Upgrade a 401 heating system?

[Geoff Kingston]

In a few weeks time I will be stripping out the heat exchangers blower and pipework for the cabin heater and screen demister and am thinking now is the time to think about improved demisting and better heating.
Any thoughts and suggestions would be most welcome either to improve what is there or to modify the whole set up with a more powerful modern under dash unit such as those sold by Holden's or Car Builder Solutions.
The car when it does get back on the road will be kept in use during the winter and our wet Welsh summers! so good demisting is going to be as important as a decent heater.
Geoff.

[dave dale]

Hi Geoff,
For what it might be worth, here is my contribution: When I first got my 403 in the late nineties, there was hardly any heat available in the cabin. I had the heat exchanger radiators in the footwells backflushed and all the pipework, valves etc. cleaned or replaced. Although there was much better heating, I was still a little disappointed. After everything was checked again I posted the question on the BOC forum. I was advised by someone who had been through the same problem to always leave a window slightly open. Result – a huge improvement! I was also reminded by the adviser that the Drivers' Manual states that a window ( rear quarterlight is recommended if I remember correctly ) be left slightly ajar. I was reminded again of something that I already knew but had forgotten – " when all else fails then read the instructions "! Anyway, it is so hot in the cabin now that I often drive in the dead of winter, as is my preference, with the driver's window fully open
( except when my girlfriend is a passenger, of course ). Another interesting little discovery is that, for some strange reason, leaving the nearside front window slightly open directs cold air to the driver only, without impinging on the passenger, and vice versa. It also demists the screen rapidly. As a consequence, when I have my girlfriend in the passenger seat in winter, she cooks gently in the cabin heat whilst I drive in shirtsleeves with cold air keeping me comfortably cool from the slightly open nearside window. I also fashioned some quick – release radiator blinds from clear perspex which clip onto the outside of the radiator grilles. Makes warming up quicker and maintains a higher coolant temperature. A few years ago I drove the 403 to the former East Germany in the dead of winter. Temperatures were consistently well below zero but the cabin stayed as warm as toast, which leads me to suggest that there would be no need for you to replace the original heating equipment.
Good luck. Dave Dale.

[Geoff Kingston]

Hi Dave,
I had seen something about this a while back so having seen your advice I looked up the relevant section in the 401 handbook and explains the reason why this works and how vents open windows shut creates a slight cabin pressure which is useful apparently if you want to keep dust out of the car when driving on dusty roads but not if you want heating or to recycle or as they put it in the handbook recondition the air inside the car.
The only reason I was thinking about possible changes was that I remember someone years ago telling me they had changed the system on a customers car. This might have been to allow blower assisted air into the cabin as well as for demisting. I will have to take everything apart as the water hoses are perished and the heat exchangers and valve have not had any water in them for over 40 years so I will probably have the exchangers reconditioned when I have the main radiator I intend to use done. I might just put it all back and see how it works, its so long since I used a 401 in the winter that i really could not remember if the system was good or bad, I do remember a heat exchanger bursting on a 401 once that was quite spectacular and it was a good job the carpets were old and there was no passenger on board at the time.
Thanks for you help.
Regards,
Geoff.

[ahaugland]

I just purchased a Bristol 401 which had been modified by a previous owner with a blower motor controlled by a separate switch that fed into a split duct and into each of the air intakes for the heater. The original mechanism relied on airflow created by forward movement of the car to push air through the heater matrices. The blower motor theoretically should allow you to keep constant heat independent of motion. I can't say yet really how well it works as I am still sorting out a couple of things in the car. The entire assembly mounts in front of the radiator, potentially shrouding the top section of it so I also don't know what impact it will have yet in hot weather. The system has, however, been on the car for at least the last fifteen years, through the last three owners and several thousand miles so I'd suspect that it works OK.

--Alex Haugland
Eugene, OR
USA
1953 Bristol 401

[Geoff Kingston]

Hi Alex,
That sounds an interesting set up, the standard 401 set up has the blower mounted by the right hand heat exchanger and is used for demisting only, the 403 has a sliding panel in the air distribution system to allow this air under pressure from the blower to be diverted to the under dash area not just the foot wells. I had considered adding another blower by the left hand heat exchanger with ducting to the under dash area or as there is plenty of room there one of the new compact heaters as used in a lot of kit and classic cars to provide heating.
I think what I need to do first is get the existing blower working and see how well that actually pushes air to the screen.
Another option suggested is to fit heated screens which I must admit I had not considered, John Lawley is going to talk to a potential supplier about this.
Knowing how well these can work on modern cars that and an alternator conversion might be worth considering and leaving the standard heating system unaltered.
Geoff.

[ahaugland]

My car still has the blower for the demist as well, but as the added fan effectively blocks the intake for the heater when it isn't running, both would have to be on in order to demist the car.
A heated windscreen would be an interesting option. Jaguar on the Mk2 and S-Type (the 60's version) with a generator had an optional heated rear screen, with a somewhat comparable area of glass heated. They do work (at least it does on my 3.8 S-Type) and don't draw enough voltage to overrun that generator, so you may be fine with the stock generator on the Bristol without installing an alternator. I'm not sure how it's output compares to that of the Jaguar's, however. Heating elements do draw quite a few amps, but the demisting elements don't need to generate much heat to be effective.

--Alex Haugland
Eugene, Oregon
USA
1953 Bristol 401