Re: air bubbles in engine oil

Thread approved.

Re: air bubbles in engine oil

First, some bubbles visible immediately after shutting down is to be expected, especially for a motorcycle engine where the oil not only gets thrashed by the crank but churned by the transmission. However, there is at least a chance that something is wrong. In that case, two possibilities come to mind:

1) Too much oil in the crankcase. If there's too much, the oil can't spread through the engine as easily, so the oil can't lubricate, and also the bubbles can actually act as an insulator, causing the motor to run hot and maybe become damaged. Verify that the oil level is correct, and remove a little if necessary; it's best to try to get the oil level exactly between the full/add marks rather than have it sitting right at either one.

2) You have a small amount of water (mainly condensation) in the oil. This can happen if you do a lot of short-distance riding. You can fix this by going for a long ride so the oil gets really hot, and the moisture can boil off through the crankcase breather vent.

Re: air bubbles in engine oil

Hi, I have a Pulsar 150 Neon and have been facing a similar kinda issue like the OP. I have 1353km on odo, second service done, but now using Shell AX5 20w50 Mineral Oil and after riding say 9kms the engine becomes quite hot and oil starts bubbling as though its boiling (not foaming). Along with this oil I added 20ml of Motul 3100 20W50 oil from a container that had few drops of Liqui Moly Engine flush. Should I drain this oil now or keep it? I changed oil as engine became really hot even on relaxed riding on Bajaj oil.

Re: air bubbles in engine oil

Can you share a picture of the spark plug ?

Re: air bubbles in engine oil

Thanks for the reply. Here's the pic of the left spark plug:-


I recently got it tuned from the ASC as the bike once nice and hot would stick to 2100 RPM and wont go down until left for an hour. They set it to 1000 RPM thinking I'm a cheapskate xD so I myself turned the AFR screw half a rotation to get 1200 RPM idle. Still the bike overheats quite easily.

As for oil bubbling like its boiling, what do you suggest?

Re: air bubbles in engine oil

To me the spark plug looks a little lean, making your engine run hotter than usual.

Aim for brown instead of that grey.

For bubbling -
Check engine oil level, check if there are any noises from the engine (unusual noises)
If all is good, then ignore it, it's normal.

Re: air bubbles in engine oil

What idle RPM do you suggest as I don't want to set the AFR screw to zero then set it whatever turns you suggest. It has been quite finnicky before. It's DTSi so one spark plug is oughtta run lean than the primary one as per the CDI right?


Oil level is just shy of max level.

Engine has this "chrrrrr" sound when hot, don't know if its normal or not. Have another engine soudn issue for which I have created a new thread, awaiting Mod approval.

Re: air bubbles in engine oil

New pulsars run 5 map CDI so I am not sure if one plug is meant to run lean.

On my pulsar, both the plugs run almost correct, by almost I mean almost. The right plug is brown and I am good to go.
I have set idle to 1200-1300rpm since years and that has been convenient for me. Bike starts in minus degree C temperatures in one self ( one thumb of the starter ) and after a little warmup it's ready to climb the roads. ( we have uphill and downhill roads mostly )

Hope this helps.