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MG MGB Technical - Oil Level High

I have just done a multi day rally in my '73 BGT. I check the oil and water every morning. Each day of the rally ( about 220 miles ) involved some track runs and a couple of 20 or so minute sessions at high revs. It does not normally use any oil during the events, but does use a bit on motorway runs.

No change after the first 2 days then it was very slightly up on day 3. On day 4 , driving home day it had dropped to 'min' so I topped it up.

300 mixed motorway and A road miles later, we got home and the next day the oil level was high - by about the same amount as the difference between min and max.

I cannot smell any petrol on the dipstick and the oil on it will not ignite. No sign of any coolant loss or milky stuff in the filler cap.

Any ideas what it might be and what I might check next?

Mike
Mike Dixon

Heat expansion?? Just a WAG. Jud
J K Chapin

On day4 when you checked it and it was down, then topped up, maybe the car wasn't sitting level when you dipped it-or- the flat washer and seal on the dipstick is floating around on the stick or got itself jammed on the tube giving you a false reading
William Revit

I always check it stone cold so heat is not it, but I wondered if it could be 'user issues' as well, it often is in my case!

The car was not totally level but not enough to make that sort of difference. Having said that it went up over the full level( which is where I would have expected it to be on previous performance) by about the amount of oil I added.

It is due an oil change anyway so I will do that and take it for a drive to see what happens. Only thing I can think of prior to that might be a compression test?

Mike
Mike Dixon

On my 73 the dipstick drops down onto a reinforcing plate in the bottom of the sump with a definite clonk, so I would notice if it didn't go down far enough when topping up, only for it to be down next time and then read high.

Other than that as well as temperature and angle how long the engine has been standing after switch-off also affects the reading, there have been discussions about whether you should check when hot, cold, or something in between! Given the distance between Max and Min and that it's not going to blow up if you go a millimeter over or under so it's not a big issue.

In this case just keep an eye on it, and the other fluids as normal. You can do a compression test but I don't see that showing anything in relation to this if there is no coolant scum on the dipstick or oil in the radiator.
paulh4

The only thing I can think of and it's a vague thought, is that the oil filter is sometimes draining back into the sump. Some filters have a better anti drain down valve. I always use Mann, as they seem better, and engines so fitted, take less time to build pressure when fired up!!
Allan Reeling

From my topping-up the filter holds nowhere near the amount between Max and Min, sources indicate one Imperial pint. Agree with the comments about anti-drain-back valves in the filters themselves, and Mann.
paulh4

Well that oil filter emptying could add some variation. Apart from fuel dilution and evaporation, and a dodgy dip stick I currently can't think of anything else.
Allan Reeling

Just a thought Mike. Could it be that your dip stick has a curl/bend in it and sometimes it sits properly on the bump/shelf in the bottom of the oil pan and other times it misses the bump and goes further down to the bottom of the pan giving you the overfull reading----------

willy
William Revit

This thread was discussed between 08/11/2023 and 11/11/2023

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