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MG MGB Technical - Smoke coming from oil cap

Hello.
Bit of a novice, but here goes...
I took my week old (!) 1971 B out again last night (a five min trip to pick up some engine oil turned into a half hour drive) and on the way back, TWO mins from home noticed 'smoke' coming from front of car, plus a slight buring smell.
Got home lifted the bonnet and there was high pressure smoke (although not black or anything, almost steam I suppose) coming from the oil filler cap.
The engine oil was low, I topped it up and run the car again for a few minutes (no sign of smoke, although would imagine it will need another half hour+ run if it is to happen again).
Will be changing oil and filter tomorrow, to eliminate that, but understand the previuos owner had it serviced a year ago (but it has only done 800-ish miles since).
Anything to be unduly worried about?
Thanks,
Rob
Rob Silkstone

One thing I should mention is I'll only be using this car for the 2 mile trip to work and back, although the car will get at least a half hour run every other evening or so and the regular weekend jaunt.
I imagine the oil isn't getting up to optimal temperature during the week so would envisage having to change the oil more than I would normally, say every four to five months?
Am I right in thinking the car won't suffer as a result of short trips, only that I may need to change the oil more regular?
Thanks,
Rob
Rob Silkstone

It sounds like a crankcase ventilation problem. You should have two locations for ventilation. The side tappet cover and the valve cover. Make sure these are free flowing and are piped to the proper locations. The valve cover is piped to the charcoal canister and the side tappet cover is piped to the carbs. There are plenty of online diagrams to help. Maybe someone else has more advice for you. Good luck. -Brian.
Brian Johnson

>One thing I should mention is I'll only be using this car for the 2 mile trip to work and back
I know B's are fun to drive - but get a bike!
.

> I know B's are fun to drive - but get a bike!

I know bulletin boards are fun to fill in, but please - fill in all fields!
Rob Silkstone

To whomever is using my "mark" - get your own. The mark .,. is as specific to me as your name is to you.

Rob,
What color was the smoke ?
How does the oil look on the dipstick - dark, amber, white ?
.

Short trips cause premature wear on engines and are really rough on exhaust systems. Condensation and acid build-up are two primary reasons for this. The bicycle comment may be appropriate.
George B.

The smoke was quite light in colour, I would almost describe it as steam but there is a slight dark tint to it.
The engine oil colour on the dipstick looks pretty usual to me, dark in colour, almost black.
Thanks Morse.
Rob
--
If I wanted to buy a push bike I would. Perhaps the people who don't understand the love and thrill of owning a classic British sports car would refrain from 'helping'.
Rob Silkstone

Your smoke may well have been steam from evaporating condensation. Keep an eye on it and keep the oil topped up.

Things to watch -
replace all heater and radiator hoses, or at least buy them and carry them with you until you have time to replace them.
replace belt, do not overtighten
Change all fluids; differential, transmision, coolant, ...

most important - regularly watch the countryside. This will keep the car and owner happy and in good shape - I'M NOT JOKING ! These cars run better if you actually use them.

Enjoy your MG.
.

Many thanks.
Just got back from a 40 minute spin (only because I can't leave it alone yet and the brief journeys to work and back will be the very least of this car's life!) and no sign of smoke/steam.
I topped up the oil last night (think I put just short of a litre in) so will keep an eye on it.
Many thanks,
Rob
Rob Silkstone

Rob
I have a B the same vintage as yours which likes to smoke and drink(oil) a bit too. Don't worry just keep the oil topped up and it will carry on for tens of thousands of miles yet. Sounds like your crankcase breater is blocked to me. Get some new pipes (about £5). You will also then need to get the front tappet chest cover off to clean the wire gause oil separator. This is a bit fiddley if you don't take the carbs off. Thats straightforward too, but tie them together with string to stop the linkages dis-assembling themselves. Don't forget to buy new gaskets for the carbs and tappet chest (about £2). I cleaned my gause with petrol, white spirit and then left it soak in detergent for a couple of days, that unblocked it completly. Some people take the gause out, but I can't help but think this is bound to increase your oil consumption. You can buy a new tappet chest cover and separator for about £15. Glue the cork gasket to the cover with gasket goo, it makes it a lot easyer to put back. Finally you will need a new filler cap about £4. Whole job could take you a couple of hours.
Paul Hollingworth

If your crankcase breather is blocked, the engine will try and find a different location to release the pressure, rather than dumping it into the carbs. On my 74B I repacked the gauze in the crankcase breather, but was a little bit too liberal in the amount used and the resulting pressure build up forced it to use the rear main seal as it's exit point, letting a fair bit of oil drain with it. You should be able to blow a mouthful of air into the small hole on the oil filler cap, and then cover it with your thumb. If the crankcase breather isn't venting properly, you should notice that the air that you blew into the valve cover wants to come right back out, making a little bit of noise. If it doesn't come back out and there is no pressure at the oil filler cap, then everything should be good.
Now I know that most of us don't want to wrap their lips around an oily orifice, but it is a quick way of determining that the air is venting in the correct direction (to the carbs). And besides, it sure beats riding a bicycle!
With the number of short trips that you are making driving to work, I'd err on the side of making more frequent oil changes, such as every 2 months or 2,000 miles. The worst things that will happen is that you'll always have nice clean fresh oil, which never hurts.
SteveO

Many thanks guys.
Plenty to go on there, will investigate this weekend and let you know what it was.
Thanks again,
Rob
Rob Silkstone

This thread was discussed between 01/05/2002 and 02/05/2002

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.