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How Long will Engine Last with Low Compression in all cylinders

My '97 Subaru Legacy 2.5 GT is burning oil, about a quart every 500 miles, so I recently asked my mechanic for a compression test. All four cylinders have loss of compression, 30-50% of normal - with the difference between each cylinder being within spec. (between 5-20psi). The spark plugs also show signs of burning oil on the electrodes.

This car has 244K on it. I would love to postpone the purchase of a new car and drive this old, beloved Legacy until it dies completely. It drives fine for me in its current condition. It has had the heads serviced not that long ago, timing belt replaced, suspension is good. Except for the fact that I have to add oil, I have no complaints. Since I added an oil stabilizer to thicken the oil, I no longer notice much smoke or smell and I suspect I’ll be adding less oil. I’m in a temperate climate and I don’t have to submit to emissions checks.

However, the car needs some safety work, such as brake pads, rotors, tires. I’m trying to decide how much longer it will reasonably run like this, so I can amortize the cost of those repairs. If I can get another 60K out of it, I’m all for it. But if it’s only going to be running another 6 months, I’m not putting any more money into it.

If anyone has any experience driving a vehicle with low compression (keeping the oil topped off, of course) I’d love to hear it. How much longer would you guess this engine has? Thanks, in advance!!

Getting another 60000 miles out of this is close to impossible. The brakes and tires will be more than the vehicle is worth. I would bail as soon as I could.


my personal opinion formed without any empirical evidence is that it will be a lot closer to 6 months than to 60,000 miles. Even if you don’t have a catastrophic failure you will reach the point where you are fouling the spark plugs or the catalytic converter.

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Try this to see if it raises compression and reduces oil burning.

I’ve had very good results with this product.


My view is somewhat different. If it’s running fine for your needs, and you don’t mind adding oil regularly, keep on keepin’ on. Nobody can predict how long it’ll keep going, but in the old days I’ve known oil burners to keep on going for years. The biggest difference with new cars is that the burning oil will probably (likely) shorten the cat converter’s life, and perhaps the MAF sensor and the upstream O2 sensor as well, but hey, like everyone else I’m only guessing.

Yours is exactly what additives like the one suggested by Tester are good for… prolonging the life of an old buggy that’s still getting you where you want to go.

HOWEVER, you MUST fix the safety items.
If the engine wears out and you can no longer get up that hill it’ll ruin your day.
If the car fails to stop or suffers a blowout in a bad spot, it can ruin the rest of your life as well as the lives of everyone else touched by the resultant accident. You could easily kill someone’s mother or father or even yourself.
Please, please, please get the safety issues addressed.


Given the choice of 6 months or 60k miles only I’d have to go with 6 months. As mentioned, with that kind of oil consumption the converter is toast.
The compression does not have to drop to zero before the engine fails to start. It varies but once it starts getting near 100-110 PSI it could leave you stranded.

It’s definitely not a car to take on a long trip.

The additive mentioned is certainly worth a shot at this point.

I would argue that once it begins to fail to start reliably, that’s when it could leave you stranded! The compression readings when it begins to behave like this will vary from engine to engine… and climate to climate.

Bottom line, when it begins to be hard to start and the battery and spark plugs have been eliminated as the cause, you need to start shopping. Until that happens, or until you become unhappy with its performance, keep on truckin’!

My son owns a 2001 Acura TL that had similar issues at about 220K miles. We used the stuff “Restore” that Tester suggested and had outstanding results. Almost a year later he still drives the car to work every day, about 60 miles round trip and it sounds great. He also had to add a quart of oil every 500-600 miles or so. He now adds a quart every 1000 miles. That’s very much acceptable to him. His mechanic told him the same…get rid of the car it will break down. I guess every car and situation is different.

4 tires and a brake job cost you about $700 if you do the brakes yourself. Better than stuck with new car payments.

One of my previous cars had very low compression . . . 105psi, I believe . . . and it was actually a very reliable car. According to the service manual, minimum compression was supposed to be 180psi, so the engine definitely wasn’t in great shape.

No problems starting, in fact it started quickly. It never left me stranded. In all the years, it just needed routine maintenance and wear-and-tear items. It never needed a starter, alternator, or anything like that

I monitored the oil level regularly, adding as necessary

it passed the smog inspection every year, in spite of some oil consumption

In rural areas where there is no annual emission check many owners of beaters just remove the cat, tape over the service engine lights and drive the vehicle into the ground, so to speak, by just adding oil as needed. .I did that to a car while in college in the 50s.

If you live in an area with annual checks, you will fail and the car will be condemned .

So, the 6 months suggested is probably accurate.

I think it could last 60k if you take really good care of it, but it may not be economical to do that. You might be at that point where it becomes a money pit. Brakes and tires today, in a couple of months, struts. After that some suspension parts, then a transmission. Add a couple of CV joints and before long you have some very serious money tied up in it. The the engine goes so you need to replace it in order to get back the money you have already invested. It becomes throwing good money after bad.

In economics, this is called the point of diminishing returns.

Might as well try the Restore product and see what happens but what will you save by delaying replacing the car that is now worn out? So you get another year out of it. You still will have to trade at some point so all you are doing is putting off the inevitable cost. Just seems to me you should re-think the actual savings of waiting a year versus just doing it now. And if the Restore works, you might even get a better trade-in price than what the junk yard would give you.

You’ll finally know when the compression gets too low – The engine will not have enough compression to start.