Moss Motors, Ltd

As with Ed in his post, my 77 'B' is using/leaking oil, but unlike his car mine is not producing any noticeable smoke.  I've let my wife take it a couple of times when she was able to pry the keys out of my fingers and as I watched her drive off, there was no trace of smoke.  It is leaking - as my garage floor will attest - and that may be the problem, but if it is it has to be the rear seal.  The rest of the exterior, other than the oil filter mount, is dry.  And I have a replacement o-ring for the filter mount.  It may be necessary to install a replacement transmission in the not too distant future and I will take the opportunity then to replace the rear seal, but for now she takes about a quart every 600 miles.  Those 600 miles are daily interstate miles traveling at 70 to 80 mph. This past weekend, I attempted to do a compression check, but I think my 30+ year-old compression tester may not be any good.  I ended up with basically 60 psi on two cylinders and 50 on the other two.  That doesn't make sense as she has adequate power and accelerates nicely when getting on I-75.  And if the compression were that bad, wouldn't I be using a LOT of oil?

zach

zach,

A quart every 600 miles IS a lot of oil. Get another compression gauge to make a comparison. Strangely, you don't have to seee a lot of smoke to be burning oil. And at highway speeds, when fully warmed up, things a very different for you engine than when pulling away from the hacienda still cool from resting. What oil are you using? I've seen this have a profound effect on consumption. Let's hope it's just all that leakage.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

motorbill,

I'm using Castrol 20w50.  If I put a bottle of STP oil treatment in, it reduces the oil consumption. What does that mean?

zach 

zach,

It means you're burning STP instead of oil! Seriously, the gloop raises (temporarily) the viscosity of your oil. That could keep it from either burning or leaking quite as fast, but in the end it breaks down and to continue using it is most likely a false economy. How much does it reduce the consumption? When I was younger I used to use the stuff in a couple of MGs I had which were oil burners, and it did indeed do something to lessen the smoke and oil use.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

Zach, thickening the oil is an attempt to compensate for wear on components of the engine. Things like piston rings, valve guides, connecting rod and crankshaft bearings. You will also be raising the oil pressure due to the increased resistance to flow.

Just my opinion, but 1 quart of oil per 600 miles may be considered excessive if your engine has less than 60k miles,but that doesn't seem too bad considering the speed that you are driving. How much of that is leaks? Do you think it may be a half pint in that length of time? If so you may actually be burning or blowing a quart every 800mi.

 I would do a good compression test both dry and wet and you may be able to get a fix on rings or valves leaks. But it doesn't sound like you are quite ready for an engine rebuild; just keep oil in it and an eye on the oil pressure.

 I have a 74 TR6 with 96k . Yeah, there's a lot of wear, occasionally a light puff at start up. I don't notice any when following my wife either,except some unburned fuel when she pulls away from me in 3rd. None when she lets up on the throttle at speed, yet I add a quart before 500 miles go by.

 I use Castrol 20w50 and 1/2 bottle of Lucas oil stabilzer at changes then the other half of the bottle when low the first time, then the Castrol from there on.  

Zach - your oil problem does echo with mine, and I'm itching to get it fixed.

What I'd like to know is what oil useage should be considered "normal" for an engine in good condition? For example a (properly) rebuilt & reconditioned engine that has had a couple of thousand miles to run in.

Cheers,

Ed

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I want my MGB

Guys,

600 miles to the quart is a lot of oil usage, wherever it's going. My customers usually go 2000 to 2500 miles at least. Many don't have to add at all between changes at 3000 miles.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

That's pretty good, Motorbill. Sounds like somebody has built them right. Know of any engines still running with 90k plus that I could compare my old TR6 to, leaks and all?   ken

Yep.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

motorbill,et al.

As for the leaking oil, the distributor wires have oil spray from around the oil filter mount and the underside of the engine and transmission are dripping with oil. This weekend, I'm going to try to get around to replacing the o-ring on the oil filter mount and the oil pan gasket (just because I have a new one) and then see what that does to the oil useage. Then I will re-check the compression using a different compression tester and I'll report back.

zach

Zach - it sound's like your problem might be simpler than mine, well at least I hope so.

On the other hand, I'm all set for a dirty weekend under the "hood" (I still have trouble with these American names for car parts). Never mind, what I spend in parts, I'll save on oil...

 Good luck,

 Ed

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I want my MGB

Zach, be extra diligent when putting in the oil filter o-ring seal. The old one may be hard, fooling you to think there is not one in there. 2 can spell disaster as you will loose your oil in short order. If the old one does not come out intact be sure to clean all reminants out or you will loose your oil, again,in short order. A thin blade works good for lifting the old one out.

 Another thing that contributes to "abnormal" leaks is a malfunction of your crankcase/ valve cover ventilation.I admit that I am unfamilar with the ventilation of your model but it would be wise to check it out. Pressure will build up in the crankcase itself and force oil out in various places.

 After the engine is warmed up and running, pull out the dipstick. If oil sputters up the vacant hole, you've got a ventilation problem.

  Good Luck and let us know how things turn out.    ken

Post Script: if you are not familar with the proper way to do a dry/wet compression test, be sure to familarize yourself with the technique.  

Thanks all, for your suggestions.  My in-laws were here this past week, so needless to say, I haven't had an opportunity to do anything to the MG. But, I have read up on how to do the compression test, and I'm going to rent a good gauge from the local auto parts store, hopefully this weekend, and I will report on my findings.  Also, at the same time I'll change the oil and replace the o-ring and we'll see what that does to the leakage problem.

If you are still with me on this, I have a new problem.  I hope I just got some bad gas, but the car won't idle at all.  She'll run and drive fine, but the minute I take my foot off the gas, she dies.  And if I'm going downhill with the car in gear but not pushing on the accelerator, she burbles and backfires a little.  This just started Friday.  I had filled the tank in the morning, and that evening on the way home from work, she started acting up. Not on Interstate 75; just on the back roads when I had to downshift and stop for stop signs,etc.  Is it just bad gas, or do I have other problems?

zach

Yeah, we are still with you!  You might take a look at any tube or hose that is attached to the carb or intake manifold.With the exception of the fuel line, these will be vacuum lines. Trace their route for complete connections at their respective points of termination and any coupling or union inbetween.

A vacuum leak will cause rough idle.   ken 

The only vacuum line on the car goes from the base of the carburetor to the distributor.  It's in good condition.  No leaks at all. I pulled the fuel line off the carburetor and turned on the ignition.  There is plenty of gas being pumped to the carburetor.

zach