My prelude every now and then will let out a puff of blue smoke maybe a couple times per my 35 minute commute. It is enough for me to notice in my rearview mirror. I decided to replace the spark plugs, change the oil, and do a compression test. The compression test numbers are as follows:

Cyl 1 - 195
Cyl 2 - 185
Cyl 3 - 185
Cyl 4 - 180

These numbers are good and lead me away from thinking piston rings/headgasket/bent valve(s).

I also checked oil for the milkshake and checked the coolant for oil. Both coolant and oil were fine.

Here is a picture of the spark plugs i pulled:


They look OK, if not a little rich.

I also checked the PCV valve and it rattles as it should. Here are a couple more facts about the car:

- daily driven, i doubt it has seen redline in over a year
- Still currently returns 30mpg mixed driving
- idles fine, no issue there
- no CEL
- seems to run fine/smooth as far as i can tell
- the car has a test pipe
- stock exhaust, stock intake, stock header
- the car does leak a little oil (couple drops per day) from what i believe to be the rear main seal

What are your thoughts? Could this be an egr issue? Should I invest in a catch can? I would assume that if my valve guide seals are bad it would be more consistent, no?

Thanks

 

I would def say bad rings and or valve seals. How many miles do you have on your car/engine?

 

155k

 

Dude, those plugs are done, replace them.

You need to fix all your leaks and then determine how much oil you're burning between oil changes since all Honda's can burn up to 1qt between chnages (that's going by the newer cars that have a 5k+ interval so a little over half a qt will be in your range) and this is considered completely normal by Honda's standards.

Also, don't THINK it's the rear main seal, don't EVER look from the bottom when you have leaks, start from the top and if you can, pressure wash the engine before you start hunting. More than likely cam cap, VTEC or dizzy o-ring since they're super common on older Honda's and will leak down the clutch housing and right where you're seeing it in the rear side of the engine making you think the rear main is bad. That engine better be spotless and dry everywhere else other than the clutch housing before assuming the rear main is leaking since it's the last thing on a car that will leak.

 

Blue smoke on a 155k engine is really hard to believe but I guess not outside the realm of possibility. Swap out the plugs and see what happens.

Vtec engines always run rich though. It might actually just be normal smoke especially if it's happening in the upper rpm ranges(while in vtec)

mine does smoke up a bit in vtec and i got 260 compression straight across on my jdm

 

Thanks for the tips, I will def narrow that leak down. I also did replace the plugs with new NGK iridiums.
Blue smoke on a 155k engine is hard to believe? I've posted this elsewhere and I keep getting replies saying its the rings. A full leak down test is in order.

 

222k on a 96 prelude si and no blue smoke whatsoever. Pulls extremely strong. But I still use a can of restore at every oil change just to give it extra protection.

 

Because it seems to only do it after cruising it might be a vacuum getting oil passed through the valve seals.