Motoring Discussion > Cooling in rear engined vehicles?	Miscellaneous
Thread Author: movilogo	Replies: 26

Wed 16 Mar 11 09:47   Cooling in rear engined vehicles? - movilogo

In one Fifth Gear episode, they tried to see if gearbox explodes if a car is continuously driven in reverse. The result showed gearbox remained intact but lack of air caused engine to overheat. So, in rear engined vehicles (e.g. Porsches and most coaches/buses) how the engine is cooled? In mid/rear engined cars (Ferrari/Porsche) there are cowlings at an angle on the sides of the car which does allow some air flow. But what about heavy vehicles where no such cowlings can be seen? Reply to this message | Report message

Wed 16 Mar 11 09:55   Cooling in rear engined vehicles? - L'escargot

Hillman Imps had a conventional radiator and an engine driven fan with ducting/cowling to ensure that all the fan-produced air went through the radiator. Reply to this message | Report message

Wed 16 Mar 11 15:30   Cooling in rear engined vehicles? - Kithmo

>> Hillman Imps had a conventional radiator and an engine driven fan with ducting/cowling to ensure >> that all the fan-produced air went through the radiator. >> And they often overheated. Reply to this message | Report message

Thu 17 Mar 11 09:03   Cooling in rear engined vehicles? - L'escargot

>> >> Hillman Imps had a conventional radiator and an engine driven fan with ducting/cowling to >> ensure >> >> that all the fan-produced air went through the radiator. >> >> >> And they often overheated. >> Hillman Imps, like all Rootes products of that era, were designed to be able to be driven at a continuous maximum speed (and at a continuous maximum torque in 3rd) in an ambient temperature of 40°C without the coolant boiling or without the engine or gearbox oil temperature reaching an unacceptable level. Any sample which wouldn't conform to those parameters was defective in some way. Last edited by: L'escargot on Thu 17 Mar 11 at 09:05 Reply to this message | Report message

Thu 17 Mar 11 10:22   Cooling in rear engined vehicles? - Zero

> >> Any sample which wouldn't conform to those parameters >> was defective in some way. Or the design was flawed. Reply to this message | Report message

Thu 17 Mar 11 10:36   Cooling in rear engined vehicles? - Auristocrat

My father thad two Imp variants - one the estate (the Husky) and an Imp Super. Both were owned for four years, and neither had an issue with over-heating. Both had their water pumps replaced due to them beginning to leak, and the king-pins were also a weak point. Reply to this message | Report message       1

Wed 16 Mar 11 09:55   Cooling in rear engined vehicles? - Rob81

Some rear engined, water cooled vehicles have a radiator at the front and pipe cooled coolant all the way back to the engine. I guess most also have massive fan in the engine bay to keep things a bit cooler. Reply to this message | Report message

Wed 16 Mar 11 10:53   Cooling in rear engined vehicles? - spamcan61

>> Some rear engined, water cooled vehicles have a radiator at the front and pipe cooled >> coolant all the way back to the engine. I guess most also have massive fan >> in the engine bay to keep things a bit cooler. >> SWMBO's Skoda Estelle was like that, although the fan wasn't massive Reply to this message | Report message

Wed 16 Mar 11 10:58   Cooling in rear engined vehicles? - Armel Coussine

>> Skoda Estelle was like that, although the fan wasn't massive Estelle had a normal-size electric fan behind the front radiator. Only worked when needed (e.g. when stuck in traffic). There was no fan in the engine compartment. Reply to this message | Report message

Wed 16 Mar 11 11:08   Cooling in rear engined vehicles? - spamcan61

>> >> Skoda Estelle was like that, although the fan wasn't massive >> >> Estelle had a normal-size electric fan behind the front radiator. Only worked when needed (e.g. >> when stuck in traffic). There was no fan in the engine compartment. >> A right thanks, that's why I can't remember what it looked like! I recall the thermostatic switch on the radiator failing on SWMBO's, so I just mounted a switch on the dash, and had manual electric fan actuation. That would probably be tricky to do on most modern cars. Reply to this message | Report message

Wed 16 Mar 11 16:43   Cooling in rear engined vehicles? - bathtub tom

The Estelle rarely needed a cooling fan. The ducting for the front mounted radiator meant the air came in high and exited low in an 'S' shape. When stationary, convection would play a major part in cooling (as well as the pipes running the length of the car). The first time I drove my daughter's in rain, I was convinced it had a holed radiator. I stopped in traffic, the 'stat opened and hot water caused the rad to steam off the rain water which rose in front of the car. Imps tend to clog their radiators by blocking them with detritus sucked up by the fan. Those that use them off-road (particularly on grass) know to keep them clear. Reply to this message | Report message

Wed 16 Mar 11 17:06   Cooling in rear engined vehicles? - spamcan61

>> The Estelle rarely needed a cooling fan. The ducting for the front mounted radiator meant >> the air came in high and exited low in an 'S' shape. When stationary, convection >> would play a major part in cooling (as well as the pipes running the length >> of the car). >> True, I only recall having to use my manual override switch about half a dozen times over a couple of years. Reply to this message | Report message

Wed 16 Mar 11 17:15   Cooling in rear engined vehicles? - Iffy

When I was doing breakdowns off the motorway, we used to expect a cooked Imp or two if it was a hot day. To be fair to the little car, it worked well enough if properly maintained. It had an aluminium engine, and the year-round benefits of anti-freeze/corrosion inhibitor were not well understood. The plastic cowling linking the rad to the cooling fan often split and fell off. Home bodgers wouldn't replace it, resulting in a boiling Imp on a hot summer's day. Reply to this message | Report message

Wed 16 Mar 11 09:58   Cooling in rear engined vehicles? - VxFan

>> So, in rear engined vehicles (e.g. Porsches and most coaches/buses) how the engine is cooled? Radiator still in the front, IIRC. Unless it's an aircooled engine (eg, VW Beetle, campervan - which have cooling fins on the cylinder heads) Reply to this message | Report message

Wed 16 Mar 11 10:28   Cooling in rear engined vehicles? - Skoda

On a Porsche 911 (996), as well as the normal radiators (there's 2 at the front, either side with the central radiator being an oil cooler for the autobox) there's ducting underneath the car scooping air into the engine bay. Reply to this message | Report message

Wed 16 Mar 11 10:48   Cooling in rear engined vehicles? - Armel Coussine

>> cooling fins on the cylinder heads) ... and a huge, noisy, power-sapping fan... Reply to this message | Report message

Wed 16 Mar 11 11:17   Cooling in rear engined vehicles? - lancara

Remember Beetles and VW campervans in Kuwait (rear engined cars good traction on sand) were mainly driven with the engine cover propped open permanently Reply to this message | Report message

Wed 16 Mar 11 13:15   Cooling in rear engined vehicles? - jc2

Rear-engined Renaults had the rad at the back.Most rear-engined buses/coaches have side mounted rads. Last edited by: jc2 on Wed 16 Mar 11 at 13:16 Reply to this message | Report message

Wed 16 Mar 11 16:49   Cooling in rear engined vehicles? - Bellboy

theres an extra cooling fan in the air intake behind the drivers door on those hairdressers mg rover tf thingies Reply to this message | Report message

Wed 16 Mar 11 21:37   Cooling in rear engined vehicles? - jamesh764

My Fiat X1/9 had the radiator and cooling fan in the front, and pipes running underneath the car to the engine in the back. Additionally there was another fan in the back which blew cold air onto the carburettor - I think it was some kind of mickey mouse bodge job to prevent fuel vapourisation or something. Reply to this message | Report message

Wed 16 Mar 11 21:41   Cooling in rear engined vehicles? - Number_Cruncher

The only place you don't really want the radiator to be is in the turbulent wake behind the car where the relative speed of the air flow is very low. This is exactly what you will get if you run a standard car in reverse. On a rear engined car, the air can be sourced from an area where the flow isn't in the wake, and/or you can oversize the fan, or, you can admit defeat, and move the radiator to a forward position where you can take the input from a relatively high pressure region, and arrange the outlet to be in a low pressure region - best exemplified by the Lotus Elise. Reply to this message | Report message

Thu 17 Mar 11 01:01   Cooling in rear engined vehicles? - VxFan

>> The only place you don't really want the radiator to be is in the turbulent >> wake behind the car where the relative speed of the air flow is very low. Hence why some banger racers mount the radiator where the rear windscreen used to be. Not only does it get plenty of air blowing through it, it also stops it getting crunched during racing ;) Reply to this message | Report message

Thu 17 Mar 11 08:02   Cooling in rear engined vehicles? - IJWS14

Rear engined cars are designed to cope with being driven forwards with the engine at the back. Front engined cars are not designed to do long distances in reverse with the engine at the back, just as rear engiend cars are not designed to run in reverse for long distances (in their case engine first). Try driving a 911 in reverse and see what happens - it will cook. Reply to this message | Report message

Thu 17 Mar 11 09:03   Cooling in rear engined vehicles? - DP

>> Front engined cars are not designed to do long distances in reverse with the engine >> at the back, There was a video on YouTube of someone experimenting with this using an old scrapyard bound mk2 Cavalier. It really didn't take long for the thing to expire in a cloud of steam. A couple of minutes at most. Reply to this message | Report message

Thu 17 Mar 11 09:48   Cooling in rear engined vehicles? - bathtub tom

ISTR someone doing research on airflow over car radiators many years ago (America IIRC). They came to the conclusion that maximum cooling efficiency was achieved with an airspeed of 12 MPH over the radiator. Reply to this message | Report message

Thu 17 Mar 11 10:17   Cooling in rear engined vehicles? - L'escargot

>> They came to the conclusion that maximum cooling efficiency was achieved with an airspeed of >> 12 MPH over the radiator. >> It depends on how you define "efficiency". In general, heat transfer between the coolant and the airflow increases as the air velocity increases. You'd need an extremely high air velocity for the reverse to happen. Reply to this message | Report message

Thu 17 Mar 11 10:21   Cooling in rear engined vehicles? - L'escargot

>> Front engined cars are not designed to do long distances in reverse with the engine >> at the back, ............ How could you have a front engined car with the engine at the back? Reply to this message | Report message