MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Oil level.

This is probably a simple question, but i've just purchased a 73 B roadster. This past weekend i changed the fluids.

I used 3.5 quarts of oil, after running the engine and then allowing it to settle for a few minutes (per the owners handbook), the level on the dipstick was just below the half way point. The next morning the level was at the maximum mark.

When should I be checking the oil, I have checked the oil level of all my previous cars when they have been standing for several hours but it seems on the B I need to check the oil minutes after standstill.

P.S Good board, it has helped me a great deal in buying my car.

Thanks.
F1Fan

I have always found that it takes awhile for all of the oil to drain back down to the sump after running the engine, so I noramally check the oil after the car has been sitting overnight.

Does your the pseudonym you are using indicate that you own a F1 Magna in addition to the MGB by any chance?
Cheers - Dave
David DuBois

Agreed. All of the oil takes a while to drain back after the engine has been run. So, for the most accurate reading of the dipstick, waiting at least 15 minutes after shutdown is an excellent idea. Taking the reading in the morning, or before the car has been started for the first time that day, as Dave suggest, will give you the most accurate reading possible--assuming the car is on a level surface.

Make sure you use a good quality oil filter. The Mann W 917, available through BAP stores in Arizona, is an excellent one to use.

If you are in the Phoenix area, there is a large Brit car show at Falcon Field this weekend. Not sure whether it is Saturday or Sunday, but www.azmgclub.org should have the information. Les
Les Bengtson

The first time I changed the oil in my 67 I thought there was a black hole in the oil pan. I kept pouring oil in and finally after 6 quarts it was filled up. The manual said 5. Correct dipstick too. Go figure.
Mike MaGee

"The next morning the level was at the maximum mark."

The problem is that oil is draining out of your filter when it shouldn't be. The Mann filter that Les recommends will hold its oil for a weekend or more. If you get that filter on your car, then the level change overnight should be negligible.

I say this because it's always been accepted practice to check the oil with the engine at operating temperature. I haven't read the manual, but have assumed MGB's are no different.

When I was in auto shop (back in the days of bias-ply tires), I was taught that oil, as a liquid, will expand as it heats. So if you top up the oil level cold, you may have more than maximum at operating temperature.

I was further taught that the problem with too much oil is that the crankshaft is too deep in the oil puddle and can whip air into it. I must say that I've never seen this syndrome demonstrated, nor experienced it. It's only learned info.

To loop back to the original topic - I'd recommend changing to the Mann filter and checking the oil level hot - say a few minutes after shutting down. That's a more realistic measurement as far as operating conditions go.

Opposing opinions welcome.

Matt Kulka

As I understand oil filter operation on the MGB, oil comes from the fitting at the right rear of the engine through the long hose to the oil cooler, through the cooler then through the shorter hose to the fitting on the bottom of the oil filter adapter. It then goes through the oil filter and out center standpipe to the engine main oil gallery. I don't see how any filter will drain back through the anti-drain back valve, unless oil runs up hill. It would have to drain back through the bottom of the filter adapter and back through the cooler and lines to the rear block fitting. The long oil line is higher than the top of the filter where it runs through the radiator support. Oil from the filter will eventually drain down to the standpipe level through the oil galleries and the bearings after the engine is shut down. Clifton
Clifton Gordon

Matt. The problem with too much oil in the crankcase is that the crankshaft will actually hit the excess oil several thousand times a minute. This is like standing in a swimming pool, or sitting in a bath tub, and hitting the surface of the water with your open hand. If you do it hard enough, you will hurt your hand. Water and oil are both relatively incompressible and, the crankshaft hitting the excess oil is going a lot faster than you hand would be in the pool. Thus, while most people know about the foaming effect that can be created, consider the damage to the crankshaft and bearings which would also be taking place.

Now, when the oil is circulated through the system, the oil level in the sump goes down. This is why we have to wait a while to obtain a proper reading. My experience is that if the oil level is not above the Max line, hot or cold, there will be no problem with the oil being struck by the rotating crankshaft (at least on a regular basis--that is why windage trays are added for racing/rally use where it might be a problem on a regular basis). I have checked the oil ten minutes after shut down, one half hour after shut down and after allowing the car to sit all night. I found that the oil level a few minutes after engine shutdown, was lower than it was a half hour after engine shutdown.

You are quite correct that this can be caused by a bad oil filter anti-drain back valve. However, assuming that one has a good oil filter, this represents oil that is up in the cylinder head or in some of the oil galleys draining back into the sump. Thus, my belief that you need to allow the engine to sit about 1/2 hour after running to get the most accurate reading. Whether such a reading is more accurate than letting it sit over night and taking a reading in the morning, I cannot say. I do not know how much oil will expand when hot, nor do I know whether there is an expansion rate difference between the petroleum based oils and synthetic oils.

Bottom line. I have never had a problem topping up with a cold engine. I can see where topping up a warm engine, if it has been about 1/2 hour since running might be, very slightly, more accurate. I believe it is more important to pick a method and use it consistantly, then make it a practice to only fill to the bottom of the Max line, than it is to debate hot vs. cold readings. But, I am still learning. Les
Les Bengtson

What and where is the oil filter anti-drain back valve? How does it go bad, what are its symptoms/fix? It there one on a hanging canister filter?

Paul
Paul Hanley

The anti-drain back valve is in the filter. Fram filters are the worst for drain back properties. I just bought some Valvoline filters that looked quite well made in this regard.
Mike MaGee

I have two MGBs. The engine in one has only a few thousand miles on it. The engine in the other has 99,000 and some change. The cars are driven infrequently and a few days after being last driven the oil level in both would rise beyond maximum and take several seconds for oil pressure to build at restart. Tiring of this I installed a gear-reduction starter in each and then installed a Moss hang-down filter converter in both cars. Now the pressure builds to max in a second or less even after sitting for a week or two.
Charles Edwards

Ah yes the anti-drain back valve. I have a puralotor on my car with anti-drain back valve only because I have heard it's the "right choice". And I have also heard that Frams are the worst choice. What I don't know is how the anti-drain back valve works. I would assume it is some sort of check valve in the filter. Was it designed to accomodate a filter that is installed upside down as in the MGB? Does it keep the oil in the filter hence showing a filter's worth of oil low on the dipstick after start up. Things that make you say hummmm?
Dan H.
Dan Hanson

The anti-drain back valve is shown in this URL, scroll down to the first photo.
http://www.ntpog.org/reviews/filters/filters.shtml
It is supposed to prevent oil from leaking through the filter inlet holes around the filter base. In the MGB with an oil cooler the inlet is fed from the oil cooler. The oil cooler is fed from the oil outlet at the rear of the block. The oil lines run through the radiator support in chrome bumper cars. One of the oil lines is at a higher elevation than the top of the oil filter. I always thought that liquid will not flow up hill?

The MGB oil filter adapter for inverted filters has a two inch tall stand pipe in the center. Oil is fed to the oil galleys through the stand pipe. Oil can drain into the engine through the stand pipe, there is no valve to keep oil from flowing through the outlet, however it should not go below the top of the stand pipe. With a tall filter that could equal around half the oil in the filter. I use only short filters, Motorcraft FL-300, Purolator L10017 or some other short filter. I don't use Fram in any car I have.

My 74 MGB has the hang down filter, it cannot leak down, the 68 GT has the inverted filter. I have not experienced time lag with oil pressure build up in either car.
Clifton Gordon

Clifton, all,
I also use the Purolator filters on my '69 (although I use PL14670, which is externally identical to L10017...) I have no lag in oil pressure at startup. Previous to switching to Purolators, I used Unipart, and with those I *did* have a lag. Prior to that, I used the original cartridge setup and had lag with that as well.

I haven't studied the oil flow and didn't realise that the oil had to go up to go down, so to speak. The only thing that I can think of that would explain my observations is that there is some siphon action occurring that is pulling the oil up through the cooler hose and down into the sump...

HTH!
Rob
Rob Edwards

I sometimes worry in my very simple approach to most things in this complicated life. Regarding oil level, I just check the dip stick each time I start the engine.

This, of course, allows all oil to drain from the top into the sump, and provides me with assurance that there's a reasonably correct amount of oil.

As to filters, since they are changed every 3,000 miles or so, (with cleaning the magnetic sump plug), going with a premium filter is a bit too extravegant for me. And, have not found any major faults or failures of the Fram filter.

Using the Moss spin off conversion with a part number 3614 filter on an 18GA engine.
glg

"Fram filters are the worst for drain back properties"

Interesting, the MGOC has just started selling Fram filters for the MGB with what they call 'an improved anti-drain back valve' i.e. improved over other manufacturers, and I'm sure I have read many people say Fram are one of the best. I have not yet had any problem with either Unipart or Champion filters draining back but someone posted a few weeks ago that new purchases of both types wouldn't hold any oil even if the filter was removed immediately after switching off the engine. He tried a couple of each before fitting something else (Fram? Volvo?) and had no more problems.
Paul Hunt

A pricier alternative is the K&N Gold filter.
It took perhaps 3 seconds to get oil pressure
with the Unipart filter on my 79B. With the K&N
I get pressure starting to come up as soon as I
start cranking. But at $13 a filter there
are probably cheaper ways to go.

Ronald

Paul,
What I found with the Unipart filters is that when I removed them after 3k miles or so, the anti-drainback valve had gone all wavy. There's no way it could have sealed....
Rob Edwards

I have Unipart on both mine at the moment and will change them in the spring. If I remember I'll fill them with old hot oil, plug the centre hole, invert them ... and see what happens.
Paul Hunt

This thread was discussed between 13/11/2003 and 16/11/2003

MG MGB Technical index

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