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MG MGB Technical - 1972 B GT Starting to play up

Hi all
looking for a bit of advice on possible causes / cost of repair for a few issues.

1. Blue smoke visible from exhaust in occassional bursts.
2. Temp gague only getting to 1/4 and not getting to mid postion ie 'Normal'

Thx a lot :)
J McCaughey

Blue smoke is burnt oil, so it could be piston rings/bores, or valve guides, amongst others.

You really need to do a compression test, wet and dry, to try to diagnose.

As for the temp gauge, you need to establish whether it's the gauge that's playing up, or something else.
Dave O'Neill 2

Temperature gauges, sometimes, read differently. On my two 79Bs, one ran with the temp gauge below normal, the second ran with the temp gauge just above center. Reading cylinder head temperature and radiator temperature using an infa-red thermometer showed the two running within a few degrees of each other. Actual testing of the temperatures would be an excellent idea and, in your case, can be done using a meat thermometer inserted into the filler opening in the radiator. Remove the radiator pressure cap, start the engine, run it at a fast idle until you get up to your normally indicated operating temperature and read the temperature on your thermometer.

As Dave notes, blue smoke is oil being burned, black smoke is rich mixture, and clouds of white smoke is coolant being burned. Worn valve guides and leaky valve seals with allow an "occasional burst of blue smoke", most commonly when the car is first started after having been sitting for a while or on acceleration. Keeping track of your oil consumption, and checking for oil leaks which will have an effect on oil consumption, is a good starting place. But, again as Dave suggests, a compression check is always a good thing to do. I do a compression check, and note the readings, as part of the annual maintenance.

If you are burning large amounts of oil, the spark plugs will show oil fouling which can cause misfiring.

Les Bengtson

Thx Gents. good starting points for me.
J McCaughey

Blue smoke on startup only usually means your valve guides are worn. When the engine is shut off for a while, oil leaks down through the worn guides. If that's all you have, it's not terribly significant or mechanically "threatening". Just means you'll need a valve job in the not too far distant future. I agree with the others, nothing like a thorough compression test.

MGB gauges have never received any awards for accuracy, but you don't want to overheat your engine and be unaware of it. Have you checked the thermostat? Is it stuck open or not installed at all? A quick check without removing the thermostat would be to place some cardboard in front of the radiator, drive it a bit and see if the temperature comes up. If so, it's probable that your gauge works reasonably close to correct, but you need a thermostat.
Rick Penland

The oil burning could also be due to a breakdown of the seperation part and letting too much oil 'mist' through under high crankcase pressure scenarios (like when you give it a 'quick burst'). I'd personally look at your rings going though, sadly it's more likely :(

I'll also add my +1 for a faulty thermostat. True the gauge could have gone wrong, but it's just as likely the stats stuck open, either partally or fully. Do the radiator blocking trick on a small run to test it out (don't cook your engine though!)

This thread was discussed between 30/03/2011 and 01/04/2011

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