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MG MGF Technical - heater box replacement

I was wondering if anyone knew how difficult a job it was to replace the heater box on the front of the F

After numerous attempts at fixing it, It STILL LEAKS
:0( i will give sealing it one more go but i think i may need to change it, i have been told that rover charge a fortune to do this and wondered if it was a job for the very novice, novice :0)
Nick Walters

Did you manage to get the sealant I suggested?
Bruce Caldwell

I did M8 and i pulled it into the back as hard as i could. What i did do though is to double it so it was thicker, so it may have been to big to get into the gap. I will try it one more time but this time just using a single strand that may help.
I am not sure.
Nick Walters

It must be a big leak then! Perhaps as you suggest it is best to get the box out and replace the seal. This requires removal of the fresh air trunking under the dash inside the car.
You can then remove the screws holding in the box; two under the bonnet at the front bottom edge and some more inside the car I believe. This is the extent of my knowledge on this because I have never reached this stage nor found anyone else who has. My car has aircon which further complicates the issue. In my case I believe it would require draining the aircon system to remove the condenser unit.
Just to re cap on your leak.
Does it occur when you move off or when stationary?
PS have you also sealed around the grommets where the harness passes through the bulkhead?
Bruce Caldwell

Thanks for replying Bruce.

My leak happens more when i move off but still leaks when stationary, i can see where it is coming in, i poured a watering can of water down the windscreen and looked under the dash (with seat removed and carpet pulled back) and i can see it dripping from the heater box, a round foam like seal. I dont have aircon so should be an easyish job but like i say i am a very novice, novice :0).

If i do need to replace the box does anyone know the part no... as we all know what rover parts depts are like :0)
Nick Walters

I have just spoken to Rover who have quoted 500 to replace the box so i really need ot look at replacing it myself now.. so any help would be appreciated

I appologise as i know this is a tiresome subject :0(

Nick Walters

Crumbs Nick- not sure how many people could really advise you on this. I'd give Mike Satur a call- mainly because he has rebuilt a number of MGFs from scratch.

The cause of the leak according to a recent article in Safety Fast is a result of a problem during the car's manufacture- the seals often become distorted during the installation process. Obviously the easiest solution is to seal the box in situ. Is replacement really going to be necessary? I ask because on the production line, the order of installation sees the heater box installed before the dashboard is installed around it. Therefore to remove the heater box would involve comprehensive dismantling of the interior- hardly a job for the faint of heart.

Have another look at the options before embarking on the replace route- and Mike might be a good person to chat with. B&G may be able to help too?
Rob Bell

Check the archive - there's a full DIY instruction for replacing the heater box COVER (which is all you need to do) with the new, modified part.

I'd give you clues as to what to look for, but my printout of the thread's at home - but I'd try "heater" and read through what it finds...

I must get around to looking at mine before the winter rains as it leaks too...

NNW 49 (97 VVC)


I got a quote for the heater air intake box about a month ago (the seal is between the horizontal bulkhead and the bottom of the box).

The cost of the part was 28 I think that was plus VAT.

Didn't need it in the end as I took the whole box out and sealed it back in place with black silicon sealant 7 approx. The hardest part was getting the box out from under the bonnet and over the brake servo.

Worth checking under the passenger carpet and sound proofing material. Mine took two days to dry right out I recon it must have been leaking for months/years with the previous owner.


Russ Fitz

Thats why i am sick of it Russ as everytime i seal it i dry out all the carpet and the soundproofing, then it leaks again making puddles everywhere :0(
Perhaps i should leave it as an on board paddling pool :0)
Nick Walters

Hit the "archive" link at the top of this page (5th link from the right).

Search for "Leak Through Heater" in the MGF technical archive.

Has full instructions and the part number you need (if you can't manage to get the existing cover to seal with mastic)


I tried removing the box with no luck as the brake cylinder got in the way. I just lifted the heater box up slightly and forced silican sealant in and then fixed back in position (this was done from inside the car). I also removed the blanking cover for a LH drive car and added sealant there aswell.
Hopefully this has cured the leak.

Tom Randell

Alright nick, for a start you do not have to replace the whole heater box just the foam gasket which if you can not get one you can make one ,which is probably better than the original anyway.And to remove the box is not very hard at all,
1. remove the under bonnet trim,2 10mm plastic nuts on the right and a plastic screw fixing on the left. will now see the torsion tube leading to the brake servo remove the 'R' clip and tube washer on the left.
3.Witha 13mm spanner loosen the 13mm bolt at the back of the servo on the right.
4.With a long extension ratchet and 13mm socket go between the wheel arch and wheel to loosen the lower 13mm bolt(you may need to jack the car up slightly to gain access if the suspension has dropped slightly).
5.With a shorter extension remove the 2 13mm bolts on the left side of the servo.
6.once removed remove the servo vacuum pipe by pulling the lift the servo up untill the 2 loosened bolts are clear of there mountings and pull the servo forward slightly,this should give you enough room to remove the air box.
7.go in to the passengers compartment and remove the glove box,2 screws underneath and 2 inside,also remove the electrical connectors from the bulb holder and switch 4 in total. remove the air duct to the heater box 2 10mm nuts then pull downwards.there you will see the bolts to remove the box.remove clean and refit with a new sponge gasket,refit carefuly not catching the new gasket.
9refit in reverse order.
hope this helps you.
Dave mgf tech

Sorry i haven't replied before i needed time to do the work and now i can say Dave mgf tech, i do actually believe you are a genius, i went to rover this morning to ask about replacing the box, when i asked if it was a stock item he just laughed so i went to halfords and bought some car silicone sealer, the box is a doddle to remove if the instructions are followed carefully, my foam gasket was ripped and a bit missing from one corner so i would assume thats where the water was getting in, so a lot of silicone was applied, when the box was replaced the silicone pressed out of the sides so i know a good seal is made.

i would say these instructions need to be put somewhere like the FAQ as i know a lot of ppl will need to do this... and i am sure these instructions will help..

All i need to do now is to wait a couple of days to let the silicone dry properly and then i will test it..

A big Thank you
Nick Walters

Did it work?

Bruce Caldwell

It has rained here and there was no water inside the car so i guess it is ok, i am putting off pouring water down the windscreen though just incase.
I guess i will have to soon though before the winter sets in..
I am pretty sure there will be no leaks though :0)

Nick Walters

This thread was discussed between 23/08/2001 and 05/09/2001

MG MGF Technical index

This thread is from the archive. The Live MG MGF Technical BBS is active now.