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MG MGB Technical - oil loss

Ok, I know that I could look in the archives, but I want a quick answer!

Its a 1978 b roadster, showing 89,000 miles. it runs great, but is showing some signs of age.

On start up, the oil pressure can take up to 8 seconds before the needle moves, the oil can go from full on the dipstick to below min in 150 miles. Its not smokey except when you change gear (my dad followed me 130 miles in it!) Oil pressure is at just over 50 on the gauge.

I'm guessing its a tired oil pump, worn piston rings and big end bearings? BTW it doesn't drop/leak any oil at all!

What can I do? it drives great, performance is fine, its just the oil consumption that worries me, as well as the non moving oil pressure gauge (my midget jumps around to 70 on the oil gauge at cold start up as soon as it fires!)

If I need a new engine, does anyone have a cheap one/2nd hand thats good etc. within reasonable travelling distance of Birmingham?

Thanks
John
John Collins

Some others here will certainly have more helpful comments than I, but here goes:

The best way to start your cold engine is to run the starter for a few seconds without the choke (I.e. not starting) that way, the mechanical pump will start bringing up the pressure. Then, you can pull the choke and properly start the car

The smoke during gear change is most likely coming in through your valves. E.g. worn guides or seals.

I would not worry about the pressure as such. Over 50 is fine. The more important test is how quickly the pressure goes back to 0 when you shut the engine off. If this is quick, your bearings may be showing wear. Worn bearings also show other symptoms like knocking and even so, they wouldn't cause you to use 4pints/150 miles.

Your oil loss is worrysome. I know you say there's no apparent leak, but obviously, it's going somewhere. That much burning would show a lot of blue smoke. Most likely, it is indeed dripping out and you just haven't noticed where yet. It may only happen when driving which makes it tricky.

First things:

1. Check if another oil filter makes any difference to the speed of the oil pressure coming up.

2. Check your coolant. Is the oil in there?
3. Do a compression test (wet/dry).
4. Take a good look at your emission setup, specifically the tube coming out from your side vent left of the carb. If this is freeventing, you may have the culprit. (Guess how I know...) There's tons of this and how incorrect setups lead to overpressure and oil loss on the archives.
Philip

John. Try a Mann W917 oil filter. Oil pressure comes up with a few seconds, less than five, indicating the oil drain back valve is working and keeping oil within the filter. Your problem sounds like the oil filter is allowing the oil to drain back into the sump. This shows up as an oil level at the "Max" mark when the engine is cold and, after it has shut down, but before the oil has drained out of the cylinder head and oil filter, a below "Min" reading. I have seen this happen with filters having a bad anti-drain back valve. The Mann filter is used on the Volvo and some other applications and has worked well in the MGBs for years.

If you are loosing oil through burning, it will show up as an oily residue on your spark plugs.

Other oil loss areas are the tappet covers and the valve cover gasket. Clean the area throughly and, after a drive, inspect for leaked oil. I recently had to pull an engine I had installed four years ago. Left had motor mount had broken, the tranny/engine stay rod rubbers were broken down to the consistancy of sponge rubber and the two rubber grommets, which help the rocker arm cover to seal were completely oil soaked and broken down. The original products lasted much longer than their modern replacements. Hence, do some checking for leaks, even if you have replaced some of these items in recent memory.

Les
Les Bengtson

HI,

thanks for all advice, I've found out where the oil is going! its coming out of the oil filler cap as a fine mist, so I'm guessing that its crankcase pressure, and probably caused by worn rings?

John
John Collins

There should be a slight vacuum in the crankcase when running if the breather system is good. If it is blocked pressure may well blow oil out of the filler cap, which is vented on UK cars of that vintage. Remove the cap with the engine running and there should be a slight change in idle speed. Put a sheet of paper over the filler neck and it should be held down on to it. If it flutters off maybe the breather system from the front tappet cover via a Y-pipe to the carbs is blocked so check that first. If that is OK do a compression check, dry then wet. Cylinders should be within 10% of each other, and if you get a big increase in wet over dry t implies worn rings/bores.

OTOH the cap could simply be knackered, mine used to leak oil as well and I had to have a 'scarf' round the filler neck to stop oil running down. Worth sticking a new one on just to see what difference it makes.
Paul Hunt 2

This thread was discussed between 26/09/2006 and 28/09/2006

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