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MG MGB Technical - Coolant leak – heater?


I have just fitted a new radiator to my 73 BGT, having done a thorough flushing of the system including the heater.

Just been out for the test drive:

- I have coolant coming into the drivers foot-well, by the look of it out of the heater vent - which has the heater above it?

- There is probably even more coolant dripping from Tom’s knob, externally. The chamber in which Toms Knob runs through is dry (access hatch cut earlier) so its probably just because it’s the lowest point.

Any thoughts? If the heater has developed a leak ( flushing damage?) can I bypass it in the short term? A heater change is not top of my list with a rally imminent …….

Mike
Mike Dixon

Mike. Yes, the heater may be by passed with no problem. In fact, a heater was an option over most of the life of the MG marque.

No, unless you used some inappropriate cooling system flush, the flush that you performed was not the root cause of any heater leak. It might, however, been the "last straw" of an old heater core that was on the very verge of break down. Since you flushed the system, refilled it, then carefully checked for any leaks or other problems, you did not have this happen, unexpectedly, on a long trip somewhere when you might have damaged the engine.

The best method of testing out the cooling system is to use a radiator pressure tester, which is pressure pump with a dial indicator (psi) on the front and a rubber line coming out the front attached to a pressure cap that is mounted on the radiator. Some people here have mentioned that such things are not common in the UK, but I wonder if that is true? Here in the US, such a device is not uncommon in the tool collection of the serious hobbyist and is a mandatory part of the collection of any professional mechanic. Someone should have one available to you so that you may test your system.

It is possible to test the heater core by attaching a longer heater hose to one side and a shorter, plugged, heater hose to the other. Use a bicycle foot pump to pump the core up to cooling system pressure (the pressure of whatever radiator pressure cap you normally run) and see if the heater core holds pressure. If not, make sure the hoses are tight and, if they are, assume a bad heater core.

Les
Les Bengtson

Thanks Les.

So I just need to run some hose from the heater valve to the water return pipe? Do I have the heater valve open or closed?

Mike
Mike Dixon

Mike,
if you're bypassing the heater then you might as well have the heater valve open.

Normally you can wire them to be fully open or fully closed but not both, by that I mean when you select either fully open or fully closed it will be one of those but not both, it doesn't matter either way in use you can chose so you might as well have open (to its fullest whatever that is).

Do I take it you didn't remove the matrix to flush it?

Are you absolutely sure it isn't just a leak at the matrix hose connections, a small split perhaps, or loose jubilee clip - always, always start at the basics and with the simple stuff first.

Are there grommets around the matrix inlet and outlet pipes to the heater box case?

You might be unlucky and have a leaking matrix but I think that's a lot more unusual than one that is more blocked.

I would certainly have been one of (or the one) to say over here you can't normally just nip in a garage ("shop") and ask to borrow or for a test with a pressure tester (for free?) but it might be more friendly in Wiltshire. You can buy them or make one yourself certainly.

Let us know how you get on, unless you can syphon the coolant out there'll always be residue in the matrix unless you remove it from the vehicle and give time and patience to getting it fully empty and dry, same for the radiator (and engine and gearbox).

Nigel Atkins

Mike. Yes, just run a hose from the heater control valve to the pipe for the heater return water. Valve position makes no true difference.

As to the pressure checker, most mechanics will do a basic pressure check for relatively little money. The mechanic I use for my regular cars is quite generous in doing tests such as this for free since he regularly maintains our other cars. If you have a shop you regularly deal with, they might also do such a test as a gesture of good will. If not, the test is quick, easy, and should not be expensive to have performed.

Nigel is partly correct when he states that you cannot get either the heater core or the radiator completely dry without removing them and putting them out in the sun for a few days. However, you do not have to dry them out when flushing the cooling system. Simply flush the system, completely, with fresh water, drain all that you are able, then refill with a water/anti-freeze mix and you will have no problems.

Unless you have owned your car from new, there is no way to ensure that previous owners have taken as good a care of your car as you do. Hence, there is always a possibility of poor maintenance in the past which will show up in the future. One of the things one has to live with until you sorted all of the previous problems. By the time you do, new problems will crop up. This is the same with any classic vehicle and MGs more than reward the time, trouble, and expense.

Good luck. Les
Les Bengtson

With residue in this case I was thinking that even if the matrix is bypassed that if it does have a leak and it's at the bottom, and sloping end at that, without the system pressure the leak might continue to drip for quite a while. Or take a while to transfer through an internally clogged up matrix to the leak part. Days after you think it's stopped you drive hard round a corner and when you park up more damp the next day.

With residue from draining for any cleaning I like to get out as much as possible each time to make each part of the operation as efficient as possible. Same for oil changes. Whatever residue is left in at any stage is diluting the effectiveness of the following and final stage.

For a one off thorough clean I'd have the radiator and matrix out of the car (engine block drain scraped) and shake/turn/blow/suck as much fluid out as possible but life's far too short and more interesting to waste too much time on these overpriced and overvalued old cars so I wouldn't worry about some being left in. I'd want to do a thorough job but only once, then just hot thorough drains as required.

I don't have classic car or marque rose-tinted glasses so my experience is different to others and I don't think the time, trouble and expense is always fully rewarded, often it's wasted but I only enjoy driving the cars and nothing else. The everything is sweetness and light doesn't wash with me as I've 30+ years of using various classics as dailies so I have lots of experience(s) without blindness to the many pitfalls of ownership (I struggled with putting the p on the end there). 😊
Nigel Atkins

Heater valve open or closed won't make any difference with just a hose from the valve to the return pipe.

It's quite possible for hardened crud to be covering a leak, but it would take a pretty aggressive flush to remove that and reveal the leak.

If it's dripping from Tom's Knob then really something should be visible through the grille as you can look right down on it. But with the heater matrix in front of and partly below the air box it's more likely a case of running into the box-section below the air-box and from there down the outside of Tom's Knob. For coolant to come out of the footwell vent there would have to be quite a lot in that box section. At a lower level than that is the mounting plate for the demister tubes, and leaks from there would get onto the top of the tunnel and down the sides into the footwell.

Any road up, as they say, it's almost certainly heater out time. It's said you can bend the cover away from the matrix ports and lift that out with the heater in-situ, but that still leaves the corner of the matrix tucked down below the top of the heater shelf, without further surgery to the heater case. The rubber block the post-1970 (or so) demister pipes fit into (the attached is the earlier arrangement) can be the biggest problem, not so much in getting the heater out but in refitting it with a new block as the old one is likely to be crumbling away. More info here http://www.mgb-stuff.org.uk/heatertext.htm#remove


paulh4

Thanks - further investigation with a mirror revealed a steady drip from the heater matrix. I will bypass it for now and investigate further in slower time - it might be something quite simple.

I would be nice just to be able to just get the matrix out if that is all that is required and is possible . But should I have to take it all out I suspect there will be bits and pieces to sort out/paint once I have, so I will need plenty of time.

I have a 'tame' local mechanic who gives me loads of advice and even lends me tools, so I may get it pressure tested - I will be passing his way to get my hose.....

My wife/navigator suspects its another user induced maintenance failure, but I am putting it down to coincidence as I think a couple of you are. As Les says better now than in the middle of an event/holiday so she is being very good about it.

I recall it was much easier on my midget!

Mike
Mike Dixon

Mike,
I cleaned and replaced the heater matrix on my BGT well before the days of the useful advice on forums such as this and just worked my way through it so if I could do it anyone can.

It's exactly the same principles as with the Spridget, renew/replace the seals as required but whatever you do it won't be as effective as a Spridget heater because of the cabin and fresh air vent, I'd try to seal that vent door, the manufacturer and factory didn't always do the best design and work.

I can't remember having any problem with that rubber block but I do remember not being able to find anyone who could tell me how to get in the screw under the fan arch of the heaterbox. On here someone suggested using an allen key headed screw.

It's just Sod's Law that as you didn't take the matrix out now you have to - but DO check that you actually need to and it's not just a leak from one of the hose connections getting into the heater box.

If you're bypassing the heater then you might as well have the heater valve open - if it makes no difference what's the objection, you're on a rally in summer why not have full circulation without the bother of the heat in the cabin.
Nigel Atkins

"user induced maintenance failure" is a bit unfair with cars this old.

It's change to what I wrote earlier but it depends on what your rally involves. If pushing it in high temperatures (if only) then having the heater valve open will have some coolant bypassing the radiator and its cooling. Some of us have found it necessary to have the heater on to assist the radiator in high temperatures.
paulh4

Mike,

I removed the heater box & replaced the heater box about 3 years ago. Don't underestimate how long it will take you , never mind the bad language & cut fingers. If you are intending to use the car in the very near future you may find it expedient to go down the temporary by pass route & do it in the autumn / winter if able! Paul referred to the rubber block at the bottom which the demister tubes go in to . I had to perform key hole surgery through the heater vents in the footwells to break it up so that i could lift the heater box out from it's location in the boxed section just in front of the air intake on the scuttle.It is made all the harder trying to do it when the engine is in -situ as you can't stand in the engine compartment & lift it straight out!


Cheers,

Charles
Charles9

I think the imminent rally will be ok - no big climbs but I will open the heater valve. I have a clear month after that before a more arduous one in September so that could be the chance to fix the heater.

If it means removing the 3 screws along the front of the heater box that also serve to clip down the brake pipes I think I might be paying for some help for those alone - I know I cannot shift two of them and that by the look of it is only the start of the potential problems. It never ceases to amaze me how something I have been faffing around with for hours takes my local mechanic 3 minutes to do when I finally admit defeat.

I will do some calling around in the morning to book in some help at an appropriate time. I assume I can drive it a few miles with the heater out so I can get home to do the titivation and then, if required return for help with re-installation - that would make the whole thing doable.
Mike Dixon

I can't remember it being that much of an awkward job on my 1974 BGT and I still be moaning about it now if it was. Perhaps, no probably, the new parts were better made then.

For the screws (there are 4 or 5, definitely one under the fan housing parts of the heaterbox that needs an Allen key head) for a week in advance of doing the job soak them in PlusGas or GT85 overnight then try to slightly tighten to break rust/crud/muck seal then try to loose, if it doesn't work repeat for the next night and following if required. I can't ever remember it failing me - let the chemical do the hard work not your wrist.

As someone put earlier not all Bs had a heater so no problem driving with out one but they did have a blanking plate to stop engine bay fumes getting into the cabin so you'll want fix something up temporarily to block the large aperture left by removing the heater box.

As the navigator your wife really ought to be assisting in the repairs and is she prepared to push the car out of deep mud and check depth of water crossing to save the car. My wife refused to push the car anymore a couple of decades back, and it wasn't like I wasn't doing the steering.

We went on a charity day of 4 rallies one Sunday with the likes of Paddy Hopkirk setting a route and (not on his route) one of the checkpoints was a pub that wasn't open to serve ale, never done one since!
Nigel Atkins

Mike
Before you bypass the heater, I'd have a real good check around where the hoses fit up to the heater
There have been plenty of people caught out by having a leaking hose joint, with coolant tracking from the end of the hose down into the heater box--specially if you happened to have one or both of these hoses off during your recent flushing process.
If you're going to bypass the heater for a rally, there's two trains of thought
#1 tap open---hot water from the head/tap is recirculated back into the waterpump and back into the engine--
#2 tap shut--normal cooling

With a heater in the circuit- 'sometimes' it can be an advantage to turn the heater on if your engine is starting to overheat as this uses the heater matrix as an extra mini radiator and also has a bit extra coolant in the circuit,-- but with the heater bypassed ,if the engine starts getting hot, opening the tap will make it worse as there will be hot water entering the pump inlet instead of cooled coolant from the radiator
My vote is---leave it shut/off
willy
William Revit

This is why I asked about the grommets, rubber on the case front might reduce ingress and show more signs of leak from hose on the outside of the heater box, whereas the foam type inside the heaterbox, or none at all, might hide the leak from the hose.

My thinking with heater valve open is, the cooling system has been cleaned and hopefully fully checked and fully working so shouldn't need any assistance of having the heater matrix on but having the valve open gives a more constant heat which the stat and cleaned system should be able to cope with.

The bypass hose does provide a little chance of heat transfer from engine - but of course this heat goes into the engine bay, where the engine sits. If the bonnet has the standard sound deadening that will also keep more heat in the engine bay.

In summary it doesn't make much or perhaps any odds either way so you can have a preference but if you forget or don't bother it doesn't matter.

Checking the valve is open might find if it leaks there too - stealth instruction/advice. 😊
Nigel Atkins

Mike,
My car acquired from new did not have any grommets over the heater matrix pipes where they pass through the "lid" of the heater box. When i removed & refurbished the box i obtained the grommets which were listed under MGA spares. (It maybe your year of MGB had grommets but i don't think so)!
I suspect they would be difficult / impossible to fit with every thing jammed in place & you would end up wrecking the lid by bending it forward.
I recall using a mole wrench / WD 40 & suitable posi-drive screwdriver to get the heater box mounting screws out.
Cheers,
Charles
Charles9

Charles,
I've got grommets on the heater box of the Midget but I put them there, I can't remember what if anything was there before. They also help to hold the matrix inlet and outlet pipes a bit when pushing on or pulling off the hoses. The ones I used IIRC were just spare for use on house electric metal sunken boxes.

I can't remember what was on the Bs I had if anything but the grommets Moss sell look the same/similar as the ones I used on the Midget.
Nigel Atkins

BTW - I wasn't suggesting to fit the grommets, well not at this point, only asking if they were fitted.

If ordinary WD40 worked then great but it's not so good as a penetrating fluid hence it sits on and coats a surface to repel water. PlusGas I've always found works, before that Rapideeze but that's no longer available and I also use GT875 for lubricating so try that too and no doubt other stuff also works and there might not be that much between them but as I put I've always had success with PlusGas though I suspect that it's not as good now as before it was made elsewhere.


Horses for courses, each to their own.
Nigel Atkins

I did bypass the heater and all was well, but given the advice above I reconnected the heater just on the off-chance and gave it a really good run; no leaks!

I had not disconnected the pipes from the heater as part of the flushing - I can only think I disturbed the seal pipe /heater in moving them around to get water through them. My bypass hose will be safely stashed in the boot though.

Thanks all - just saved me hours of 'fun' . Beer credits added should we ever meet!

Mike
Mike Dixon

Well done Mike, that's the sort of end to a job I like, instead of car-farting-about.

After removing hoses and clips do check before and again after a good run that they all tight, even the ones you didn't touch.

Check all clips for tightness, no need to go mad on them though, for jubilee clips slightly loosen first to make sure they're not stuck in one position then tighten, it may be you can only tighten by how much you have just loosened but that's OK at least you know for sure. On a jubilee clip I find a socket (usually 6 or 7mm) on a short solid screwdriver type handle give me more feel than with a ordinary "slot" or "cross" screwdriver.

Of course I just have to put for my own selfish pleasure -
you probably wouldn't have the leak had you had the rubber grommets on the heaterbox as they hold the matrix more. 😁

(Of course you could come back and say they are fitted whether they are or not, it's all just fun).
Nigel Atkins

I only discovered the grommets from someone else after many years. Not listed in the Parts Catalogue for the MGB, some suppliers show them but others only for the MGA. I fitted them when refurbing my V8 heater and they finish it off nicely, 7H1993.

paulh4

I am in agreement with Paul. See my refurbished box ready to go back in with the grommets. An additional modification i made was to modify the top mounting bracket so that it became a moveable "L bracket" with a welded bolt through the top of the box which made it easier to slide under the lip of the scuttle ,attach a nut & then fit the screw holding the box to the engine side fire wall.(Particularly given that the later RB cars re-routed the brake lines to under the lip & it saved scratching fresh paintwork)
Cheers,
Charles


Charles9

This thread was discussed between 07/07/2021 and 10/07/2021

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