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MG MGB Technical - heater fan output

Hi

Driving home sunday evening in cold damp conditions and couldn't see a darn thing out the windscreen through all the condensation?

i've read the posts about bobs heater valve mod - is this just concerned with heat? What i would really like is a bit more airflow. Mine seems to trickle through - its hot once engine gets warm but there isn't enough of it!!

is there a bigger fan/twin speed motor i can fit or any mods to stock equipment?
Blind?

Blind,

Too bad you're not a member of this group, there is considerable info on this subject in the archives. To summarize that info, a TR-7 blower may provide more air flow with very little modification or you can increase the wire size to your current blower circuit and get a little more boost.

Also, there are some inexpensive checks that you can perform on the air delivery system in your car. The ducts tend to get brittle with time and crack, apply duct tape to the holes. The felt seals on the air direction baffles come loose causing the baffles to leak, it can be glued back into place. These tests can be done with the dash in place, but its easier with the dash out.

A little more costly is the removal of the heater housing and replacing all the seals associated with it. If you go this route, be sure to clean the dust off the fan blades. Once you know you have no air leaks it will be easier to determine whether or not you need a larger blower motor.

Doug
D. Cook

Blind:
My page you mention is concerned only with the valve and its ability to deliver hot water. However, as you have judged, there is more to the problem than that one item.

I am going to post a cross section view of the heater box on my webpage, http://hometown.aol.com/akamrmg/MGPhotoShare.html , maybe this may help folks visualize how the air flows thru the heater. Look for it by tomorrow. There are other things that could be causing your heater to not deliver heat or where you want it.

D. Cook mentions several, other, less obvious ones are reverse polarity of the fan motor electrical wires; blockage of air intake at the air intake plenum (air entry hole next to squirrel cage fan opening); broken, disconnected, or plugged up defroster vent hoses or dash level diverters, slipping squirrel cage fan on the motor shaft, or possible control cable breakage or disconnect.




Bob Muenchausen

Bob, that cross section photo doesn't seem to have the spongy seal around the demister pipes. I have read that that can be a pain to replace, and others have left it out. I recently pulled my heater box and I did not have that seal. As far as I can tell the box had never been out of the car. What's your opinion on that seal.

Doug, thanks for the tip on the TR7 Squirell Cage! I new someone had done that mod with a Triumph part, but I didn't know which Triumph model. Does it fit right on the existing blower motor shaft?
J Moore

If you don't mind, my 2 cents..a good heater seal is essential. Recently I got carried away and removed, restored and renovated my car's heater box while the cylinder head and block were at the machine shop. After reinstallation I found that the what I believed to be a windshield leak was a leaking heater box. Not only do I get greater flow to the defroster outlets, but, the heater really blasts away even with a 160 stat.

rn
RN Lipow

John,

I have not tried the TR-7 modification myself, I was only trying to summarize a thread from the archives. It is my understanding from that thread the mod is a complete swap of motor and all; the TR-7 being similar in size and shape but with a more powerful motor. But it's been a while since I read that article.

Doug
D. Cook

RN - Thanks, anyone's advice appreciated. I'm doing the same thing, my engine is off at the machine shop!
J Moore

John,
I recently asked about that seal (the thick one at the bottom). Like you, I think my heater has never been out and it does not and seems to have never had that seal. I looked at it and could see no purpose that it served. Someone -- Chris Betson, I think -- explained that on the earlier cars like ours, the two fibre demister pipes serve the function that the seal serve in later cars.... The BL parts book lists it for all MGBs (at least up to Sept 76, the end date of the book), but I've certainly known parts books to be wrong! I've since noticed something else as well. The BL MGB parts book lists the seal but makes no mention of the demister tubes. The BL MGC body parts book shows the tubes, but does not list the seal. Perhaps the tubes were superceded by the seal?
Rob Edwards

Thanks Rob! Unless someone comes up with a better reason not to, I plan on leaving it out.
J Moore

To the best of my knowledge today, I do not recall having replaced the sponge seal you mention which goes around the demister pipes, and is/was wedged between the heater shell and the firewall panel, as I recall. It was probably a good idea, but apparently it was not completely necessary as I have always gotten good air flow since rebuilding. Getting hot water to the core was always a bigger problem for my car, and once I opened up the valve and modified it, I had that too. FWIW.
Bob Muenchausen

Oooooh, he wants more than a trickle of air, does he! Mr. Special thinks he's better than everyone else. Why should HE have a functioning demister? An MG with a winscreen defroster that really works - boy talk about your NONORIGINAL MGs.

Next he'll be wanting his wipers to clear the rain off the windshield.

Seriously though, this problem is easilly solved by inhaling from inside the car and exhaling out the side window, inhaling from inside the car and exhaling out the side window, etc.

On the constructive side, I have thought about the small in-line fans that I've seen at racing supply stores. Anyone have experience with them?
Fred H

I'd start with making sure your heater box is making good heat - that enables the moisture at the windscreen to evaporate quicker.

My cars ability to clear its windscreen without the use of a rag, increased ten-fold when i bought a new heater matrix and replaced the seals to the heater box.

Doesn't matter what thermostat i now run, the car is warm within minutes of setting off and the windshield clears very rapidly. Further to this, i threaten physical violence! ;-> to anyone who touches the inside of my windscreen with fingers/rags etc. the fan cant work as efficiently with a greasy/unclean windscreen.

Clean the windscreen properly with warm water with a little vinegar mixed in and rub with brown paper on a dry day with either a heater on in the car or with car in direct sunlight. Dont use those "windscreen cleaning" sprays, they just smear grease not cut through it.

Then afterwards never rub window with rags or fingers - espcially when damp as this builds up oils which promote misting up. Use the fan instead and periodically (in dry weather again) wipe the windscreen with more paper to get rid of any dried moisture droplets.

You can add a relay to the fan, which may or may not increase power - if you fit relays to the headlights, then the fan seems to pick up a bit anyway. You can also buy an uprated output heater fan from the MGOC. Not needed since i bought a new heater matrix however. Oh yeah, and do Bobs Mod! ;->

~PHIL
Phil

Fred,
elaborate on the inline fans you mention - like where you have seen them, etc.

I have always wondered why, at this point in time, modern car makers have not introduced small high output heating elements into the demister air stream which would come on only when the car was cold, and cut out when the hot water would begin to flow. Having hot air immediately at start up would not be a bad thing. Modern electrical systems probably could handle these little heaters, but they may be too expensive or impose other requirements that manufacturers don't want to pay for.
Bob Muenchausen

Fred et All,

I just installed Bob's "alternative" heater valve
(many thanks to Bob for his help). I have the stock heater core and motor, and what a difference the valve made. It hasn't been terribly cold here yet, maybe high 30's, but the heat almost drove me out with the fan on. It's comfortable with the fan off and heater vent closed when the valve is open!!

I did clean out the heater core when I rebuilt the engine two years ago. Also have installed my winter (195) thermostat. I guess my point is that increasing the flow of hot coolant to the core really makes a difference.

Cheers, Doug
Doug Keene

Bob, the major downfall of an electric heater is amperage requirements. A very small heater, say 500 watts, would require almost 40 amps of current. I'm not sure there is an alternator that would put out that kind of power at idle - at least not one that would make for an affordable upgrade. You may also have problems with seals degrading, as well as the need for thermal proving switches for fan operation. It would be an interesting project, but the only real payback would be the ability to say "I did it first." Sometimes that's all we really need, isn't it? Well, that and a clear windshield.

Actually, it seems to me like the best solution for more airflow is to have a smooth metal pipe rather than the plastic or foil type pipes supplied from the factory. Pvc has too much airflow-friction, as do the factory units. I would suspect an airflow increase of anywhere from 30-40%. Hmmm.....
Jeff Schlemmer

You mean there's a fan in a MGB? I thought it was just a bunch of mice running around under my dash :)
Mike MaGee

Bob, Behling Racing Equipment has them, but I can't locate my catalog.

Their phone is 262-783-7474 if you want to order a catalog.
Fred H

Actually, it's a hamster panting on your foot.... ;-)
Rob Edwards

HA! Found it. It's cylindrical with what looks like 3" ends for venting and the middle is abou 4" dia. Looks about 8-9" long judging by the picture.

$30 inline blower - 3"
Fred H

Perhaps I missed something, but the first thing that I would look at is the shutter that switches air between the cockpit and the windshield. If you happen to be a newbie, that shutter can be viewed from the right-side heater outlet. It could have been mis-adjusted by a DPO. Twenty years ago, mine separated the flap from its control --- I had to re-solder it.
Dan

Jeff,
You are probably right about the amperage being too much, especially at idle. Lord knows I found that to be true in my GT with just its OE alternator and all electrical on in the worst of winter driving (and not even a rear window defogger to sap the juice away!)

Thanks, Fred for the info on the inline fans. There are several things I can think of that these could be useful for on our cars. Every new resource is a new possibility for doing things better.
Bob Muenchausen

Bob, some modern cars do sport an instant heat from cold system. Some of the more up-market vehicles equipped with climate control use the air-con unit as both a chiller and a heat-pump. You can extract plenty of heat from the outside air even when said outside air is well sub-zero. No doubt this arrangement will trickle down-market as things do.
I remember once seeing an article where somebody had done a similar mod to an MGB GT. They removed the (redundant) heater assembly, covered the scuttle air intake and installed the heat-exchanger in the space created after some additional chopping. A second heat-exchanger at the front, two pancake fans and some ducting later and all working. The controls were cleverly adapted to work from the existing knobs on the dash, although a new fan switch was required to cater for the four speeds now on offer(!)
T J C Cuthill

Why not just get hold of the period windscreen heating elements, as seen fitted to (amongst others) the monte carlo Minis... They were metallic elements stuck to the window which were used to defrost instead of heater air.

These are also fitted to latest fords etc as tiny little metallic strips inside the windscreen laminate.

~PHIL
Phil

This thread was discussed between 17/11/2003 and 19/11/2003

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