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MG MGA - Dramatic increase in Oil Consumption


A couple of weeks ago I mentioned that rebuilding my carbs had dramatically improved performance (until the dizzy gave out that is).

Additionally I noted that after revving up past 3000 rpm and letting off the gas I was getting a back pressure sound (vroommm pop pop pop pop gargle. Nobody particularly posted in response and it sounded about right for a small sports car however I've noticed a dramatic increase in oil consumption since the carb rebuild.

I'm wondering if that noise and the backpressure is some how sucking oil out?

Obviously I need to do a compression check but does anybody have any thoughts?

By dramatic I'm talking 2 quarts in under 500 miles.
T McCarthy

See if your choke is stuck on.
mike parker

Can't get my head around that theory Mike? how does the choke being on affect oil consumption.
What I would be curious about is how much oil did it use before you sorted out the running?
Whilst 2 quarts is a lot It is far from extremely excessive. I have known a number of fresh engines that have used that amount before bedding in. Other than that the original style valve stem seals were very poor on the MGA and will account for high consumption if fitted.
Bob (robert) Midget Turbo


Did that. All good.


There are two reasons Mike could be asking that 1) is I've heard that the popping noise can be a result from a rich fuel mixture 2) is that if there is gas washing the walls it dramatically reduces the oil viscosity and I could envision that could cause more oil to get past rings and seals. Let's see what Mike has to say.

It used to go through about a quart per/500 miles prior to this.

One other thing that may be a clue is that I've never needed a clamp for the breather hose out of the valve cover however ever since the carburator repair I've had a noticable trickle of oil from the hose down the valve cover.
T McCarthy

Excessive choke can cause a lot of trouble, not just poor fuel economy.
Throw a vacuum gauge on the engine and check your engine vacuum. Check whether the breather tube in the air cleaner is plugged, or otherwise obstructed.
mike parker

If the choke were on during driving, the breather tube would not really be under vacuum, and could cause excessive pressure buildup in the engine. (This is what I was looking for before, but forgot to write.)
mike parker


This is going to be a REALLY dumb question. But where would I attach it?

With the breather hose and the overflow tube isn't this an open system?
T McCarthy

Pull the dipstick, smell the oil on it. If it stinks like fuel your float bowls are sticking open or the jets are sticking down when the choke is released. If there is no fuel in the oil you may have developed a new leak somewhere. Check the plugs, if they are black and sooty its way too rich, if they are also oily it is being washed off the cylinder walls by the fuel and or some is comming down the valve guides. Since it started right after your carb rebuild I would look there first.
J Heisenfeldt

I don't think it is a really dumb question. Since my vehicles are in such pristine condition (not running), I had to go out to double check. Car number one: no engine-forget that. Car number two: no carburettors, ditto for that. Car number 3 & 4 couldn't get the hood open for a while, but I finally did. Car number 3: no air filters. Car number 4, the only car I did get the engine running on, voila! Although the air filter base is on the wrong carb,there is a tube on the air filter housing. I did a quick check in my MGA Service Parts book, and the tube is shown in the inset.(see attached)

mike parker

Mike, I don't see how choke affects the breather tube at all. The only reason it's connected to the air filter element on the front carbs is to supply the crankcase with filtered outside air. In theory if you left the tube completely off it would have the same ventilating effect, only allowing unfiltered air in. The draft tube under the engine is what creates the vacuum, at speed. The MGBs had different ventilation setups through the years, perhaps that's what you're thinking of?

However, that's not to say that there isn't pressure buildup in the engine. If it's blowing oily mist back up that vent tube and into the air filter then there's a problem. I wouldn't attribute it to the carbs though. Are you burning the oil, or perhaps losing it somewhere? My Magnette has a 3-main 1800 and doesn't drip more than your normal MG, but after a hard run it will sometimes vacate a rather large puddle when parked. One of my theories is that blowby is forcing oil out of the rear scroll and into the bellhousing. Either that or a machinist buggered up the crank scroll, I won't know until it's apart.
Mark J Michalak

I may have made a mistake here. My theory was that since the choke was closed, the breather tube wouldn't pull gases and it would cause buildup. As soon as I read your comment, I realized that only one carb is choked, which might negate my comment. I just don't know offhand which carb is choked. (yes it was based on other vehicles than the MGA)
mike parker

When I had a similar issue I found that the oil filter housing seal had been nipped and when hot managed to spray a very fine jet of oil onto the ground.
Interestingly it did not show up as a large (or larger than usual!!) puddle of oil on the ground. The only way I found it was by sticking my hand under the car when the engine was running.
Something to check at least.

Neil Purves

This thread was discussed between 05/08/2008 and 11/08/2008

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