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MGB MGB Oil Consumption

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Jonnyc

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Hi, this is my first post in this forum, and I hope someone can help me. I own a 71 MGB, and this year I've been doing some upgrades to improve the appearance and performance. In doing so, I replaced the Valve cover with an Alunimum cover without a breather vent. It came with what they claim was a breather cap instead. I also removed the emission pump (bad anyway), gulp valve and all additional emission related hoses. Again, I've done a few things to this car, so I'm not sure what is causing my problem.

Heres my problem. This year I'm losing about 1 quart of oil per 200 miles! This car NEVER used that much oil in the past, and I very nervous what is causing it.

Could the breather cap be the culprit?? I've read that this can be a problem because of increased pressure in the system.

Any other advice would be helpful. Thanks in advance.
 
Jonny,
Welcome to the forum. You are almost certainly correct about crankcase pressure causing the problem. Somewhere in your series of changes Something is wrong. It is likely related to the breather vent system.
D
 
It could be breather related but I don't think it has anything to do with the valve cover. I have the same valve cover on two of my cars and don't have the problem. I would suspect ring, or valve guide wear. Another thing would be a clogged crank breather.
 
That's great, it sounds like a pretty simple fix then - right? Can I just buy an over the counter breather cap from a local parts store? Or do I need to buy it from somewhere like Moss? Why is the breather cap that came with the new Alunimum cover so inadaquate? And is this a common issue with after market Valve covers.

Thanks again for the fast reply!!
 
Tom, this car never lost any oil per Summer let alone every 200 miles. I did most of my recent work on this car about 1000 miles ago (nothing internal), and last week I notice my oil was down about 2.5 quarts! Very alarming indeed! I first suspected internal engine wear, but I couldn't figure out why all of a sudden the engine would just fall apart so fast. I'm hoping it's just something simple like the breather cap. What do you think.
 
Guys, you are the best.

I removed all emission equipment as recommended by a very reputable local shop that specializes in MGB's and other british cars. Now I'm starting to think they advised me wrong.

I'm looking at my Bently "Complete Official MGB" service manual, and I'll list what I took off. It appears I have a variation of the "Exhaust Air Injection" system on my car.

* Air Manifold (tube running to each cylinder)
(Plugged all holes with allen screws)
* check valve and and air pump
* vacumm sensing tube (plugged hole)
* Gulp valve

I say this is a variation of the Exhaust Air Injection because I had a breather tube coming from the Valve Cover (not shown) and I didn't have the Crankcase emission valve which is listed in the diagram.

I'm sure there were some other hoses I reconnected direct instead of to the part which was removed. Keep in mind, I'm just a home MGB hobbiest, not a real mechanic.

I get the feeling this is where the problem is after researching and talking to you guys.

Let me know what you think, and what needs to be reinstalled.

I have a side question for you as well. How much damage do you think I did to my engine running it 2.5 quarts low. I noticed something was wrong because my oil pressure was extremely low (around 25) when driving. Everything seems fine, but my valves were clattering louder than normal. I reajusted my valves to .13 (spec is .15) and it seems very quiet now

Thanks again for the help.
 
"I say this is a variation of the Exhaust Air Injection because I had a breather tube coming from the Valve Cover (not shown) and I didn't have the Crankcase emission valve which is listed in the diagram."
-----------------------

Jonny,
You need to closely check the references that I gave you. There HAS to be a pcv/vacuum system connected to the engine somewhere or the internal crankcase pressure will cause big oil control problems. "Crankcase emission valve"?. I really think that restoring the pcv/hose/vacuum system would be best. I don't know what parts were on it when you started. Maybe some are missing.

The only substitute is a separate breather hose connected "somewhere" & dumping into a catch can. Or a large flow vented filler cap Which will blow oil out.

Removing the air injection as you did shouldn't cause problems.

I doubt if there was any engine damage due to low oil.
D

[ 08-09-2003: Message edited by: Dave Russell ]</p>
 
Thanks again. I'm sorry if I'm a little slow on this, but emissions have never really made sense to me - guess I'm going to understand it now though.

I did read the references you pointed me to. The "side plate cover" discussed in the first link wasn't something I knew about or completely understood. It looks like an aftermarket fabrication to fit on MGBs. Still trying to figure out if I need it or not.

The other link describes the hoses going to the carburetors. Those were not touched and are still hooked up exactly like they were. So the crankcase is vented through the carbs just the way it describes.

The link also said: "In 1970 a non- vented oil cap was introduced with breathing now taking place through a charcoal canister". This is where it gets confusing. The charcoal canister is still in place but only the fuel line is going in and out of it. The only thing that was removed from the canister was the breather hose coming from the valve cover to the canister. I guess that's why I'm focusing in on the valve cover vented cap which is suppose to replace the function of that hose.

I re-examined all parts I removed and I'll try to explain exactly what I took off.

These are the components and nothing else: The air manifold (removed and all holes plugged) which connected to the checkvalve (removed) which connected to the air pump (removed). the air pump went to the gulp valve (removed), which had two hoses going to the intake manifold. Both holes in the intake manifold (which again were connected to the gulp valve) were plugged. What I just described is all one system conected by hoses to each other. This is the only part of the emission system I removed.

So, you already mentioned the air manifold shouldn't have caused this. That leaves the two plugged holes in the intake manifold (which went to the gulp valve) are the cause (doubtful?). Or the breather on the valve cover going to the canister is the cause. Or I've got bigger problems!

Again, I've pulled out all parts and this is exactly what I did... no more guessing or trying to just remember...that's it. Hopefully that helps a bit more.

One more think I want to make clear. The car doesn't smoke and never did. But it does spit black soot out of the exhaust pipe (residue on the pavement) when it's started cold. I assume this is somewhat normal and not related due to the rich mixture when choked. Someday I would like to figure that out too, but this oil comsumption is more important right now. Unless you think it's related in some strange way.

Again, I know I'm not up to speed on this stuff. I truly appreciate your time.

[ 08-10-2003: Message edited by: Jonnyc ]

[ 08-10-2003: Message edited by: Jonnyc ]</p>
 
I may have an idea -- wonder of wonders!

Part of the referenced info says;
"As gases are withdrawn by inlet manifold pressure, a vented/filtered oil filler cap provides a supply of fresh air through a restricted orifice (9/64" dia.)."

If your new ventilated filler cap opening is too wide open, more than the equivalent of a 9/64 hole,-- then the vacuum vent system (carbs) can't pull a proper vacuum on the crankcase & things won't work. This is not just about emissions but also about engine oil leak control. To explain further, With a slight vacuum in the crankcase, the engine will leak less oil out of the seals & gaskets & less oil will bypass the oil rings.

Try plugging the filler cap vent with something that has a small (9/64) hole in it.

The exhaust soot & some water in normal on a cold start.
D

[ 08-10-2003: Message edited by: Dave Russell ]</p>
 
Hi guys....just getting into this late and I may have missed it in your writing above, but:

Did you remove or plug your PCV valve? (it's not clear when I read your posting...but you mention "removing hoses") The PCV valve is esentially "a controlled vacuum leak"...and the carb is jetted to compensate for it. If the PCV is eliminated (and instead, the crank is vented to the open air), you'll run rich. Rich mix will cause oil consumtion, especailly on high mileage or well-worn engines (the extra gas washes oil off the cylinders). At 200 miles per quart, your engine should be smoking quite a lot...is it?
This assumes that you are burning oil and not leaking it (again, not clear from the quick read I just did). If you're leaking, you need to be sure that you're crankcase has a good vent...you could just leave the oil cap loose to create a good vent (held on with duct tape and a bit of wire temporarily)...It may be a bit messy near the valve cover, but if it cuts down on oil loss (due to crank pressure), you could go from there.
Running an MGB engine 2.5 quarts low should not hurt it, if oil pressure was maintained...fast or hard driving while low will cause the oil to slosh around, allowing the oil pump to "pump air"....not good. I'm unsure about the tapping sound you mention: MGBs have mechanical valves (not hyraulics), so they don't respond to low oil level the way a "normal" car does. I'm hoping that the sound wasn't connecting rod bearings running "dry"...watch your oil pressure and oil level extra carefully for a while.
 
Isn't the PCV valve on most cars a small device that plugs into the valve cover? I can remember a few cars we simply pulled it out and shook it to see if it still rattled - if it rattled it was good. My MGB has no such device, and I believe the PCV system is simply a hose coming from the engine block to the carburetors instead. Is this correct? If so, is there some sort of device that could have become plugged? Again, all hoses from the crank to the carbs are still there untouched.

About the carbs running rich. My carbs are very difficult to adjust because of a vacuum leak in the throttle shaft of the front carb. I've read this is very common on this car, and I'll need to rebush it some day. I don't think it's running so rich it would cause a 200mile per quart consumption.... or could it? You'll have to let me know.

I think I'll probably just reinstall the old valve cover for a while with the hose to the canister. See if that fixes it. I assume the rest of the emission equip is ok to leave off - unless you think I should just put it all back.

I really like this site. I've posted my problem on a few MGB boards and had very little if any response. It's good to see a place where there are knowlegeable MGB enthusiests!
 
Hi Tom,

You are probably right. I have chased my tail before, never caught it though. Since J. claims that the problem just started after the changes I would "assume" that the problems are related, but maybe not. I think that the only breather on his car is the connection from the front side cover to the carbs & a restricted hole on the original filler cap, am I wrong? In any event I'm tired of tail chasing.
D

[ 08-10-2003: Message edited by: Dave Russell ]</p>
 
The only way he is going to know for sure is to replace the stock valve cover and drive it. If the problem goes away then he has found his problem. I don't see how it could, but that's waht I would do.
 
Thanks guys for all the advice. I'm going to remove the Y connector and check for any blockage like you advised. I'm also going to keep an eye on all oil consumption very closely.

I want to clear something up though. I would hate to take up everyones time helping me with this unless I'm sure about the problem and sequence of events and what could have caused it. I just realized this morning I may be jumping the gun.

I had an oil change a few months ago (about 1500 -2000 miles ago), and I suppose it's possible that they didn't fill it up to level correctly. Then I did the removal of the emissions about a 1000 miles ago. Last week I noticed the oil down 2.5 quarts (which NEVER happened before for an entire summer of fun). Filled it up. Yesterday, I checked the oil and it was down 1 quart after 200 miles. That's why I thought 1000 miles would lose approx 2.5 quarts at the rate I was loosing it, and brought me back to the emissions removal/new valve cover timeline.

But guess what, that was a no no! I should have waited for a cold engine to check the oil, right!! This morning I checked it again, and it was up to level. Didn't know a whole quart would sit in the top of the engine when warm.

So, in closing, I will keep an eye on everything and cross my fingers that the person who did the oil change didn't fill it up correctly. Hopefully this is just a big misunderstanding.

I'll keep everyone posted!!
 
hmmm i usually check my oil after the car has idled for a couple of minutes. shut off engine Then check oil.


is this proper? it is the way i was taught. and makes sense
 
If you check oil while engine is warm or just after running, there's oil still up in the engine/head...I always check in morning before starting engine...that way, I see what's in the sump...checking oil at filling station or just after running causes one to think its low when it isn't - & also causes one to add oil when its not needed....too much oil is just as bad as too little.
 
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