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mrfixitrick
mrfixitrick, Mechanic
Category: Car
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Experience:  Over 35 years of full-time, hands-on, automotive repairs to all makes.
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I have a 1999 Subaru Forester which has been using a lot of

Resolved Question:

I have a 1999 Subaru Forester which has been using a lot of oil lately, and today the check engine light came on, so I took it to a friend who does some car repairs and the diagnostic test said the 4th cylinder was misfiring. After he replaced the spark plugs and changed the oil, air filter and oil filter, he did a compression test on the cylinders and found the cylinder #4 was only 70 compared to the others which are 140. He found oil also in the tailpipe. The engine still starts, but the whole engine shakes, so I'm not driving it to avoid further engine damage. My friend said it probably has a leaky piston ring or bad valve and the head gasket will need to come off to repair it, but I'm hoping they don't have to remove the whole engine to repair it to avoid a huge bill. What do you think is the problem and how much should I expect to pay for this type of repair, and is it possible to do it without removing the engine? Thanks for your help!
Submitted: 5 years ago.
Category: Car
Expert:  mrfixitrick replied 5 years ago.
HiCustomerand welcome to JustAnswer!

My name is XXXXX XXXXX I'd like to answer your Subaru question.

Your friend's diagnosis of rings/valves could easily be correct. However, there should be further testing to determine the exact problem before resorting to removal of the heads or engine, which will be required if that is the case.

Applying compressed air to the #4 cylinder through the spark-plug hole while the piston is kept at Top Dead Centre is one way of determining what is going on with that cylinder. You will be able to hear where the air is escaping. If the exhaust valve is leaking, you will hear the hiss in the exhaust pipe. If the intake valve is leaking you will hear through the intake manifold and throttle body.

If the piston rings are leaking in the low cylinder, the pressure test above will build pressure in the crankcase, and you will feel and/or hear hissing in the oil fill opening (leave oil cap off, or the air will come out through the PCV valve system and intake manifold instead). A spoonful of engine oil can be added to the low cylinder for the compression test to confirm that rings are the problem. (compression will increase)

The valve adjustment for #4 cylinder should be checked in case it has backed off or tightened up. There is a chance that a valve adjustment could restore at least some compression to the low cylinder, especially if it passed the piston ring test. However, the oil in the tailpipe generally points to a more severe problem than a valve adjustment, such as a broken piston ring or missing valve seal.

Do you notice blue smoke in the exhaust? This usually indicates a piston ring or valve seal problem.

Anything more than a valve adjustment will require removing heads and possibly the engine, at a cost of $1000 -$2000 likely for repairs.

How many miles/kilometres are on this engine?
If your engine mileage is excessive you may need to look for a good used complete engine as a replacement. (perhaps $1500-$2000 installed)

You could also consider a rebuilt engine, but the total costs will likely be double that of the used unit.

Let me know if you have any questions about this info at any time; just return to this question to ask.


mrfixitrick, Mechanic
Category: Car
Satisfied Customers: 143
Experience: Over 35 years of full-time, hands-on, automotive repairs to all makes.
mrfixitrick and 13 other Car Specialists are ready to help you
Customer: replied 5 years ago.
Thanks for your response. So do you think the further testing that you recommended could be done by my friend (who is an airplane engine mechanic) who did the compression test for me today (and installed new spark plugs), without having to remove the engine or put the car up onto a lift (which he doesn't have)? Would there be any risk of doing further damage to the engine by doing these tests or should I take it to an engine specialist or the Subaru Dealer (mega-bucks that I don't have) to do these other tests that you have suggested (before they remove the engine)? I really don't have $1,000 right now to spend on repairs, so I sure hope it will turn out to be a less serious problem than what the possible scenarios you described might cost me... do you think that some shops might take installment payments for really expensive repairs like this?
Expert:  mrfixitrick replied 5 years ago.
It's important to check whether a valve adjustment will improve the compression and then if necessary determine whether it's a piston ring or a valve problem. I'm sure your friend could do the additional cylinder "leak down" tests, and it will not hurt the engine. It will require an air compressor or portable air tank, and an adapter fitting to fit the air hose to the spark-plug hole.

If it's a valve or head gasket problem, the removal of the cylinder head work can be done with the engine in the vehicle. If only the bad side head is done, and the corresponding piston/ring is ok, then expenses could be considerably less than the $1000 I quoted, perhaps half of that. It's hard to tell the full damage without removing the cylinder head and looking at the piston and cylinder walls.(although they do make mini-cameras just for this purpose, not many mechanics will have one....)

I doubt shops will take instalment payments for the work done...unless they keep your vehicle until the work is paid in full. Perhaps you can talk your friend into becoming a Subaru apprentice by working on your car??

mrfixitrick, Mechanic
Category: Car
Satisfied Customers: 143
Experience: Over 35 years of full-time, hands-on, automotive repairs to all makes.
mrfixitrick and 13 other Car Specialists are ready to help you

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