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MG MGB Technical - Substance oozing from head gasket? Oil or coolant?

I have a 73B of which the engine was rebuilt 3000 miles (2 yrs)ago. Pretty much since the first startup I have noticed that there is a black oily substance that is oozing out of the head gasket area below the number 2 and 3 cylinders. I've been told that the only likely fluid that this could be is coolant, but the stuff looks and feels alot more like oil. Being that the oil passage to the head is on the other side in the rear corner of the block, is it possible that what I am seeing is oil? It seems oil would have to travel quite a distance across the block to come out where it is. Initially I thought it might be coolant that has mixed with sealing compound applied to the head gasket, but now I'm not so sure.
Since the rebuild its using a pint of oil every 100 to 200 miles. I do not see appreciable smoke or oiliness in the tailpipe or exhaust, but the sparkplug side of the engine is quite wet (I see maybe one small drop on the garage floor after a run though). When the engine is running, this substance bubbles at the block/head interface, and has left a fine black spray on the underside of the hood.
I hope that this is in fact oil, because I have to remove the head for some work, and will use a Payen gasket which I hope will solve the oozing and oil use problem - am I hoping in vain, and do I have to look elsewhere regarding the oil consumption?

Thanks in advance for any comments.

Erick
Erick Vesterback

I have a 73 BGT and gave it a top overhaul about ten years ago. It was the first time the head had been off and after reassembly I noticed a slight ooze and bubbling from the same area as you. However, that was 40k miles ago and it's still oozing but not enough to worry about. I would be concerned about using a pint of oil every 200 miles as even when I was commuting 60 miles a day I wasn't using anything like as much as that. But if you have enough fluid leaking to leave a spray on the hood that leak is probably to blame. I would change the head gasket and see how it goes afterwards.
Miles Banister

Erick. There are oil passages on the right hand side of the engine, plugged off with brass plugs. One is near the distributor and some have had problems with oil leaks there. The valve cover gasket has long had problems with oil leaks, especially some of the newer gaskets which seem to be made of inferior quality cork. I would throughly clean the engine exterior, take the car for a half hour drive, then examine to see where the oil is coming from.

Anything bubbling from the head gasket area is a bad thing. Even if it were oil from another source, the fact that there are bubbles indicates there is a problem with the cylinder head or the gasket. Fel-Pro makes a very good gasket set for the MGB engine as uses a resin head gasket marked "Made in England". I have used these on three rebuilds with excellent results.

It is possible to take a cold engine and use a cooling system pressure gauge/pump to put the system under pressure. If you have a cooling system leak, it will show up by the system not being able to hold pressure. If you are lucky, you will be able to see where the leak is.

With these tests performed, you should have a better idea of what the leak consists of and where it might be coming from.

Les
Les Bengtson

I have a Payen gasket, which from what I can tell is also called Fel-Pro which I plan to use - it has a length of extra material along the sparkplug side of the gasket to improve the sealing on that side. I've heard of John Twist using strands of copper wire on that side to seal it up as well, but I expect the Payen/Fel-pro should do the job. Should that gasket be installed dry, or would some type of sealant be a good idea?

I will try to rig something up to pressurize the coolant system and see if that causes the bubbles to form or shows evidence of a leak.

Thanks Les and Miles for your help.
Erick Vesterback

Erick. The resin style gasket should be installed on a clean, dry surface. Do not forget to check the cylinder head nut's torque after initial run in, then a couple times more over the first 1K miles. I retorque at 200, 500 and 1K miles.

Les
Les Bengtson

I don,t have the archive thread, but I recommend checking under leak down test. Check compression and see if the cylinders are equal. If they are, do the leak down test.

Like Les said, if it is the head, then it needs fixing.
Bruce-C

Do you have access to a black light? I'm pretty sure that I still have a few vials of flourescent dye additive for oil. You clean everything, pour it in the oil and drive a while. Turn all the lights out and shine a black light in the area and everything that is oil that has leaked since you put the dye in will glow yellowish. If you want to try it let me know.

Tom Lea
tom

I measured compression a few months ago, and got the following:
dry/wet
1 - 162/185
2 - 160/185
3 - 155/180
4 - 170/200

I was a little surprised that number 4 was so much higher than the others.

Bruce - From what I understand, the leakdown test measures how quickly air escapes from the cylinders using compressed air into the sparkplug holes? I don't have a tester, but saw plans somewhere for building one. I do have a compressor - is the idea that you do the test at various crank positions to see if the leakage changes with piston position in the bore? How does one change the piston position without the compressed air turning the engine over (apparently the engine will want to spin if the piston moves even alittle off TDC).

Tom - I have tried the dye before, but I have found that the coolant and the oil seemed to glow equally under the black light, so I wasn't sure what I was seeing. Even the Castrol Diesel 15W40 that I use seems to glow without the dye under the light that I have. I'll take a look at it now with the black light, clean it up, then add some more dye to the oil, and see if it gets brighter, and conclude that its oil.

The head has a small crack above #3 spark plug, and leaks coolant at the rate of 1 drop per minute. Actually it doesn't leak coolant right now because I covered the area with Marine Tex, which seems to have stopped it. I suppose that the same crack could be leading to oil leaking out of another spot in the head, which is coming out at the head gasket. I have another head being assembled (has been crack-tested) which will go on within the next month. I just hope I don;t have the same oil consumption after it goes on so want to rule out other possibilities now. Thanks to all who have replied so far.
Erick Vesterback

I think David DuBois, Bremerton, WA, USA ddubois at sinclair dot net had posted information on the leakdown. It was a way of pressurizing the cylinder and checking for valve or ring leakage, but it should also be able to show a head leak.

If the car was leaking when you did the compression tests, it would not look like there could be a significant leak. 15% difference is what I read as considered normal so even at 170, your low is not that far off.
Bruce-C

This thread was discussed between 09/02/2008 and 12/02/2008

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