That’s low.
https://www.koptimatfhev.com/compression_test-2080.html
Tester
Did you test the compression with the throttle plate fully open?
Are you sure? That is for a 2016+ hybrid version, mine is a 2013 non hybrid. The engine in the pics doesn’t look like mine.
I found this one that looks more accurate, what do you think? Kia Optima: Repair procedures - General Information - Engine Mechanical System - Kia Optima TF 2011-2022 Service Manual
… I’m pretty sure I didn’t. Does that make a big difference? What does it even do? Also I think the compression numbers might not be that off, see my last post.
I read that I could try checking the compression then putting some oil in the clyinder and checking it again. Better pressure after adding the oil would indicate worn rings/pistons/cylinder walls I guess? How much oil should I put in?
Not having it open results in lower compression numbers. So I bet your compression is ok, and the problem is with the injection system.
Opening the throttle plate allows more air to enter the cylinders. More air to compress equals higher compression.
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Ah okay. Do you know of any way to test to see if injectors are leaking? Or maybe I should be looking at something else? It looks like testing GDI systems maybe requires expensive equipment?
Ah so if you don’t press the gas it just basically pulls a vacuum and compresses the air that was behind the throttle plate?
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I don’t know what’s needed to test the GDI system.
I’d sell Kia and buy a Toyota. Scotty K.
on some GDI engines, “gas in oil” condition may be caused by fuel leaking in the high-pressure pump, it leaks right under the valve cover
I would entertain the idea of this pump defect too
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Hmm, that looks easy enough to take off. You mean it could be leaking into the engine from the bottom of the hpfp? Down past the cam follower?
I’m not sure how I would tell if it’s leaking other than taking it off and smelling the bottom lol, and that’ll be hard because the whole thing would smell like gas I assume haha.
Could I do this?
- Remove fuel pump relay
- Start and run car until it stalls
- Disconnect the metal line that goes to the fuel rail
- Leave the line from the fuel tank connected
- Remove hpfp from engine
- Put the hpfp in a bucket or something
- Turn the key enough so it primes the fuel system (will it spray hard? will it stop eventually?)
- See if it leaks out of the bottom
I’ve thought about it haha. I couldn’t sell it to someone in good conscience without telling them about this though so I wouldn’t get as much as I’d like. I’ve thought about trading it in at a dealer but worry about them asking me if it has any issues I know about, saying no, and it coming back to bite me in the ass somehow.
Very seldom do they ask if your vehicle has problems . They already know that hardly anyone will tell them or the person might not even know if their are problems . Once they take it and either send it to their shop or auction why would they even bother to contact you .
This is a lousy time to purchase a vehicle so why not just have a shop look at this thing and give you a real estiment on what it needs then decide ?
Yeah I’m going to if I can’t figure it out after I check if the hpfp is leaking from the bottom (if I can figure out how to haha).
I suggest you redo that compression test as those 135-140 numbers mean the engine is on the way out.
Low compression numbers means overly rich incomplete combustion. An engine like yours in good condition should be in the 190-200 range; depending on application.
For what it’s worth, I’ve done some compression tests with throttle plate open and closed and it did not make that much difference. Even at 150 it’s dying.
Still, the plate should be open. If the numbers come back at 135-150 then it’s major decision time and compression is not the only issue.
Gasoline is a poor lubricant and heavily diluted motor oil will wear out all other internal engine parts along with additional ring/cylinder wear. Same principle with engine coolant mixing with transmission fluid. Trouble brewing in mere minutes.
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I will check the compression again, I did check it when the engine wasn’t fully warmed up last time. I’d guess that could make a difference?
Where do you see it should be 190-200? I found this that says between 135-156. Kia Optima: Repair procedures - General Information - Engine Mechanical System - Kia Optima TF 2011-2023 Service Manual
You should never rely on published specs. Those are “will it run specs” from tech writers who have never run a compression test in their life and I have seen this for many makes of cars. I’ve even gotten crossways a few times with service school instructors and phone talks with the tech depts… You ask where do I come up with my numbers. For 2 reasons.
Near 50 years of tests on everything in the inventory. Compression tests were mandatory at every dealer I worked for when a problem existed, plugs out, etc. In cars with difficult plugs a vacuum gauge was used first to verify a compression problem.
Two is the rule of thumb. Good compression is roughly 20 X the Compression Ratio with slight variances for altitude, barometric pressure, ambient temps, etc. Again, that difference is so slight as to not matter.
The only engines I’ve seen in which 120 could be said to be great was the old VW air cools. The reason for that is the very low compression ratio of 6 to 1. One of my antique Harleys is the same way. Little compression as it is 5 to 1. VWs and HDs are air cooled and that is why the low compression; to hold the heat generation down.
I suggest that if you run the comp. test again you also run a wet test after the dry one. This means maybe half teaspoon of oil into each cylinder before retest. If the 135 number for example jumps to 155,etc this means a ring problem unfortunately. If it remains around 135 it means cylinder head valve issues. The latter is not likely IMO since the first results are roughly even across the board. Hope this helps.
Okay, thanks. I will try the dry/wet compression tests.
Do you have any thoughts on how I could check if the hpfp is leaking into the engine from the bottom?
If you trade it in to a dealer, they are the professionals, and it is on them to determine if the vehicle has any issues, not to depend on you to disclose. Get an oil change right before you bring it to the dealer for trade in. If whoever is evaluating the car asks you if it has any issues, say “I don’t know”.
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