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MG MGB Technical - Cooling system leak questions

My 74.5 "B" has just overheated. I found that the heater core must be leaking because both passenger and driver footwell carpets are saturated with coolant. Looking into this I've got a couple of questions.
1) Is this coolant going to ruin my carpet or just dry and be sticky? If so, should I flush the footwells with water? Suggestions welcome.
2) I replaced the radiator cap last summer but today I noticed that both my old one and the new one (10lb from Moss) have a slit or cut across the face of the rubber seal that mates to the inner neck on the radiator. The old one is pretyy uniform but the new one looks more like a rip. None of my other cars have this cut. It goes completely across the seal. Is this normal?
3) Are the heater cores usually repairable?
4) While running the engine I also see "spits" of water coming out of what the parts catalogs call the "Front Cover w/ Oil Separator". This is a roughly 2" by 4" by 0.5" deep cover that is on the side of the block and has a steel emissions system pipe coming out of it. Most of the emissions system was removed from this car so it just sits open now. Any idea what this is covering, why there would be water in here and is it OK to be left just open or should I seal?
Thanks,
Tom
Tom Gillett

Tom - sounds like you need a new heater matrix. Rinse the carpets in the bath and put them on the line/airing cupboard. Talk to Moss about the rubber gasket. On the cover prob. can you be a mit more specific - what engine - precisely where it sits ??
Roger

Roger,
Thanks for the response. The car is a 1974 and 1/2 MGB with the 1800 engine. The engine cover is on the drivers side at the front of the engine under the intake manifold.
Tom
Tom Gillett

Tom - That cover is part of the emission system that should be hoked up to the intake manifold via a PCV valve (if you have HS4 carburetors) or via a Y fitting to the carburetors (in the case of HIF carburetors). Are you sure it is water (coolant) and not oil oil that is "spitting" out of that pipe? You should not be getting any water "spitting" out of there as the cover is over the tappet chest and open to the crankcase (where no water should be). Cheers - Dave
David DuBois

David,

I forgot to mention that someone replaced the original carbs with a downdraft Weber so all the emissions hoses, injectors, air pump, etc. were removed before I got the car. I don't see a place to route it into the Weber. My wife and kids got me the car for my birthday. Fortunately, there are no emissions tests in this part of Virginia yet. Thanks
Tom Gillett

1. Definitely sounds like something ripping the seal, it should be a smooth continuous rubber disc.

3. I wouldn't bother, given the trouble of removal and replacement I would never fit a repaired unit, and I would pressure test a new one before fitting! Adding a leak sealer to the cooling system could be an option, but as you can't see the leak you won't know whether it has worked for a while, and they can block up other parts of the cooling system.

4. PCV valves were replaced by the far better carb breating system in September 68, and HSs from then on had the crankcase breather ports, as did the HIFs that followed them. Only if you had HS carbs earlier than that would you need a PCV valve with SUs. Whilst export cars got HIFs with the 18V engine in 71 the UK continued with them until the 74 model year. Webers don't have the breather ports and so do need PCV valves or you have no crankcase ventilation and can get internal corrosion. With water (if that is what it is) spitting out of the front tappet chest cover port you either have significant condensation, or maybe a head gasket leak allowing coolant into the combustion chambers and from there past the pistons into the sump, or a leak from a water passage to the oil passage for the rocker gear. Unfortunately this is quite possible having overheated due to lack of coolant.



Paul Hunt 2

Been away - the news/advice meantime must sound disheartening. It sounds as if you need a new filler cap - and a cylinder head gasket.
I am guessing the gasket is blowing - this often has the effect of increasing water pressure - the extra pressure then looks for the weakest points - in your case the heater matrix (the water from the cover is another side effect).

Although not infallible, the way to check out a blowing cylinder head gasket is to run the engine up to operating temp with the radiator cap off the car. The bubbles coming out of the radiator filler are an indication of a blowing head. A lot of bubbles will tell the tale - a few bubbles could be the outcome from a hotspot causing boiling because of the lower pressure.

Do you want to give it a go and let us know what happens ?

It's an MG - hope youre in this for the long haul.

Roger
Roger

Well, who needs a heater! I'm bypassing until I iron out this whole problem. So, what should I see if I take this engine side cover off? I don't have a replacement gasket handy yet so will I get a large amount of oil leakage if this seal is not perfect which will be the case when I reattach the cover after inspection?

Also, because the new radiator cap seems to be no better than the old one (actually much lower quality seal) I had to get a 13 lb unit locally instead of the recommended 10 lb unit. Is this dangerous or no big deal?

Thanks,
Tom
Tom Gillett

Tom

I would have done the same with the rad cap - but change back when you can get a good quality 10lb unit.

The side cover provides access to the cam followers - the view is underwhelming - everything you need to know is coming out of the tube. Hopefully oil vapour and not too much steam.

I meant to say in my last post that the head test needs the rad to be full - use the throttle a little to test the head gasket.

Good luck - Keep us posted.

Roger
Roger

Tom. When a Weber conversion is done, the front tappet cover is connected to a 90 degree elbow that is fitted to the air cleaner at the bottom of the lower chrome piece.

If it is, truly, water coming out, you have a significant problem as this means there is water in the oil passages. A compression check and a cooling system pressure check need to be done to see where the problem might be. Bad head gasket or cracked cylinder heads are the two most common sources of oil/water mixing.

Plan on on oil and filter change, immediately, to preserve the engine's bearings.

As to radiator pressure caps, the MG uses the same size pressure caps as the older small block Chevy engines and they are available from quite a number of sources.

Les
Les Bengtson

13lb should be fine, the factory fitted 14lb caps eventually. Only if the system is pressurising for any reason i.e. a defect should it reach cap pressure, I had a 20lb cap on my V8 for a while when it was pressurising and one day the bottom hose exploded in spectacular fashion.
Paul Hunt 2

Les,

Can you recommend a good source for the correct air cleaner assembly? Mine has a hole but no pipe and the filter doesn't fit. It is simply two, 7" diameter, round, tin plates with a filter sandwiched in between and i can't fing replacement filters from Moss or VB.

Also, the compression test revealed no leaks. Can a Miti-Vac be rigged to help with the cooling system pressure check? If not, how is this performed?

Sorry for the delay in responses. I don't get much time to work on the project.
Thanks,
Tom
Tom Gillett

Tom. Your local BAP store, and most VW specialists, have air filter assemblies for the Weber DGV series carbs. Similar in style to the K&N and you can use the K&N cleaning and oiling kit when needed.

A cooling system pressure check requires a handpump having a pressure dial and an attachment to the radiator filler neck/expansion tank. You pump up the system to the rated pressure, determined by what pressure your original pressure cap was rated at, and see if the system will hold pressure. If not, you look to see where coolant is being forced out from. Hopefully, it is simply a bad or loose hose. The tool costs about $100 the last time I purchased one, making it somewhat expensive for the hobbyist. But, most mechanics will have one available and should not charge a great deal for performing the systems check. It can also test the function of the radiator's pressure cap to see if it will hold pressure properly. A bad cap can cause an overheating condition. The MGB uses the same size cap as the 1970's vintage small block Chevy engines. Get the one nearest your required pressure rating.

While talking to a good mechanic, ask where you can get some hose to connect up the air cleaner to the tappet cover. Heater hose will work, but is not designed to hold up in an oily environment. There are hoses designed to work in such an environment, but they are not commonly stocked at the discount parts houses. NAPA should have it available.

Les
Les Bengtson

Some autoparts stores rent the tester Les mentioned. It looks like a bicycle pump.
Kimberly

Let me see if I can attach a photo the the cooling system pressure tester in use.

Les

Les Bengtson

No leaks ? steam coming from the vent ? or oily vapour ?

Further Pressure tests with the engine hot !

Good luck

Roger
Roger

This thread was discussed between 29/03/2008 and 13/04/2008

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