Bad compression or maybe something else?

20

Asked by Nov 26, 2017 at 01:09 AM about the 2001 Toyota Corolla

Question type: Maintenance & Repair

I bought a Toyota Corolla and after a 120 mile road
trip I got it home and did a compression test and it
was low in 2 of the 4 cylinders :(
I gave it 4 hours and did a compression test again,
but now all 4 cylinders run great compression.  I
took it for a good drive to warm it up and test the
compression again and it still reads good
compression.  It has a misfiring issue and says it
runs lean.  Could anyone explain why the
compression randomly got better? Maybe I just
tested it wrong the first time but I was pretty
confident I did it all right. any other advice is great.
Thanks!

8 Answers

220

Were the two bad cylinders adjacent?Possible beggining of head gasket leak.

2 of 2 people found this helpful.
20

That was my thought. I really just wanted the engine out of the car so when I bring out the engine would it be easy to replace the head gasket?

1 of 1 people found this helpful.
220

I would do the teat a few more times before I condemn the head gasket.it is not absolutely necessary to pull the engine to replace the head gasket. Was it two cylinders next to each other? Check for vacuum leaks and check injectors and injector Orings

2 of 2 people found this helpful.
220

Sorry for the typo.That should read "I would to the TEST..."

1 of 1 people found this helpful.
220

How many miles are on this car?

1 of 1 people found this helpful.
20

They were the two adjacent cylinders in the middle. I would also mention the spark plugs that were in the middle had white tips so the engine definitely got very hot at some point. I just don't understand how the compression somehow just became normal does anyone have input on that? And also thanks so much for all the quick input

1 of 1 people found this helpful.
75,765

White tips on the spark plugs is an overly lean air/fuel mixture. Either too much air or not enough fuel. The low compression on the two adjesent cylinders is a head gasket. Possibly when the engine is cold and everything contracts the head gasket is sealing. When the engine is warm/hot everything expands and the head gasket isn't sealing properly. What are the readings of the two low cylinders? Sounds like they're still firing, but lean. HTH. - Jim

Best Answer Mark helpful
220

I had a Lancer that had a similar head gasket problem. The cooling system was full of rust(bad design). It seems the circulating rust would seal the head gasket for awhile,then get dislodged. And on and on.Like a bad chemical sealent However, Js08016s Cold/warm theory is probably correct. Head bolts and theyre torque could also be a factor. You still havent mentioned how many miles are on this car?

1 of 1 people found this helpful.

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