MGB: Down Three Quarts. You Read That Right.

I just checked my oil yesterday, and I was down three full quarts! How could that be? I usually top up a quart every couple of months (I don't drive it that much), so I don't usually think much about it. Obviously not the best approach.

I thought I'd checked it more than apparently I had. Now I realize I must not have checked the oil in at least a few months. I've been driving the MGB a little more lately, sometimes 20-30 miles once or twice a week, but no more than that. Recently, I've noticed a very little oil smoke and some oil splatter on the rear of the car. Not much, though, and hardly noticeable. There are more drops of oil than usual on the driveway and in the garage. Nowhere near three quarts, though.

Where did those three quarts of oil go? Am I burning it or leaking it? Or both? There's no puddle of oil on the garage floor, just a lot of drops.

What do I check first? Is this a simple fix or am I in for a major overhaul? Can I keep driving now that I've topped up the oil? I will be checking the oil at least weekly from now on.

I would drive it but I think I would ck. the oil everyday until you know what is going on.


Dwight

You must be burning it if there's not a big puddle under the car. Look at your spark plugs. You could have bad rings or bad valve guides. A leakdown test will help point out the culprit. But if there's no puddle under the car, it's getting close to time for a rebuild. Sorry. Basil
[I'll save you money on the parts if you need them]

My first check would be the plugs. If they are black and oily, then you're burning some oil.

You could also be leaking oil which is spreading under the car and only dripping off when you stop. It may not look like much of a leak but it's surprising how much can disappear that way.

Having a good look at the underside will soon tell you if you have a leak.

From the mileage you are doing and the oil loss, it sounds quite considerable, but as long as you keep it topped up there's no reason why you shouldn't drive it.

I take it you own your own oil well. :D

leaking enough to spatter the back of the car is leaking enough to describe the amount of oil You had to add.

Drew, the difference between the MIN and MAX marks is closer to one Imperial Pint than to a quart. If you get down to the MIN mark and dump a quart in you are overfilling the sump and just asking for leaks, among other things.

I am not saying that this is where ALL of your oil is going or why but it should be taken into consideration.

Jack

If you were down three full quarts, you'd only have a quart in the sump. I wouldn't think you'd have hardly any oil pressure. Did you?

I suppose some leaks are only really significant when the motor is running (rear or front seal). You might be leaking a good bit "under steam" and not see it on the drive. That would probably be the issue if you have oil on the frame behing the motor.
FWIW, I thought I was low on oil and waaaay overfilled the sump because the dip stick wasn't bottoming out on the pan.

If you're using up a quart every, say, 500 miles on an old worn LBC engine then it's not that far out of line. But if you're using a lot more than that then you've got to start looking into things and figuring out what's going on. Good luck with it.

Oil Consumption is cause by leaking or by burning

If the engine is leaking it WILL leave drops after a hard run. A drop or two the size of a dime is one thing -- a puddle the size of a saucer is quite something else.

If the engine is not leaking, then it is burning.

The engine burns oil for three reasons: the engine is pressurized, the valve guides are faulty, or the rings are bad. It's nearly always the rings. Start your diagnosis with the PCV system. Make sure the engine can breathe. Drew, you hae a 90 degree hose leaving the front tappet inspection cover which is connected to a plastic Y piece (12G2134) which then vents into each of the HIF carbs. If that hose becomes plugged, then the inside of the engine cannot vent and the oil consumption skyrockets. If the valve guides are faulty then the car will smoke - SMOKE - at idle or upon acceleration after a deceleration (from high manifold vacuum). To repair this, you can fit Felpro umbrella seals on the valve stems (SS 70373) in place (not having to remove the cylinder head). But, in the end, you'll find that it's the rings. To repair this you need to remove the head and sump, cut the ridge from the top of the cylinder, hone the cylinders, use a glazebreaker to set up a 60 degree crosshatch, and fit new rings. This is a perfect time (as the sump is off) to fit new rod bearings, three of the five main bearings, oil pump internals. Then, if you have the cash ($1200) get the head ported and polished for an additional 5-10 horsepower.

There are always unusual situations. I had a customer who drove across Ohio in February -- he said his temp gauge remained on C even through he was using a 190 F thermostat -- it was THAT cold. His 200 mile trip used two quarts of oil. It had never burned before, it never burned after.

Hope this helps

John

These guys have hit it all, but don't forget that any improperly hooked up breather arrangement can cause that level of oil consumption. When I hooked up my non-standard breather arrangement I made a few mistakes. The car seemed to run well but when I checked the oil it had used about 1 qt in 75 miles.

Most useful item of information was the difference between the MIN and MAX level on the dipstick - I think I have been over-filling the car with oil, assuming that it was greater than just a PINT!

Oh well, free undercoating and rust-proofing if leaking that much.

You can lose a qt every 250 miles through the side plates and not have much in the way of underside oil or drippage on the floor; some but not much. The oil just blows away while you are moving. This has happened to me twice now, once with the yellow 74 and currently with the blue 73. Both have been cured by tightening the retaining bolt. Hope that is your problem too (cheap fix).

I'm not saying this is how everyone should be, but if I noticed ANY oil loss in my B I would rectify it immediately.

Thanks for all the good ideas on this oil burning/leaking issue. It's a new one for me. I'll check underneath for oil leaks and check the spark plugs for fouling. Should have done that right away. I'll also check the PVC system for clogging.

I doubt it's valve guides since I haven't really had any smoke -- just a little, pretty normal for these cars, but no cloud of oil smoke. After doing all that, I'll assume it's the rings, as John and others have suggested.

I have done zero work on the car since before the oil loss, so it's not likely some adjustment I made that's the cause of this. But hoses can get clogged and things can come loose.

As far as oil pressure goes, I check that gauge constantly and it's been normal with no drop in pressure that I've noticed -- even with the engine down three quarts. A little surprising?

As I said, I haven't seen much smoke and very little oil dripping -- a little more than usual, basically lots of drops underneath the car instead of just a few. No puddle of oil. And the minimal, but noticeable, oil splatter on the rear of the car, as I mentioned. That could be either from burning oil which is then going out the tailpipe or from dripping underneath the car and blowing back toward the rear, though that latter seems less likely to me somehow.

When I filled the oil, it was to near the top fill line, but not all the way up to it -- since I didn't want to overfill. It did really take three full quarts. Imagine my surprise when each quart made the oil rise very little. Guess I'd better get this checked out. If I do need a rebuild, maybe it's time for the "works". "Oh, honey . . . "

[quote=DrewM]
I doubt it's valve guides since I haven't really had any smoke -- just a little, pretty normal for these cars, but no cloud of oil smoke.[/quote]

I wouldn't say that smoke is "normal for these cars". Sometimes you see a little puff of too-rich exhaust if you've left the choke on longer than you need, but that's different than smoke from oil.


[quote=DrewM]
As far as oil pressure goes, I check that gauge constantly and it's been normal with no drop in pressure that I've noticed -- even with the engine down three quarts. A little surprising?[/quote]

What numbers are you seeing on the oil pressure gauge? Cold idle, cold fast, hot idle, hot fast? You would expect all those numbers to be different. What are you getting?

Do yourself a favor and perform a leak-down test.

[url=https://www.mobiloil.com/USA-English/MotorOil/Car_Care/DIY/Engine_Leakdown_Test.aspx][color=#FF0000]engine leakdown test[/color][/url]

[url=http://www.automedia.com/Engine_Leakdown_Test/ccr20080301lt/1][color=#FF0000]leakdown test[/color][/url]

does one doe this test onesself or hire it done, , next time i see a mechanic i will sak if he has the proper device.

Do it yourself if you have the tool (or are willing to buy or borrow one), otherwise hire a mechanic.

Drew,

I would check the car from underneath for oil leakage. May be it is fixed by checking some bolts at the sump or at the blanking plate for the fuel pump or the side covers. If so, do not overtighten anything! When there is oil at the bellhousing or at th front cover, new seals should be fitted soon.

Another idea from your last posting was to imagine the filter was renewed and the oil changed and toped up nearly to the limit of the max. mark before the engine had been fired ip and run for a few seconds.
Running the engine after oil and filter changes, the filter will fill up and the reading at the dipstick might be alarming within a few miles!
Remember, when using the right filter element, the oil will stay inside the filter and not drain back into the sump.

The oil at the rear valance of your car should be lost through a leak, it is not from the exhaust as there is no blue smoke and you did not mention any changes in exhaut sound.

I run my engine in the roadster without valve stem seals and the forged pistons have a different clearence to the workshop data. The CR of this engine is well over 12.5:1. Generally speaking it is a stage 6 with some additional mods and it burns some oil when taking it over the 6K rpm but not that much as you think to have observed at your B.

30 years ago, I had a GT that had done 100K mls within a few years of service and it had allways been forced to high rpm by the PO, even when the engine had not warmed up. The bores were ready for a rebore and the car burned nearly 2 gal. between regular changes. No oil on the rear too but big blue clouds!

Check for leaks and top up after some minutes of running when oil and filter was chaged.

Ralph

P.S. What kind of oil did you use? 20W50 or some modern synthetic oil? Modern oils in old engines can cause problems...

Drew, I hope you post your ansewr when you find it; I'm betting on a side cover leak but it is always nice to know what the final answer was.

Oil pressure is stable at about 60-70 pounds where it's always been.

And, I found a little time this evening to check a few of the simpler things.

1. I looked for clogs in the hoses connecting carbs to engine, thinking a blockage might be the source of too much pressure. But no luck. All hoses and the plastic Y fitting are pretty clean. I sprayed them inside with carb cleaner to make sure they're really clean and put it all back together.

2. I removed each spark plug and looked for oily residue, but all of them looked fine. The plugs were dry and light grey in color with no darkness or staining or oil visible on any of them.

3. I ran the engine for ten minutes, then placed a clean white sheet of paper an inch or so behind the exhaust to see how much oil residue might accumulate. After about a minute at normal idle, the paper had some moisture that looked like water vapor. But no oil at all. No smoke, either. I did notice a little oil spotting the floor which might have come from the tailpipe at some point earlier. Maybe it spits oil only when it's just been driven? Not sure how that would work.

4. Crawled underneath partway, had a nice rest, and also looked for oil drips with engine off and engine running. There are a lot of oil spots on my driveway and garage floor, but I saw no dripping from the engine. It is dripping, but I can't tell from where. There's no puddle or large oil stains on the floor, either. Maybe it drips oil mainly as a I drive it when it's under pressure or when the engine is being flexed. If so, that suggests something is loose, maybe a bolt somewhere, or maybe a gasket needs replacing.

I'll drive it some more this weekend and see if I can get the oil to leak out more noticeably from somwhere. Then I'll jack it up and check bolts for snugness and look some more for obvious oil leaks.

After that I'll get my mechanic friend to do leakdown and compression tests and so forth, to determine if I need a ring job. I'll fill you in when I find something.

[quote=DrewM]
Oil pressure is stable at about 60-70 pounds where it's always been.
[/quote]

Is that hot idle? cold idle? hot, at-speed? cold, at-speed? If you're not getting different readings under those different conditions then perhaps your oil pressure gauge isn't working properly.

Top up the oil and give the engine a good cleaning to remove any existing residue.
Drive the car and when you park it slide a sheet of paper or cardboard under the car
to show up any fresh drips.
Then, just keep an eye on your oil and look out for any leaks.

Go to the autopart store and get your self a bottle of engine oil dye and black light. Dump it in the oil and drive for a while. Pull back in the garage shut the door and go all csi on the engine. Stuff is killer for finding the source of leaks.