Do I have to replace my engine if 2 of 6 cylinders have only 1/2 recommended compression pressure ?

Question

I read that even the front O2 sensors are under the car in a 96 ford taurus so i decided to go to a mechanic (especially since the car was smoking today). He said 2 cylinders out of 6 dont have enough compression and i need a new engine. Is it true theres no other way to repair the cylinders except by replacing/rebuilding the engine?

Answer 1

First thing I would do is take it to another garage. Tell them the symptoms and let them troubleshoot and diagnose the problem. Don't tell them that someone else said the engine was toast, because 9 times out of 10 they will barely give it a glance.
It is true that SOMETIMES an engine might have to be replaced when it has low compression. Is that the only test that was done? If so please go to another garage.
Other causes of low compression include:
Cracked cylinder head
Blown head gasket
Warped valve
If compression readings between any two adjacent cylinders are unusually low, the cause is almost always a blown head gasket.

If compression readings are low in one or two nonadjacent cylinders, the most likely cause is burned exhaust valves. Other possibilities include broken valve springs, bent pushrods, rounded cam lobes, broken rocker arms, broken top compression rings, cracked pistons or scored cylinders.

If compression in all cylinders is low, the piston rings and/or cylinders are worn and the engine needs to be rebuilt or replaced.

Wet Compression Test
When a cylinder shows low compression, a "wet" compression test can be used to see if the problem is a worn cylinder or rings, or a leaky valve or head gasket. A wet compression test is done by squirting a little oil (about a tablespoon full) into the cylinder to temporarily seal the rings. The engine is then cranked and compression is measured a second time. If compression is unchanged and is still low, the problem is not the rings or cylinder, but a bad valve (usually the exhaust valve) or head gasket. On the other hand, if compression is higher, the problem is the cylinder or rings.

Running Compression Test
Compression in individual cylinders can also be tested while the engine is running. This is done by attaching a threaded compression gauge attached to one cylinder at a time (remember to ground the spark plug wire, too).

Running compression test readings will be lower than cranking compression numbers because a running test measures volumetric efficiency. At idle, typical numbers are 60-90 psi. At 2,000 rpm, the numbers will drop to 30-60 psi.

This test can be used to diagnose valve-related problems such as weak valve springs that may seal the valves fine at low rpm, but not at higher rpms. Worn cam lobes will also cause low readings.

Cylinder Leakage Test
A cylinder leakage test can be performed to pinpoint where a compression loss is occurring in a cylinder. The test is performed by feeding regulated compressed air through the spark plug hole into the cylinder, watching the "leak down rate" on the leak down tester gauge, and listening to hear where the air comes out.


To do the test, the crankshaft must be rotated so the piston in the cylinder being tested is at top dead center (TDC) on its compression stroke. In this position, both valves will be closed.

An acceptable leakage rate is usually less than 10-15%, although some engines may still run reasonably well with cylinder leakage rates of as high as 25-30%.

If a weak cylinder has low compression but shows little leakage, the problem is in the valvetrain (a rounded cam lobe, bent pushrod or excessive valve lash). The cylinder is sealing, but the valve(s) are not opening properly to admit air.

If compression is low overall but all cylinders show little leakage, valve timing may be retarded or the valves may not be opening (check for a slipped/broken timing belt or chain).

If a cylinder has high leakage and air comes out of the exhaust pipe, the cylinder has a burned exhaust valve, broken exhaust valve spring or insufficient valve lash.

If air comes out of the throttle, the cylinder has a bent intake valve, broken intake valve spring or insufficient valve lash.

If air comes out of the oil filler cap or PCV fitting, the problem is a cracked or burned piston, broken or worn rings, or a damaged or badly worn cylinder.

If bubbles are observed in the radiator, there is a crack in the combustion chamber, block or a leaky head gasket.

Hope that will help. Good luck.

Answer 2

When rebuilding the heads or cylinders on an engine on any car, the engine must be pulled from the car. There's nothing to be done about that. You're going to pay the money to have the engine pulled.

Well, you can get a new engine for $1200 and dropped in for $600 if you go to the right guy. Make sure you have another compression check done by another mechanic.

If you decide to have the engine rebuilt, they have to pull it out anyway, so that's already $600-1000. Then on top of that they've got to remove the heads and hone your cylinders. You'll have to buy 6 new fitted cylinders, piston rings, and probably valves. Normally if more than one cylinder is bad, it's not just the valves. When it's the pistons and rings getting blow-by, you've got to replace all your pistons and rings at the same time. There's no way around it.

Now, if you go to Autozone and ask about their Tough Ones engines, you'll be sure to find an incredible deal, I promise. I just dropped a very nice 351 Windsor in my eddie bauer bronco for a total of $1900 including labor. They sell you the engine as a long block, which means it comes with the heads already on it. The mechanic will just transfer all your components from the old one to the new one.

Keep in mind though that the Tough Ones engines are REBUILT engines. They are in immaculate condition and are usually slightly more powerful than they were before they were rebuilt. They come with a 150,000 mile warranty. Paying for the warranty is worth $2000 by itself, much less for it to come with a new engine!

Answer 3

Yes, the engine is toast. Repairing it will certainly cost too much and a new engine will cost too much too. We are talking about a '96 Ford Taurus afterall. That would be ten years old and if you drive the national average of 15,000 miles per year, you have around 150,000 miles on it... in other words, it's plumb wore out... It isn't a Honda.

I would say to call the local junk yards and see what one would cost there. I bought a whole transmission once for $150 and would bet that Taurus engine wouldn't set you back $500 with all sorts of stuff attached. Typically, they would come with a 90 day or even a 6 month warranty. It would cost you about that amount to remove and replace it as well so you are still looking at ~$1000 to go this route but I would bet it would drive just fine.

Good luck!

Answer 4

I have a 1992 mercedes 500 sl that had a hose leak and caused a cylinder to go bad and is burning oil. I found an engine for 1000 bucks online.What would be involved after pulling the engine and put another in? Cost? is it worth it? car only had 96K miles

Answer 5

If the two cylinders are right next to each other, I suspect that you may just have a blown head gasket - a fairly common problem on old Taurus V6's from what I've heard. This is repairable, although not exactly a cheap fix. Other than that, either you need another motor or another mechanic.

Answer 6

Did you actually see him do a compression check on those two cylinders ? If it's true replacing the engine is the best thing to do.You couldn't justify the labor cost to tear an engine down and only rering two cylinders.there are too many other considerations also.

Answer 7

There are other ways to fix it, but none cheap. You can re-ring the cylinders, but that leads to everything else. Might be better in the long run jut to get another car

Answer 8

one cylinder reading 0 compression what do i need to do

Answer 9

Im afraid your mechanic is right. It is smoking due to oil burning in the dead cylinders.

Answer 10

get rid of the car the motor is junk and replacing it will cost double what he vehicle is worth