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Toyota Corolla low compression

I have a 2009 Toyota Corolla with 138,000. Check engine light shows a misfire cylinder 4. Mechanic today said cylinders 3 and 4 showing low compression. The only thing I noticed is car wants to idle a little rough when in park or stopping suddenly. Power seems fine when driving. It is not using oil. Mechanic said rebuild or engine replacement is only fix. I’ve been reading about the product engine restore and most comments report cars with low compression using a lot of oil. Mine is not using extra oil. Will engine restore help bring up the compression?

Restore is pretty good, there are other brands of miracle in a can that others like. You can buy a few more miles and quiet a noisy engine but not cure anything. None of these will fix a misfire. The coils sit right on top of the plugs and are easy to replace. If you have not replaced the plugs, now is a good time to do it. Use Denso brand, Toyota’s are finicky about plugs, don’t use a generic equivalent.

What is the maintenance history on the car? Have you kept up on oil changes?

I am surprised the mechanic is leaning to replace/rebuild the engine. Is there information not shared with us that will help get a better understanding of this?

If cared for this engine will last a long time.

Reduced compression in a cylinder will definitely cause misfiring. Do you know the compression numbers of all four cylinders? If so, post them here, as that will help clarify the severity of the situation and your alternatives.

I have used Restore on old worn-out engines, and saw a noticeable improvement. I even owned a car with one dead cylinder, which shook a lot at idle but otherwise ran adequately. Those were pre-1996 models, so getting through emissions testing was not a problem.

The question for you is what, if anything can be done to get this vehicle through its next required emissions test. You can experiment with disconnecting the battery to clear all codes, and buying a cheap scanner to see if there is a distance which you can drive after clearing the codes which will allow enough monitors to set as “ready” without setting the CEL so you can pass emissions. If there is no required emissions testing where you live, I would just add Restore, and drive it until it becomes too difficult to start, or stalls out. That is a lot cheaper than rebuilding/replacing the engine.

I wonder if the problem is in the valves. One can do a compression test on the suspected cylinders, squirt some oil in the cylinder and repeat the test. If the compression doesn’t increase, the problem most likely is in the valves. If the compression reading increases, then the piston rings are suspect. Another possibility since two adjacent cylinders have low compression may be a bad head gasket. I would think that a valve job would be less expensive than a new engine.

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Hmmmm low compression on neighboring cylinders. That says Hello you have a blown head gasket here!

If your mechanic’s solution to this is a new engine, find a better mechanic.

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Gotta wonder, though, why a Corolla head gasket went bad. That’s very unlikely if the car has been well maintained. What else could be behind a bad head gasket on one of the most reliable cars ever made?

Thanks for feedback. Compression in cylinders 3 and 4 are 75 each. Cylinders 1 and 2 are 125. I didn’t mention with initial post that the valves rattle or tap when motor is under increased strain. Mechanic today said it may be fixed by a valve adjustment. I imagine that is cheaper than a replacement used motor. I have received estimates for motors from 1,100 to 1,500. I would like to keep this car running correctly not just running it until it quits

Reply to your question about cylinder compression. 75 in cylinders 3 and 4. 125 in cylinders 1 and 2. Thanks.

This Corolla is a two owner car. Previous owners had a lot of routine maintenance work done. With 138,000 miles, I expected I was getting a good car. Never thought something like a bad head gasket would occur at this mileage. The previous owner did have a compression test done early 2019. Don’t know the results but maybe low compression was the reason they traded it in to carmax. I purchased it wholesale price from carmax

@Kramvols8404_156652 A valve adjustment may be all that is needed. I go back to the old days when cars had solid lifters (my dad’s 1939 Chevrolet and 1963 Studebaker are examples) where valve adjustments were part of the routine maintenance.

The valve lash could be the problem and you would be looking at about an hours labor just to check it, plus a valve cover gasket kit so maybe $150-200. If the valve lash needs adjustment, now that involves removing the cams to replace the shims in the valve buckets and that can take a couple of hours more.

The fact that you have two adjacent cylinders with the same low compression makes the most likely culprit a breached head gasket between the two cylinders. There could be some welding required if the head or block has eroded around the breach.

This kind of failure is not caused by poor maintenance, mostly it is just one of those things. If the engine has had good maintenance, it would be worth doing the repair.

I suspect that the engine has been over heated and the cylinder head is warped, does this car have a new radiator or any new cooling system parts?

Multi-layered stainless steel head gaskets don’t go bad or breach, when over heating occurs the cylinder head will warp first. If that is the case a used engine is usually more economical than repairing the damaged engine.

All cylinders are too low.I suspect if a wet compression test was done you would find a ring problem showing. The mechanic should have done this. As it is he only did half a test.

Concur w/OK above, all 4 cylinders – assuming the measurement reported is accurate – are too low for the engine to ever run well. It seems very unlikely this can be corrected by a simple valve clearance adjustment. For that to be the case all of the valves would have to be too tight. I own a Corolla also, older than yours, and I’ve never had a case where a valve was too tight. In every instance where the valve clearance was slightly out of spec, it was too loose.

That said, just measuring the valve clearances isn’t that difficult. Takes around 45 minutes as I recall. Might cost $100-$200, and could provide a clue. I’d double check the valve clearances in this case if I had that problem myself; I’m a diy’er and can make that measurement in my driveway, so there’s no $$$ expense to me for that info. Could provide a clue. If I had to pay $200, I would probably be thinking however it is best to call it quits on this engine and spend the $200 towards another used engine or rebuilding this one.

Recommendation: Start looking for a compatible used engine from a rear-end wrecked 2009 Corolla.
You have one huge plus going for you, your choice of vehicle: Corollas are probably the biggest selling car in the USA, so there should be a lot of used engines available. For example just the San Jose North PickNPull site has a Corolla on blocks for almost every model year from 1991 to 2009.

@Kramvols8404_156652 I am having the same problems right now with my 09 corolla. Low compression in 3 and 4 (both in the 60’s) with 1 and 2 being 125. Stalls when I slow down or idle. Not having any problems with temperature/overheating. Already check ignition coils and spark plugs. Almost 180,000 miles.

Did you ever get your car fixed? What fixed the issue?

Again, a wet/dry test will tell if it’s a valve or ring issue.
A leakdown test would do it too.