removing oil cap whilst engine is running

cyclonebri1

skiddlydiddly wrote: »

I thought it was to check for excessive blowby in the cylinders ie gases escaping past the rings?

The correct repy at last, :T:T:T, and yes the fact that the engine ran differently does indicate a less than perfect engine. Did it belch oil fumes from the rocker cover??.

Testing this way is normal.

gaz_jones

Never knew abotu this test. Might try it on my car at lunch out of interest.

Do I literally start the engine, let it run for a minute then take the oil cap off and hope there's no change at all?

Gloomendoom

cyclonebri1 wrote: »

The correct repy at last, :T:T:T, and yes the fact that the engine ran differently does indicate a less than perfect engine. Did it belch oil fumes from the rocker cover??.

Testing this way is normal.

I disagree. Removing the oil cap can allow air to bypass the mass airflow sensor. This will mess up the fuel/air mixture and the engine will run poorly even if it is otherwise in perfect condition.

I do agree that oil fumes belching out of the oil filler is a bad sign.

Pew_Pew_Pew_Lasers!

Gloomendoom wrote: »

I disagree. Removing the oil cap can allow air to bypass the mass airflow sensor. This will mess up the fuel/air mixture and the engine will run poorly even if it is otherwise in perfect condition.

I do agree that oil fumes belching out of the oil filler is a bad sign.

I wouldn't buy a car where air and exhaust gasses are swilling around outside the rocker cover.

Flying-High_2

Gloomendoom wrote: »

I disagree. Removing the oil cap can allow air to bypass the mass airflow sensor. This will mess up the fuel/air mixture and the engine will run poorly even if it is otherwise in perfect condition.

I do agree that oil fumes belching out of the oil filler is a bad sign.

But usually in this case the crankcase is vented into or near the throttle body...i.e Vauxhalls X20XEV and its gummy throttle bodies and ISVS..... Not before the MAF. Imagine how long the MAFs would last with Oil Vapour being blasted at them.... Then you'd have running problems.

Gloomendoom

Flying-High wrote: »

But usually in this case the crankcase is vented into or near the throttle body...i.e Vauxhalls X20XEV and its gummy throttle bodies and ISVS..... Not before the MAF. Imagine how long the MAFs would last with Oil Vapour being blasted at them.... Then you'd have running problems.

Eggzackerly. If they vented before the MAF then then it would take into account the extra air being sucked in and the fuelling would be adjusted to suit. If it is vented anywhere after the MAF then the ECU is unaware of the extra air being fed in.

Oily air kills hot-wire MAFs. Some K&N filter owners have found this out to their cost.

skiddlydiddly

Gloomendoom wrote: »

I disagree. Removing the oil cap can allow air to bypass the mass airflow sensor. This will mess up the fuel/air mixture and the engine will run poorly even if it is otherwise in perfect condition.

I do agree that oil fumes belching out of the oil filler is a bad sign.

As I understand it though, the pulsing fumes from the oil cap hole will be stronger than normal due to the extra pressure from the escaping cylinder gases.Also it would smell of exhaust fumes.That's what I look for really when doing it.
Can a mechanic confirm this or dismiss an wives tail?

Lum-I too have and SR20(DET), cracking engines.

Gloomendoom

skiddlydiddly wrote: »

As I understand it though, the pulsing fumes from the oil cap hole will be stronger than normal due to the extra pressure from the escaping cylinder gases.Also it would smell of exhaust fumes.That's what I look for really when doing it.
Can a mechanic confirm this or dismiss an wives tail?

I don't think that is under dispute.

C_Mababejive

Its nothing to worry about.

Lum

skiddlydiddly wrote: »

Lum-I too have and SR20(DET), cracking engines.

I don't have one. Have an RB20DET, and a CA18DET in the GFs car.

For some reason we both prefer the older design. I also have a philosophical objection to pushrods :P