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MG MGB Technical - Overheating (catastrophe?)

Hi all,
Driving home today I suddenly heard a strange rattle come from the front of my 78B, it seemed to be from the engine bay. Almost immediately I noticed the smell of coolant and then I saw my temperature gauge start climbing rapidly. If it wasn't such a sunny day I probably would have had the roof up and not noticed until much later.
I pulled over to check. The thermostat for the fan had popped out of the radiator. Coolant had escaped and splashed over the front of the engine.
Halfway between home in the middle of nowhere. No water, just a bottle of Red Bull which I'm sure wouldn't have helped much.
I let it cool down until the temperature gauge was below halfway before attempting to drive it slowly home. Made it barely to my street with the temperature not quite reaching the red mark, but it conked out anyway and I had to push it around the corner and into my driveway.
So I let it cool down to halfway again before firmly replacing the thermostat and refilling the coolant very slowly.
I've started the engine okay and let it warm up a bit, now I notice a very small leak coming out an invisible crack in the engine block just in front of the 3rd spark plug.
Have I warped my cylinder head as well? How do I check? Is this a total catastrophe worthy of the cheap bottle of red wine I'm considering consuming to drown my sorrows tonight?
Any help (or condolences) appreciated.
Cheers,
Dave
P.S. On a side note, I thought the gauge was stuck so I tapped the glass. It broke the glass. Not my day, eh?
D O'Brien

Trouble is when you loose that much coolant the temp gauge will not give an accurate figure as the sender will be in steam AND the top of the engine will cook very quickly without water. Is the leak in the head or the block or on the head gasket line? If you're very lucky warping is all you've done!! The over-heating and then not letting the engine go stone cold before re-filling may well have cracked the head.
Not a great fan of the rad switch on R/B's. Either seal the hole off and use a sender in the top hose or a properly soldered in and threaded boss in it's place, with a screw in sender.
Allan Reeling

Damn. I certainly didn't let it go stone cold before refilling and that could be where I did the most damage.
The crack appears to be just above and to the right of the 3rd spark plug. I can only see the crack when the engine is running and the green coolant starts to leak through.
As for the sender, I always thought that rubber grommet seal wasn't going to hold it in if the pressure built up. I guess I was right. I will definitely be soldering in a proper threaded boss now.
D O'Brien

Allan is right, coolant loss doesn't show on the gauge until it's too late. I had the bottom hose on my V8 develop a pin-hole on the M6 and the only way I knew was that there was slight miss-fire when accelerating. Oil and temp gauges were spot-on, but I decided to pull into the next services anyway ("Listen to your car, it is talking to you"). It was only when I slowed right down I could hear it hissing like the Royal Scotsman. After that and another longer-term cooling system issue I fitted a coolant level warning light, which I can't quite bring myself to remove even though I solved the problems years ago. Later 4-cylinder cars had a clip which positively holds the sensor in the gasket, I'm not sure whether that is directly compatible with the earlier unit.
PaulH Solihull

Dave,
That's a classic spot for cracks to develop. they usually start at the plug hole then go to the head bolt boss, or the edge of "the lump". If you take the head off you might also see that the crack has gone through to the valve guide. Your head has probably got "the lump" between 2 and 3, but these heads still crack. If so it's scrap I'm afraid.
Allan Reeling

Hi Dave, I had a similar issue with the temp switch on my '80RB. The switch had moved in the rubber seal so that the one arm of the metal holder JUST engaged the switch body. When it let go I was fortunate enough to have removed my head from a close inspection of the distributor. Could have been nasty.
I used thin steel wire to secure the metal holder ( clip as referred to by Paul) so that the two "arms" are in effect locked at a fixed distance, over the body of the switch which stops the switch moving our under pressure. Has been that way for about 4 years BUT I do check it when I check the water level about once a month. A few of my friends with MG Bs have done this a precautionary measure, simple, cheap and effective.
As you may have a top end rebuild looming could be best to go the whole hog a get a soldered in unit.
Cheers Ray
R. E Bester

Dave- Speaking first hand, I can testify the holder clip does not guarantee squat. On my brand new mega rebuild for the SC car, I started having heating problems during breakin. I thought it was friction heat build up and would taper off as the engine wore in. Well, in traffic slowdown, on the freeway, I saw the temp gauge creeping up. Scrambling to the next off ramp, I pulled over, left the engine running and opened the hood. The fans were not on, the temp was saying 200*, and as I was using the IR thermometer to read radiator manifold, sender, and head temp, the sensor blew out the radiator top as I stood there watching, dumbfounded, and dripping with 50-50%.
Whereas I share Paul's vestigial suspiscions for these cars after 40 years of marriage to them, I went to the trunk and grabbed one of the 2 gallons of water I always carry in each car, along with every tool known to man, and spare parts stashed in every corner. Wiping things down while the engine went "stone cold", I replaced the brand new Moss supplied sensor, grommet and holding clip. Two hours and some friendly phone chat later, I refilled things, and finished my drive no problem.
Next day after warmup, I'm checking things out and the temp is rising again. I'm reading temp spots with the IR and have my friend, a gentleman who actually worked at Abington, building MGB's in the late 70's, advising me. The fans are not coming on again. I wiggle the trip wires, but get nothing. I pull the wires and use a paperclip to jump and start the fans. With the engine idling, fans turning, Lawrence standing there, I go to shut down engine. The bulb, grommet and clip all blow out again, as 50-50% erupts like a geyser, drenching again, the new engine. After wiping things down...................

Cheers, Vic
vem myers

My STERLING had the same arrangement but they had small bracket soldered to the header tank and after inserting the switch there was a "U" shape clip that was inserted behind the bracket to hold the switch in place.
It should not be hard to duplicate it.
No photos available as the car is long gone
DARNOC31

Dave,
small consolation - you have written off the cylinder head. With modern engines, by the time you realize you have an overheating problem and pull over into the slow lane - you need a new engine. A small engine from the Gothenburg factory cost my wife £4000 and the fitting.. another £600 on top. Bentley or Kia it's the same story only the price varies.
Bad luck.
Roger
R Walker

Alas. I should have known better. I normally carry all my tools but I had them in my other car as I've been doing work at my girlfriend's house.
So now I need a new cylinder head. I hope I haven't damaged anything else major.
Looking at the list of heads from Heritage MG (the local supplier in Australia) I'm a bit confused which one is for the 1978 rubbernose UK-build. Their list is at http://www.mgspareparts.com.au/index.php/store-catagories/engine/head-list
I can rule out the MGBV8, MGA, MGC and midget heads. From the remaining MGB it isn't clear which one is for the 78 model.
The prices range quite a bit and this close to Christmas I'm trying to keep the expense down as much as I can.
D O'Brien

Hi Dave, Sorry about the head. I cannot help you with which one to use but have been dealing with Heritage for years. There listing I think is expertly designed to totally confuse. You have their phone number give them a call. They have always worked out the correct part for me and you will probably have options as complete head or bare. See if there is any casting numbers before calling, it may help.
Good luck
Ken
K Stuckey

Dave,
I think the later R/B engines went back to the smaller 1.57" inlet valves, but the large valve head 1.625"will fit but may need the bores modifying to clear the exhaust valve.
Allan Reeling

Dave - I would follow Ken's advice; if yours is a near UK spec (engine-wise), your head was probably a 12H4735. By now it would have been modified to burn leadfree and/or ethanol - so you want an updated 4735. If they don't instantly know what you are asking for - go elsewhere - it's a bit of a minefield.
Roger
R Walker

Dave,

Don't rush this or it could cost a bundle. Firstly, there are a number of other reliable suppliers of heads/parts generally in or around Sydney. Consider:

Sportsparts P/L Normanhurst phone 02 9875 1144
Very good with helpful advice and can source difficult parts. MG sports driver owner really knows his stuff. May be a little dearer than some others but well regarded for quality.

Nepean Classic Cars Penrith phone 02 47 323 211
Have a website as well. Long time car and parts supplier to MGs. Changed hands a few years ago but generally well regarded.

There is another business at Granville, very well regarded but I cannot find a contact. They do advertise in Australian Classic Car magazine though, so you will find them there.

There is also a sportscars business up on the peninsular somewhere. Again, from memory they also advertise in the same mag.

Not knowing anything about your car other than the year/model you gave, important in deciding on a head replacement will be to know what head AND block are presently in there. The original might have been swapped for another. Any amount of work may have changed original specs of the head or the block eg bore size. You will need to know and understand the present mix of specs to make the best and most economical choice.

As a starting point, probably need to lift the head at least to check chamber characteristics and access bloc details. Head casting nos are on top, under rocker cover. Block nos are on stamping block on RHS (from drivers seat) of block.

Good luck.

Regards
Roger
R Taylor

FWIW, and not trying to hijack this thread, I am pulling the radiator, braising off the bulb hole, and using a Corvette sensor switch which will screw into the top of the 76-80 thermostat housing. That should do it. No u clips required.
Further, FWIW, we've had good luck repairing head cracks with pins, and/or high temp kiln welds. Cheers, Vic


vem myers

I've also had great luck with repairing cracked heads with pins. I took a BMW head to my local machinist after getting a quote of $1,300 for a new, bare head. He was able to drill out and pin the crack at the exhaust valve. That was several years ago and it has held up perfectly. RAY
rjm RAY

Hi
i also have a similar problem..

see this video..http://www.youtube.com/watch?feature=player_detailpage&v=QjzQT_qzoC4

but i think the engine is running lean..the spark plugs are light grey..

Alfredo


a rodrigues

Do you have other symptoms? I can't see anything wrong in either of those.

All I can see in the radiator filler is the circulation of coolant by the pump, with a tiny amount of 'froth' which is probably from turbulence. The plug looks fine - http://www.atlanticjetsports.com/TechTalk_Images/spKPlg_colorchart1.jpg. If it is weak it is only fractionally, and incidentally running with the oil filler cap removed does weaken the mixture (not that I'm assuming you actually drive the car with the cap removed).
PaulH Solihull

Paul
the car over heats, and throws the coolant out, i got new radiator,cap, water pump, thermostat,head gasket,just over a 1000kms ago, i though those bubbles had something to do with compress air going out to coolant lines..
also the oil cap being badly rust..
if i ride with radiator cap just half closed then its ok...
see todays ride...http://www.youtube.com/watch?v=kMoo9N4dJso&feature=youtu.be
thnks
Alf
a rodrigues

Dave: when replacing the cylinder head, I recommend you replace the head bolts as well. The bolts may have lost their tensil strength and may either snap, or stretch upon re-assembly thus creating an additional failure. MG cylinder head cracking is not uncommon. Mine was replaced with and alloy head and has been excellent ever since. That was 7 years ago.

Keep us postd on your progress

cheers

Gary

79 Mgb
gary hansen

Alf,
If you run with the cap half closed, you will reduce the temperature at which the water boils. Boiling means steam and steam means hotspots leading to distortion etc. The easiest way to see if you have a gas leak is to fill right up to the top of the filler neck - rev the engine and see if it bubbles. The alternative is to put chemicals into the coolant which change the colour of the water if exposed to gas. Someone here will tell you what it is called and where to buy it.

On the bright side - a new cylinder head gasket is no big deal. Less than a days work on the 1800.
Roger
Roger W

Alf, did you replace all that stuff because of the problem? And the problem is unchanged? Or has that problem arisen since those changes? I note the temp gauge was bang on N in your video. Does it boil when driving? Or only shortly after switching off a hot engine? What pressure cap do you use?

As you close the rad cap the tabs on the cap ride along ramps on the neck gradually tightening it, then drop into recesses to lock the cap in that position. So the cap is on tighter just before it is fully closed, than when it is fully closed. If you really do mean half closed, then that should be less tight than when fully closed, leading to what Roger says. If that *stops* it boiling then that says to me that there is something wrong with the cap or the neck, or both, but you seem to have changed both hence my questions.

As sold by the MGOC 4Life coolant is said to have an indicator of head gasket failure by changing colour, although other sites I've looked at mentioning that coolant don't say it. Alternatively there are combustion leak detectors that use a chemical to show the presence of combustion gases at the top of the radiator http://www.amazon.com/Lisle-75500-Combustion-Leak-Detector/dp/B0007ZDRUI

PaulH Solihull

Hi Roger/ Paul
the video was done after i found that problem, so the radiator cap was half closed( first lock step) it did reach the N mark stays there.
with cap fully closed it went over that mark and when turn off the engine it did not stop imidiatly, like if its timing was advanced.
the stuff i mentioned was replaced together,new radiator, cap, water pump, and head gasket.
the reason for that it was overheating, but it was ok for while, i donot do many kms a year maybe about 500kms ,i take the car out a few times a year for short rides say 40 to 50 kms.
there is 10 stamped on the cap, not sure what it means.
I will try to get the gas test fluid to make sure that is not the problem.
i have enriched a bit the fuel nut 3 flats down the su4 carbs.
thanks for your feedback.
Alf
a rodrigues

"when turn off the engine it did not stop imidiatly, like if its timing was advanced"

That does sound like overheating, causing hot-spots in the combustion chamber, and running-on. If it isn't spitting coolant out of the overflow then it's not boiling-over as such, but you could be getting localised boiling around the combustion chamber which means water is no longer conducting heat away. It could be a combination of factors. I'd be inclined to retard the timing a degree or two. I think you need to do a pressure test as well. You can get adapters that fit between the rad and the cap that you can pump up and check for leaks as well as the pressure of the cap, but given your situation with the cap I'd be more inclined to do something involving the top hose, like one chopped in half and and adapter fitted between the two halves, like some electric fan sensor switches do. As well as the static test I'd also do a running test with a cabin gauge in the adapter so you could monitor pressure both running and after switch-off.

Caps are usually marked in PSI as well as the metric equivalent, like this one which is a 20lb cap.


PaulH Solihull

Alf,
Late model B's used 15lb rad caps, GHN 4/5 used 10. Running on is a problem all B's have had, the latter ones seemed worse. There are things which make it worse, including; too hot a grade of plug, weak mixture, carbon in the combustion chamber, too high a compression ratio (skimmed head/block or wrong head!!), poor fuel, to name some.There are lots of things which cause overheating, depressurising the system is only giving you a false gauge reading, you will still be losing water and the sender end of the gauge will not be in water. If coolant is being spat out, then the system is either boiling because it's not pressurising, get a 15psi cap and check for leaks, or it's over-pressurising either due to a warped head, a cracked head or leaking gasket. The bubbles in your video would seem to suggest the over-pressure theory.
Allan Reeling

i took the car for MOT just now, i had to lean the mixture a bit o pass, while was standing and engine running for some time the needle gauge went up to 3/4 full and built some pressure so when i stoped it throw some fluid out even with half closed cap.
I thing the next step is to take to a workshop and do the pressure test to eliminate that possibility or not.
my cap could well be 20lb type since there is no indication of psi just a 10.

thanks for feedback and picture.. i will keep on posting the results.
Alf
a rodrigues

Mine ('70 Roadster) was doing a similiar thing. Would be fine for 30 miles or so the temp would head to the top end and stay there the water level would be very low. As I have the 'crook neck' rad I guessed the level a bit and put the vent pipe from the rad cap into an empty bottle (1l Tonic water! No longer god for Gin!) bottle. The catch bottle would have water in at the end of a drive if the temp stayed 'Normal' but would suck it back in on cooling. but if the gauge went hot then the bottle was empty. I borrowed a pressure tester and found a VERY tiny leak on the top hose round my Kenlowe fan seal. A new jubilee clip and the pressure tester stayed steady so I hope the problem is cured. It would appear that as the water level dropped (vented via leak) then the top hose was empty, once the thermostat opened, eventually the temp sense bulb (Guage) would be in steam rather than water hence the rapid guage rise. Also as I had no anti freeze the expelled water was dissappearing in the airflow and leaving no trace so I had no idea that the leak existed! Once the rain stops for more than a day I'll be able to go for a decent test run but I have my fingers crossed
Bernie
B Anderson

I tought of leaving a picture of the cap here.


a rodrigues

As a general point, the cylinder head gasket is prone to leak - very often this will be when the revs are higher - after cooling down the seal is remade and a test at idle reveals nothing. This is not solely MG/BL/BMC. They all fail eventually, it was mainly 1970s MGs that failed straight out of the factory. When Peter Burgess sorted the head on the 18V for unleaded fuel, he recommended a Payen gasket tightened slightly higher than the manual recommended. Peter if you are reading, many thanks, you did a good job. Can you tell these folks the torque you recommended.
Roger
Roger W

I intend to pressure test my cooling system (1980 MGB standard UK spec). I plan to insert a temporary tee connector in the pipe that connects the header tank to the rad, then connect a tyre valve to the tee-off point. This will allow me to apply 15 psi pressure using a foot pump (which has a pressure gauge). Will this work?
Brian Shaw

Alf - It's unlikely to be a Kpa cap as 10kpa is a tiny psi. As an Imperial cap then it's only 10psi anyway, not 20. Surely no manufacturer would put a '10' on the cap to mean something else, and not pressure ... or would they?

Don't use a 20lb cap in an attempt to solve a problem, I did and the bottom hose burst shortly after a hot switch-off. You shouldn't get anywhere near that when everything is right, working properly my V8 only got up to 11psi just as the fans cut in i.e. about 1/3rd the way from N to H.

Brian, yes it will, that is exactly what I did and it is easy with the expansion tank, less so without. I used the same method for a cabin gauge to it so I could monitor the pressure while driving while I had a cooling system problem. Pump it up cold and leave it overnight and there should be very little if any pressure loss next morning. As well as testing the cap pressure your foot-pump should be able to display the real pressure i.e. hot running if you run it at a fast idle (by wedging the throttle, not pulling the choke).
PaulH Solihull

Pressure test done. Pumped it up to 15 psi. The following morning it was 5 psi and about a quarter pint of coolant on the floor. Found a small leak at top hose/thermostat housing. Hopefully it's nothing more serious than that.
Brian Shaw

A bit late on an update, but it's been Christmas holidays and after my new cylinder head was installed the car was running like a dream (until this week, but that's another story in another post).
I did end up getting it from my usual supplier as I've always had success with them. I won't name names, but one of the other suppliers recommended by R Taylor was a no-go for me after a ery bad previous experience with them.

Anyway, I handed the job over to my usual mechanic and organised the parts for him. He did a bit of checking of his own and confirmed I had the right part. He has lots of experience with British cars, although Minis are his main game rather than MGs.
He told me the new one had single springs whereas the one I was replacing had double. He explained the differences and what I took from it was basically the single springs might be noisier. I drive with the top down anyway so I can't hear anything.
He did a very thorough job tuning everything, including the twin SUs. It felt like I was driving a new car. In fact I don't remember it ever driving so well. The engine seems to run extremely smoothly and power/acceleration is more than enough to bring a smile to this leadfoot's face.

I learned my lesson about putting cold coolant into a hot engine. An expensive lesson but the end result is a big improvement. I can't complain... except for the new problem you can read about in my other thread. :)

Thanks again for all the insight and advice. As always it has been invaluable.

Dave
D O'Brien

This thread was discussed between 04/12/2012 and 15/01/2013

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