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Massive oil burning under load but barely any at slow speeds - seems better with thicker weight oil

I recently got my hands on a 1994 Geo Metro 1.0L 3 cylinder. Actually I got TWO of them. One had a bad engine (burned valves) but was otherwise a good car while the other was junk (expect for the engine) and I am amazed the suspension didn’t separate from the body due to the rust. So, I decided to swap the engine from the junk car to the good car. I replaced all seals and gaskets external to the engine plus the PCV valve and gave everything else a good cleaning. The only seals and gaskets not replaced were the intake gasket, head gasket, and exhaust gasket as the engine was swapped in a complete manner. I also did the timing belt and water pump while I was in that far as well as did the plugs/wires/cap/rotor when putting it back in. I also ran an oil change through of cheap oil and some Seafoam and Marvel Mystery Oil to clean out any sludge as it looks like oil hadn’t been changed real well in this engine. This oil came out pretty dirty after like 30 minutes of idling.

This little car runs amazing overall and keeps up with traffic and is way more peppy than I would ever imagine! It is also getting somewhere between 50-55 MPG and is fun to drive kinda like a big go kart. There is ONE MAJOR issue! If I get on a highway and try to maintain speeds of 65MPH or faster on big hills, I am guaranteed to get massive smoke clouds from the valve cover area filling with oil and puking it through the PCV/breather assembly right into the intake. I tried more oil changes with synthetic oil and this kept happening. I also ran Seafoam and MMO through the oil and drove it like 30 miles before the change. The oil came out really black each time. I can now actually see bare metal on the inside of the valve cover area through the oil fill where before it was all black after all these oil changes. I also replaced the PCV once again for good measure as it was like a $6 part.

I drove about 100 miles on the highway and started getting massive smoke screens every time I got a long uphill grade and tried to maintain speed, especially if I stayed in 5th gear. The car had more than enough power to make it up the hill in 5th but would smoke under the load. This began to make me suspect I had a serious blowby problem. I had a quart of oil in the car and added all of this during a couple stops on the way. I was at or slightly below the low mark when I decided to head home so I found a parts store and purchased a quart of the cheapest store brand 10W40 oil I could find and used this to get home. It still smokes quite a bit but maybe not like on the way there. I also had the wind at my back so I figured part of this was load dependent.

I was at or just below the fill mark on the dipstick when I got home so I added some more 10W40 oil I had sitting around for an ATV I no longer own. I know this is formulated for motorcycles and ATVs but figured I wouldn’t hurt the engine any more. I also added some auto trans fluid as I know some people say the detergents in this can free stuck rings and work wonders in a neglected engine. Again, how can I do more damage to this engine than has already been done? The car calls for 5W30.

I have pretty much resigned myself to the fact that this little engine had 170K of not the best maintenance and is due for a rebuild. My plans are to keep driving the car while rebuilding the other engine with bad valves. I am glad I kept the old engine around. The car seems to be doing a lot better on the mix of thicker oil and ATF but wonder how long it can go like this. I took it out on the highway and really pushed it hard to see if I could make it blow smoke and it would not. It MAY have consumed some oil on the dipstick but I am even not sure about this. I am not adding any until I can see a definite drop in the level.

Here is my next question. What is likely the solution I found? Thicker oil sealing worn rings better? ATF dissolving crud around stuck rings? When/if I change the oil before I get to the rebuild, what weight should I use? 5W40 maybe?

Also, these engines are notorious for burning valves if a thicker oil is used as the hydraulic lifters don’t allow them to close completely. Should I worry about this or not?

Anyway, these engines are cheap and easy to rebuild and I can do most of the work myself besides any machining that the engine/head I have might need.

I feel I am on borrowed time and shouldn’t get my hopes up that things are going well but wanted to get a second opinion. I feel I must have a blowby issue and am tempted to start ordering parts to rebuild the old engine. Even if thicker oil fixes the burning/smoking issue, I now worry about the valves. I just find it amazing I have this problem when the little car runs so well otherwise.


Along with the PCV valve, there is a large vent tube from the valve cover to the air filter housing. Any obstruction in that vent will cause such problems.

Yeah, the hose from the PCV has a branch. One side goes to the air cleaner housing while the other goes to the valve cover. The hose was FILLED with goo when I started on the engine. I cleaned this up and don’t see how I could have any issues there.

This is a load and duration of load issue. Sustained headwinds and long uphill grades bring this on. Short hills do not.

Besides this issue, the car runs great. I checked compression and it checks out well within spec.

I still wonder if there is crap around my rings causing this and that my rings are not stuck but “sticky”. When I first started having this, I had it to the floor and couldn’t cause the issue. Moderate loads did. Now I cannot get it to happen even when I try!

These engines are known for this. Geo Metro forum posts refer to it at “oil farting.” Many things can cause it including PCV/breather issues, stuck relief valve on oil pump at high RPM, blowby around the rings, etc.

I thought I had blown the engine the first time this happened as we are not talking about just a little bit of smoke. I am talking about enough smoke that people on the highway pull over! Either way, I will drive it with the wrong oil if this solve the issue while I rebuild the other engine.


Is smoke easily passing through that vent to the filter housing?

I never imagined these cars as “peppy.” Could it be that the engine had been modified, causing the problems? (Please feel free to tell me if I am wrong about the possibility of a modification causing the problem.)

“it looks like oil hadn’t been changed real well in this engine”

Sounds like a classic case of worn rings or gummed up oil control rings.

Have the compression checked, if they’re all low (my guess) it’s worn rings.

The smoke isn’t passing through the vent/tube. Large quantities of liquid oil are being pumped through the tube where they directly enter the intake through the breather hose. The smoke is a result of this oil burning in the engine! We aren’t talking about little bits of smoke. This is like the kind of smoke you would expect if your engine blew but then it clears and the car runs just fine! I mean I could see some cars behind me not completely obscured by the smokescreen actually pulling over!

I had the air cleaner totally cleaned out and dry of oil and crud. Oil was pooled inside it after these episodes. I burned like 1/2 quart in 10 miles one time when I was really pushing it. Oil isn’t burning much past the rings, if at all. This isn’t to say that the rings are ok and that massive blowby isn’t causing the oil to fill the valve cover area under load. This is definitely load and not RPM dependent so I don’t think it is an oil pump/oil drainback issue.

I don’t think any major modifications have been made besides the fix up/routine maintenance I did when I swapped the engine. This is one of the few cars that I feel I could pick up the engine and swap all by myself. I did all the work and nothing was done to the internals before as far as I know. It isn’t a race car by any means but I made sure everything I could do to make it run efficiently was done like having a good tune up. I can easily maintain the speed limit on hills except the the oil smoke issue.

Several have told me to keep driving it with good oil and some ATF and that one of two things will happen. 1. “Sticky” rings will free up over time and the issue will reduce or go away. 2. The engine will eventually burn valves due to me using thicker oil or building on the stems from oil burning.

I will steam clean with water to keep it going if I can and use a thicker weight of oil if that keeps the smoking to a minimum. I have had none of the nasty blasts in quite a while. If it doesn’t clear up soon, I plan to definitely rebuild the other engine I have sitting in a shed. I have actually been pretty impressed with this simple little car and love the gas mileage. Sure, I could buy a brand new Prius but it would cost a lot more and I know it wouldn’t be so easy to work on.


All three cylinders came out at 170-180psi. Minimum is 156 or so and max is 199 or 200. Now is probably not the time to check if it is running well and not blowing smoke. I wonder if the rings are “sticky” but not completely stuck and will free up or have freed up. Either way, it seems to run so well besides this issue.

I wonder if the rings are “sticky” but not totally stuck because it will not do this if I floor it on a long hill. It is only under moderate but extended loads. I wonder if the full throttle runs put enough pressure to cause the rings to seat fully.


I suggest that you remove your valve cover and look for the oil drain back holes that allow oil to drain back into the pan. I think you will find that these are really gunked up. You may need to spend the better part of a weekend mechanically removing all the gunk from the valve area on top of the head.

When you get done, pull the oil plug and pour a solvent or kerosene over the head and down into the pan to flush out any loose chunks. Then fresh oil and oil filter should get you on your way. If not, then you have bad rings.

Your compression may be high because there is a great deal of carbon buildup in the cylinders. You are adamant about the volume of smoke and that is almost certainly blowby. And you say the smoke is not flowing out the vent to the breather while oil is running out. Maybe you could study on that issue and see what’s going on there. That smoke is almost certainly building pressure in the crankcase and forcing oil past the rings.

I didn’t read everything but check the ignition timing.

Yes, I feel that the smoke is NOT coming from the crankcase through the PCV, etc. Oil is being burped through the breather hose into the air cleaner housing and in LARGE quantities where it is then burned in the engine, resulting in a tremendous amount of smoke! I am adamant about the smoke because it is enough to smokescreen an entire road. As indicated, some of the cars I could actually see behind me were pulling off to the side of the road to avoid the smoke or maybe they just couldn’t see a thing. I pulled over the first time this happened and noticed a ton of oil in the air cleaner housing. The splash pattern indicated it came through the breather/PCV hose.

I think it is blowby causing high crankcase pressures and the inability to drain oil back through the head due to the pressures. The drain back holes seemed ok when I had the valve cover removed to replace the gasket. Now there were some head gaskets with the holes too small or not exactly centered where they should be and this is a possibility.

I don’t think this is related to the oil drain back holes in the head as it isn’t RPM dependent. It is based on the load I put on the engine. For example. If I maintain 70 mph on an uphill grade in 5th gear, I am more likely to blow smoke than if I am in 4th gear going the same speed. I have also done engine braking on long downhills which gets the RPMs up but not one bit of smoke. The oil pump on these engines is like a timing cover on engines with a timing chain. The oil pump is very simple and an impeller keyed directly into the crankshaft that rotates within this cover. There is a pressure relief valve and sometimes this gets stuck closed, causing too much oil to go into the valve cover area. This problem is RPM dependent. The faster the engine turns, the more oil builds up and the more likely you are to get smoke so I don’t think this is my issue.


sounds like you need to replace your rings

I did not read all the posts carefully, but in case no one has mentioned it, there should be an oil separator at the inlet to the PCV hose - often some baffles that may be permanently attached to the underside of the valve cover. When those baffles get full of sludge, the oil droplets build up to a pool that gets sucked out through the PCV and burned. Heavier oil tends to burn less because it has less of a tendency to form very fine droplets that get carried up to the oil separator.

I had my valve cover off during the intial workup of the engine in order to replace the VC gasket. The baffles are on the VC and didn’t look filled with crap although I soaked the entire part to remove the sludge, etc.

I have been looking into getting an identical spare engine rebuilt over the past day or so. There is a guy not too far from me that specializes in these little cars and will do a very complete rebuild for $400-500 less than buying a reman from a parts store and will likely do a better job too. I was thinking about doing it myself but it sounds like he really knows what he is doing and plan to drive this a while and want it done right.

As for the current engine, I plan to drive it a while as is with thicker oil if needed to prevent this severe smoking/oil burning. I have been told that thicker oil can cause the hydraulic lifters to stay a little too open and cause valve burning. If I change the oil again before a rebuild, I will give it a complete fill of the specified 5W30 and then add 10W40 to makeup anything if it gets burned. Oil burning is also horrible on the valves due to deposits causing them to stick open and hot spot formation. It is a balancing act between trying to not burn oil and using too thick oil in order not to burn the valves.


i agree with both Keith and Rod Knox i think they our on to something

From the amount of sludge you seem to be describing, I am surprised that the oil drain back holes are clear, but you had eyes on and I do not.

So now, I am going with the rings. BTW, compression checks can sometimes fool you. I had a 64 Rambler that was burning oil much as your car is now. I did a compression check and got 180 psi in every cylinder, wet or dry, but it continued burning oil. One thing different though was that it made more smoke on deceleration and going down hill than acceleration or going up hill. The high vacuum tended to suck more oil into the cylinders.

Anyway, despite the good compression readings, when I pulled out the pistons, the compression rings were worn down to glitter riding on the carbon built up in the ring grooves. The oil control rings were encased in solid carbon as well.

BTW, what is your rate of oil consumption? The Rambler was about 50 miles/qt. Is the smoke gray or black? If it is black and only occurs going up hill, and your oil loss is not very high, maybe the problem is not related to the oil but to a fuel problem. I also had a 66 Ford 240 ci I6 that did not lose any significant oil between 5000 mile oil changes, yet would always soak the air filter in oil, even with a new PCV valve, I never figured out why.

“All three cylinders came out at 170-180psi. Minimum is 156 or so and max is 199 or 200”

@cwatkin - just to be sure I understand, your engine’s three cylinders all tested within 10 psi of each other? And the 156 min/200 max is just the specifications, right?

Correct, my cylinders came out to 170, 175, and 180 (forget the order) so the compression is pretty balanced. Yes, the 156-200 is what would be considered acceptable from the factory.

I am going to redo a compression test to see if anything has changed.