effectively above the bumper), poorly disguised as a spare wheel carrier, or on the roof, poorly disguised as luggage on a roof rack. Others which require major vehicle modification before whether they work or not can be proven, such as behind the rear seat in a Beetle with air ducted in and out via major ducting modification to the windows and body, or large quantities built in the UK with a ridiculously large, unducted radiator between the engine and the rear valance which we have comprehensively proven cannot work without relying on fans far too much.

Each to their own, but almost all customers are looking for something less subtle than that. I.e. they want their VW to still look air cooled, and they want to achieve that in a proven way with minimal modifications to the VW. There are very few locations where both that and correct functioning without relying on fans under normal driving conditions can be achieved. In a Beetle and many of the Beetle based other VW models, the only viable radiator location is in the front, in the spare wheel well, due to the absence of enough space anywhere else where enough air flow is available. In a split screen bus, or a bay window in which the owner doesn’t want to fit the (generally regarded as very ugly) 1.8 Mexican built T2c front mounted radiator system the only suitable location is under the floor.

Two radiators mounted either side of a VW bus engine compartment, and how we detemined that this arrangement cannot work:

During our research into where to put the radiator for our bay window or split screen bus cooling system back in around 2006, the original plan was to put one small radiator either side of the engine in the engine compartment, with ducted air from each scoop behind the rear windows. We abandoned this location in favour of under the floor because of the difficulty of providing a header tank location higher than the radiators. The only way to achieve this which would work in all bus models would have been to fit a hatch into one of the ducts from the vent behind a rear window, to access the filler cap from inside the bus., also this location would have required relocation of the battery, or often batteries in campers, which is far from ideal. The on;y alternative locations would be inside, and all space inside a VW camper is better used for camper related things.

Many years later we got to help a customer to test this system which he’d built and was having trouble with, and the change of location for our system proved to have been the right move. By spending maybe a day helping the customer to work out why the system he had build wasn’t working properly, and what, if anything, could be done to make it work, we gained the results of that testing without having to build anything or spend any money. His system was well built, effectively exactly the same as what we had originally planned to build, and his timing was perfect, as it coincided with about the highest temperatures we ever get in the UK. The results comprehensively proved that the customer’s ‘either side of the engine compartment’ radiator arrangement cannot work satisfactorily. We did get it to cool without relying on fans in the low 30’s degrees C ambient (this is not a high enough ambient temperature for a well designed cooling system), but this required comically large extensions to the inlet duct size, and the engine lid removed, and 100% impractical radiator air exit ducting extending back behind the rear of the body into the low pressure air behind.

One radiator mounted between the engine and the rear valance in a VW bus, and why this arrangement cannot work:

Going back way before we started work on radiator installations for bay and split screen buses, we’d been contacted by many people in the UK who had radiators in this location, and which were not effectively cooling the engine. They would rely on the fans being on at most times including when driving at high speed. This is not acceptable, as the purpose of electric fans on any modern engine is to increase cooling when coolant temperatures are higher than they should be – i.e. in abnormal running conditions. With the fan(s) already on trying to achieve cooling under normal conditions, there is no extra cooling in reserve for the abnormal conditions which cause coolant temperatures to rise in any car (e,g towing, very long hills in hot weather, having to slow or stop suddenly on the motorway on a hot day, etc). Under all other circumstances, the natural air flow from vehicle movement will be sufficient to keep the engine cool with a well designed cooling system. Most modern water cooled vehicles have more then one level of additional cooling which can be applied when the coolant temperature is abnormally high. This includes most T25 / T3 / Vanagon models, and all post MY92 Subaru’s, which have two.

In a well designed cooling system, the fans should hardly ever come on, and when they do, they should always knock the temperature back down quickly, and therefor turn off again. This should happen in cycles if things get really hot, as the temperature rises, the fan(s) turn on and the temperature reduces repeatedly (the temperature sensors or software controlling the fans intentionally have quite a lot of hysteresis). The fan(s) staying on constantly, as they do in some of these inadequate Subaru powered VW cooling systems, is proof that the fan system is ineffective – it is either not powerful enough to control the temperature, or something has gone very wrong with the engine, causing an extreme temperature rise (detonation, running lean, or other causes of likely imminent engine death).

The reason for there being many Subaru powered VW buses in the UK with radiators between the engine and rear valance is that a ‘specialist’ routinely fits them there. Their attempts at making this arrangement work are a joke. They use insanely thick radiator cores, with about the same frontal area as a standard Subaru radiator, apparently oblivious to that fact that the thicker you make a radiator core, the harder it is to get air to flow though it, and by the time any air that does get through to the back of the core, it will no longer be much colder than the coolant). It is no coincidence that the trend in OEM radiator cores ha been for them to get thinner and thinner. The ‘specialist’ or their customers also cut holes into the rear valance and / or engine lid (typically hiding the latter by mounting the number plate on stand offs). They also hide colour changing maximum temperature indicators on the engines they install, typically on the bottom of the coolant manifolds, or or at least used to. Apparently, this is in an attempt to wriggle out of any (inevitable?) warranty claims for engines damaged by overheating by claiming ‘look, you’ve let the engine get this hot’, as if the customer had a choice when the cooling system is incapable of cooling the engine.

The big problems with this location are:

  • There is no room for any ducting on the inlet side of the radiator, as the engine is in the way
  • As well as restricting the airflow, the engine and gearbox can only slightly increases the temperature of any air which does make it through the radiator core
  • Lack of space for air to exit the radiator, requiring external bodywork modifications
  • Lack of engine access. Not too big a deal if the VW is a late bay with an engine hatch, but a big problem if it is a split scree, and early bay or a type 1 engined late bay, as they didn’t get the hatches.

See how much effort it took when we helped a customer to get his otherwise well engineered ‘radiator either side of the engine compartment’ cooling system to work above in “Two radiators mounted either side of a VW bus engine compartment, and how we determined that this arrangement cannot work”. A totally impractical amount of additional ducting both scooping up air behind the rear windows, and venting it through the engine lid hole past the bumper into the low pressure air behind the bus. And that only achieved cooling without the fans being on up to the low 30’s degrees C. A good cooling system design needs to be capable of running insignificantly hotter ambient temps than that before it relies on the fans being on. Similar ducting would be required to get the ‘radiator between the engine and the rear valance’ location to work, except there is no space there for any of it.