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MG MGB Technical - MGB heater motor

I have looked in the archives but was wondering if anyone has found a direct replacement for the original heater motors. My car is back on the road after a 3 year rebuild and the defroster is just not great. I have checked the wiring, ensured the defroster tubes are connected, the intake is clear and ensured that hot water is getting to the heater but I don't dare go out without a cloth to clean off the windshield. I don't remember it being this bad before but it is just like the old VW that I used to own now. The volume of air that it moves is pathetic.

I am aware that it is not going to be like a new car but surely we can do better than that.

Brian
1974 MGB GT
Brian Smith

Brian, there's no "direct" replacement that I know of. The best upgrade I've seen is to a GM three speed motor and fan assembly. It's not difficult to do, takes a little modification to the heater box and some wiring, but really puts out the air. I did a similar upgrade on my midget and really like the results. http://www.mgexperience.net/phorum/read.php?1,519704 should take you to the article which describes the mod.
Bill Young

brian
moss europe do an uprated heater assembly that is bigger and stronger than the standard one
it is deeper than a standard heater box though
ste
Ste Brown

"I don't remember it being this bad before ..."

But it's been 3 years. These things weren't very efficient when new. Have you tried closing the foot well vents? Is your vent (selection) control cable adjusted properly?

I've driven roadsters and GT's in winter (up north). Both were terrible in providing warmth to the body and keeping the windshield clear. My GT's were a bit better on cabin heat, but condensation on the inside seemed worst than experienced with my roadsters (e.g., trapped higher humidity from my breathing). To lessen some of this problem, I would open the pop out side windows until the little beast had things under control.
Steve Buchina

Make sure the motor is rotating in the right direction.I replaced the fan/motor with one from a Mini Minor. It was bigger & stronger. Another trick is to wire the motor directly to the 12V+ (brown) cct. via a relay.I'm not sure how this would work with atwo speed motor though. Barrie E
Barrie Egerton

MGOC offer a replacement/upgrade. Have a look on their website get back if you can't find it
Stan Best

I have tried wiring the motor "backwards" and no difference. This is a single speed motor so maybe I will try checking out the voltage getting to it. I drove this car daily all year round for many years until I retired and decided that it deserved to be rebuilt. I never really had a problem with defrosting the windows or heat but it is clearly not the same now. The windows fog and unless I use the cloth to clear them, they stay that way and it doesn't even get warm now although the line to the heater and the return are both good and warm.

Brian

Here is a link to the rebuild of the car.
http://www.island.net/~btsmith/
Brian Smith

Try one of those grill covers that lets in fresh air. The one that's located at the center of the windscreen. That keeps out a lot of cold , fresh air and allows the innards of the heater box to stay a bit warmer.

G L Gimbut

A replacement or upgraded motor, fan or matrix will have little benefit if there are other issues with the heater system. I have counted at least 10 areas any one of which with a problem will contribute to poor performance, and you could have any number of those ten areas with problems. My roadster heater burns my feet, and my V8 will clear mist off the screen in seconds. I've measured the heat output from my screen vents at 140F/60C with an ambient of 50F/10C. You might like to have a look at http://www.mgb-stuff.org.uk/wn_heaterframe.htm for some ideas.
Paul Hunt 2

This thread was discussed between 20/02/2008 and 23/02/2008

MG MGB Technical index

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